Polymeric stabilizers for polyvinyl chloride resin

A polyvinyl chloride composition having superior processing and thermal stability properties is prepared by blending with the polyvinyl chloride a copolymer of an .alpha.-olefin and an unsaturated epoxy monomer, or a terpolymer of an .alpha.-olefin, an unsaturated epoxy monomer and an epoxy-free monomer, such as an acrylate ester.

BACKGROUND OF THE INVENTION 
Polyvinyl chloride (PVC) is presently used in myriad useful applications; 
some such applications involve the introduction of hot substances into 
containers molded from a PVC composition. Conventional PVC compositions 
contain additives such as liquid epoxy type stabilizers (e.g. epoxidized 
soybean oil). These stabilizers, when blended into the PVC resin, have a 
tendency to reduce the glass transition temperature (Tg) of the PVC 
compound; thus decreasing the softening temperature of the processed PVC 
product. This decrease in softening temperature leads to problems where 
hot substances are introduced into PVC products such as bottles; the 
bottles tend to sag and distort. 
The instant invention overcomes these problems by blending with PVC, an 
epoxy type stabilizer system that results in a PVC composition with a Tg 
equal to or greater than the Tg for the PVC composition without the epoxy 
type stabilizer. More specifically, the instant invention teaches blending 
with PVC either a copolymer of an .alpha.-olefin and at least one 
unsaturated epoxy monomer or optionally blending with PVC a terpolymer 
comprised of the aforementioned copolymer plus an epoxy-free monomer 
wherein the epoxy-free monomer can also be an .alpha.-olefin. 
Copolymers of unsaturated epoxy monomers and ethylene have been long known 
in the art. For example, U.S. Pat. No. 3,383,372 (Spivey) discloses a 
copolymer comprised of ethylene and glycidyl esters such as glycidyl 
acrylate, glycidyl methacrylate and glycidyl ethacrylate. These 
copolymers, as taught by Spivey, are either used alone or are modified 
with fillers and plasticizers as molding compositions for the manufacture 
of films and coating. 
Another reference to copolymers of unsaturated epoxy monomers is found in 
U.S. Pat. No. 3,201,497 (Heino). This reference relates to epoxy resin 
adhesive compositions comprised of an epoxy resin, a copolymer of an 
ethylenically unsaturated epoxy monomer and an ethylenically unsaturated 
epoxy-free monomer and a curing agent for the epoxy resin. 
SUMMARY OF THE INVENTION 
It has surprisingly been found that when copolymers of an .alpha.-olefin 
and an unsaturated epoxy monomer or a terpolymer of an .alpha.-olefin, an 
unsaturated epoxy monomer and an epoxy-free monomer (which can also be 
another .alpha.-olefin) are blended with PVC, a composition is produced 
having superior processing and thermal stability properties. This new PVC 
composition also has a softening temperature higher than that for 
conventional PVC compositions containing liquid epoxy type stabilizers, 
thus enabling the production of a PVC container which will have less 
tendency to sag or distort when filled with hot substances. For example, 
the maximum use temperature for a PVC bottle produced from a conventional 
liquid stabilizer such as epoxidized soybean oil is about 55.degree. C to 
about 65.degree. C whereas the maximum use temperature for a PVC bottle 
produced with stabilizer systems of the instant invention would be about 
65.degree. C to about 75.degree. C.

DETAILED DESCRIPTION 
The term "PVC" as used in this invention is meant to include both 
homopolymers of polyvinyl chloride and co- and ter-polymers of vinyl 
chloride with comonomers such as vinyl acetate, vinyl formate, alkyl vinyl 
ethers, ethylene, propylene, butylenes, vinylidene chloride, alkyl 
acrylates and methacrylates, alkyl maleates, alkyl fumarates, etc. 
Preferably, at least 80%, and more preferably 100% of the monomers to be 
polymerized will be vinyl chloride monomer. These resins have a number 
average molecular weight of about 35,000 to about 120,000; preferably from 
about 45,000 to about 75,000. Inherent viscosity (as measured by ASTM 
D1243-60; Method A) will generally be in the range of about 0.5 to about 
1.5, preferably in the range of about 0.7 to about 1.2. The method of 
preparation of these resins is not critical and, for example, any of the 
well known suspension techniques may be employed. 
Unsaturated epoxy type monomers suitable for use in the instant invention 
are those which will free radically polymerize with .alpha.-olefins. These 
include but are not limited to glycidyl methacrylate, allyl glycidyl 
ether, glycidyl acrylate, vinyl glycidyl phthalate and allyl glycidyl 
phthalate. The preferred unsaturated epoxy monomers are glycidyl acrylate, 
and glycidyl methacrylate. 
The epoxy-free monomers suitable for optional use in the present invention 
include, but are not limited to acrylate and methacrylate esters of 
C.sub.1 to C.sub.18, preferably C.sub.1 to C.sub.12 alcohols such as 
methyl methacrylate, ethyl acrylate, butyl methacrylate; styrene and 
substituted styrenes; acrylonitrile; vinyl esters of C.sub.1 to C.sub.18, 
preferably C.sub.1 -C.sub.12 aliphatic monocarboxylic acids such as vinyl 
acetate, vinyl propionate and vinyl stearate; and .alpha.-olefins. 
Preferred are the alkyl acrylates and methacrylates and most preferred are 
the low molecular weight acrylates and methacrylates such as methyl and 
ethyl acrylate and methyl and ethyl methacrylate. 
.alpha.-olefins suitable for use in the instant invention are generally the 
C.sub.2 to C.sub.20 .alpha.-olefins. Preferred are ethylene and propylene. 
A typical formulation for the instant composition is as follows: about 1 to 
about 50 parts, preferably 2 to 20 parts of a copolymer of an 
.alpha.-olefin and an unsaturated epoxy monomer; or about 1 to about 50 
parts, preferably 2 to 20 parts of a terpolymer of an .alpha.-olefin, an 
unsaturated epoxy monomer and an epoxy-free monomer, based on 100 parts of 
PVC. It is also understood that other ingredients such as pigments, dyes, 
fillers, flame retardants, impact modifiers, lubricants, processing aids, 
stabilizers and other conventional compounding ingredients can be 
incorporated into the vinyl chloride resin compositions in any convenient 
manner, for example by the use of high speed mixers or internal mixers. 
It is to be understood that the copolymers and terpolymers of instant 
invention can be either prepared by copolymerization or by grafting the 
epoxy and/or epoxy-free monomer onto a polyolefin. It is also within the 
scope of this invention that the .alpha.-olefin and epoxy-type monomer can 
be first copolymerized and subsequently grafting the epoxy-free monomer 
onto the resulting copolymer or vice versa the epoxy-free monomer can be 
copolymerized with the .alpha.-olefin to which the epoxy-type monomer is 
grafted onto the resulting copolymer. 
The compositions of the present invention are produced by first preparing 
the epoxy/.alpha.-olefin copolymer or terpolymer by procedures known in 
the art. For example, these copolymers can be prepared by polymerizing 
mixtures of .alpha.-olefin and unsaturated epoxy monomer either in tubular 
or autoclave reactors at pressures above about 30 atmospheres, for 
example, about 500 psi to about 2500 psi; preferably at a pressure of 
about 1100 psi and at temperatures from about 37.degree. C to about 
210.degree. C. Where the copolymer is a graft copolymer, the polypropylene 
or polyethylene may first be fed into a plastics extruder wherein it is 
pressed and heated to a flowable or molten condition at temperatures 
between 130.degree. and 250.degree. C, and above the crystalline melting 
point of the polymer, under pressure. The epoxy monomer and initiator is 
then fed under pressure into a midsection of the barrel of the extruder 
and into contact with the heat-plastified or molten polymer. 
Initiators suitable for use in the instant invention include: organic 
peroxides such as caprylyl peroxide, lauroyl peroxide, benzoyl peroxide 
and ditertiary butyl peroxide; organic hydroperoxides such as t-butyl 
hydroperoxide and cumene hydroperoxide; azocompounds such as 
azo-bis-isobutyro-nitrile; pivalates such as t-butyl peroxy pivalate; and 
peroxy dicarbonates such as diisopropyl-peroxydicarbonate. Preferred are 
the organic peroxide and hydroperoxides. The amount of initiator suitable 
for use in the instant invention is about 0.01 to about 2.0 percent based 
on the total weight of monomer. 
It is preferred that the above-aforementioned epoxy-.alpha.-olefin 
copolymer or terpolymer be prepared so as to give a product in powder 
form. Any conventional process known in the art for giving the powder form 
of said polymer can be used. Such a polymer in powder form allows a more 
convenient procedure when blending with the PVC resin compound which is 
also preferred to be in powder form. It will be evident to those skilled 
in the art that the practice of this invention is not limited to the epoxy 
copolymer or terpolymer or even the PVC resin being in powder form. The 
materials of the present invention may also be in pellet or any other 
conventional form and it will also be evident to those skilled in the art 
that the type of blending apparatus is determined by the form of the 
material before blending. 
Before the epoxy polymer is incorporated into the PVC compound, the PVC 
compound is first prepared by conventional means known in the art. If the 
ingredients are in the preferred powder form, they are dry blended on a 
high speed mixer such as a Papenmeier; or Henschel mixer at mixer speeds 
ranging from about 500 rpm to about 5000 rpm. It is preferred that the 
mixer speed be about 500 to about 1000 rpm during the first minute of 
mixing and thereafter the speed increased to about 1000 to about 2000 rpm 
for the remainder of mixing time; overall mixing time usually ranges from 
about 5 to about 30 minutes. The order of mixing is, however, not critical 
and variations may be made if desired, but a typical order of mixing is 
shown in Table I below. 
TABLE I 
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Temperature Time 
Order Additive (.degree. C) 
(Min.) 
______________________________________ 
1 Resin 32-38 1 
2 Stabilizer, 60 5 
(processing aid) 
3 Impact Modifier 82 5 
4 Copolymer or 90-110 5 
terpolymer 
5 Transfer from hot 
70-95 5 
mixer to cool mixer 
______________________________________ 
If the epoxy polymer is in powder form, it may be dry blended with the 
above PVC resin and various ingredients in a high speed mixer. If the 
epoxy polymer is in pellet form or any other bulk form, then it is evident 
to those skilled in the art that such materials can be blended in a 
Banbury, an extruder, a rubber blender or even in a Brabender as used in 
the examples of the instant application. 
The term glass transition temperature (Tg) as used in the instant 
specification and claims means the temperature at which the amorphous 
domains of a polymer take on the characteristic properties of the glassy 
state; that is, brittleness, stiffness and rigidity. In other words, it is 
the temperature at which the polymer changes from a plastic state to a 
brittle, vitreous state or vice versa. 
All glass transition temperature measurements of the instant invention were 
made on a Perkin Elmer Differential Scan Calorimeter (DSC model 1B). All 
samples were vacuum dried for 36 hours at 0.1 mm Hg before analyzing. 
BRABENDER STABILITY TEST 
The Brabender Heat Stability Test used to determine the long range 
processing stability of the instant PVC compounds was performed on a 
Brabender torque rheometer fitted with a 30 ml roller head (5/2) and a 5 
kg ram weight. A Moseley Autograf Model 7101B recorder was used to 
continuously monitor the temperature. 
The Brabender conditions were as follows: 
Head Temperature:177.degree. C 
Sensitivity:5:1 
Zero Suppression:to keep pen on scale 
Damping at X 1:15 secs. (1000-100 mg) 
Rotor Speed:35 and 143 rpm 
Scale:X 5 
Sample Charge Weight:22 g 
The Brabender was set at 35 rpm and 22 gr of PVC compound was charged 
through a cooled chute wherein the ram weight was applied. When the ram 
weight reached bottom, the Brabender and Moseley chart were simultaneously 
started. One minute after fusion, the rotor speed was increased from its 
original speed of 35 rpm to 143 rpm as quickly as possible. When the 
torque rose 100 meter grams, the test was discontinued. 
BRABENDER FUSION TEST 
Another test used on the compositions of the instant invention is the 
Brabender Fusion Test. This test was performed on a Brabender as 
previously described in the Brabender Stability Test. The Brabender 
conditions for the Fusion Test were as follows: 
Head Temperature:215.degree. C 
Sensitivity:5:1 
Zero Suppression:to keep pen on scale 
Damping at X 1:20 sec. (1000-100 mg) 
Rotor Speed:25 rpm 
Sample Charge Weight:23 g 
The Brabender was set at 35 rpm and 23 gram of PVC composition was charged 
through a cooled chute wherein the ram weight was applied. When the ram 
weight reached bottom, the Brabender and Moseley chart were simultaneously 
started. Two minutes after fusion torque peak, the test was discontinued. 
The invention will be further understood by reference to the following 
description and examples. 
EXAMPLES 1 - 5 
A dry blend according to the Basic Formula in Table II was prepared in a 
high speed Papenmeier mixer by first mixing at a speed of 1200 rpm for 1 
minute then further mixing for an additional 2 minutes at a speed of 3600 
rpm. 
TABLE II 
______________________________________ 
BASIC PVC FORMULA 
Ingredient phr 
______________________________________ 
PVC resin.sup.(a) 100 
Impact Modifier.sup.(b) 
15 
Processing Aid.sup.(c) 
3 
Stabilizer I.sup.(d) 2 
Stabilizer II.sup.(d) 
1 
Lubricant I.sup.(e) 1.25 
Lubricant II.sup.(f) 0.25 
Lubricant III.sup.(g) 
0.5 
Lubricant IV.sup.(g) 0.5 
______________________________________ 
.sup.(a) Resin of PVC homopolymer with a number average molecular weight 
of about 50,000. 
.sup.(b) Mainly polymethyl methacrylate - an impact modifier. 
.sup.(c) Methyl methacrylate - butadiene - styrene terpolymer (MBS) - a 
processing aid. 
.sup.(d) Organotin - thermal stabilizers. 
.sup.(e) Glyceryl monostearate - lubricant. 
.sup.(f) Low molecular weight polyethylene - lubricant. 
.sup.(g) General lubricants such as stearates or stearic acid. 
To the basic formulation above, four separate samples were prepared 
according to Table III. 
TABLE III 
______________________________________ 
Additions to Basic Formulation 
Sample 
______________________________________ 
E-1 Basic formulation only 
E-2 Basic formulation plus 5 phr Epoflex 945 (an 
epoxidized soybean oil). 
E-3 Basic formulation plus 5 phr of a copolymer 
of polypropylene and glycidyl acrylate (2 wt %). 
E-4 Basic formulation plus 5 phr of a graft copolymer of 
low density polyethylene and glycidyl acrylate 
(1 wt %). 
Sample 
E-5 Basic formulation plus 5 phr of a terpolymer of 
polypropylene, polyethylene (6 wt %) and glycidyl 
acrylate (2 wt %). Made by grafting glycidyl 
acrylate onto a polypropylene polyethylene 
copolymer. 
All weight percentages based on the total weight 
of the co- or terpolymer. 
Brabender stability and fusion tests were run ac- 
cording to the method previously set-forth, and the 
results are found in Table IV and V. 
______________________________________ 
TABLE IV 
______________________________________ 
Brabender Stability Test 
Time to Breakdown 
Sample 
Breakdown, min. 
Torque,mgm Temp., .degree. C 
______________________________________ 
E-1 14.5 1530 216 
E-2 17.0 1300 217 
E-3 20.1 1250 212 
E-4 13.5 1430 218 
E-5 18.2 1210 209 
______________________________________ 
This table shows that the use of copolymers of this invention with PVC 
composition generally results in an increase in stability. Also evident in 
this table is that for stability purposes, the epoxidized soy bean oil 
when used as a stabilizer in PVC compositions is substantially equivalent 
to the co- and terpolymers of the instant invention. 
TABLE V 
______________________________________ 
Brabender Fusion Test 
Fusion Torque Peak 
Sample Torque mg Temp. .degree. C 
______________________________________ 
E-1 2200 320 
E-2 2200 310 
E-3 1120 295 
E-4 1690 314 
E-5 1400 301 
______________________________________ 
This table shows the advantages of using the copolymers of the instant 
invention as indicated by the lower torque values needed to reach fusion 
peak as opposed to the composition containing the epoxidized soybean oil 
or the base composition without the use of any additional stabilizer. The 
lower torque values can be interpreted to mean that such compositions 
would require less work to flux and therefore easier processability. 
Glass transition measurements were performed on samples E-1 to E-5 by use 
of a differential scanning calorimeter (DSC). The results are found in 
TABLE VI below. 
TABLE VI 
______________________________________ 
Glass Transition Determinations 
Glass Transition 
Sample (Tg, .degree. C) 
______________________________________ 
E-1 72.0 
E-2 63.5 
E-3 74.0 
E-4 77.0 
E-5 74.5 
______________________________________ 
This table illustrates the most critical aspect of the instant invention, 
which is, the fact that the glass transition temperature of a PVC 
composition is not lowered when the stabilizers of the instant invention 
are used. In fact, the glass transition temperature is surprisingly 
increased. This increase in glass transition temperature is important 
because it also correlates to an increase in softening temperatures, which 
also correlates to a PVC container which will less likely sag or distort 
when filled with hot substances. 
EXAMPLES 6 - 8 
24 grams of glycidyl methacrylate were placed in an autoclave 1 gallon 
reactor along with 1050 ml of cyclohexane into which 1100 psi of ethylene 
was introduced over a period of 1.5 hours at a temperature of about 
105.degree. C. 10 grams of lauroyl peroxide were introduced into said 
reactor over a period of 1.5 hours. The copolymer was recovered and its 
physical properties measured; the results are shown in Table VII. 
TABLE VII 
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PROPERTIES OF COPOLYMER OF EXAMPLE 6 
Product Weight 156 g 
Melting Point 102.degree. C 
Saponification No. (ASTM D-94) 
25.8 
Glycidyl Methacrylate (GMA)wt% 
6.5 
Epoxide Equivalent, moles/kg 
0.65 
Calculated wt % GMA In Resin 
9.0 
______________________________________ 
The Epoxide Equivalent was determined by dissolving 1.7 g of the above 
prepared copolymers in methyl ethyl ketone and refluxing for 10 minutes 
and subsequently titrating with 1 normal HCl. The following formula was 
used to calculate the Epoxide Equivalent: 
##EQU1## 
Two separate blends were prepared by dry blending 5 phr of Epoflex 945 
(E-7) and 5 phr of the previously prepared ethylene/glycidyl methacrylate 
copolymer (E-8) with the Basic Formulation of Table II in a high speed 
Papenmeier mixer by first mixing at a speed of 1200 rpm for 1 minute then 
further mixing at a speed of 3600 rpm for an additional 2 minutes. E-6 
represents only the Basic Formulation of Table II. 
Brabender stability and fusion tests were run as previously described and 
the results are shown in Table VIII and IX. 
TABLE VIII 
______________________________________ 
Brabender Stability Test 
Torque 
Fusion Time to Before 
Peak Torque Breakdown 
Breakdown 
Sample Time,sec mgm min mgm 
______________________________________ 
E-6 40 3150 10.5 1600 
E-7 45 2850 17.2 1500 
E-8 240 1200 17.6 1450 
______________________________________ 
TABLE IX 
______________________________________ 
Brabender Fusion Test 
Fusion Peak 
Sample Time,sec Torque,mgm Temp, .degree. C 
______________________________________ 
E-7 12 2050 165 
E-8 18 450 169 
______________________________________ 
These tables also show the advantages of blends of the instant invention as 
evidenced by the lower torque values required to reach fusion peak as 
opposed to the torque value required when a liquid stabilizer such as 
epoxidized soybean oil is used. The melting point of the ethylene/glycidyl 
methacrylate copolymer (102.degree. C) is also high enough so that it will 
not lower the glass transition temperature (softening point) of the 
finished product when blended with the PVC composition of the instant 
invention. 
It is to be understood that this invention is not restricted to the 
foregoing examples which serve only to illustrate the present invention. 
Numerous variations may be devised without departing from the scope of 
this invention.