Polystyrene Compressibility

Klein and co-workers have documented the remarkable lubricating attributes of polymer brushes tethered to surfaces by one end only [56], Studying zwitterionic polystyrene-X attached to mica by the zwitterion end group in a surface forces apparatus, they found /i < 0.001 for loads of 100 and speeds of 15-450 nm/sec. They attributed the low friction to strong repulsions existing between such polymer layers. At higher compression, stick-slip motion was observed. In a related study, they compared the friction between polymer brushes in toluene (ji < 0.005) to that of mica in pure toluene /t = 0.7 [57]. 

Fabrication. Acetal resins are most commonly fabricated by injection mol ding. A homogeneous melt is essential for optimum appearance and for performance of injection molded parts. A screw compression ratio of no less than 3 1 is advised and the size of the injection molded shot should be 50 to 75% of the rated capacity (based on polystyrene) of the barrel. 

Fig. 3. Effect of density on compressive modulus of rigid cellular polymers. A, extmded polystyrene (131) B, expanded polystyrene (150) C-1, C-2, polyether polyurethane (151) D, phenol—formaldehyde (150) E, ebonite (150) E, urea—formaldehyde (150) G, poly(vinylchloride) (152). To convert...

Fig. 4. Load vs compression for plastic foams (149). A, polystyrene, 32 kg/m (2 lbs/fT) B, polyethylene, 32 kg/m C, latex mbber foam. To convert...

The particular type of thermoplastic elastomer (TPE) shown in Figure 3 exhibits excellent tensile strength of 20 MPa (2900 psi) and elongation at break of 800—900%, but high compression set because of distortion of the polystyrene domains under stress. These TPEs are generally transparent because of the small size of the polystyrene domains, but can be colored or pigmented with various fillers. As expected, this type of thermoplastic elastomer is not suitable for use at elevated temperatures (>60° C) or in a solvent environment. Since the advent of these styrenic thermoplastic elastomers, there has been a rapid development of TPEs based on other molecular stmctures, with a view to extending their use to more severe temperature and solvent environments. 

Table 16.5 Typical mechanical properties of compression-moulded polystyrene plastics as measured by appropriate ASTM tests...

In the 1990s this approach became more common in order to ensure sufficient compressive strength with the trend to lower bulk densities. Furthermore the proportion of SAN to polyol has been increased to about 40%. This may lead to serious stability problems and care must be taken to control the size and distribution of the particles and prevent agglomeration. Polymer polyols using polystyrene as the polymer component have recently become available (Postech-Shell) and are claimed to exhibit good stability, low viscosity and less discolouration as well as providing price advantages. 

Assemble the polystyrene cassette filter holder, using the appropriate filter for the sampling method. Compress cassette by using a mechanical press or other means of applying pressure. Use shrink tape around cassette... 

S-B, S Polystyrene 1,2-polybutadiene Polystyrene Polybutylene Enhanced compression set... 

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