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NATIONAL BUREAU OF STANDARDS REPORT

5967

Report on Project 4881

Properties of Plastic Films for Use as

Waterproofing Materials in Underground

Heat Distribution Systems

by

A. G. Roberts

for

Office of the Chief of Engineers

bureau of Yards and Docks

Headquarters U.S. Air Force

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
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NATIONAL BUREAU OF STANDARDS REPORT

MBS PROJECT MBS REPORT

1003-12-4881 July 11 , 1958 5967

Properties of Plastic Films for Use as

Waterproofing Materials in Underground

Heat Distribution Systems

by

A. G. Roberts

Plastics Section

Organic and Fibrous Materials Division

IMPORTANT NOTICE

NATIONAL BUREAU OF ST

Intended fur use within the

He additional evaluation and i listing of this Report, either

She Oltke of the Director, Nr however, by the Government

to reproduce additional copit

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

progress accounting documents

formally published It Is subjected

g, reproduction, or open-literature

tssion Is obtained in writing from Such permission is not needed,

y prepared If that agency wlshee

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

Properties of Plastic Films for Use as Waterproofing

Materials in Underground Heat Distribution Systems

by

A. G. Roberts

INTRODUCTION

A difficult problem in the engineering of underground

heat distribution systems is the long-term sealing of the

system against external water and moisture that can impair

or destroy the heat barrier property of the insulation.

Water can also cause serious corrosion to the heat carrying

pipe, or to the outer metal shell often used in such systems.

In a typical heat* distribution system conforming to

present recommended^) good engineering practice, the heat

carrying pipe is surrounded by an adequate thickness of

thermal insulating material held in place by a non-watertight

wrapping which permits diffusion of water vapor from the

insulation to a surrounding air space enclosed by a masonry

or metal outer shell. Waterproofing of the outer shell

against earth has generally been best accomplished by use of

coal tar bitumastic materials. While these materials are

excellent waterproofers as long as they remain in place,

difficulties arise from their tendency to flow at elevated

temperatures, such as might occur in the event of a heat pipe

break or if seepage of external moisture reduced the

insulating value of the insulation. Also, the adhesion of

the bitumen (or other material) is sometimes poor because

of the difficulty of obtaining in the field the cleanliness

of surface required for good adhesion.

The use of tapes or sheet wrappings of pressure sensitive

polyvinyl chloride or polyethylene sheeting materials has

been considered an adequate alternative' 1 ' to the use of the

bituminous or other coating materials. Here also, trouble

has been encountered because of the limitations of these

plastic sheet materials at the elevated temperatures often

met with in service and because of adhesion and bonding

problems in the field.

The rapid technical advances that have characterized the

plastics field raise the possibility that new plastic sheet

materials may be developed, or may already be available, having

improved properties making them more suitable for use as

exterior waterproof membranes in heat distribution systems.

*Numbers in parentheses refer to the Bibliography at the

end of this report.

2

To determine the present status of plastic film or_ sheet

materials in relation to the waterproofing requirements of

modern underground heat distribution systems, an extensive

survey was made of the available literature and technical

information on the physical and chemical properties of

plastics. The results of this study are summarized in this

report.

Asphalts, coal tar pitches, and impregnated felts,

although good waterproofers within certain temperature limits,

were outside the scope of the present survey on plastic films.

Adhesives are considered only to the extent that they

constitute essential adjuncts to the use of plastic film.

Pressure-sensitive tapes, since they consist of a film plus

adhesive, also are treated as secondary to the basic

problem of developing a suitable film material.

Concise descriptions are given of the test methods

generally employed in evaluating the properties of plastic

films. Application techniques for plastic film materials

are discussed. An extensive, selected bibliography is given.

Chief emphasis has been placed, however, on the most

important properties of the plastic materials themselves.

Indications are that among the new materials that have or will

soon become available, there are several which give excellent

promise of fulfilling, at reasonable cost, the rigorous

requirements of application in underground heat distribution

systems.

PROPERTIES OF FILM MATERIALS

The film properties considered to be of greatest

importance for the intended application in underground heat

distribution systems are as follows:

WATER RESISTANCE

Water vapor permeability

Water absorption

TEMPERATURE RESISTANCE

Flow temperature or melting point

Maximum service temperature (220°F required)

Minimum service temperature ( 0°F required)

Heat seal temperature

- 3 -

RESISTANCE TO SOIL CONDITIONS

Acids, bases, and salts

Fungi and bacteria

Rodents and insects

NATURAL WEATHERING RESISTANCE

Resistance to oxygen and ultraviolet radiation

STRENGTH

Tensile strength

Elongation

Bursting strength

Folding endurance

TOUGHNESS

Abrasion resistance

Puncture resistance

Tearing strength

ELECTRICAL RESISTIVITY

Volume resistivity

SPECIFIC GRAVITY or DENSITY

COST

In considering the above properties in relation to

available plastics, it was possible immediately to eliminate

a large number of materials as unsatisfactory, so that

attention could be concentrated only on potentially suitable

materials. Thus, thermosetting plastics in general were'

ruled out because of their rigidity and non-availability in

film form. Elastomeric materials were not considered because

rubber-like stretch is not an advantageous property in the

present application. Among thermoplastic materials, the

cellulose derivatives were eliminated either because of

poor moisture resistance, poor fungal resistance, or poor

resistance to elevated temperatures. Vinyl chloride-acetate

copolymers are unsuitable because they soften at relatively

low temperatures. Polyvinyl alcohol is soluble in water.

Rubber hydrochloride film (Pliofilm) has a rather high water

absorption and softens at moderately elevated temperatures.

After due consideration, the following types of plastics

were selected as worthy of detailed study for purposes of

their possible usefulness in underground heat distribution

systems. Those marked with an asterisk (*) are new and highly

promising materials:

- 4 -

Polyester (Mylar)

Polyethylene (conventional type)

*Polye thylene (high-density type)

*Polypropylene

^Polycarbonate (Lexan)

Polyvinyl chloride

Vinylidene chloride-vinyl chloride copolymer

Polychlorotrif luoroe thylene (Kel-F

)

Polytetraf luoroe thylene (Teflon)

Polyamide (Nylon)

Polystyrene

Acrylonitrile- styrene copolymer

Polymethyl methacrylate (Lucite or Plexiglas)

The important properties of the above materials are

summarized in Table I. A discussion of the information

developed during the data-gathering survey mil now be

presented, first from the viewpoint of the properties

themselves, and then from the standpoint of the materials as

they embody these properties.

PROPERTIES

Water Resistance

This is the fundamental property which is being sought in

the present application. To have good water resistance, a material must combine the following basic factors: 1) insolubility in water, 2) low water absorption, 3) low water vapor

permeability.

Insolubility implies that the material will not be attacked

or degraded under conditions of continuous immersion in water.

Absorption of water into a plastics material causes

swelling and often reduces strength through a plasticizing

action. When the swollen material dries, shrinkage occurs.

Alternate wetting and drying produces a swelling and shrinking

cycle which constitutes a fatigue process that eventually

weakens the material through rupture of polymer chains.

Although the literature does not contain information about

the resistance of specific materials to the effects of

alternate wetting and drying, such as might readily occur in

underground heat distribution systems, it is evident from the

foregoing discussion that good durability in this respect would

be associated with a low water absorption coefficient.

- 5 -

Low water vapor permeability is, obviously, a property

of prime importance in a material to be used as a waterproofing

medium. It should be noted, however, that this property does

not necessarily go hand-in-hand with a low water absorption

coefficient, or vice versa. Both properties must be independently

assessed in evaluating the water resistance of the material in

que stion.

It happens that many plastic film materials possess good

water resistance, so that this property has not been a limiting factor for purposes of the present application in

underground heat distribution systems.

Temperature Resistance

Resistance to elevated temperatures has been the property

most difficult to obtain in plastic film materials. For use'

in underground heat distribution systems, the barrier film

should be able to withstand temperatures up to 220°F without

appreciable softening or deterioration. Temperatures this

high, or perhaps even higher, might be reached in the event

of a break in the high pressure steam pipe. In this circumstance, hot water and steam would pass through insulation,

wrapping, and air 'space to the outer masonry or metal that

is in contact with the plastic film.

Until recently, no practical plastic film material

capable of continuous service at temperatures up to 220°F

was available. Now, however, several suitable materials

have been developed. They are described later in this report.

An important consideration in the elevated temperature

behavior of a plastic film is its heat seal temperature. As

will be further discussed, heat sealing promises to be a most effective way of bonding the plastic film or sheet into

a sealed waterproof system. For this purpose, it is

desirable that the film material be sealable at a temperature

that it is practical to achieve with field equipment.

Maintainance of flexibility at low temperatures is also

an important requirement of plastic films for the present

application. Good handling and toughness, properties are

essential at least down to 0°F. Most of the plastic films

considered here easily meet this requirement, and are in

fact useful at temperatures far below this -- in some

instances as low as -200°F.

Resistance to Soil Conditions

- 6 -

For good

must be abl

conditions '•

service underground, a plastic barrier film

to withstand many corrosive and destructive

present in the soil environment.

Acids and alkalies (strong bases) seldom occur in the

free state in nature because of their great chemical reactivity,

which results in salt formation. Salts, of course, abound in

the earth's crust. In the presence of water, which is also

abundant, these salts may yield an acidic or basic environment almost as destructive as that produced by the free acid

or base. It follows that materials possessing good resistance

to acids and bases will usually also have good resistance to

salts. Many plastic film materials with good acid and

alkali resistance are available and are de scribed -herein.

Moisture in the soil provides an environment which often

supports the growth of fungi and bacteria that may attack

plastics. Although many plastics are not in themselves

susceptible to fungal attack and neither hinder nor support

the growth of fungi, the materials with which the raw resins

are compounded may be very susceptible. Plasticizers, for

example, which often are incorporated into plastics (especially

films) in substantial proportions to impart the requisite

flexibility, may be highly susceptible to fungal attack.

Destruction of the plasticizer can leave the film brittle and

unusable, even though its resin base may be unharmed.

Although an extensive literature exists on the general

aspects of fungal and microbiological deterioration^

)

? reliable information on the resistance of specific materials

is relatively sparse. In the procurement of film materials

for use as moisture barriers in underground heat distribution

systems, a fungus-resistant plasticizer should be specified.

Ordinarily, the manufacturer should be able to supply such

materials on the basis of available information. If not, then

an experimental program should be carried out to obtain the

necessary data. Incorporation of suitable fungicides can

also contribute greatly to the durability of plastic films

underground

.

Although rodents and insects are capable of causing

damage to plastic films there are few reports in the

literature of rodent or insect damage to plastics underground,

such as buried plastic pipe or buried plastic electrical

insulation. Many insects that could harm plastics are not
II ' ‘
- 7 -

found far underground. Termites, though voracious eaters,

have a decided preference for wood cellulose and are not

likely to be a hazard to plastic film underground. Rodents

can gnaw through plastics in quest of food, but do; not eat the

plastics. Film around metal or masonry would not be a particularly attractive target. In rodent-infested regions,

potential damage from these pests could be minimized* by incorporating rodent repellents and rodenticides” >

5

) q n the

plastic film.

Weathering Resistance

Good weathering resistance, basically, stems from good

resistance to oxygen and ultraviolet radiation. The presence

of moisture is also an important factor in the deterioration

of materials because of the profound effect which water

exerts on so many chemical reactions. Ozone and corrosive

dusts and droplets also have a deteriorative influence on

many materials above ground. Below ground, many of the

effects associated with natural weathering are minimized,

.but the corrosive action of water and oxygen remains.

Plastic materials differ greatly among themselves

with respect to their inherent resistance to outdoor

weathering. Thus methyl methacrylate plastic is almost

immune to the effects of weathering over long periods of

time, whereas polyethylene is quickly degraded outdoors

unless stabilized. The words "unless stabilized" are the

key to successful use of plastics outdoors. A great many

special-purpose stabilizers have been developed for specific

materials which have greatly increased the longevity and

usefulness of ^plastics materials in outdoor applications.

Where plastic films intended ultimately for application

in underground heat distribution systems may be exposed to

sunlight during periods of storage in contractors yards or

while awaiting sealing or burial after being applied to the

heat distribution conduits, it may be desirable to provide

the same stabilization as for outdoor applications in

general, to assure the maximum durability. Effective

stabilizers against ultraviolet light, oxygen, and heat are

available for polyvinyl chloride, polyethylene, polyvinylidene chloride, and other plastic materials of interest in

the present investigation.
.
Strength

- 8 -

Film strength, while secondary in importance to water and

temperature resistance, is nevertheless an important property.

Only those strength properties considered most relevant to the

present application are listed ip. Table I.

Good tensile strength is of basic importance in any

material that may be subjected to stress and strain during

handling or service. A moderate elongation is desirable

for ease in handling and fitting film materials, and for

keeping stresses generated during installation or service at

relatively low levels.

Bursting strength as given by the Mullen tester is of

interest as a supplement to the tensile information. Values

were not available for all the materials in the table.

Folding endurance, as given in Table I, was determined

either with the M.I.T. tester (ASTM), or the Schopper

bending tester. Although numerically the two methods are

not directly comparable, they both give useful information

about the fatigue strength of the material. Good fatigue

strength may be an important attribute for resistance to

the weakening effects of alternate wetting and drying.

Toughne ss

The property of toughness, while closely related to

strength, implies certain additional qualities of particular

relevance to abrasion resistance, puncture resistance, and

tearing strength. From a theoretical viewpoint, toughness

is often interpreted as the area under a stress-strain

curve

.

Data on toughness Is given in Table I, where available.

Some information on this property also appears in the

discussion of the individual plastic film materials which is

given later. Most of the materials considered in this

report possess adequate toughness for the intended

application in underground heat distribution systems.

Electrical Resistivity

All the plastic film materials described here possess a high electrical resistivity. Volume resistivity for the various

materials ranges from lO 1 ^ to 10 1 ' ohm-cm. Since good moisture

- 9 -

resistance was one of the prime criteria by which the most

promising materials were selected, the volume resistivity

of this group would not be expected to drop greatly even in

the wet state.

Measurement of insulation resistance is a rapid, sensitive

criterion of microbial attack on plastics'^). Fungal attack

can be indicated by a severe drop in insulation resistance

before visual damage or strength loss become apparent. In

many instances, however, visual growth on the specimen provides

a reliable testw). In investigations of the breakdown

of electrical equipment under high humidity conditions, a drop in insulation resistance has been attributed to moisture

rather than to fungi^’

,

the fungal growth being considered

more as a warning of dysfunction than as deterioration in

itself

.

Specific Gravity

For practical purposes, the specific gravity (ratio of

weight of material to weight of an equal volume of water at

a given temperature) is numerically equivalent to the density

expressed in grams per cubic centimeter, and both terms are

used with equal frequency in the literature.

Ehe specific gravity is useful not only as a measure of

relative weight, but also as an indication of the yield per

unit area to be obtained from a given weight of material

made into a film of unit thickness, and as a means of

following physical changes in a material or as., a criterion of

uniformity or purity.

Polyethylene and polypropylene are among the lightest

of plastics materials.

Cost

Cost f igures^ 1 ^’ 11 ^ for the various plastic film

materials are expressed in Table I both on a weight basis and

in terms of the cost per 1000 square inches of a. 1-mil thick

film. In estimating the over-all cost of materials, however,

a number of additional factors must be considered. Thus,

some film materials may be used in a smaller thickness than

others because they may be inherently stronger. Polyethylene

terephthalate (Mylar) film, for example, is as strong in a 1/2-mil thickness as polyethylene film of 1 1/2-mil thickness.

Application costs, whether by heat-sealing or adhesive, also

influence the relative cost of materials.
.
10

Although the cost of some of the materials is prohibitive,

as in the case of polytetraf luoroe thylene (Teflon), others,

such as high density polye thylene , are low enough in cost to

be feasible ‘for the present application. Still other materials,

expensive at present because of their newness (e.g.,

polypropylene), may become economically practical with

increased production.

MATERIALS

The various film materials will now be described

individually, in terms of the properties that have been

discussed

Polyethylene Terephthalate (Mylar)

This is a relatively new material belonging to the

polyester family of plastics. It possesses a combination of

properties that makes it worthy of serious consideration for

the present application in underground heat distribution

systems. These properties include good water resistance,

heat resistance to 300°F , and exceptional tensile strength,

as well as good chemical resistance. Chief disadvantage of

Mylar is its relatively high cost, about $2.25 per pound

j

this cost can be offset somewhat by using it in the lower

thickness permitted by its high tensile strength.

Bonding of polyethylene terephthalate can be accomplished

with adhesive s^l^' or by heat“*-sealing , although the latter is

somewhat difficult and cannot , be x done by conventional means.

A method using benzyl alcohol^ ^ has been effective in heatsealing Mylar. Also, Mylar can be laminated readilynto

other plastics, such as polye thylene ^or Saran^ > , to give

combination materials possessing good heat-sealing characv

terfstics as well as other enhanced properties.

A new amorphous type polyester film^ 1 ^ 1 ?), called

Videne A, was recently announced by the Goodyear Tire and

Rubber Company. It is serviceable from -kO to 200°F and

is easily heat-sealed with conventional equipment. It

becomes adhesive at 250°F and could be laminated to Mylar to

impart good heat seal characteristics. It melts at 350°F,

and is easily laminated to many other materials by heat and

pressure. It possesses the greatest known abrasion resistance

of any film surface -- even greater than that of melamine

plastics. It is available, at present, only in limited

quantities at $ 2.25 per pound, but will be cheaper later as

production is increased.
•*
11

Polvthvlene (conventional type)

Conventional polyethylene is produced by processes that

yield' a relatively low density material ( 0.92 g/cc) with a degree of crystallinity of 60-65 percent and only moderate

heat resistance. Although possessing excellent moisture and

chemical resistance, and low in cost, its maximum service

temperature of 200°F is inadequate for the more severe

temperature conditions that might be encountered in underground heat distribution systems.

Deterioration of polyethylene by sunlight (ultraviolet)

occurs in only a few months outdoor exposure in the unstabilized

material: however, by incorporation of suitable carbon-black

pigment

s

' 1 ° ? 19 )

9 deterioration of polyethylene can be

prevented for many years. Stabilization of polyethylene

against heat is accomplished by incorporation of an antioxidant.

Most commercially available adhesives for polyethylene

have low bond strength^O). Surface treatment with chromic

acid improves its ability to be bonded with an adhesive.

Polyethylene possesses excellent heat-sealing characteristics,

however, and this is the preferred method of bonding it, both

for ease and economy. Polyethyle

techniques to be discussed later^

Polyethylene (high-densitv type)

le . is

11 ) also easily weiaea, oy

The new high-density polye thylenes that have come into

prominence recently are superior to conventional polyethylene

in many physical and chemical propertie s

(

22 ?

)

0 They are

characterized by improved heat resistance, greater rigidity

and tensile strength, increased puncture resistance and low

temperature toughness, greater resistance to environments:!-

cracking, and decreased permeability to gases and chemibals.

Electrical properties remain excellent. Transparency is

somewhat reduced. The improved properties of high-density

polyethylene s may be attributed to their relatively high

degree of crystallinity (about 80 percent) compared to that

of conventional polyethylene (60-65 percent).

High-density polyethylene s are produced by new low

pressure processe s

v

24 j m.ade possible by the use of special

catalysts developed by the Phillips Petroleum Company in

the United States and by Dr. K. "Ziegler in Germany. Both

the Phillips and the Ziegler processes yield similar high-

12

density materials. The Ziegler process and properties of the

Ziegler polyethylene are described in a number of articles

in the literature (25,26, 27, 2o, 29 ,30,31) . Production of

Ziegler-type polyethylene has been undertaken by a number of

licensed manufacturers, including Farbwerke Hoechst producing

"Hostalen" (32

)

? Ruhrchemie making "RGH Polyethylene "U33 jB^)

? Koppers Company with "Super Dylan"(35) ? and Hercules Powder

Company with "Hi-f ax" (36; . The Phillips type, designated

Marlex, is discussed in a bulletin(37) and in a paper(3o).

Both Phillips and Ziegler types are discussed in other

article

s

( 22 , nh

)

# a number of large manufacturers in the

United States have obtained -Ziegler license s (39

)

? including

Du Pont, Bakelite, Monsanto, Goodrich, Gulf, Dow, and others,

so that a tremendous production of high-density polyethylene

can be expected in the near future.

Another type^of high-density polyethylene ("Alkathene HD")

is being made by I.C.I. by a modification of I.CJ.'s

conventional high-pressure process in the same equipment and

plants that make conventional high pressure polyethylene (^0).

The properties of this material lie between the Phillips and

Ziegler low pressure types and the conventional high pressure

type, but are much closer to the new low pressure (highdensity) types.

High-density polyethylene is serviceable at temperatures

up to 250°F or even Higher. It has the excellent heat-dealing

qualities of conventional polyethylene although the heat-seal

temperature is about 50°F higher.

The excellent combination of properties possessed by

high density polyethylene, including water resistance,

elevated temperature resistance, ease of application, and

low cost, make this material worthy of prime consideration

for purposes of the present application in. under ground heat

distribution systems.

Polypropylene ~

The polypropylenes are a new family of thermoplastics

with unique and superior properties, beyond that of the highdensity polyethylenes( 1+1

?

tf‘2, 1+3y . Polypropylene has exceptional

heat resistance; it may be used up to 300°F. Its melting

range is from 32,5 to 3^-0o F. It can be fabricated by conventional techniques and yields a clear film heat-sealable with

conventional equipment.

- 13

Although the polypropylene s promise to be reasonably

priced when production increases, their present cost is high

and quantities are limited. They are of great interest for

the future but not yet ready for wide use in underground

heat distribution systems.

Polycarbonate Resin (Lexan)

Polycarbonate resin is a new, tough, heat-resistant,

dimensionally stable thermoplastic material^** ? ^5) . It

has been named "Lexan" by General Electric Company who

developed it. Among its outstanding properties are low

water absorption and heat resistance to 300°F. It can be

cast or extruded into films or sheets that are heat-sealable,

or which can be welded with a hot air torch. Solvent

cementing is also feasible.

The only adverse physical property of polycarbonate for

purposes of the present application is its poor alkali

resistance which might lead to attack and decomposition in

some soil environments.

The present cost of polycarbonate is $2.50 per pound

in pilot quantities.

Polyvinyl Chloride

Among the older plastic materials, polyvinyl chloride

has been widely Used as a vapor barrier material, even in

applications requiring elevated temperature resistance. Its

maximum service temperature of 200°F is inadequate, however,

for reliable performance under conditions that might be met

with in underground heat distribution systems. Although

resistant to oxidation, it is very susceptible to deterioration

by heat and light unless stabilized (^6, M-y, ko

)

. fortunately,

a number of effective stabilizers are available (^9 ) . Among

the most effective heat stabilizers are heavy metal soaps,

which react with the hydrogen chloride liberated during

degradation and form harmless chlorides. The hydrogen

chloride, if not removed, catalyzes further decomposition.

Highly promising new stabilizer s ( 90) will soon be available.

Polyvinyl chloride has excellent resistance to moisture

and to chemicals that might be present in an underground

environment. Its fungal resistance is good (51* 52). Rodentrepellent chemicals for vinyl chloride plastic ( 53) are

available if required for use in areas where infestation of

these pests might be a problem.

- lb -

Polyvinyl chloride film can be bonded with special

purpose cements (5*+) or by heat-sealing. A rapid method for

bonding lengths of vinyl chloride plastic tubing in the field

by the use of quick-fit couplings and a small torch has been

successfully applied (55); it will be further discussed in

the section on bonding methods.

Although polyvinyl chloride, like conventional polyethylene, has in the past been one of the best (but not completely adequate) materials available for the present application, both polyvinyl chloride and conventional polyethylene

can now be supplanted with the new high-density polyethylene

which promises to fulfill all the requirements for a vapor

barrier in underground heat distribution systems.

Polvvinvlidene Chloride-Vinyl Chloride Copolymer (Saran)

Saran is a tough, moisture-resistant material with

generally good aging resistance and good resistance to fungi

and bacteria (2) 0 Like polyvinyl chloride it has limited

elevated temperature resistance. Its heat-sealing properties

are excellent.

It is a less desirable material than polyvinyl chloride

for use in underground heat distribution systems because of

its higher cost and its susceptibility to attack by ammonium

hydroxide which may be generated in certain soil environments.

Polvchlorotrif luoroethvlene (Kel-F

)

This material possesses properties that exceed the

requirements of the present application (56). Since it is

high in cost, and adequate cheaper materials are now available,

the use of polychlorotr if luor oethylene in underground heat

distribution systems is neither necessary nor desirable.

Polvtetraf luor oethylene (Teflon)

This is an expensive premium material which far exceeds

most of the requirements for use in underground heat distribution systems. It is mentioned here because of its uniquely

superior chemical and physical properties (57, 58, 59) rather

than for its practical usefulness in the present application.

Although pressure-sensitive Teflon tape has been produced,

the problems of bonding the material are formidable. Teflon

is not heat-sealable.

- 15 -

Polyamide (Nylon)

Nylon is 'tough, abrasion-resistant, fungus-resistant, and

resistant to strong alkali and most solvents, but it has a rather high water absorption and poor resistance to acids (2,

58,59)* its maximum service temperature depends on the type

of polyamide. It tends to oxidize at elevated temperatures.

The poor water and poor acid resistance of nylon make it unsuitable for the present application.

Polystyrene

Polystyrene, whiie resistant to water and soil chemicals,

is relatively more brittle than other thermoplastics and

possesses only limited resistance to elevated temperatures

(60). This latter limitation alone makes it an unsuitable

material for the present application.

Acrvlonitrile-S tvrene Copolymer

This material, while possessing many useful properties,

fails to quality for use in underground heat distribution

systems because of its relatively poor resistance to elevated

temperatures (57).

Polvmethvl Methacrylate

Polymethyl methacrylate film, like polystyrene, is relatively more brittle than most other thermoplastic film materials. It has superior resistance to outdoor weathering and

is biologically very stable, being reportedly unattacked by

fungi, bacteria, or insects (2). It has good resistance to

water and to acids, bases and salts.

The usefulness of polymethyl methacrylate film in the

present application is limited chiefly by its relatively

poor physical strength at elevated temperatures.

Laminated Films

Many of the plastic film materials that have been discussed can be bonded to other plastics, fabrics, or metal

foils to give a laminated film that possesses the desirable

properties of both materials. The bonding can be accomplished

with suitable adhesives or by heat and pressure 0 Thus, Mylar

can be bonded to polyethylene or to Saran to combine the heat

resistance and strength of the former with the heat- sealable

16

qualities of the latter. Or, polyethylene can be bonded to

aluminum foil to increase the heat resistance of the former

and the strength of the latter. A mirror of aluminum, deposited on a plastic film, could provide valuable heat reflective properties in some applications.

A laminate of high-density polyethylene and aluminum foil

might well provide the ultimate in a moisture-proof, heatresistant film for application in underground heat distribution systems.

Sources of Supply for Plastic Film

For information on manufacturers of plastic film materials,

and on trade names of such materials, it is recommended that

standard reference works, such as the Modern Plastics

Encyclopedia ( 57 ) be consulted. The magnitude of such a list

is beyond the scope of this report.

TEST METHODS

The more important test methods generally employed to

evaluate the properties of plastic films will be briefly

described in the following sections. For a detailed description of a given method, the bibliographic reference

should be consulted.

In many instances a standard A.S.T.M. test is available.

In other cases a Federal test method or a satisfactory commercial method is employed. For some properties, no standard

procedure is available; for example, the heat-seal temperature

is largely the consensus of information accumulated by manufacturers and fabricators concerned with this process.

Water Vapor Permeability

This property is usually measured by the procedures of

ASTM Method D 697 (6l). Two procedures are specified

s

Method A. Desiccant Method : The desiccant (e„g„,

anhydrous magnesium perchlorate) is placed inside a test

dish of specified size and shape. The specimen is placed

over the opening of the dish and centered on the supporting

ring or flange. A circular metal template with a beveled

edge to which petrolatum has been applied is centered over the

- 17 -

specimen and dish opening. Molten wax, consisting of equal

parts of beeswax and rosin, is flowed into the annular space

around the beveled edge to seal the system. The template is

removed as soon as the wax has cooled and solidified. The

assembled test dish is weighed on an analytical balance and

placed in an inverted position, so that the desiccant is in

direct contact with the inner face of the specimen, on the

test rack in a chamber . maintained at constant temperature and

relative humidity ( 73

»

1+°F , 50$ R.H.). A fan is used to maintain a current of air flowing over the exposed face of the

test specimen. Weighings are made at intervals of several

hours until a constant rate of gain is attained. Plotting

weight increase against time gives a curve whose slope is a measure of the water vapor permeability.

Method B 0 Water Method ; This differs from the desiccant

method in that water is used inside the dish, which requires

that the test be carried out with the dish in an upright

position. Since there will be a layer of air between the

surface of the water and the under side of the specimen,

through which water vapor will diffuse at an undetermined

rate, it is necessary to standardize on such factors as the

ratio of water surface area to test area (should be 1:1) and

the distance between the water surface and the under side of

the film (should be 25 mm). The rest of the procedure is the

same as for Method A.

Water Absorption

This property is measured in accordance with ASTM Method

D 570 (62). Specimens 1- x 3-inches in size are conditioned

by drying in an oven for 24 hours at 50°C, cooling in a desiccator, and weighing. The conditioned specimens are completely

immersed in distilled water maintained at 23°C (73.4°F). At

the end of 24 hours, the specimens are removed one at a time,

all surface water wiped off with a dry cloth, and weighed

immediately. If the specimen is l/l6th inch or less in

thickness, it should be put into a weighing bottle immediately

after wiping and weighed in the bottle.

When materials are known or suspected to contain appreciable amounts of water-soluble ingredients, they should be

reconditioned again for 24 hours at 50°C and weighed. If this

weight is lower than the original conditioned weight, the

- 18 -

difference is considered to be water-soluble matter lost during

immersion and is added to the weight increase on immersion when

computing the total water absorption value.

Tensile Strength and Elongation

Measurement of these properties of plastic films is usually

made by ASTM Method D 882, Method B (63), in which a constant

rate of jaw or grip separation is employed. The test specimen

is a strip of uniform width and thickness and 4 inches or more

in length. The width of specimen should be chosen to allow

failure to occur well within the load capacity of the machine.

A rate of cross-head motion of 2 inches per minute is used for

film with an ultimate elongation less than 100 percent, and a

rate of 20 inches per minute for film with an ultimate elongation of 100 percent or more. Thickness and width are measured

at several points and the minimum cross-section is recorded.

Tensile strength is calculated by dividing the maximum load

in pounds by the original minimum cross-sectional area in

square inches.

While the specimen is being elongated, the displacement

of initial gage marks on the specimen is followed with

divider points. The percentage elongation is calculated

by dividing the elongation at the moment of rupture by the

original gage length and multiplying by 100.

Bursting Strength

Bursting strength as given in Table I was determined

with the Mullen Bursting Strength Tester according to the

procedure of ASTM Method D 774 (64). In this test, the

specimen is clamped over a circular orifice beneath which

is an extensible membrane that expands into the film specimen under steadily increasing hydraulic pressure applied to

the system. The specimen is stretched into what approaches

a hemispherical shape. The pressure in the system at the

instant of rupture is indicated by a maximum-reading dial

gage; this pressure is taken as a measure of the bursting

strength of the specimen and is reported as Mullen ''points"

rather than psi, because the true bursting strength of the

specimen involves other factors (for example, the distensibility of the specimen) in addition to the pressure in the

system (65).
I

r

*‘
19 -

Tearing Strength

Two different methods are in general use for measuring the

tear strength of plastic films:

(1) A.S.T.M. Method D 689, or the Elmendorf tear strength

method, determines the average force in grams required to tear

a sheet by measuring the work done in tearing a number of

sheets together through a fixed distance after an initial slit

of specific length has been made in the test specimen with a sharp blade ( 66 ). The testing machine is of the pendulum impulse type with a means for holding the pendulum in a raised

position, a means for releasing it instantaneously, and a means for indicating the maximum arc through which the pendulum

swings when released. The specimen is clamped in a plane perpendicular to the plane of swing of the pendulum. The difference in amount of swing with and without the specimen in the

path of the pendulum provides a measure of the work done in

tearing through it, as computed from the geometry and mass of

the calibrated instrument.

(2) In A.S.T.M. Method D 1004, using a static-weighing

method and a constant rate of grip separation, tear strength

is determined by measuring the maximum load required to tear

through a specially-shaped die-cut specimen, or through a bundle of such specimens, and is expressed as the pull in

pounds per inch of thickness required to tear a single specimen

( 67)0 The specimen has a 90° off-set, rounded on the outer

edge and forming a right angle at the center of the inner

edge, so that a high stress concentration is produced at the

center of the specimen when the load is applied. The tear

strength value is therefore an indication of the notch sensitivity of the material as well as a function of its tensile

strength, elongation, and shear strength. Where bundled

specimens are employed to bring the tearing strength value

within the range of the instrument, the thickness value for

computation purposes shall be the average of the individual

thicknesses of the sheets that make up the bundle, never the

apparent thickness of the bundled specimen.

20

Volume Resistivity

Measurement of the electrical resistance of insulating

materials such as plastics or plastic film, because of the very

high resistance of such materials, is subject to large errors

unless specialized methods are used. Suitable methods are described in A.S.T.Mo D 257 ( 68

)

0 The details of the methods are

too lengthy and complex for treatment here, except to consider

the basic concepts and usefulness of the measurements.

The Volume resistivity of a material is defined by the

A.S.T.M. as the ratio of the potential gradient parallel to

the current in the material, to the current density. In the

metric system, the volume resistivity is numerically equal to

the volume resistance when measured between two electrodes

which cover opposite faces of a centimeter cube of the material. The volume resistance between two electrodes which are

in contact with, or embedded in, a specimen is the ratio of

the d-c voltage applied to the electrodes to that portion of

the current between them that is distributed through the

volume of the specimen.

The volume resistivity of an insulating material, such as

plastic film, can provide an indication of the uniformity of

processing of the material, detect traces of impurities that

might affect the quality of the material, and indicate the

existence of deterioration or foreign matter (e.g., fungal

growth) in the material.

Specific Gravity

The specific gravity of a plastic film is measured by

weighing it in air and when immersed in water. Details of the

method are given in A.S.T.M. D 792 (69). A wire of suitable

length is hung from the pan support of an analytical balance

and tared. The specimen is then attached to the wire so as

to be suspended about an inch above a pan straddle supporting

a beaker, and the weight in air (a) is determined. The specimen, still suspended by the wire, is then immersed (by filling

the beaker) in freshly boiled distilled water at the reference

temperature, and the weight (b) again determined. Finally,

the specimen is removed from the wire and the weight with the

same length of wire immersed in the water is determined. The

21

specific gravity is calculated from the following formula:

Sp 0 Gr 0 = a where c is the loss in weight

a - b - c of the wire on immersion.

Folding Endurance

The procedure for measuring folding endurance with the

Schopper tester is given in A.S.T.M. D 643, Method A (70).

Test specimens are 15 mm in width and 10 cm in length. The ends

of the specimen are gripped by two horizontally opposed clamps

provided with calibrated spring tension which varies during the

folding cycle as a slotted folding blade, through which the

specimen is inserted, folds the specimen while the blade slides

back and forth between creasing rollers. The specimen is folded

at a uniform rate of approximately 120 double folds per minute

until it is severed at the crease. The number of double folds

required to sever the specimen is recorded as the folding endurance . Method B of A.S.T.M. D 643 describes the procedure for use

of the MIT Folding Endurance Tester. Experience (71) with this

test method has indicated that it is not adaptable for testing

all types of plastic films, particularly those of interest in

the present investigation, such as vinyls, polyesters, and polyethylene. Therefore, data by this method have not been reported

herein.

Weathering Resistance

Conditions for the exposure of plastic material to outdoor

weathering are defined in A 0 S.T.M. Method D 1435, wherein are

discussed the method by which the material is to be exposed,

the general procedure to be followed, and the climatological

information to be recorded (72). The method does not cover the

methods of test to be used in evaluating the effects of exposure, except for visual appearance and dimensional changes.

Specimens for exposure are mounted on racks at an angle of

45 degrees to the horizontal and facing true south. Racks

are located at a variety of climatologically different test

site's including temperate, arctic, desert, tropical, salt air,

and industrial locations. The appearance and dimensions of the

22

specimens before weathering and after various periods of exposure are recorded. Other properties of the material, involving destructive tests, can be evaluated by exposing a sufficient number of specimens.

Artificial or accelerated weathering tests, although

they do not provide a direct correlation with natural weathering,

give a very useful indication of the type of outdoor service to

be expected from a given material, and such tests are widely

employed

.

Recommended practice for an accelerated weathering test

using the S-l bulb and a fog chamber is given in A.S.T.M. D 795

(73) 9 and also in Federal Specification L-P-406, Method 6021.

Test specimens are mounted on a modified phonograph turntable

operating at approximately 33 rpm beneath the S-l bulb. Periods

of radiation are followed by periods in a fog chamber. The

radiation and wetting cycles for each 24-hour period are as

follows: 2 hours in the fog box, 2 hours irradiation, 2 hours

in fog box, and 18 hours irradiation. The duration of the test

is usually 240 hours, although any length of time may be specified as circumstances warrant.

An artificial weathering test using fluorescent sunlamps

and a fog chamber is described in A.S.T.M. D 1501 (74). The test

is performed in an enclosure in which a turntable and five

fluorescent sunlamp bulbs are installed, so that the specimens

are three inches below the lamps. The fluorescent lamps employed must have been aged for at least 50 and not more than 1050

hours. The turntable operates at 30 to 40 rpm. Hot air at 55

to 60°C is blown over the specimens at a rate adequate for maintaining them at that same temperature. The fog chamber consists

of a closed, shallow box with a spraying unit and baffle to prevent direct impingement of the spray on the specimens. The

specimens are exposed continuously for 240 hours, unless otherwise specified, by repetition of the following 24-hour schedule:

2 hours fog, 2 hours ultraviolet radiation and hot air, 2 hours fog,

and 18 hours ultraviolet radiation and hot air. A visual

examination of the specimens is made after each step of the

testing procedure. At the end of the test procedure, various

optical and physical tests may be made on the specimens to

evaluate the effects of the weathering process; such as, luminous transmittance, haze, flexural strength, etc.

23 -

Chemical Resistance

The resistance of plastics, including films, to acids,

bases, salts, and other chemicals jjs determined by immersion

in various standard reagents for 7 days at 23°C, or other

specified temperature, as described in A.S.T.M. Method D 5^3

(75) - The length, width, thickness, weight, and appearance

of the specimens before and after the immersion period are

noted. Specimens removed from the various solutions are wiped

with a dry cloth and weighed immediately in a weighing bottle.

The dimensions of the treated specimens are measured immediately

after weighing.

Fungal Resistance

A variety of methods are used to evaluate the fungal

resistance of plastics (6,7,76), including visual, optical, and

electrical methods. The specimen is placed in a warm, humid

environment and inoculated with any of a variety of fungal

cultures. Visual observation of fungal growth is often an

adequate test. In other instances, the microscope can be used

to establish the existence of fungal attack. Measurement of

Insulation resistance is usually one of the most sensitive tests

of fungal attack; fungi, and the moisture associated with them,

can cause an enormous drop in insulation resistance even when

visual indication of attack is completely lacking.

Abrasion Resistance

Information on the abrasion resistance of plastics in film

form is not generally available in the literature. The Taber

Abraser which, despite a number of drawbacks, is widely used

to evaluate abrasion resistance (77), is not suitable for use

on films. Several A.S.T.M. test methods (78,79,80) are available which can give information on abrasion resistance of plastics.

The Abrasive Jet Method (8l) developed at the National

Bureau of Standards, although designed for testing organic

coatings, is well adapted for measuring the abrasion resistance

of plastic films taped or bonded to a metal substrate; in

fact, a film is used as a reference standard in calibrating

the instrument. It gives a measure of abrasion resistance in

24 -

terms of the time required for a jet of fine abrasive particles

to abrade through a unit thickness of film. Although data on

a variety of films has not been obtained with this equipment,

such information could be obtained if desired.

Insect and Rodent Repellents

Test methods for evaluating the efficiency of insecticides

and insect repellents usually involve the use of those test

insects most likely to do damage, and are conducted till death

of all insects is obtained (88;. For insecticides, a sample

of treated material is given to the insect as its exclusive

food, except for tap water. Usually the insects are paralyzed

and die before even trying to eat the material. Repellents

are tested in a 3-compartment box which requires the insects

in a first compartment to walk or land on the treated material

in a second compartment in order to reach food in a third compartment. A good repellent will keep the insects in their

original compartment where they will die of starvation.

Rodenticides and rodent repellents are tested by using

treated material as a partition to separate rats from food

(88). Satisfactory rodenticides or rodent repellents will

prevent even voracious recently-caught field rats from getting

to the food.

A.S.T.M. Committee D-l4 on Adhesives has prepared two

methods that may be used to test plastic films. One is for determining susceptibility to attack by roaches (88a) and the

other by laboratory rats (88b).

Other Test Methods

Other A.S.T.M. test methods, not directly utilized for

the data given in Table I, but of some interest in connection with the properties of plastic films, include a heat

distortion test (82), a method for measuring the tensile and

elongation properties of bulk plastics (83), a method for

determining brittle temperature (84). and several penetration

or puncture resistance tests (85,86,87). Bacteria have also

been known to attack some plasticizers in vinyl plastic films.

A.S.T.M. Committee D-l4 on Adhesives has developed a test

method for determining the effect of bacteria which may be

applicable (87a).

- 25 -

APPLICATION METHODS

In addition to possessing the required physical and chemical

properties, a material for use in underground heat distribution

systems should be capable of being applied by readily available

techniques that can be relied upon to produce a complete and

durable sealing of the system. Plastic films are available in

the form of tapes, sheets, and rolls, in a variety of widths.

Although application techniques will vary with the nature and

form of the material, the general principles involved in applying plastic film materials can be given:

Tape s Plastic tapes for the present application must be of the

pressure-sensitive type. The tape is applied by wrapping it

around the conduit in an overlapping spiral, while maintaining

strong tension to provide the adhe sive -activating pressure.

The bonding efficiency of a pressure-sensitive material depends

on the temperature; therefore, care must be taken to apply the

material within the temperature range recommended by the manufacturer.

A possible serious limitation of pressure-sensitive tapes

for the present application is the difficulty of formulating a pressure-sensitive adhesive that is efficient over the 'entire

temperature range (0 to 220°F) in which it is expected to perform. The existence or non-existence of such a material was

not established during the present survey. Considering the

inherently difficult nature of the problem of formulating a material that must be tacky at 0°F and yet not flow at 220°F,

it is believed that pre ssure- sensitive tapes are not the best

materials for use in underground heat distribution systems.

Adhesive-bonded Sheeting or Film

In the form of discrete sheets or as continuous film from

a roll, flexible plastic vapor barrier material can be applied

around the conduit system and sealed with a thermoplastic

adhesive that bonds overlapping ends of the material. A thermoplastic adhesive is specified because such an adhesive can

closely approximate the properties of the film materials

26 -

under consideration here and is likely to better withstand the

stresses developed during the expansion and contraction that

will occur over the wide operating range of temperature to be

encountered. Such adhesives dry by solvent evaporation,

leaving the solid adhesive in place. The nature of the adhesive

required is determined both by the temperature and other physical

requirements of the application and by the nature of the material to be bonded.

The field of adhesion and adhesives, besides being too

vast in itself for review in the time available for the

present survey, is not directly relevant to the basic

problem of a suitable plastic film. Since a plastic film

with the requisite properties appears to be available, as

mentioned elsewhere in this report, the development of a suitable adhesive should be largely a matter of applying the

same knowledge in a modified form, and is a problem that may

with confidence be entrusted to the experienced adhesive

f ormulator

.

For many of the film materials described in this report,

proven adhesives are already available. A recent article by

Riley ( 89 ) discusses the application techniques involved in

solvent cementing, adhesive bonding, thermal welding, and

mechanical fastening, and also gives tables of specific adhesives for particular applications. A report by Faunce (90)

discusses test procedures and performance criteria for an

adhesive for vinyl chloride plastic and for polyethylene

barrier materials and describes a new neoprene-diisocyanate

type adhesive that has proved effective. Information as to

the suitability of certain adhesives for particular applications and their method of use is readily available from

adhesives manufacturers.

The use of adhesives in the field requires careful surface

preparation and cement application, besides involving fire and

toxicity hazards. Considering the amount of work involved y the

skill required, and the cost of adhesives in general, it is

felt that adhesive-bonding of plastic film for the present

application, while entirely feasible, is neither the easiest

nor the most economical way of accomplishing the task. Instead, most serious consideration should be given to one of

the several methods of heat-sealing plastic film which are

described in the next section.
*
27 -

Heat-sealing Sheet or Film

Of the various methods available for bonding plastic film

for underground heat distribution systems into a sealed system,

the most promising from the viewpoint of economy and ease of

application as well as efficiency of seal are the heat-sealing

techniques. A rapid efficient system may be visualized in

which continuous lengths of plastic sheeting or film are laid

in the conduit trench before laying down the piping (or inserted under the piping if already installed) and then turned

up and sealed in a continuous process with mobile heat-sealing

equipment.

Polyethylene, including the high-density type so promising

for the present application, is among the easiest of materials

to heat-seal. In addition to lending itself to the conventional

heat-sealing techniques, it can be welded using a heated air

torch. The hot gas, produced by gas or electric heating within

the torch, is directed against a round polyethylene filler rod

and the sections to be joined (91). The welding proceeds at

a rate of about 5 inches per minute.

The electronic welding of vinyl film is discussed in (92).

An effective method for bonding lengths of vinyl chloride

plastic pipe in the field, which may be applicable in cases

where discrete sheets, after being sealed lengthwise, must

be joined to other sheets, has been developed (55). In this

method, the end of one length of tube is heated on the inside,

with a small torch, to soften it, and the softened end is then

stretched backwards over a ring previously placed around the

tubing. The end of the other tube is then heated and pulled

over the ringed piece, and a pressure yoke is pulled over the

belled-out portion of the tubing to make a strong, waterproof

seal.

Heat-sealing methods include flame, hot gases, hot wire

(impulse heater), electronic high frequency, electrical (resistance) heating, hot metal band, etc. (59,93,9^)0 In all heatsealing methods, temperature, pressure, dwell time, and cooling

time are all important. A recent study of the dielectric heatsealability of films (95) makes use of an apparatus in "which

the various heat-sealing parameters can be closely controlled

for a systematic study of their effects.

28 -

Of the various heat-sealing methods that are available,

electronic high-frequency heating appears to offer the best

promise for fast, efficient, and relatively economical use in

the present application for sealing film in underground heat

distribution systems. Mobile field equipment for generating

the necessary RF power is available and could be put to effective use in the continuous sealing process envisioned in the

first paragraph of this section.

Heat-sealing is used for bonding thin materials and

welding for bonding thicker sheets. Thus, if it is decided

to use sheeting that is too thick to heat-seal readily,

welding can be used.

SUMMARY

An extensive survey of the literature on plastic film

materials has been made to establish the suitability of such

materials for use as exterior waterproofing membranes in

underground heat distribution systems. Relevant properties

of conventional plastic film materials and of promising new

materials are tabulated and discussed. Test methods commonly

employed for evaluating properties of plastic films are concisely described. Application techniques for plastic film

materials are considered. A selected bibliography is given.

RECOMMENDATIONS

On the basis of the information developed during the

literature survey on plastic films, and after careful study

of the properties of a wide variety of films in relation to

the performance requirements of underground heat distribution

systems, it is recommended that prime consideration for the

present application be given to the new high-density polyethylene materials. These materials have excellent water

and chemical resistance, are serviceable from -105 to 250°F,

possess good strength and toughness, are easily applied and

heat-sealed, and are low in cost.

It is believed that high-density polyethylene film, applied

as continuous sheeting which is turned up around the conduit and

then heat-sealed in a continuous process by mobile sealing equipment, may offer an effective, rapid, and economical means for

waterproofing underground heat distribution systems.

BIBLIOGRAPHY

(1) "Underground heat distribution systems", Building Research

Institute. Washington 25, D c C., Technical Report Ho. 16,

March 195°.

(2) Greathouse, G. A., and Wessel, C. J. , "Deterioration of

Materials", Reinhold Publishing Corporation, New York,

N. Y. , 195^.

(3) Barail, L. C., "Packaging Engineering", Reinhold Publishing Corporation, New York, N. Y. , 195^ •

(4) Modern Packaging 28, 21 6 (1955).

(5) Modern Packaging 2j?, 130 (1952).

(6) Blake, J. T., and Kitchin, D. W. , "Effect of soil microorganisms on rubber insulation", Ind. Eng. Chem. 4l,

1633 (1949).

(7) Blake, J. T., Kitchin, D. W. , and Pratt, 0. S, , Elec.

Eng. 62, 782 (1950).

(8) Leutritz, John, Jr., and Herrmann, D. B. , "The effect of

high humidity and fungi on the insulation resistance of

plastics", ASTM Bull. 1^8, 25 (1946).

(9) Titus, A. C., "Fungus growths and electric apparatus", Gen.

Elec. Rev. 48 (8), 19 (1945).

(10) "Cost table; Papers - Films - Foils", Modern Plastics 35

(5), 104 (Jan. 1958).

(11) Quarterly Price List, Special List, Chem. Eng. News,

April 2, 1956.

(12) Angier Adhesives (Adhesives for Mylar), Division of Interchemical Corporation, Cambridge, Mass.

(13) Lanning, D. D. , "Mylar - a high-strength film", Prod. Eng.,

July 1956.

(14) "Boiled in film", Modern Plastics ^4 (2), 136 (Oct. 1956).

- 30 -

(15) Kelley, M. E», Jr., Roth, S. F., and Bailey, H. R. . "Saran

coated films", Modern Packaging ^0, 151 (June 1957).

(

1

6 ) "A new polyester film", Modern Plastics 331 (7), 94 (March

1958).

(17) "Heat-seal polyester film laminates to wood, metal", Materials in Design Eng. 4Z (5), l4l (May 1958).

(18) Elec. Mfg. 61, 10 (May 1958).

(19) Modern Plastics 33. (2), 100 (Oct. 1955).

( 20 ) Schrader, W. H. , and Bodnar, M. J. , "Bonding of Polyethylene", Samuel Feltman Ammunition Laboratories, Picatinny

Arsenal, Dover, N. J. , Tech. Report 2401, March 1957.

(21) Haim, G. , and Neumann, J. A., "Manual for plastics welding,

Vol. II, Polyethylene " , Industrial Book Co. (Affiliate of

Industrial Publishing Co.), Cleveland, Ohio, 1954.

(22) Neumann, J. A., and Bockhoff, F. J. , Modern Plastics 32

(12), 117 (Aug. 1955).

(23) Raff, R. A. V., and Allison, J. B. , "High Polymers, Vol. XI,

Polyethylene", Inter science Publishers, Inc., New York,

N. Y. , 1956. (Especially Chapter VI).

(24) Campbell, J. B. , "Rigid heat-resistant polyethylene s"

,

Materials & Methods 42 (1), 88 (July 1955).

(25) Ziegler, K. , Kunstoffe 4£, 506 (1955).

(26) Ziegler, K. , Holzkamp, E., Breil, H„ , and Martin, H.

,

Angew. Chem. 6/7 , 426 (1955).

(27) Ibid. , 62, 5^1 (1955).

(28) Grams, E., and Gaube , E., Angew. Chem. 6£ 9 548 (1955).

(29) Schultz, G. , and Mehnert, K. , Kunstoffe 43_, 4l0 (1955).

(30) Krause, A., Chemiker-Ztg. 657 (1955).

- 31 -

(31) Sollenberger , G. H. , Plastics Industry 12 (10), 16 (1 955).

( 32 ) Farbwerke Hoechst, A.-G., Preliminary Bulletin "Hostalen"

April 1955.

(33) Ruhrchemie, A.-G., RCH Hochmolekulare Polyethylene, Bulletin,

1955.

(34) British Plastics, 28, 440 (1955).

(35) Koppers Company, Inc., Bulletin C-5-216, ’’Super Dylan",

1955.

(36) Hercules Powder Company, "Hi-fax", Bulletin, 1956.

(37) Phillips Petroleum Company, "Marlex-50", Bulletin, 1955.

(38) Jones, R. V., and Boeke, P. J. , paper presented at the

129th meeting of the American Chemical Society, Dallas,

Texas, April 8-13, 1956.

(39) Modern Plastics 21 (l), 85 (Sept. 1955).

(40) Chem. Eng. News ^4, 1470 (1956).

(41) Properties of polypropylene", Materials in Design Eng.

46, 164 (Dec. 1957).

(42) Crespi, C., "Propylene - a promising new plastic", Materials

in Design Eng. 42 (1), 110 (Jan. 1958).

(43) Ottolenghi, M. , and Crespi, C., "What's with polypropylene?",

Modern Plastics 25. (7), 89 (March 1958).

(44) Goldblum, K. B. , and Thompson, R. J. , "New plastic gains on

metals' properties", Gen. Elec. Rev. 60 (6), l4 (1957).

(45) Thompson, R. J. , and Goldblum, K. B 0 , "Polycarbonate resin",

Modern Plastics 2^ (8), 85 (April 1958).

(46) Fox, V. W., Hendricks, J. G. , and Ratti, H. J. , "Degradation and stabilization of polyvinyl chloride", Ind . Eng.

Chem. 4l , 1774 (1949).

- 32 -

(47) Scarbrough, A. L. , Kellner, W. L. , and Rizzo, P. W. , "The

role of hydrogen chloride in polyvinyl chloride degradation", Modern Plastics 22 (9), 111 (May 1952).

(48) Chevassus, F., "Natural and accelerated weathering tests

and their influence on vinyl compounds", Ind. Plastiques

Mod. (Paris) 2 ( 7 ), 38 (1957).

(49) Lally, R. E., and Hansen, F. R. , "Stabilization of polyvinyl chloride", Modern Plastics 22 (4), 111 (1949).

(50) "Epoxy plasticizer s-stabilizers" , Ind. Eng. Chem. 50 « 86l (June 1958).

(51) Berk, S. , "Fungus tests on polyvinyl chloride films plasticized with three plasticizers", U. S. Frankford Arsenal

Philadelphia, Pa. Pittman-Dunn Laboratory Report R-889,

Jan. 1949.

(52) McKinley, R. B. , and Seaberg, C. H. , "Moisture vs rubber

insulation", Gen. Elec. Rev. 21 (^) 9 58 (1952).

(53) Modern Packaging 22, 130 (1952).

(54) Schwartz Chemical Co., "Plastic pipe cement", Heating,

Piping and Air-conditioning 22 (4), 199 (April 1958).

(55) "Portable ditch", Modern Plastics 2k (3), HO (Nov. 1958)

(58)

McKnight, F. , "Kel-F helps beat problems of electronics

industries", Plastics Ind. 2 (8), 13 (1951).

(57) "Modern Plastics Encyclopedia", Plastics Catalogue Corp.

,

New York, N. Y. , 1957.

(58) E. I. du Pont de Nemours and Co., Polychemicals Dept.,

Bulletin, 1957.

(59) Shack, W. , Editor, "A manual of plastics and resins",

Chemical Publishing Co. , Inc. , Brooklyn, N. Y. , 1950.

(60) Dow Chemical Company, Plastics Bulletin, 1957-

- 33

(61) ASTM Method D 697, now superseded by ASTM Method E 96 , "Test for measuring water vapor transmission of materials

in sheet form", Part 6, 1955 Book of ASTM Standards, p.

1655.

(62) ASTM Method D 570, "Test for water absorption of plastics",

Part 6, 1957 Supplement to Book of ASTM Standards, p. 57.

(63) ASTM Method D882, "Test for tensile properties of thin

plastic sheets and films", Part 6, 1957 Supplement to Book

of ASTM Standards, p. 412.

( 64 ) ASTM Method D 774, "Test for bursting strength of paper",

Part 7, 1955 Book of ASTM Standards, p. 914.

(65) "Bursting strength of doped fabrics", Federal Specification

TT-P-l4lb, Method 629.1, June 26, 1952.

(66) ASTM Method D 689 , "Test for internal tearing resistance of

paper", Part 7, 1955 Book of ASTM Standards, p. 886.

( 67 ) ASTM Method D 1004, "Test for tear resistance of plastic

film and sheeting", Part 6, 1955 Book of ASTM Standards,

p. 204.

(68) ASTM Method D 257, "Tests for electrical resistance of

insulating materials", Part 6, 1957 Supplement to Book of

ASTM Standards, p. 97.

( 69 ) ASTM Method D 792, "Tests for specific gravity of plastics",

Part 6, 1955 Book of ASTM Standards, p. 396.

(70) ASTM Method D 643, "Test for folding endurance of paper",

Part 7, 1955 Book of ASTM Standards, p. 859.

(71) Slone, M 0 C., and Reinhart, F. W. , "Properties of plastics

films", Modern Plastics jLIL? 203 (tune 1954).

(72) ASTM Method D 1435, "Recommended practice for outdoor

weathering of plastics" , Part 6, 1956 Supplement to Book

of ASTM Standards, p. 64.

(73) ASTM Method D 795, "Recommended practice for accelerated

weathering of plastics using S-l bulb and fog chamber",

Part 6, 1955 Book of ASTM Standards, p. 365.

- 34 -

(74) ASTM Method D 1501, "Recommended practice for resistance of

plastics to artificial weathering using fluorescent sunlamp

and a fog chamber", Part 6, 1957 Supplement to Book of ASTM

Standards, p. 6l.

(75) ASTM Method D 543, "Test for resistance of plastics to

chemical reagents", Part 6, 1955 Book of ASTM Standards,

p. 349.

( 76 ) Harvey, J, V. , "Testing the fungal resistance of plastic

coated fabrics and plastic films", U. S. Quartermaster

Depot, Philadelphia, Pa., Microbiology Series Report 13 , April 1949.

(77) ASTM Method D 1044, "Test for resistance of transparent

plastics to surface abrasion", Part 6, 1955 Book of ASTM

Standards, p. 232 .

( 78 ) ASTM Method D 673, "Test for mar resistance of plastics",

Part 6, 1955 Book of ASTM Standards, p. 251.

(79) ASTM Method D 1242, "Tests for resistance to abrasion of

plastic materials", Part 6, 1955 Book of ASTM Standards,

p. 235.

(80) ASTM- Method D 1300 , "Tests for laminated thermosetting

decorative sheets", Part 6, 1955 Book of ASTM Standards,

p. 119.

(81) Roberts, A. G. , Pizer, R. S. , and Crouse, W. A., "Abrasive

Jet Method for measuring abrasion resistance of organic

coatings", ASTM Bulletin No. 208, Sept. 1955, p. 36.

(82) ASTM Method D 648, "Test for heat distortion temperature

of plastics", Part 6, 1955 Book of ASTM Standards, p. 296 .

( 83 ) ASTM Method D 638 , "Test for tensile properties of plastics",

Part 6, 1957 Supplement to Book of ASTM Standards, p. 27.

(84) ASTM Method B 746, "Test for brittleness temperature of

plastics and elastomers by impact", Part 6, 1957 Supplement to Book of ASTM Standards, p. 18.

(85) ASTM Method D 781 , "Test for puncture and stiffness of

paperboard, corrugated and solid fiberboard", Part 7,

1955 Book of ASTM Standards, p. 933.

- 35 -

(86) ASTM Method D 876 , "Methods of testing nonrigid polyvinyl

tubing", Part 6, 1955 Book of ASTM Standards, p. 598.

( 87 ) ASTM Method D 1117, "Methods of testing nonvoven fabrics",

Part 7, 1957 Supplement to Book of ASTM Standards, p. l48„

( 87a) ASTM Method D 1174, "Test for effect of bacterial contamination on permanence of adhesive preparations and adhesive

bonds", 1955 Book of ASTM Standards, p. 1148.

(88) Barail, L. C., "Packaging Engineering", Reinhold Publishing Corp. , New York, N. Y. , 1954.

(88a) ASTM Method D 1382, "Test for susceptibility of dry adhesive films to attack by roaches", Part 7, 1955 Book

of ASTM Standards, p. 1213.

(88b) ASTM Method D 1383, "Test for susceptibility of dry adhesive films to attack by laboratory rats", Part 7,

1955 Book of ASTM Standards, p. 1211.

( 89 ) Riley, M. W. , "Joining and fastening plastics", Materials

in Design Eng. 42, 129 (Jan. 1958).

(90) Faunce , R. D. , "Establishing test procedures for an

adhesive for barrier materials", Reynolds Metals Company

Report to Picatinny Arsenal, Dover, N. J. , Samuel Feltman

Ammunition Laboratories, Ordnance Project No. TB4-621D,

Nov. 1954.

(91) Same as reference 21.

(92) "Hot subjects heat- sealing" , Modern Plastics (8),

85 (April 1958).

(93) Modern Packaging Encyclopedia, Packaging Catalogue Corp.,

New York, N. Y. , 1957, p. 496.

(94) Farkas, R. D. , "Electronic Heat-sealing", Modern Plastics

31 (7), 109 (March 1958).

(95) Addis, G. I., Rosenthal, L. A., and Flowers, E., "Dielectric

heat-sealability of films", Plastics Technology 3., 542

(June 1958).

- 36 -

( 96 ) B. F. Goodrich Chemical Co., Geon Division, Bulletin, 1957.

(97) Rohm and Haas Co., Plexiglas Bulletin, 1957c

(98) "Technical data on plastics", Manufacturing Chemists'

Association, Inc., Washington, D. C. , February 1958.

(99) ASTM Method D 79*+, "Recommended practice for determining

permanent effect of heat on plastics", Part 6, 1955 Book

of ASTM Standards, p. 373«

(100) "Flexible moisture-vapor barrier sheet", Air Force-Naval

Aeronautics Material Specification AN-B-20.

(101) "Barrier material; water vapor-proof, flexible", Military

Specification MIL-B-131b.

(102) "Vinyl lining prevent? water seepage", Modern Plastics 33 « 180 (July 1956).

(103) Simonds, H. R. , Weith, A. J. , and Bigelow, M. H. , "Handbook of plastics", D. Van Nostrand Co., Inc., New York,

N. Y. , 19^9.

(104) Seymour, R. B. , and Steiner, R. H., "Plastics for corrosion

resistant applications", Reinhold Publishing Corp. , New

York, N. Y. , 1955.

(105) "Technical data on plastics", Plastic Material Manufacturers

Association, Washington, D. C. , 195*+.

(106) Lever, A. E., and Rhys, J. , "The properties and testing .of

plastic materials", Chemical Publishing Co., Inc., New York,

N. Y. , 1958.

(107) Kinney, G. F. , "Engineering properties -and applications of

plastics", John Wiley & Sons, Inc., New York, N. Y. , 1957.

(108) Sasso, J. , "Plastics handbook for product engineers",

McGraw-Hill Book Co. , New York, N. Y. , 19*+6.

(109) "Plastics Engineering Handbook of the Society of the Plastics

Industry, Inc., Reinhold Publishing Corp., New York, N. Y.

,

1954.

- 37 -

(110) Barail, L. C. , "Biology of plastics, SPE Journal (1),

l4 (Jan. 19531.

(111) Nelson, A. I., Hu, K. H. , and Steinberg, M 0 P. , "Heat

processible ' f ood films", Modern Packaging, June 1956,

page 173.

(112) McGrew, F. C., "The polyolefin plastics field - present

technical status", Modern Plastics 2J1 (7), 125~ (March

1958).

(113) "Plastics for building", Building Research Station

Digest No. 103 (Oct. 1957).

(114) "Properties of plastic films", Materials in Design Eng.

46, 149 (Dec. 1957).

(115) Ball, W. H. , "Application of insulation and vapor barriers",

National Research Council, Division of Building Research,

Building Note No. 24: Ottawa, 1956 (The Council).

(116) "Plastic coatings for buried pipe", Corrosion Technology

1, 179 (June 1958).

- 38 -

TABLE I. PROPERTIES OF PLASTIC FILMSa

Property

A.S.T.M. b ’ h

Test Method

Polyethylene

Terephthalate

(Mylar

)

WATER RESISTANCE

Water vapor permeability0 D 697

Water absorption, 24 hr. , l D 570

0 . 05- 0.15

<0.5

TEMPERATURE RESISTANCE

Flow temp. (melt, pt.), °F

Maximum service temp. , °F

Minimum service temp. , °F

Heat seal temperature, °F

RESISTANCE TO SOIL CONDITIONS

Acid s Base s S alts

Fungi and bacteria

Rodents and insects0

WEATHERING RESISTANCE

Resistance to oxygen plus

ultraviolet radiation

STRENGTH

Tensile strength, psi

Elongation, %

Bursting strength (Mullen) 6

Folding endurance

D 543

M

II

D 1435 (outdoor)

D 795 (S-l bulb)

D 1501 (fluorescent)

fD 882,

(.Method B

D 774

D 643, Method A^

482-490

300

-80

490 (coated}

Good

Good

Good

Inert

Fair

17000-24000

35-110

45-60

20000

TOUGHNESS

Abrasion resistance

Puncture resistance

Tearing strength, grams D 689 b 10-27

"

"

, lb/in. D 1004

j

650-1740

ELECTRICAL RESISTIVITY

Volume resistivity, ohm-cm. D 257 lO 1 ^ SPECIFIC GRAVITY D 792 1 . 38- 1.39

COST 1

' Per pound, dollars 2.25

Yield, sq. in. per lb. 20000

(1-mil thick film)

Per 1000 sq. in. , dollars 0.112

(continued on page 2)

- 39 -

TABLE I. (continued) - page 2

Property*

(abbrev. ) Polyethylene

(conventional

)

Polyethylene

(high-densitv) PolvDronvlene

WATER

Perm.

Absorp.

0.04-0.08

0- 0.8

0.02

TEMP.

Flow 230 265-300 325-340

Max. 200 250-275 300

Min. -70 -105 to -190 <44

Seal 200-375 250-400

SOIL

Acid Excellent Excellent Excellent

Base Excellent Excellent Excellent

Salt Excellent Excellent Excellent

Fungi Unaffected Unaffected Unaffected

Ttodents

WEATHER

Oxygen

+ UV

Good if

stabilized

Appears good Probably good

STRENGTH

Tensile 1100-3500 2500-6000 3900-5700

Elong.

Burst

Fold

50-800

48

Very high

10-1300 500-750

TOUGHNESS

Abrasion

Puncture

Tear, g

Excellent

60-200

"

, lb/in. 65-575 600-1300 * 840-1000

ELEC. RESISTVol. resist. >io^5 ^lO 1 5 7IO16

SPEC. GRAY. 0.92 0.93-0.96 0.90-0.91

COST

Per lb. 0.53 About % Promises to

Yield 30000 higher than reasonable

1000 sq. in. 0.018 conventional

*See first page of table for full designation,.

(continued on page 3 )

TABLE I. (continued) - page 3

Property*

(abbrev.

)

Polycarbonate k- (Lexan)

Polyvinyl

Chloride

Vinylidene

Chloride - Vinyl

Chloride Copolyme:

(Saran;

WATER

Perm. 3xl0 _o 0.35-2.0 0.01-0.03

Absorp. 0.3 Nil Nil

TEMP.

Flow 514 290-310

Max. >300 200 200

Min. -135 -50 -50

Seal 250-350 275-320

SOIL

Acid Fair Excellent Excellent

Base Poor Excellent Excellent

Salt Fair Excellent Excellent

Fungi Good Good

Rodents

WEATHER

Oxygen

+UV

Appears

good

Good Very good

STRENGTH

Tensile 9000-10500 1400-5600 1800-15000

Elong. 60-100 150-500 5-250

Burst 20-40 35

F old Good >500,000

T OUGHNESS

Abrasion

Puncture

Excellent Very good

10- >100

Tear, g

"

, lb/in.

60-1400

110-490

80-465

ELEC. RESIST.

Vol. Resist. 2xl0lb 10 12 -1014 1013

SPEC. GRAY. 1.20 1.23-1.29 1.68

COST

Per lb. 2.50 in pilot 0.87 1. 04

Yield quantitie s 21500 16300

1000 sq. in. 0. 040 0.064

*See first page of table for full designation,

(continued on page 4)

- 4l -

TABLE I. (continued) - page 4

Property*

(abbrev.

)

Polychlorotrif luoroe thylene

(Kel-F

)

Polytetraf luoroe thylene

(Teflon)

Polyamide

(Nylon)

WATER

Perm.

Absorp.

0.00

0.00

0.00

0.00

0.3-1.

8

1 . 0 - 1.

5

TEMP.

Flow

Max.

Min.

Se al

420

390

-80

415-4^0

500

-200

180-350

-60

SOIL

Acid

Base

Salt

Fungi

Rodents

Excellent

Excellent

Excellent

Good

Excellent

Excellent

Excellent

Good

Poor

Excellent

Fair to Good

Good

WEATHER

Oxygen

HJV

Excellent Excellent Good

STRENGTH

Tensile

Elong.

Burst

Fold

6300-6600

90-200

42 (2 mils)

1500-3500

100-300

9000

Orients

TOUGHNESS

Abrasion

Puncture

Tear, g

"

, lb/in.

200-350 10-100

ELEC. RESIST.

Vol. resist. 10l8 lO1 ? 5xl018

SPEC. GRAV. 2,1 2. 1-2.

2

1.1

COST

Per lb.

Yield

1000 sq. in.

12000

10.00

12800

0.78

1.43

24000

0.060

*See first page of table for full designation.

(continued on page 5)

- 42 -

Property*

(abbrev.

)

TABLE I. (continued) - page 5

Acrylonitrile - Polystyrene Styrene ConolvmerPolymethyl

Methacrylate

WATER

Perm. 0.5-0.

7

0.4-0 .

5

0.5

Absorp. Nil 0.3-0.

4

TEMP.

Flow 220-250 255-305

Max. 175-200 185 155-190

Min. -50 to -70 -60

Seal 220-300

SOIL

Acid Good Good Good

Base Excellent Excellent Good

Salt Very good Very good Good

Fungi Good Good

Rodents

WEATHER

Oxygen Good Excellent Excellent

+-UV

STRENGTH

Tensile 7100-12100 10000-15000 8200-8800

Elong. 3-10 4-12

Burst

Hold

TOUGHNESS

Abrasion

Puncture

"

, lb/in. 270-495 340-380

ELEC. RESIST.

Vol. resist. 101 /-10l9 >10l4

SPEC. GRAY. 1.05-1.08 1.18-1.19

COST

Per lb. 0.35 0.55

Yield 26100 25400 23400

1000 sq. in. 0.013 0.023

*See first page of table for full designation.

(continued on page 6)

FOOTNOTES:

- ^3 - TABLE I. (concluded) - page 6

aSources of information are indicated by the following references

to the bibliography: (2,10,13,22,24,34,39,42,43,57,58,59,60,71,

89,93,96,97,98).

^Unless otherwise indicated.

cExpressed in grams per 24 hours per square meter per millimeter

thickness at a pressure differential of 1 centimeter of mercury

(g/24hr/m2/mm/cm Hg).

^Specific information on individual materials not available. See

text for a general discussion of the problem.

eExpressed in Mullen Points, for a 1-mil thick film.

fCost figures are the latest conveniently available at time of

survey, and usually are as of January 1958. In view of changing

costs, especially for newer materials, current manufacturers’

price lists should be consulted.

^Tests made with Schopper Bending Endurance Tester, using 1-mil

thick film unless otherwise noted.

h-Other A.S.T.M. test methods, of interest but not utilized directly

for the data given here, are discussed in the text and referred

to in the bibliography.

^Elmendorf test; gives pull required to continue tear of 1-mil

thick film after starting.

^SPI-ASTM static weighing method; yields pounds of force required

to tear through a 1-inch thick film.

^Properties are for the molded resin; data for films not available

but should be similar <>

*"Water permeability of polycarbonate resin is expressed in

g/cm/hr/cm^/mm Hg. (cf

.

, footnote "c").

USC 0MM- NBS -DC
.
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