Moulding Flexible foam

Aminoplast dispersions, in spite of the accessibility and low cost of raw materials, are not produced industrially, due to the risk of toxic formaldehyde elimination, especially when the resulting aminoplast polymer polyol is used for slabstock foams and, of course, for moulded flexible foams used for seating or interior automotive parts. 

Not only are these reactions of importance in the development of the cross-linked polyurethane networks which are involved in the manufacture of most polyurethane products but many are now also being used to produce modified isocycuiates. For example, modified TDI types containing allophanate, urethane and urea groups are now being used in flexible foam manufacture. For flexible integral foams and for reaction injection moulding, modified MDIs and carbodi-imide MDI modifications cU"e employed. 

Polymers Unsaturated fatty-acid chains offer opportunities for polymerisation that can be exploited to develop uses in surface coatings and plastics manufacturing. Polyunsaturated fatty acids can be dimerised to produce feedstocks for polyamide resin (nylon) production. Work is also ongoing to develop polyurethanes from vegetable oils through manipulation of functionality in the fatty-acid chains, to produce both rigid foams and elastomers with applications in seals, adhesives and moulded flexible parts (see Chapter 5 for more information). 

The global consumption in 1997 was 7 x 1()6 t. The market is dominated by flexible foam (49 % in the USA, 38 % in Western Europe) and rigid and semi-rigid foam (28 % USA, 35 % Western Europe). Reaction injection moulding (RIM) products account for about 6 % and cast rubbers 2 %, and about 15 % is used as thermoplastic rubbers, surface coatings, sealants, adhesives and synthetic leathers. 

Parkinson, J.C., "Moulding Flexible Polyurethane Foam", British Plastics, 27 (3) 146-147 (March 1964). 

The polyether triols are the most important class of polyether polyols and they are used in flexible PU foam fabrication. The majority of polyether triols used in flexible foams are copolymers of PO-EO. Random copolymers are used in continuous slabstock flexible foams and block copolymers (PO-EO), with terminal poly[EO] block, are used in moulded foams (hot moulding and cold cure moulding processes). 

It can be seen that moulded flexible PU foams using EO capped polyether polyols (block copolymers PO-EO with terminal poly[EO] block) represent only 22% of total worldwide consumption and that the majority of foams are flexible slabstock PU foams which use random copolyethers of PO-EO. It can therefore be concluded that the most important polyols for flexible PU foams production are in fact the random copolyethers PO-EO. 

This polyether triol hybrid structure block [PO] - random [PO - EO]- block EO, with a MW of 3000 daltons, was used successfully for hot moulded flexible PU foams with... 

The polyether triols (PO-EO block copolymers with terminal poly[EO] block) are very reactive polyols due to the presence of a high percentage of primary hydroxyls. These polyether polyols with terminal poly[EO] block, are used preferentially for moulded flexible PEI foams. 

Basic polyurethane chemistry was discovered by Otto Bayer in 1937, but polyurethane polymers were first developed as replacements for rubber at the start of World War II. Numerous applications followed including fibres, rigid and flexible foams, mouldings and elastomers (Brydson, 1999). The preparation of polyurethane polymers occurs via a reaction process intermediate between those of addition and condensation (Brydson, 1999). Like addition polymerization, there is no splitting off of small molecules, but the kinetics are otherwise similar to condensation polymerization. 

Figure 3.11 A modular oval conveyor for flexible foam moulding. It can be easily extended, adding modules of track and pairs of mould carriers, when higher productivity is required.

Flexible moulded polyether foam is widely used in the transport, furniture and packaging sectors. In many cases flammability is of great importance and so the effects of suitable flame-retardant agents on such foams has been widely studied. One piece of work by Chestnut Ridge Foam in Pennsylvania, using Cone Calorimetry, studied the heat release characteristics of various combinations of commercially available additives, plus the CO emission and time to ignition. 

Bayer markets a dimethylpropane phosphonate-based FR called Levagard VP SP 51009 to enable rigid PU foam to meet fire regulations. Clariant offers liquid phosphorus polyols for the protection of polyether flexible and slabstock moulded automotive foams. Flexible PU is also commonly flame retarded in Europe with chlorinated phosphate esters. Borates have not shown... 

Suprasec VM 50 2-5 Low viscosity liquid polyisocyanates. High density flexible foams. Structural foams. Foam-backs for carpets/vinyls. Computer cabinets and other moulded articles. 

Several kinds of polyurethanes are of commercial significance and are conveniently classified into the following major types - flexible foams rigid foams elastomers fibres and moulding compositions surface coatings and adhesives. These various types of material are considered separately in this chapter after an account of the development of polyurethanes, the raw materials involved and the general reactions of isocyanates. 

The water-isocyanate reaction forming carbon dioxide is commonly used to form open-cell flexible foams. Trichlorofluoromethane (TCFM) is a physical blowing agent relying on heat from the urethane reaction exotherm to boil this is used to form rigid closed-cell foams and most self-skinned moulded products. There is considerable concern over the effect of fluorocarbons on the Earth s ozone layer, and suitable replacements are actively being sought. 

Figure 11.2 Production of hot cure moulded flexible PU foam...

Conventionally, almost all flexible foam mouldings are used in the automotive industry, although difficult furniture shapes are also moulded. 

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