J. F. Beachen

The Role of synthetic resins and plastics in the modern world is enormous. It is growing rapidly and is far from static in nature. New materials are being developed and offered for use with great regularity by the giant supply houses of the United States, United Kingdom and Europe. A chemist in this sphere is faced with a rapidly changing range of products and must continually keep abreast of literature published throughout the world. With the considerable weight and techniques of advertising available to most suppliers, it becomes a major task to separate the product with genuine advantages from those with no advantage at all, or even detriment to his own product.

Synthetic resins and plastics are end products that differ widely in their application, but generally are composed of similar basic materials. The main resins and plastics used in New Zealand Industry are:—

(1) Alkyds

(2) Phenolics

(3) Acrylics

(4) Vinyls

(5) Urethanes

(6) Epoxy resins

Alkyd resins

Alkyd resins are the backbone of the surface coating industry. The estimated distribution of alkyd resins in coatings is approximately 10 per cent. These resins are the basic vehicle for such paints as gloss enamels and undercoats for interior and exterior surfaces, for both household and industrial purposes.

The properties of these resins are governed by the ratio of three basic compounds used in their preparation. The three compounds, or building blocks, are polyhydric alcohols such as glycerine dibasic acids usually phthalic anhydride, and oils such as linseed oil. soya bean oil, safflower oil, tung oil or dehydrated Castor oil.

The resins based on these three building blocks can be divided into two groups.

(i) Alkyd resins used in the surface coating industry.

(ii) Polyester resins used in the plastics industry.

Both types are manufactured in New Zealand and used in a wide variety of applications.

(i) Alkyd resins In the surface coating industry: In general alkyds with a higher ratio of oil. about 60 per cent to 70 per cent, are more tlexible and show greater exterior durability and hence are used in synthetic high gloss enamels. The resins with a lower proportion of oil become correspondingly harder and faster drying, and are used more in undercoats and primers.

Alkyd resins arc manufactured in New Zealand in a number of plants throughout the country. It entails a chemical fusion by heat of the compounds listed above, in the presence of suitable catalysts.

The polymer formed by the reaction is essentially an ester, which point must be kept in mind when applying the resin to a particular application.

This versatile resin type is capable of many variations to meet specific problems. The surface coating chemists are constantly faced with demands to meet a particular condition or end requirement. With the knowledge and literature at his disposal this can be predicted, in theory— not always borne out in practice—and modifications to his product can be done.

The range of modifications that can be built into an alkyd resin is quite large. Alkyds are compatible or react with other groups because of:—

(1) Functional hydroxyl groups which can react with acid groups, amide groups, epoxy groups or urethanes.

(2) Functional acid groups that react with hydroxy groups or epoxy groups.

(3) Unsaturated double bonds in the fatty acid chain which can copolymerise with unsaturated monomers such as styrene. vinyl toluene, isocyanates, and various acrylate compounds.

The modifications to the alkyd structure that are carried out by New Zealand technical staff are:—

(a) Phenolic modification to improve hardness, water resistance and resistance to chemicals and abrasion, but here exterior durability suffers.

(b) Alteration in type and oil content to improve hardness, exterior durability, flexibility, speed of dry and yellowing resistance on interior application.

(c) Assessment of residual acidity. Reaction with basic pigments such as zinc oxide, calcium plumbate, white and red lead and aluminium is possible if the acidity is too high.

(d) Establishing the degree of polymerisation. Factors of film build, degree of penetration, and sag resistance are invohed here.

(e) Styrene or vinyl toluene modification to give greatly increased speed of dry but the vehicle when cured becomes sensitive to solvents.

(f) Polyamide modification to induce a "gel structure" to the paint.

(g) Epoxy modification to ungrade water, solvent, acid, alkali and chemical resistance.

All these modifications, and perhaps more, can be built in. and a new resin evolves to meet a nnrticular end requirement. The final selection of the alkyd depends on its ability to meet and nerform satisfactorily under the conditions laid down by the end user.

(ii) Polyester resins: Polyester resins are used in the plastics industry in the moulding or laminating operations usually in conjunction with fibre glass. Applications are in automotive bodies, transparent roofing, surfacing of boats, etc.

The formation of polyester resins forms a close parallel with the formation of alkyd resins. In fact polyester resins are alkyd resins without the oil modification. Whereas alkyd resins are thinned with a solvent that plays no part in the drying mechanism but just evaporates off. the polyester resin is thinned in styrene that does take part in the curing mechanism.

The formation of a polyester resin is, as above, through a reaction of a polyhydric alcohol such as propylene glycol or dipropylene glycol with phthalic anhydride or isophthalic acid.

Esterification is carried out at temperatures ranging from 350deg.F to 425deg.F. The time and temperature vary with the relative proportions of the two components. When ester formation is complete lurther modification is made with maleic or fumaric acid.

The resultant reaction product is then dissolved in styrene.

Variations in hardness and flexibility can be done quite readily to meet a particular end requirement. Modifications at the phthalic anhydride stage by replacing a moderately large percentage of the phthalic by adipic acid produces a flexible resin. On the other hand a high maleic content gives a harder brittle film by oroducing a high rate of reactivity during the film curing processes.

Polyester resins cure through the cross linking of the unsaturated groups catalysed by an organic peroxide such as methyl ethyl ketone peroxide or benzoyl peroxide. A reaction initiator is also necessary which normally is an organic cobalt salt, cobalt naphthenate. The curing reaction proceeds, provided the air temperature is not too low. rapidly, with the evolution of heat. As the film is 100 per cent reactive the product polymerises into a solid mass that is highly resistant to most solvents, acids, bases and salts.

Resin modifications are being developed in New Zealand laboratories continually. There Is not the same scope for modification as in the alkyd resin field, and once a formula has been established the product is fixed and serves a variety of similar applications.

Phenolic resins

The phenolics constitute one of the oldest resin groups. The basic make up is similar for the surface coating industry and the plastic industry. There are several New Zealand manufacturers of the surface coating type but the plastic type is mainly imported.

The phenolics are condensation products of a phenol and an aldehyde. Formaidehyde is by far the most reactive aldehyde and is almost exclusively used, as the paraformaldehyde, in commercial production. The phenol types used can be phenol. m-cresol. p-tertiary butyl phenol and a number of others. The nature of the final product is dependent of the types and ratios of the reacting ingredients.

In the paint or surfs coating industry the phenol resin so produced is [unclear: furth] modified by heat reacting on tung oil. The varnish so [unclear: duced] is used as water alkali resistant primers [unclear: sealers] and interior varnishes. Their effectiveness is not to the standards of urethanes or expoxies but adequate for most purposes.

The surface coating [unclear: che] can modify these varnishes controlling the [unclear: polymeri] and by modifying the phenolic ratio.

With phenolic plastics manufacture enfalls covering the condensation [unclear: pro] into a brittle low molecule weight compound which suitably pigmented over rollers.

This mix is then cooled the form of sheets and [unclear: gro] into moulding powder.

During subsequent [unclear: mould] enough heat is applied completely cross link phenol condensate into a insoluble and infusible [unclear: duet].

As can be seen, the difference between a paint phenol resin and a plastic phenol is the absence of a modifying oil in the latter. Phenol plastic articles are hard, and strong. They have no heat resistance and are celient insulators. Uses include handles of cooking utensil irons etc, and wash machine agitators.

Acrylic resins

The range of products [unclear: g] by the acrylic monomers building blocks is very [unclear: la] They give:

(a) Resins in solution appliance and automet uses.

(b) Resins in an emuls form for decorative [unclear: pa] and

(c) 100% reactive material the transparent sheet type of product.

The products available this group arc widely [unclear: u]. commercially because of [unclear: th] excellent properties of cher cal and weather resistar strength and clarity.

The acrylic resins are po mers of acrylic acid, [unclear: simplest] acrylate used methyl acrylate. Other [unclear: or] monomers used to fo polymers are ethyl acryli butyl acrylate, 2-ethyl he acrylate. methyl methacryl and many more.

The activity in the acry field is very intense in N Zealand and overseas. Be work is being undertaken [unclear: in] building up polymers new monomers attempting overcome defects in the [unclear: p] ticular system under [unclear: revi] The quality of surface [unclear: co ings] in New Zealand is [unclear: high] by world standards, a consequently the struggle constantly improve is [unclear: tinuous].

Taking each type in turn (a) Solution acrylics: [unclear: T] polymer resins are fori from the monomers select by a reaction mechant known as a peroxide initia free radicle polymerisati This means that the polyn is built up in solution, such xylene, and methyl [unclear: ketone], by each building [unclear: adding] on head to tall

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ad to head, until the [unclear: quired] molecular weight is [unclear: ached]. Most Industrially [unclear: ul] coating resins are pre-red from several different [unclear: omer] types conferring [unclear: eir] own special properties ese are copolymrr resins, producing copolymer resins [unclear: e] resin formulating chemist [unclear: ust] be aware of The com-[unclear: cations] and deviations that [unclear: n] aride during the poly-[unclear: erisation,] such as the differnt rates that one monomer ill enter the polymer, re[unclear: ting] in an uneven monomer stribution.

There are two types of lution acrylic:

(i) Acrylic lacquers

(ii) Acrylic enamels

Both types are produced id used in New Zealand. The [unclear: sic] development was done erseas and not a great deal [unclear: s] been done in modifying, they are tricky compounds work with. Most of the [unclear: difications] done here are way of the other additives the final paint such as [unclear: vent] blends.

The lacquer type can be [unclear: rmulat] as a typical [unclear: ample] from polymer built from methacrylic acid and ethyl methacrylate (a hard, ugh resin). The lacquers in be modified with cellulose [unclear: etate-butyrate] to aid, for camole, adhesion, plus other ds to film forming such as plasticiser, eg. butyl benzyl [unclear: thalate].

The acrylic enamels or [unclear: ermosetting] acrylics are reacing the acrylic lacquers ad conventional enamels in [unclear: e] automotive industry and ppliance fields. They are ard, durable, resistant to aining and to grease and ave excellent colour retenon and high gloss. Their igher cost is compensated or by their superior performance. The polymer is based [unclear: n] copolymers of methacrylic cid or acrylamide with ethyl crylate.

To form the enamel, after igmentation melamine form-ldehyde resin is added and [unclear: he] film baked. Cross linking etween the two resins occurs, iving a film with the out-landing properties detailed bove. Plasticising alkyd esins are also included to romote adhesion.

(b) Emulsion acrylics: This roup comprises acrylic poly-lers and copolymers in susension in an aqueous phase.

These suspension polymers re used to produce paints lor nerior and exterior brush-is "latex" types.

The basic units used in the olymerisation are methyl crylate, ethyl acrylate. 2-thyl hexyl acrylate. metharylic acid, and vinyl acetate.

It is in this field that [unclear: ctivity] is greatest. The [unclear: echanism] of polymerisation by a similar free radicle [unclear: ystem]. The basic units are mulsified in situ and the [unclear: onomers] enter the emulsiled micelle to give a polymer of the required molecular eight. The copolymer systems with vinyl acetate coupled with the ncrylates, and the pure acrylics, are both manulactured in New Zealand by this method, These vehicles form the basis of the acrylic paints of today.

The field is very wide, the chemistry of which makes an interesting study.

(c) 100 per cent reactive material for the plasties Industry: Everybody is familiar with the transparent sheeting type of material and its uses. It is formed by similar materials to those used in the acrylic lacquer, i.e. methyl methacrylate. The sheets of plastic are made by filling a space between two sheets of armour-tough plans, with the methyl methacrylate. and placing in an oven and heating until the monomer becomes nolymerised to the nolymethyl metharylate The finished sheeting is' imported ready to use.

Vinyl resins

As paint vehicles the vinyl res ns form two types:—

(i) Emulsion.

(ii) Solution.

The emulsion type, as vinyl acetate, has been discussed with the acrylic emulsions above.

The solution type polyvinyl chloride resin, is used in New Zealand but all resins are imported. Basically they arc high molecular weight, copolymers of vinyl chloride with vinyl acetate. The vinyl acetate is introduced into the polyvinyl chloride chain to ensure adequate solubility in solvents and ensure adequate adhesion. There is not a great deal of activity with the polyvinyl chloride resins for surface coatings. They are characterised by high water resistance and chemical inertness.

In the plastic field many high polymer resins available today could be classed as vinyl. The basic buildine block of CHX = CHX as nart of the molecule would include polyvinyl chloride, polyethylene, polystyrene, polyvinyl alcohol, the maleates and the acrylics. The groun comprising polyethylene, nolvstyrene and polyvinyl chloride accounts for at least half the total plastic resin market. All these materials are imported ready for use and are processed to the required article such as in calendering to produce thin sheeting, extrusion to form pipes e.g. rigid PVC guttering, and flexible PVC for floor tiles, cable covering etc.. injection moulding. e.g., high impact stvrene for film viewers, women's shoe heels tovs. and manv other articles. The field is large and all thes processes form hart of the New Zealand industry.

Urethane resins

The urethanes find their main application where extreme conditions of moisture resistance, chemical resistance, and wear resistance are required. There are several types manufactured and commercially mailable in New Zealand.

(i) The one package oil modified type.

(ii) The one package moisture cured type.

(iii) The two package type.

(iv) Foam producing or plastic type.

The basic reaction of all four types involves the reaction between an isocyanate group (R — N = C = o) and hydrogen from a hydrogen donor. Modifications of the isocyanate compound and the hyorogen donor give the diflereut urethane types listed. All these products are manufactured in New Zealand based on overseas research.

(1) The one package oil modified urethane: This compound is formed by reacting toluene difsocvanatc with the hydroxyl group of an alkyd resin, e.g. a urethane modified alkyd is produced which cures by normal oil curing processes.

(ii) One package moisture cured urethane: Here toluene diisocyanate is reacted with a polylol such as polypropylene glycol to give an excess of free isocyanate groups. Polymerisation takes place With this isocyanate in contact with moisture-from the air or the substrate to which it is applied.

(iii) Two package type: This type is similar to the moisture cured type except the polylol component contains no free isocyanate and the hydrogen is provided by a polyether or a modified castor oil derivative.

(iv) Foam urethanes: The compounds used are similar to the two-can type but trichlorofluoromet hane is present to give gaseous bubbles. Somenines water Is present to produce the bubbles. Compounds such as silicones are present to control cell size and prevent cell rupture. By varying the molecular weight of the hvdroxvl containing compound so different flexibilities are achieved. The higher the molecular weight the greater the flexibility.

The flexible foams are used m pillows, cushions, etc, while the rigid foam is used in insulation of heal and sound and in articles such as surf boards.

Epoxy resins

The chemistry of epoxy resins revolves around the ethylene oxide ring. The resins are produced by reacting a derivative of coal tar. bisphenol A with epichlorohydrin. These resins arc manufactured in New Zealand and are used in—

(i) Surface coatings.

(ii) Dies and castings.

(iii) Foams.

(iv) Laminates.

(v) Adhesive.

(vi) Body solders and patching compounds.

There is no difference between the resins used in surface coatings and in the plastics, other than the molecular weight. The lower molecular weight compounds are pourable liquids, the higher are hard solids.

These resins become very hard and tough when polymerized through reaction with various chemical hardeners, mainly polyamides.

The basic research for these materials has been done overseas.