Urethane milled glass

Table XI demonstrates the effect of fiber length on properties for a type of RIM processable material - the urethane modified isocyanurate which has low impact. Table XI ccnpares milled glass fibers with 1/8" chapped strand. The longer aspect length chopped strand provides for true reinforcement. However, it cannot be used in current RRIM equipment.

Reinforced RIM urethane using milled glass fibers (1/16 ) at 25% loading or more is now the "state of the art" reinforcement. 

Flexural Modulus. Figure 5 shows flex modulus values at 23 °C measured parallel and perpendicular to flow. The nonreinforced urethane polymer has a value of about 50,000 psi. Columns B and C show the results obtained with 8.5% and 20% loadings of milled glass fibers, respectively. Column D shows results obtained with 3.5% loadings of 1/8 chopped Integral strands. The flex modulus increased by about 20%. Column E shows data for 13.4% integral chopped strands the increase was more than 240% of the original... 

Impact Strength. Figure 6, notched Izod impact strength, shows one of the main reasons for the interest in chopped integral strands (c/s) as RRIM urethane reinforcement. The nonreinforced urethane polymer used in this study had an impact value of approximately 12 ft-lb/in. Reinforcement with 20% milled glass fibers lowers this value to about 5 ft-lb/in. (Column B). 

This process, in which a high modulus urethane elastomer is reinforced by milled glass fibers is currently commercially used in a three piece air spoiler used on the 1980 Pontiac Sunbird. The first use of reinforced RIM urethane front fenders is scheduled for use on a 1981 model car. 

RRIM machines can handle fibre-filled systems with viscosities up to 6000m Pas, which is much higher than the conventional RIM material viscosities of up to only 2000 m Pa s. The limitation to the present RRIM technology is that the process is only successful for milled glass of 0-8-6 mm screen size (average filament length of 01-0-3 mm and approximate filament diameter 0-01 mm) or other short fillers. Comparative properties of RRIM versus other structural materials are shown in Table 6.7 and a comparison of RIM versus RRIM polyurethanes is given in Table 6.8. This makes it possible to identify the features of RIM and RRIM urethanes,... 

Encapsulation is often performed with resins containing fillers such as mica, aluminum oxide, milled glass fibers, and many others. Although epoxies are the resins most generally used, polyesters, filled and unfilled silicones, urethanes, and polysulfides are also used. By the proper choice of fillers it is possible to match expansion rates of the electronic part and the encapsulant, increase the thermal conductivity of the part, and considerably upgrade the electrical and mecharucal properties of the assembly. 

Surface Quality. Class "A surface (after painting) is considered by the automotive industry as their first requirement for an exterior part. Comparing the surface quality of several reinforcements in RRIM urethane panels, it was found by visual examination that the best surface quality was the glass flakes and the worst was the integral chopped strands. Milled fiber is slightly worse than glass flakes, but it is still considered a "Class A" surface. 

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