Compression molding additives

Kohli et al. [27], for instance, showed that the tensile modulus of a highly drawn PC-TLCP composite could be modeled effectively by the simple additivity rule of mixtures, while the compression molded composite samples with a spherical TLCP morphology had moduli according to the inverse rule. In both cases, the tensile modulus of the TLCP (Ei,c) itself was assumed to be a constant value determined from a tensile test of the pure TLCP samples. But whether or not the dispersed TLCP fibers and deformed droplets have the same modulus as the bulk TLCP samples remains a question. 

The stability, growth, and transport of voids during composite processing is reviewed. As a framework for this model, the autoclave process was selected, but the concepts and equations may be applied equally effectively in a variety of processes, including resin transfer molding, compression molding, and filament winding. In addition, the problem of resin transport and its intimate connection with void suppression are analyzed. 

The data shown in Figure 7.15 were obtained from two-ply T300/P1700 unidirectional specimens that were compression molded in a 76.2 mm (3 in.) square steel mold. The cross-sections of the consolidated specimens were examined by optical microscopy and the degree of intimate contact was determined as the amount of the interply region that was in contact divided by the total area of the cross-section. Additional details of the experimental procedures are given in Reference 22. 

Additional source of information for UHMWPE acetabular cups arises from the quantitative analysis of polarized Raman spectra. Figure 17.6 shows photographs and the outcome of such analysis for two acetabular cups, which were retrieved after substantially different in vivo lifetimes. The retrieved acetabular cups were both belonging to male patients and sterilized by y-rays, but produced by different processes. One acetabular component (manufactured in 2002 by Biomet Inc.) was prepared by isostatic compression molding and sterilized before implantation by a dose of 33 kGy of y-rays. It was retrieved due to infection after 2 years 5 months. This cup will be referred to as the short-term retrieval. The other retrieval (manufactured in 1995 by Zimmer Inc.) was prepared by Ram-extruded molding and sterilized in air by a dose of 25-37 kGy of y-rays. For this latter cup, the follow-up pe-... 

Fig. 36 Fracture surfaces of thick, compressed A18749 resin sintered at 350 °C for (a) 5 min and (b) 30 min and (c) the sample in (b) reheated for an additional 30 min at 350 °C followed by slow cooling in a compression-molding press with no pressure applied...

Sample Preparation. All polymer samples were prepared from commercial general purpose polystyrene (Monsanto HF-77). The additives were incorporated into the polymer by fluxing on a two-roll laboratory mill at about 350°F. Two types of samples were molded from the milled polymer (a) 50-mil plaques, compression molded at 350°F. (b) 1.5-2.5-mil films, compression molded at 390°F. 

The additive was added gradually to the polymer fused on a two-roll mill at 170°-174°C. After addition, polymer sheets were taken off the mill and put back on the mill endwise. Several such passes were made until the sample was thoroughly mixed. The specimen was removed from the mill in thin sheets and, while hot, cut into small pieces. The polymer was compression molded at 700 p.s.i.g. and a temperature of ca. 155°C. into a 6 X 6-inch sheet of about 0.045-inch thickness. This sheet was cut into the 5 X 1/2 X 0.045-inch specimens for burning in the modified D635 test. The sample was initially evaluated with 25% additive. If the compound was effective, lower concentrations were used until the additive would not confer fire retardant activity, or until the supply of additive was exhausted. With poly (methyl methacrylate), PMMA, cast samples also were prepared. 

Additional Considerations. Compared to injection molding of thermoplastics, compression molding is less capital intensive, more labor-intensive, and takes a longer... 

However, the kind of technique used to mold these blends seems to be important in determining their mechanical properties. In fact, mechanical tests carried on injection molded samples [37] show, with respect to compression molded samples, a significant enhancement of the energy to break for all samples (Tables 20.2 and 20.3). Moreover the addition of 10wt% of SEBS to an 80 20 wt% sPS/HDPE blend involves in the injection molded samples an increase in both the energy at break and the Izod impact strength, whereas in the thermo-compressed samples no improvement is observed. Differences between compression and injection molded samples are widely acknowledged [38] and... 

The primary particle size distribution of the powder, as well as the granule shape, has an influence upon the attainable density and strength of the molded article. The static friction between the individual particles and the compression mold can be reduced by lubricating additives, which largely suppress the development of structural stress. 

In addition to Dow s own technology base 1n RIM, Injection molding and compression molding, the data 1n this study was developed from literature references and from consultation with authorities 1n the automotive Industry, material suppliers and equipment manufacturers. 

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