Molded samples

In general, polycarbonate resins have fair chemical resistance to aqueous solutions of acids or bases, as well as to fats and oils. Chemical attack by amines or ammonium hydroxide occurs, however, and aUphatic and aromatic hydrocarbons promote crazing of stressed molded samples. Eor these reasons, care must be exercised in the choice of solvents for painting and coating operations. Eor sheet appHcations, polycarbonate is commonly coated with a sihcone—sihcate hardcoat which provides abrasion resistance as well as increased solvent resistance. Coated films are also available. 

An example is poly(bis(p-carboxyphenoxy)propane) (PCPP) which has been prepared as a copolymer with various levels of sebacic anhydride (SA). Injection molded samples of poly (anhydride) / dmg mixtures display 2ero-order kinetics in both polymer erosion and dmg release. Degradation of these polymers simply releases the dicarboxyhc acid monomers (54). Preliminary toxicological evaluations showed that the polymers and degradation products had acceptable biocompatibiUty and did not exhibit cytotoxicity or mutagenicity (55). 

Measured on extmded samples, all others measured on injection molded samples. 

Similar to prepared metallographic samples, the injection molded samples were cut along the flow direction, smoothed, and polished in order to expose their internal surface. After proper etching, the treated surfaces of the flank cross-section were photographed using a polarized light optical microscopy. Based on the color differences between the TLCP and matrix, volume fraction and aspect ratio of the TLCP fibers were measured [23]. 

The release behavior depends on both the choice of polymer and on the formulation procedure. The best results were obtained with injection-molded samples. For prototypical drugs like p-nitroaniline, the drug release pattern followed closely that of the polymer degradation over a period of 9 months for PCPP. The correlation between release and degradation was still maintained in the more hydrophilic PCPP-SA, 20 80, where both processes were completed in 2 weeks. Compression molding can also be used for these polymers, but the correlation between drug release and polymer degradation is not as... 

Two other features are notable in Table III. The swelling values for the compression molded samples (CM) run consistently less than those for the solvent-cast films. Apparently there is more "entrapment" of the amorphous portions within the crystallites during and after the molding. Secondly, the degradation experienced by the polymer hydrogenated at 69°C. (see Table II) instead of 52°C. is clearly demonstrated by the higher swelling value. 

Figure 6. X-ray fiber diagram of poly(5-methyl-1,4-hexadiene) prepared with a Etj,AlCl/S-TiCl, catalyst at 0°C in pentane solvent. Compression molded sample cold drawn to four times its original length.

Preparation of Samples for Flammability Testing. Samples of the phosphorus containing terepolymers and of the polymer blends were converted to film by compression molding on a Carver Laboratory Press with electrically heated platens. The films were prepared at 250°C and 20,000 lb. pressure, using a 10 mil thick frame mold. Samples (2" x 1/4") were cut from this film for flammability testing. 

Appropriate amounts of x y resin and liquified amine were mixed together and evacuated at 60 c in a vacuum oven for t i minutes to remove air bubbles. The reaction mixture was poured into a hot (85°C) aluminum mold vhich was prepared in advance by lic tly spraying mold release agent (ISi 515, Green Chem. Products Inc.) to the inner surfaces of the mold. Samples were cured two hours at 85 C followed by two hours at 150 c (standsuxl cure). In some cases samples were subjected to eui alternate, high temperature cure of two hours at 85 C and two hours at 175 C (HT cure). After curing, samples were stored in a desiccator until use. 

Dynamic melt viscosity studies on the star blocks and a similar triblock were carried out using a Rheometric Mechanical Spectrometer (RMS) (Rheometrics 800). Circular molded samples with -1.5 mm thickness and 2 cm diameter were subjected to forced sinusoidal oscillations (2% strain) between two parallel plates. The experiment was set in the frequency sweep mode. Data were collected at 180 and 210 °C. 

The dynamic melt viscosity measurements of select star blocks and a similar triblock were carried out on a rheometric mechanical spectrometer, RMS. Circular molded samples of 2 cm diameter and -1.5 mm thickness were subjected to forced sinusoidal oscillations. Dynamic viscosities were recorded in the frequency range of 0.01-100 rad/s at 180 °C. Figure 10 shows the complex viscosities of two select star blocks and a similar linear triblock. The plots showed characteristic behavior of thermoplastic elastomers, i.e., absence of Newtonian behavior even in the low frequency region. The complex viscosity of the star block... 

Figure 5 presents the results of tensile tests for the HPC/OSL blends prepared by solvent-casting and extrusion. All of the fabrication methods result in a tremendous increase in modulus up to a lignin content of ca. 15 wt.%. This can be attributed to the Tg elevation of the amorphous HPC/OSL phase leading to increasingly glassy response. Of particular interest is the tensile strength of these materials. As is shown, there is essentially no improvement in this parameter for the solvent cast blends, but a tremendous increase is observed for the injection molded blend. Qualitatively, this behavior is best modeled by the presence of oriented chains, or mesophase superstructure, dispersed in an amorphous matrix comprised of the compatible HPC/OSL component. The presence of this fibrous structure in the injection molded samples is confirmed by SEM analysis of the freeze-fracture surface (Figure 6). This structure is not present in the solvent cast blends, although evidence of globular domains remain in both of these blends appearing somewhat more coalesced in the pyridine cast material.

Samples for irradiation crosslinking were prepared by milling in the antioxidant, followed by compression molding. Sample dimensions were 6 X 7 X 0.083 inch. Details of the milling and compression molding procedures are given in Table II. 

Thermal stability as measured by these ramped TGA experiments of the sort previously described are not the definitive test of a polymer s utility at elevated temperature. Rather, for a polymer to be useful at elevated temperatures, it must exhibit some significant retention of useful mechanical properties over a predetermined lifetime at the maximum temperature that will be encountered in its final end use application. While many of the bisbenzocyclobutene polymers have been reported in the literature, only a few have been studied in detail with regards to their thermal and mechanical performance at both room and elevated temperatures. Tables 7-10 show some of the preliminary mechanical data as well as some other physical properties of molded samples of polymers derived from amide monomer 32, ester monomer 40, diketone monomer 14 and polysiloxane monomer 13. The use of the term polyamide, ester etc. with these materials is not meant to imply that they are to be regarded as merely modified linear thermoplastics. Rather, these polymers are for the most part highly crosslinked thermosets. 

Property to be Measured ASTM Test Standard Specimen Dimensions Test Molding Sample Weight per Molding (grams)... 

Measured on extruded samples, all others measured on injection molded samples. C To convert MPa to psi, multiply by 145. 

The physical properties of polytetrafluoroethylene have been reviewed by Doban, Sperati, and Sandt and by Renfrew and Lewis, and some average properties for well molded samples are listed in Table 1. 

The graft polymers were diluted with an SAN copolymer to 20 and 30 wt % substrate. The dry blends were mixed on a two-roll mill for a maximum of 5 minutes (165° 175°C) without added lubricants. Compression-molded samples from the milled slabs were evaluated for impact and tensile strength. Figure 5 is a schematization of this procedure. 

Figure 13.13 shows such a distribution measured by Menges and Wiibken (30) for amorphous PS. They measured the shrinkage of microtomed molded samples at elevated temperatures. Figure 13.13(a) shows the longitudinal (flow direction) orientation distribution at two injection rates. The characteristic features of the orientation distribution are a maximum orientation at the wall that vanishes at the center with a local maximum near the wall. In Fig. 13.13(b), the longitudinal orientation at the wall and secondary maximum orientation are in close proximity, and the transverse orientation drops continuously from a maximum value at the surface. 

Using Porod s two-phase theory of small-angle X-ray scattering Kim140) has analyzed the intensity data for an unoriented molded sample of Kraton 101 and found that the interface between the styrene and butadiene phases is sharp. 

All experimental results reported in this paper were obtained with molded samples for a theoretical reason. These experiments should be repeated with pellet samples so that the experimental results could be more directly applied to actual extrusion operations. The energy efficiency will become an important factor in the future in designing a new extruder for a given output rate as energy cost increases. 

Equipment essential for electrophoresis includes power sources, gel molds, sample grinding trays, electrode buffer trays, reusable ice packs (or a 4° cold room), a gel slicer, staining trays, assorted glassware, variable temperature incubators), hot/stir plates, and a pH meter. Details on equipping a laboratory for electrophoresis are given elsewhere.12,17... 

Figure 3. A comparison between the mechanical properties of poly(sty-rene) and a poly(styrene) braid. ( ) Compression-molded sample of PS.

Compression-molded samples. b Ef20 = storage modulus at 20°C. 

X-Ray Analysis. Wide angle x-ray patterns were photographically recorded with 30-minute exposures from selected areas of the injection-molded samples. 

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