X-Polymers-A-Industrial Resins-1

INDUSTRIAL RESINS 

An industrial resin is a synthetic polymer which is has adhesive, film-forming or useful 

reactive properties. Many such polymers are made commercially in New Zealand and the 

following selection of these are described in this article. 

Unsaturated polyester resins

These are formed from the reaction of a diol (a molecule containing several hydroxyl 

groups) and an unsaturated diprotic acid. The resulting polyester chains are dissolved in a 

reactive solvent. The chains crosslink to form a hard, strong resin which is used in making 

the hulls of boats and in the production of "synthetic marble". 

Alkyd resins

Alkyd resins are used in many solvent-based paint systems and are a type of polyester 

made from polyols, acids and vegetable oils. 

Emulsion polymers

These are emulsions of monomers in water. As the water evaporates, the monomers 

polymerise to form a thermosetting film. These are widely used as adhesives (e.g. PVA) 

and in water-based paints. 

Amino resins for surface coatings

When molecules containing amino groups are reacted with formaldehyde an amino resin is 

formed. Their primary use is as a crosslinking agent and as such they are used in paints in 

conjuction with other polymers such as alkyds. 

Polyurethane resins

Polyurethanes result from the reaction of a polyalcohol and an organic di-isocyanate. 

They can be used as surface coatings, to make furniture and footwear and in foam form, 

for packaging. 

Polyamide-epichlorohydrin resins

These are formed in two steps. The first step involves reacting a polyfunctional amine 

with a diprotic acid to form a polyaminoamide resin. This is then crosslinked with an 

epichlorohydrin monomer. The resultant resin is used to coat paper fibres, increasing the 

strength of the wet paper from less than 2% to around 30% of its dry strength. 

Formaldehyde resins

Formaldehyde resins are made by reacting formaldehyde with any of a variety of 

substances such as urea and phenol The reagents are mixed to form a thermosetting crosslinked polymer used in reconstituted wood (e.g. plywood) and timber adhesives. 

INTRODUCTION

The term "industrial resins" refers to any synthetic polymer resin made for commercial use. 

As such it includes many substances that, chemically, have very little in common and thus 

have a wide variety of applications. Industrial resins are used in New Zealand for anything 

from synthetic leather to paint binders to imitation marble vanity tops and the adhesives used 

to hold plywood together. 
X-Polymers-A-Industrial Resins-2 

RESINS COMMONLY MADE IN NEW ZEALAND

The following section listed some resins commonly made in New Zealand, briefly describes 

the process by which they are manufactured and the uses for which they are produced. For 

some of the resins, such as polyester resins, a great variety of different ingredients can be 

used in varying proportions to produce different results. Where this is the case the types of 

variation that can occur are described. 

Unsaturated polyester resins

In general, polyester resins result from the condensation reaction between a diprotic acid and 

a polyhydric alcohol, e.g. 

HO C X

O

C

O

OH HO Y OH X C

O

OYOC

O

X C

O

+ O Y + n H2O

Any change in type or proportion of reactants results in a change in properties of the 

polymeric product so an infinite number of polyesters is theoretically possible. 

Possible variations in formulations

Unsaturated polyesters are produced from a glycol1

 and maleic anhydride2, which is faster 

reacting than maleic acid and produces less water. Some specialised resins that need high 

chemical resistance use fumaric acid3 instead of maleic anhydride because it copolymerises 

better. 

 1

A glycol is a diprotic alcohol. Propylene glycol (propane-1,2-diol) is commonly used. 

2

An acid anhydride (such as maleic anhydride) is what you would get if you reacted two moles of a 

particular carboxylic acid together and lost one mole of water, i.e. 

R C OH + H2O

O

2 R C

O O

R C O

Maleic acid is a diprotic carboxylic acid (i.e. it has two carboxylic acid groups) so in this case the two carboxylic 

acid groups of the same acid molecule react together to give the five membered ring of maleic anhydide as 

follows: 

O O O

C C

H

C C

H

O

OH

O

HO + H2O

3

Maleic acid and fumaric acid are respectively the cis and trans forms of butendioc acid: 

C C

H

HOOC COOH

H 

C C

H

HOOC H

COOH
X-Polymers-A-Industrial Resins-3

maleic acid propylene glycol

C C

HOOC COOH

H H

+ C C

H

H3C

OH

H

H

OH

O C

C

O

C

H H

C

O

O CH2 C

CH3

H

O C

O

C

H

C

H

C

O

O

Other acids are used in conjuction with the unsaturated maleic type to prevent the resin from 

being too reactive. Ortho-phthalic anhydride is the most common and is used in "general 

purpose" formulations (used in boat building, some cast sanitary-ware etc.). Isophthalic acid 

is used where better chemical resistance is required (e.g. in oil storage tanks). Adipic acid is 

used where flexibility is required (e.g. in resins for autopatch compounds). Halogenated 

acids (e.g. tetrabromophthalic anhydride) can be used to produce reduced flammability in 

mouldings. 

C

C

O OH

OH

O 

O

O

O

 

C

C

O OH

O

OH

 

O

O

O Br

Br

Br

Br

 isophthalic o-phthalic o-phthalic tetrabromophthalic 

 acid anhydride acid anhydride 

HO C

O

CH2 CH2 CH2 CH2 C OH

O

adipic acid 

Other glycols can be used, e.g. dipropylene glycol and diethylene glycol give some degree of 

flexibility and neopentyl glycol offers better chemical resistance. 

HO CH2 CH O CH2 CH OH

CH3 CH3

 HO CH2 CH2 O CH2 CH2 OH

 dipropylene glycol diethylene glycol 

Methyl methacrylate can be used as a part replacement for styrene in the monomer portion of 

the resin. This offers better resistance to yellowing on exposure to UV radiation and is most 

commonly used in resins intended for manufacture of translucent fibreglass sheeting. 
X-Polymers-A-Industrial Resins-4 

C CH2OH

CH2OH

CH2OH

HOH2C

 

CH2 C C

CH3

O

O CH3

 neopentyl glycol methyl methacrylate 

The manufacturing process

The resin is manufactured in a batch process using 1500 - 5000 L stainless steel kettles fully 

equipped for heating, cooling, pressure, vacuum refluxing and distillation. The mixture is 

cooked at up to 220oC for between 14 and 40 hours. Samples of the reaction mixture are 

taken from time to time and their acidity and viscosity measured to assess the progress of the 

reaction. After cooking the polymer is cooled and dissolved into styrene, a polymerisable 

solvent (i.e. one that can copolymerise with the polyester). 

Heating of highly flammable reactants and solvents poses practical problems. Hot water or 

super-heated steam are produced in a room detached from the kettles and circulated in jackets 

around the kettles. Thus, all likelihood of spark or flame ignition in the processing area is 

eliminated. 

Removal of water from the reaction mixture to obtain maximum yields is accomplished in 

one of two ways: 

• Sparging. Nitrogen gas is bubbled through the mixture to increase the surface area. 

The water evaporates and is carried out of the mixture and condensed. 

• By refluxing with a water absorbing solvent such as toluene4

 or xylene5. 

C

O

O O

O

C

benzoyl peroxide 

Uses of unsaturated polyester resins

The polymer resin product is used by the fibre-glass industry for building boats and car 

bodies, for encapsulating electrical components, for coating concrete to give a smooth sterile 

surface in food-manufacturing plants and for the production of "synthetic marble". In all of 

these applications the polyester-styrene mixture is poured into a mould and a free radical 

initiator such as MEKP (methyl ethyl ketone peroxide) or benzoyl peroxide added to initiate 

crosslinking. 

ROOR' RO + OR'

 peroxide free radicals 

 4

monomethylbenzene. Also called toluol.

5

a mixture of the three dimethylbenzenes. Also called xylol. 
X-Polymers-A-Industrial Resins-5

CH CH2 + OR CH CH2 OR

 styrene 

RO O C

O

C

H

C

H

C

O

CH2 C O

CH3

H

OCC

O

C

H OR

C

H

O

CH2 C

CH3

O

O

CH CH2

OCC

O

C

RO H

C

H

O

CH2 C

CH3

O

CH2 O

CH

+

Adds to further

 styrene or

polyester resin

 molecules

 

Thus polyester chains are linked together by polystyrene bridges. Polyesters can be easily 

moulded (by simply pouring the solution into a mould) and the resulting end product is 

resistant to attack and long-lasting. 

Alkyd resins

The introduction of a vegetable oil into the polyester reaction gives a product called an alkyd 

resin. Raw materials are commonly phthalic anhydride imported from the U.S.A., U.K. or 

Japan; pentaerythritol imported from Canada and soya bean or linseed oil produced locally or 

imported from Europe. The reaction is usually catalysed by an oxide, hydroxide or organic 

salt of calcium or one of the alkali (group I) metals. 

The manufacturing process

The manufacture of the alkyds proceeds in two stages. Pentaerythritol and vegetable oil are 

first heated with the catalyst for about two hours at 270o

C. The vegetable oil is an ester of 

glycerol and long chain unsaturated fatty acids, and the reacton is a trans esterification, the 

fatty acids forming an ester with the polyhydroxy-alcohol pentaerythritol. Di- and tri- esters 

of PE and di- and monoglycerides are also presumably formed. After cooling the mixture to 

150o

C, a slight excess of phthalic anhydride is added and the mixture is reheated to 240oC 

where it is held for several hours while the polyester alkyd resin is formed: 
X-Polymers-A-Industrial Resins-6 

HOCH2 C CH2OH

CH2OH

CH2OH

+ CH

CH2

O

O

CH2

C

C

O

R

R'

C R"

O

O

O

HOCH2 C CH2

CH2OH

CH2OH

C

O

R

 penterythritol (PE) vegetable oil (triglyceride) monoester of PE 

C

O

C

O

O

HOCH2 C CH2

CH2OH

CH2OH

C

O

+ R

C

C

O

O

O

O

CH2

CH2

C

C

CH2

CH2

CH2

C

O

R

O

O

The reaction is monitored by acidity and viscocity measurements. Water is removed by 

evaporating with the solvent xylol which is recycled. The unsaturated fatty acid residues 

react with oxygen to give further polymerisation in the drying of the paint or curing of the 

resin. By changing oil, acid or alcohol, a wide range of alkyd resins can be made. 

Uses of alkyd resins

Alkyd resins are used in solvent-based paints. These paints incorporate driers (e.g. cobalt 

naphthenate) which cause the alkyd to crosslink with itself using atmospheric oxygen as the 

solvent evaporates, resulting in a polymer that is no longer soluble in the original solvent. 

Alkyds are also used in stoving enamels where they are crosslinked with amino resins (see 

below). 

Emulsion polymers

These are emulsions of monomers in water that polymerise as the water evaporates. 

Examples of common monomers are given below. 

CH2 CH O C

O

CH3

vinyl acetate 

CH2 CH C O

O

(CH2)3 CH3

 

CH2 C C

CH3

O

O CH3

 butyl acrylate methyl methacrylate 
X-Polymers-A-Industrial Resins-7

CH CH2

 CH2 CH C O

O

CH2 CH3

 styrene ethyl acrylate 

A typical manufacturing process

PVA (polyvinyl acetate) glue is probably the best known emulsion polymer. It is 

manufactured by free radical addition copolymerisation6 of an aqueous emulsion of vinyl 

acetate and butyl acrylate. As the reaction is an exothermic chain reaction, the reaction 

vessel and conditions are different from the kettles previously described. The reaction is 

initiated by ammonium or potassium persulphate and bisulphite which react together to give 

free radicals which add to the vinyl monomer to initiate the free radical chain reaction: 

CH2 CH

O

CH2

C

CH

O

O

CH3

C CH3

O

.

+ CH2 CH O C

O

CH2 CH O C CH3 CH3

O

.

A section of the vinyl acetate portion of the copolymer 

The reactants are fed into the reaction vessel continuously as reaction proceeds, and excess 

heat produced is removed by cooling water. Acrylic emulsions from acrylic acid and its 

esters are made in a similar way and used for wall-paper coatings. 

Uses of emulsion polymers

Emulsion polymers are used in two industries: the paints industry and the adhesives industry. 

 In the paints industry they form the basis of water-thinnable paints, and they are used in the 

adhesives industry for wood and cardboard glues. They are also used to coat wall and 

printing papers and used in inks. 

Amino resins for surface coatings

Amino resins are produced by reactions involving formaldehyde with amine functional 

compounds such as urea, melamine and benzoguanamine. 

C

O

H H

formaldehyde 

 6

A copolymer is a polymer of the form ....AAAAAAABBBBBBBAAAAAABBBBBBBB...., i.e. one which 

consists of alternating short strings of monomer A and monomer B. 
X-Polymers-A-Industrial Resins-8 

C

O

H2N NH2

N

N

N

H2N

NH2

NH2 

N

N

N

NH2

NH2

 urea melamine benzoguanamine 

The manufacturing process

The first step in the reaction involves addition of the formaldehyde to the amine groups to 

form methylol compounds (methyl groups with one hydrogen replaced by a hydroxy group) 

by effectively adding N—H across the C=O of the formaldehyde. 

NH2

C

NH2

O

N

C

NH2

O

H CH2OH

N

C

N

O

H CH2OH

HOH2C H

HCHO HCHO

C

N

C

N

C

NH2 N NH2

NH2

C

N

C

N

C

NH2 N N

NH2

H

CH2OH

C

N

C

N

C

N N N

N

CH2OH

CH2OH

HOH2C CH2OH

CH2OH

HOH2C

HCHO 5 HCHO

The methylol compounds can react together by a condensation reaction mechanism to give 

polymers. Reactions can take place between two methylol groups or between one methylol 

group and active hydrogen atoms. 

N

H

CH2OH + HOH2C N

H

N

H

CH2OCH2

H

N — H2O

N

H

CH2OH + HN

CH2OH

— H2O N

H

CH2 N

CH2OH

This is similar to the reactions used in production of urea formaldehyde resins for use in 

production of particleboard and medium density fibre board (see below). The products of 

these reactions have limited solubility in water, are insoluble in solvents and are unstable. 

For use in surface coatings the polymers are modified by reaction with alcohols. 

N

H

CH2OH + HOR — H2ON

H

CH2OR
X-Polymers-A-Industrial Resins-9

The effect of the ether grouping is to improve the stability, modify the solubility and increase 

compatibility with other polymeric compounds. A variety of different alcohols can be used 

depending upon the properties required from the resin. 

Uses of amino resins in surface coatings

Amino resins are used as crosslinkers in stoved paint systems in combination with other 

polymeric materials including alkyds, acrylics, epoxies and saturated polyesters. They are 

used in paints in a wide variety of applications including automotive, domestic appliances, 

coil coating, metal decorating and general industrial finishes. 

Butylated urea-formaldehyde resins can be used in conjunction with alkyd resins in acid 

catalysed furniture lacquers which dry and cure at room temperature. 

Polyurethane resins

Polyurethane coating resins and varnishes offer advantages over alkyd resin systems in speed 

of drying, hardness of the film and resistance to wear. Types made in New Zealand include 

urethane oils, urethane alkyds, moisture curing polyurethanes and foams. 

A polyurethane is formed by the reaction of a polyalcohol and an organic di-isocyanate: 

HO Y OH C

O

NH X NH C

O

O O CNXNC + OYO

When isocyanates react with water, amines and carbon dioxide are produced: 

XNCO + H2O X NH C + CO2

O

OH X NH2

The amine can then react with the isocyanate to form a "disubstituted urea": 

X NH2 + X O C N X NH C

O

NH X

This can then react with further isocyanate to give crosslinks between the polyurethane 

chains, giving a durable resin: 

X NH C NH

O

X

X NH

O C

X

O

X N C NH

+ OCNX

C NH

O

X N C NH

O

X

O C

X NH X X N

O C

X

O

X N C NH

+ OCNX

The manufacture of condensed polyurethanes

Urethane oils can be formed by the addition of vegetable oil to the polyurethane. Urethane 

alkyds can be formed by reacting isocyanates with alkyds. They cure in the same way as 

alkyds, that is, by oxidative crosslinking of the unsaturated groups in the fatty acid portions 

of the molecule. 
X-Polymers-A-Industrial Resins-10 

Moisture curing polyurethanes are produced by reaction of isocyanates with polyether or 

polyester polyols. Unreacted isocyanate groups are present and these react with atmospheric 

moisture to cure the resins by forming crosslinked polyurea polyurethane structures. 

XNCO + H2O NH C

O

X OH

+

δ+

C

O

N OH

X

H C

O

N

Y

C

O

N OH

C

O

N

Y X

H

C

O

N OH

C

O

N

Y X

C H

O

N OH

C

O

N

Y X

H

etc.

The manufacture of polyurethane foam

The basic ingredients of polyurethane (the polyol and the isocyanate) are mixed together in a 

mould in the presence of a catalyst. A highly exothermic reaction occurs, producing 

sufficient heat to vapourise a liquid "blowing agent". A blowing agent is used in the 

production of polyurethane foams to cause the polyurethane to expand out so that it sets as a 

foam. In its absence a solid resin forms. Depending on the various reagents used the density 

of the polyurethane formed can vary between 6 and 1200 kg m-3. 

Uses of polyurethane resins

Urethane oils are used instead of conventional drying oils in some applications as they are 

faster-drying and give a harder finish. Polyurethane alkyds and moisture curing 

polyurethanes are used in elastomers, paints, adhesives and as thermoplastics in a variety of 

applications. Polyurethane foams have a variety of different uses depending of the density of 

foam produced. Low density foams are used in packaging and insulation and high density in 

moulded furniture. Microcellular foams are used in shoe soles, car bumpers and synthetic 

leathers. 

Polyamide-epichlorohydrin resins

These are polymeric materials which are used in the manufacture of certain grades of paper 

which require additional strength when wet (e.g. kitchen towelling). 

The manufacturing process

The resins are made in two stages. First a polyaminoamide resin is made by reaction of a 

polyfunctional amine such as diethylene triamine with a difunctional acid such as adipic acid. 
X-Polymers-A-Industrial Resins-11

n H2NCH2CH2NHCH2CH2NH2 n HO C

O

CH2CH2CH2CH2C

O

OH

H(HNCH2CH2NHCH2CH2NHC

O

(CH2)4C)nOH

O

+

In the second stage the polymer formed as described is reacted with epichlorohydrin 

CH2

O

CHCH2Cl

which reacts with available amine groups forming the amino chlorohydrin 

N

CH2CHCH2Cl

OH

which can further react by crosslinking between polymer chains or stabilise by forming a 

cyclic structure. 

The uses of polyamide-epichlorohydrin resins

As stated above, the major use of these resins is in papermaking. The resins are supplied as 

dilute aqueous solutions and are injected into the papermaking stock shortly before it reaches 

the papermaking machine. 0.5-1% solid resin (on dry fibre) can allow wet paper to retain 

over 30% of its dry strength while without the resin, the strength retention would be 0-2% 

when wet. This is used for papers that need to remain strong when wet, such as hamburger 

wrappers. 

Formaldehyde resins

Formaldehyde resins are formed by the reaction of formaldehyde with urea, phenol, 

melamine or resorcinol, and are used as adhesives. 

C

O

H2N NH2 

OH

 

N

N

N

NH2

H2N NH2 

OH

OH

 urea phenol melamine resorcinol 

The manufacturing process

The formaldehyde is produced by ICI Resins by silver-catalysed methanol oxidation: 

CH3OH ! CH2O + H2

CH3OH + 1⁄2O2 → CH2O + H2O 
X-Polymers-A-Industrial Resins-12 

The methanol is vapourised and blown across a silver catalyst. The formaldehyde gas formed 

is absorbed into water and removed continuously as a 45 - 50% solution. 

The resin is now produced in a batch process. The formaldehyde is fed into the reactor and 

heated to 60o

C. Alkali is added and then urea (produced in Taranaki - see article), during 

which time the mixture falls to 40oC. Finally the mixture is adjusted to pH 5 and heated to 

90o

C and left until sufficient polymerisation has taken place (this will depend on the desired 

end use of the resin). The reaction is then quenched with alkali and cooled. 

The reactions occuring are complex and imperfectly understood, but it is known that chains 

are formed in accordance with the following reaction scheme: 

Polymer chains with crosslinking

mono-, di-, tri- and tetramethylol urea

HOCH2NHCONHCH2 N CONHCH2OH

CH2

HO(CH2NHCONH)nNH

H2N C NH2

O

+ CH2O

NH2

C

NH

O

CH2OH

+

NH

C

NH

O

CH2OH

CH2OH N

C

N

O

CH2OH

HOH2C CH2OH

HOH2C

N

C

NH

O

HOH2C CH2OH

CH2OH

+ +

Uses of urea formaldehyde resins

The major use of these resins is in adhesives, and as such they are used in the production of 

reconstituted woods such as particleboard and plywood as well as in laminated wood. They 

are also used for a variety of other purposes including textile treatments, paints and enamels, 

glass fibre insulation binders and in the pulp and paper industry. 

ROLE OF THE LABORATORY

In all of the resins described above the end product can be substantially altered by changing 

the proportions of reactants used, the pH or the temperature. Because of this, these factors 

are monitored by the laboratory at the plant to ensure consistent quality. The final product is 

also tested using four types of routine tests: 

• Viscosity 

• acid value (i.e. the amount of acid present) 

• non-volatiles content 

• pH (only useful for some polymers, such as emulsion polymers and some 

formaldehydes) 
X-Polymers-A-Industrial Resins-13

The results of these tests do not give the composition of the final product, but they do identify 

whether the product is the same as has been produced before. In the production of industrial 

resins it is enough to know that a consistent product is being produced, and it is not essential 

to know its exact composition. 

Written by R. Biddle (Henderson High School) and John Packer, with the help of Dr. A. 

Thompson (A.C. Hatrick Limited). Updated for this edition by Heather Wansbrough 

following correspondence with John Blanchard (A.C. Hatrick Limited) and with reference to: 

• The ICI fact sheets on polyurethane and urea formaldehyde 

• The McGraw-Hill Encyclopedia of Science and Technology; McGraw-Hill, Inc.; 1992