Polyurethane foams semi-rigid

Figure 39. TG curves of unpyrolysed trimethylolpropane trimethacrylate (SR 350) (crosslinked), foamed semi-rigid polyurethane, and unpyrolysed trimethylolpropane trimethacrylate/polyurethane foamed blends (SR 350/PU weight ratio = 5.25/1, low-PU and 1/1, high-PU) under nitrogen...

Polyurethane foams may be rigid, semi-rigid or flexible. They may be made from polyesters, polyethers or natural polyols such as castor oil (which contains approximately three hydroxyl groups in each molecule). Three general processes are available known as one-shot, prepolymer or quasi-prepolymer processes. These variations lead to 27 basic types of product or process, all of which have been used commercially. This section deals only with flexible foams (which are made only from polyesters and polyethers). Since prepolymers and... 

Gas-filled plastics are polymer materials — disperse systems of the solid-gas type. They are usually divided into foam plastics (which contain mostly closed pores and cells) and porous plastics (which contain mostly open communicating pores). Depending on elasticity, gas-filled plastics are conventionally classified into rigid, semi-rigid, and elastic, categories. In principle, they can be synthesized on the basis of any polymer the most widely used materials are polystyrene, polyvinyl chloride, polyurethanes, polyethylene, polyepoxides, phenol- and carbamideformaldehyde resins, and, of course, certain organosilicon polymers. 

Another major use for semi-rigid polyurethane foams is as shoe soles. In this application, their light weight, abrasion resistance, and shock absorbing properties are important. In safety shoes, chemical and oil resistance are important. Polyether-based foams are used in applications where microbial attack is common, such as shoes intended primarily for use on soil or grass. 

We also use semi-rigid polyurethane foams to package irregularly shaped objects. Liquid reactants are injected into a plastic bag, which swells to form a custom fit that immobilizes items within an outer box. 

Rigid polyurethane foams are mostly based on polyether alcohol and are highly cross-linked. Rigid foams are many times blown by halogenated alkanes like trichlorofluoromethane. These foams have closed cell structures and are used for thermal insulation. Semi-rigid foams are used in car crashpads and packaging. 

With Amendment 1 this specification supersedes the Type II (Foam-in-Place) requirements in MIL-P-26514F described above. The requirement is for flame-resistant polyurethane foams furnished in two-component foam-in-place systems. The specification also supersedes MII P-21029B. The basic specification and Amendment 1 are Air Force (60) documents, whUe Interim Amendment 2 is a Navy (SA) document. There are 3 Gasses, Class 1 - Rigid, Class 2 - Flexible, and Class 3 - Semi-Rigid. Static-stress curves are given for Gasses 2 and 3. 

Based on the numbers in Figures 1 and 2, by 1985 RIM and RRIM will require approximately 50 M lbs. of monomeric MDI, which is about one-third of the monomeric MDI supply in 1985 (Table IX based on 20-25% of 85% nameplate capacity, excluding ARCO capacity, = 137-171 M lbs. monomeric MDI). This will leave about 100 M lbs. of monomeric MDI for cast elastomers, thermoplastic polyurethanes, shoe soles, semi-rigid foams, and some adhesives and sealants, a monomeric MDI supply which should be more than sufficient for these applications. As RRIM grows, a need for capacity expansion can be seen in the late 1980 s. No effects on the market will be seen from PUR-SMC until after 1985, and at the present time meaningful projections are impossible. 

Lignin by-products from kraft and sulfite pulping were found to constitute useful raw materials for polyols for polyurethane products. Their employment in the manufacture of semi-rigid polyurethane foams as well as polyurethane adhesives and coatings... 

To produce polyether polyols (PEP), sorbitol is reacted in the presence of a catalyst with propylene or ethylene oxide (see Figure 9.2.12). The reaetion is aimed at achieving polyols with a hydroxyl number of between 350 and 550. Sorbitol-based PEPs are then used to manufacture rigid or semi-rigid polyurethane foams by reaction with a suitable polyisocyanate. These foams are typically used in the construction industry and in packaging, industrial insulation, appliances and transport applications. 

These foams can then be extended into the area of flame-retardant materials, where methyl oleate-polyesters were used as polyols in the synthesis of silicon-containing polyurethanes [89]. Despite not strictly being foams, methyl oleate, soybean and sunflower oils have also been investigated to produce semi-rigid flame retardant materials [90]. In this instance, they were brominated, acrylated and then radically copolymerized with styrene to form the polymeric material. 

Nonwoven scrim Adhesive film/powder Chopped glass mat Adhesive film/powder Central core Adhesive film/powder Chopped glass mat Adhesive film/powder Polyurethane foam Decorative (face) fabric Typically polyester Hot melt Adds rigidity Hot melt Semi-rigid PU foam or resonated waste fibres Hot melt Adds rigidity Hot melt Present if the need for soft touch is required Typically polyester... 

A typical RIM formulation is given in Table 6.2. It is very similar in principle and design to a low-density semi-rigid polyurethane foam mix except that the more expensive linear polyester is used as the chain flexible element and a pure form of MDI is used as the strength-giving component. The functions of the various ingredients shown in the table are now described. 

Cabs are assembled using the conveyor belt system integrated with the rest of the lorry assembly line. The output of completely fitted out lorries is seventeen per day. A semi-rigid polyurethane foam filling is inserted in the roof panel to improve sound deadening. 

Disposable ear-plugs are made from glass down, plastic-coated glass down and polyurethane foam, while re-usable ear plugs are made from semi-rigid plastic or rubber. Re-usable ear-plugs need to be washed frequently. 

BMW dashboard ABS/PVC skin backed with semi-rigid PUR foam (courtesy ICI Polyurethanes). 

It may be noted here that castor oil is used as a hydroxy-compound in the preparation of polyurethanes, particularly for semi-rigid foams. Castor oil is essentially a triol, being composed largely of the glyceryl ester of ricinoleic acid. (See Table 10.4.)... 

It may be noted here that whilst most attention has been directed towards flexible and rigid polyurethane foams, intermediate products known as semi-rigid foams find use in the manufacture of car crash-pads and packaging. These products may be obtained from castor oil, polyether triols of intermediate molecular weight or moderately branched polyesters. 

Polyurethane thermal-oxidative resistance depends on the polyurethane structure and in particular on the structure of the polyol [186]. Soft-flexible standard polyurethane foams have a temperature index of approx. 90 to 120 °C the temperature index for semi-rigid systems is approx. 120 to 140 °C. These numbers can be 10 to 20 °C higher in filled systems [513]. 

MARISTICK 1750 Subfloor polyurethane adhesive from M-D Co Semi-rigid, two -component, without solvents Premium grade quick curing PUR foam adhesive Adhesion of metal, wood and ceramic tiles on horizontal and vertical surfaces Subfloor, plywood, gypsum, foamboards, block, fibreboard, drywaU, wallboard, brick, hardboard Provides elasticity of hard rubber, excellent adhesion without shrinkage, cures by crosslinking even at very low temperatures... 

Polyurethane foams cellular plastics basically of three types flexible urethane foams used for upholstery, matresses, textile linings, acoustic insulation, etc rigid urethane foams used for heat insulation (eg refrigeration), cold stores, building-panel cores, etc and semi-flexible foams used for arm rests, packaging, etc. 

The most interesting development in rigid polyurethane foams recently has been the advent of integral-skin rigid foams. These foams are formed in a similar way to integral-skin semi-flexible foams (discussed earlier) and are finding application in decorative mouldings, furniture pieces, domestic appliance cabinets and the like. In future they may even find application in the automotive industry. 

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