Polystyrene expansion

Figure 11. Polystyrene expansion during irradiation in the absence of significant stress (<10 p.s.i.g.)...

Coefficient of Linear Thermal Expansion. The coefficients of linear thermal expansion of polymers are higher than those for most rigid materials at ambient temperatures because of the supercooled-liquid nature of the polymeric state, and this applies to the cellular state as well. Variation of this property with density and temperature has been reported for polystyrene foams (202) and for foams in general (22). When cellular polymers are used as components of large stmctures, the coefficient of thermal expansion must be considered carefully because of its magnitude compared with those of most nonpolymeric stmctural materials (203). 

Steam-Chest Expansion. In steam-chest expansion the resin beads in which gas is already present are poured into molds into which steam is injected. The steam increases the temperature close to the melting point and expands within the stmcture to create beads with food cushioning and insulating properties. Expanded polystyrene is widely used in this process for thermal insulation of frozen food packaging. 

One alternative approach to the two-stage steam moulding process is that in which impregnated beads are fed directly to an injection moulding machine or extruder so that expansion and consolidation occur simultaneously. This approach has been used to produce expanded polystyrene sheet and paper by a tubular process reminiscent of that used with polyethylene. Bubble nucleating... 

Stafford, C.M., Russell, T.P, and McCarthy T.J., Expansion of polystyrene using supercritical carbon dioxide, effects of molecular weight, polydispersity, and low molecular weight components, Macromolecules, 32, 7610, 1999. 

A 50% expansion 5 years after startup is expected because of rapid growth in the use of polystyrene and the excellent choice of a site. 

Foamed polystyrene - which is also known as expanded polystyrene - is used extensively in a variety of applications, ranging from packaging peanuts to insulation board and single-use cups and plates. We produce it by two processes foam extrusion and bead expansion. Both types of expanded polystyrene consist of closed cells, i.e., bubbles with continuous walls. We can visually distinguish the two types of foam by the fact that products made by the expanded bead process consist of discrete beads that are welded together... 

Compare and contrast the bead expansion and foam extrusion methods of creating foamed polystyrene. 

In a separate study [88], we synthesized EGF fused to a polystyrene-binding peptide [101] (EGF-PSt) that could be immobilized on the surface of a tissue culture polystyrene dish. This surface also permitted efficient expansion of NSCs. Thus, EGF-PSt can be used to produce large quantities of pure NSCs in standard laboratories. 

Manufacturing Processes. By 1945 three processes were competing with each other for the further expansion of polystyrene capacities ... 

The Polystyrene Family. After 1945 there was a drastic drop in the demand for styrene monomer because the need for synthetic rubber suddenly declined. On the other hand, a big demand existed for goods in the civilian sector and this provided a strong impetus to the expansion of polystyrene. In many cases, however, the mechanical strength of polystyrene was inadequate and this initiated numerous research efforts, especially in the immediate postwar period. 

In one of several important studies on dendronized polymers [4c, 4d]. Schluter and coworkers explored the stiffening of polystyrene chains through the incorporation of Frechet-type dendrons as side chains [28, 29]. While the G-l and G-2 dendrons were not sufficiently bulky to effectively stiffen the polystyrene chain, the G-3 dendron provides enough steric bulk to force the hybrid polymer into adopting a cylindrical shape in solution [28b], In a complementary study, Neubert and Schluter demonstrated that adding charges to the dendritic wedges leads to an expansion of the chains of the hybrid copolymer in aqueous solution [29],... 

CNT can markedly reinforce polystyrene rod and epoxy thin film by forming CNT/polystyrene (PS) and CNT/epoxy composites (Wong et al., 2003). Molecular mechanics simulations and elasticity calculations clearly showed that, in the absence of chemical bonding between CNT and the matrix, the non-covalent bond interactions including electrostatic and van der Waals forces result in CNT-polymer interfacial shear stress (at OK) of about 138 and 186MPa, respectively, for CNT/ epoxy and CNT/PS, which are about an order of magnitude higher than microfiber-reinforced composites, the reason should attribute to intimate contact between the two solid phases at the molecular scale. Local non-uniformity of CNTs and mismatch of the coefficients of thermal expansions between CNT and polymer matrix may also promote the stress transfer between CNTs and polymer matrix. 

Polystyrene is an amorphous polymer and shrinkage and coefficient of thermal expansion are rather low depending on the possible rubber content. The absorption and alteration by moisture exposure are low. 

Liu and Zhong introduced a number of QSPR models based on molecular connectivity indices [151, 152], In a first iteration, the researchers developed polymer-dependent correlations descriptors were calculated for a set of solvents and models were developed per polymer type [151], Polymer classes under consideration were polystyrene, polyethylene, poly-1-butene, poly-l-pentene, poly(4-methyl-l-pentene), polydimethylsiloxane, and polyisobutylene. As the authors fail to provide any validation for their models, it is difficult to asses their predictive power. In a subsequent iteration and general expansion of this study, mixed and therefore more general models based on the calculated connectivity indices of both solvent and polymers were developed. While it is unclear from the paper which polymer representation was used for the calculation of the connectivity indices, the best regression model (eight parameter model) yields only acceptable predictive power (R = 0.77, = 0.77, s = 34.47 for the training set, R = 0.75... 

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