Rigid foamed polyurethane production foaming process

Process and Equipment. Rigid polyurethane foam processes use the same high or low pressure pumping, metering, and mixing equipment as earher described for flexible foams. Subsequent handling of the mixture is deterrnined by the end product desired. 

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... 

Similar production process to polyurethane. Has the best fire-safety properties of all the rigid foams. 

To get polyurethane foams the polymer is formed along with gas evolution. When these two processes take place simultaneously the gas bubbles are trapped in polymer matrix yielding a cellular product. Slightly cross-linked products are flexible while highly cross-linked products are rigid. Both flexible and rigid foams are of commercial importance. 

Cellular Polyurethane. Composed principally of the catalyzed reaction product of pulyisocyanatc and polyhydroxy compounds, processed usually with fluorocarbon gas to form a rigid foam having a predominantly closed-cell structure. Under investigation by regulators. 

Reaction injection molding (RIM) is a fast, low-pressure, low-temperature, low-cost process for one-step conversion of reactive liquids into large finished solid plastic products. Liquid polyol and liquid diisocyanate are mixed by impingement, pumped instantly to fill a large mold cavity, and polymerize/ cure rapidly to form a thermoset polyurethane product. The cured polymer may be a stiffly flexible product such as automotive bumper covers, front ends, and trim or a rigid foamed product such as furniture and housings (cabinets) for computers, business machines, TY and radio. 

With use of appropriate catalysts, mixtures of dianhydrides and diisocyanates were directly converted to rigid foam products without use of foaming agents [105,106]. In situ formation of imide forms like the polyurethane process, was developed by Riccitiello et al. [107]. The system contains a unique furfuryl alcohol-acid mixture which generates heat to initiate the isocyanate-anhydride reaction. 

High conversions and molecular weights are obtained because reversible reactions and side-product removal is not an issue. In RIM processes, liquid monomers are mixed using impinging jets and must quickly flow into the mold before the reacting mixture becomes too viscous. The complete cycle time for injection, reaction and umnolding (so that the mold can be used to make the next product) is often only 30-60 s. RIM is used to produce rigid molded polyurethane automobile parts and polyurethane foam seat cushions [3j. 

In a modification of the usual process for the production of rigid foam, a high proportion of isocyanurate links are incorporated into the structure to give a so-called polyisocyanurate foam. In this technique, the polyether is treated with an excess of isocyanate in the presence of an isocyanurate catalyst (e.g. an alkali metal alcoholate or carboxylate). Polyisocyanurate foams have significantly lower combustibility than conventional polyurethane foams. 

In [75,76], a method of decomposition of polyurethane rigid foams is described, using EG, DEG, and polyoxypropylenated pentaerythritol (with a hydroxyl number of 170 mg KOH/g) mixed with ethanolamines (mono-, di- and triethanolamine). Various salts of metals, such as tin, iron, sodium, potassium, zinc, calcium, copper, and cobalt were used as catalysts. The process products can be used as raw materials for the production of polyurethane plastics. 

Applications. The principal use for rigid polyurethane foams is for iasulation ia various forms utilized by a variety of iadustries. Lamiaates for resideatial sheatiag (1.2 to 2.5 cm thick with aluminum skins) and roofing board (2.5 to 10.0 cm thick with roofing paper skins) are the leading products with about 45 metric tons of Hquid spray systems also ia use. Metal doors iasulated by a pour-ia-place process coastitute another substantial use. 

The glycolysis of rigid polyurethane foams produces polyol products which can be reintroduced into the production cycle of PUR insulation materials to form materials with properties practically equivalent to dtose of materials produced using virgin polyols. Aromatic amines produced as by-products in die glycolysis process are toxic and therefore undesired side products. The most frequently observed side product is diphenylmedianediamine (DMDA), which is formed... 

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