Polystyrene characteristics

The film is fibrillated mechanically by mbbing or bmshing. Immiscible polymers, such as polyethylene or polystyrene (PS), may be added to polypropylene to promote fibrillation. Many common fiber-texturing techniques such as stuffer-box, false-twist, or knife-edge treatments improve the textile characteristics of slit-film fibers. 

Creep. The creep characteristic of plastic foams must be considered when they are used in stmctural appHcations. Creep is the change in dimensions of a material when it is maintained under a constant stress. Data on the deformation of polystyrene foam under various static loads have been compiled (158). There are two types of creep in this material short-term and long-term. Short-term creep exists in foams at all stress levels however, a threshold stress level exists below which there is no detectable long-term creep. The minimum load required to cause long-term creep in molded polystyrene foam varies with density ranging from 50 kPa (7.3 psi) for foam density 16 kg/m (1 lb /ft ) to 455 kPa (66 psi) at foam density 160 kg/m (10... 

The penetration of visible light through foamed polystyrene has been shown to foUow approximately the Beer-Lambert law of light absorption (22). This behavior presumably is characteristic of other ceUular polymers as weU. 

Sulfonation has been used to change some characteristics of blends. Poly(2,6-diphenyl-l,4-phenylene oxide) and polystyrene are immiscible. However, when the polymers were functionalized by sulfonation, even though they remained immiscible when blended, the functionalization increased interfacial interactions and resulted in improved properties (65). In the case of DMPPO and poly(ethyl acrylate) the originally immiscible blends showed increased miscibility with sulfonation (66). 

Noryl. Noryl engineering thermoplastics are polymer blends formed by melt-blending DMPPO and HIPS or other polymers such as nylon with proprietary stabilizers, flame retardants, impact modifiers, and other additives (69). Because the mbber characteristics that are required for optimum performance in DMPPO—polystyrene blends are not the same as for polystyrene alone, most of the HIPS that is used in DMPPO blends is designed specifically for this use (70). Noryl is produced as sheet and for vacuum forming, but by far the greatest use is in pellets for injection mol ding. 

Carbon Cha.in Backbone Polymers. These polymers may be represented by (4) and considered derivatives of polyethylene, where n is the degree of polymeriza tion and R is (an alkyl group or) a functional group hydrogen (polyethylene), methyl (polypropylene), carboxyl (poly(acryhc acid)), chlorine (poly(vinyl chloride)), phenyl (polystyrene) hydroxyl (poly(vinyl alcohol)), ester (poly(vinyl acetate)), nitrile (polyacrylonitrile), vinyl (polybutadiene), etc. The functional groups and the molecular weight of the polymers, control thek properties which vary in hydrophobicity, solubiUty characteristics, glass-transition temperature, and crystallinity. 

Styrene is a colorless Hquid with an aromatic odor. Important physical properties of styrene are shown in Table 1 (1). Styrene is infinitely soluble in acetone, carbon tetrachloride, benzene, ether, / -heptane, and ethanol. Nearly all of the commercial styrene is consumed in polymerization and copolymerization processes. Common methods in plastics technology such as mass, suspension, solution, and emulsion polymerization can be used to manufacture polystyrene and styrene copolymers with different physical characteristics, but processes relating to the first two methods account for most of the styrene polymers currendy (ca 1996) being manufactured (2—8). Polymerization generally takes place by free-radical reactions initiated thermally or catalyticaHy. Polymerization occurs slowly even at ambient temperatures. It can be retarded by inhibitors. 

Table 10. Characteristic Properties of Some Polystyrene Foams...

In the present work it was studied the dependence of analytical characteristics of the composite SG - polyelectrolyte films obtained by sol-gel technique on the content of non-ionic surfactant in initial sol. Triton X-100 and Tween 20 were examined as surfactants polystyrene sulfonate (PSS), polyvinyl-sulfonic acid (PVSA) or polydimethyl-ammonium chloride (PDMDA) were used as polyelectrolytes. The final films were applied as modificators of glass slides and pyrolytic graphite (PG) electrode surfaces. 

PL can be used as a sensitive probe of oxidative photodegradation in polymers. After exposure to UV irradiation, materials such as polystyrene, polyethylene, polypropylene, and PTFE exhibit PL emission characteristic of oxidation products in these hosts. The effectiveness of stabilizer additives can be monitored by their effect on PL efficiency. 

The valuable characteristics of polyblends, two-phase mixtures of polymers in different states of aggregation, were also discussed in the previous chapter. This technique has been widely used to improve the toughness of rigid amorphous polymers such as PVC, polystyrene, and styrene-acrylonitrile copolymers. 

In 1930 BASF, then part of IG Farhen, installed a plant for producing 100 tonnes of polystyrene per annum and in 1933 the first injection moulded articles were produced. In the US semi-plant-scale work at the Dow Chemical Company showed promise of commercial success in 1934. As a consequence there became available shortly before World War II a material of particular interest because of its good electrical insulation characteristics hut otherwise considerably inferior to the polystyrene available today. Because of these excellent electrical characteristics prices were paid of the order of several dollars per pound for these polymers. 

Because of such desirable characteristics as low cost, good mouldability, excellent colour range, transparency, rigidity and low water absorption, polystyrene became rapidly developed. For many purposes, however, it was considered to be unacceptably brittle and this led to the development of the rubber-modified high-impact polystyrene (HIPS) and to the complex ABS, AMBS and... 

Being a hydrocarbon with a solubility parameter of 18.6MPa - it is dissolved by a number of hydrocarbons with similar solubility parameters, such as benzene and toluene. The presence of a benzene ring results in polystyrene having greater reactivity than polyethylene. Characteristic reactions of a phenyl group such as chlorination, hydrogenation, nitration and sulphonation can all be performed with... 

The pure hydrocarbon nature of polystyrene gives it excellent electrical insulation characteristics, as a result of both the fundamentally good characteristics of the material and to the low water absorption of such a hydrocarbon polymer. The insulation characteristics are therefore well maintained in humid conditions. 

The electrical insulation characteristics of polystyrene are extremely good. Typical figures are given in Table 16.3. 

Figure 16.10. Influence of styrene monomer content of the softening point and flow characteristics of polystyrene, (After Haward and Crabtee) ...

As mentioned earlier, unmodified polystyrene first found application where rigidity and low cost were important prerequisites. Other useful properties were the transparency and high refractive index, freedom from taste, odour and toxicity, good electrical insulation characteristics, low water absorption and comparatively easy processability. Carefully designed and well-made articles from polystyrene were often found to be perfectly suitable for the end-use intended. On the other hand the extensive use of the polymers in badly designed and badly made products which broke only too easily caused a reaction away from the homopolymer. This resulted, first of all, in the development of the high-impact polystyrene and today this is more important than the unmodified polymer (60% of Western European market). 

Like polystyrene these blends have the following useful characteristics ... 

Example consider polystyrene with M = 245,000 and welded to itself at 118°C, the characteristic relaxation times are te 10 s, tro 21 min and Ty 1860 min [15], At these relaxation times, the respective average monomer interdiffusion distance is as follows [1 j ... 

Polyethylene has low density when polymerized at pressures 9,000 - 45,000 psi and high density when made with special catalysts at 250 - 500 psi. Low-density polyethylene softens 68 F lower than high-density polyethylene, which is more crystalline and stiffer. The rigidity characteristics and surface of high-density polyethylene are comparable with polystyrene. It feels like nylon, has a bursting strength three times that of low-density polyethylene, and withstands repeated exposure to 250 F, hence, it can be sterilized. 

Just as many small-molecule materials, polymers also form glasses [4]. Actually, most polymeric materials of everyday use are made of polymer glasses, polystyrene (PS) cups or compact discs made of polycarbonates, for instance. In many respects polymer glasses are very similar to small-molecule glasses, and there is nothing special about them. However, on the other hand, the special aspects of polymer materials allow specific studies beyond characteristic studies on small-molecule glasses. 

A new process to develop interface vulcanization is grafting of selective accelerators onto a polymer chain, which in the subsequent process of vulcanization acts as an effective cure accelerator for the second polymer component in the blend. Beniska et al. [6] prepared SERFS blends where the polystyrene phase was grafted with the accelerator for curing SBR. Improved hardness, tensile strength, and abrasion resistance were obtained. Blends containing modified polystyrene and rw-1,4-polybutadiene showed similar characteristics as SBS triblock copolymers. 

Addition of poly(styrene-block-butadiene) block copolymer to the polystyrene-polybutadiene-styrene ternary system first showed a characteristic decrease in interfacial tension followed by a leveling off. The leveling off is indicative of saturation of the interface by the solubilizing agent. 

An effective method of NVF chemical modification is graft copolymerization [34,35]. This reaction is initiated by free radicals of the cellulose molecule. The cellulose is treated with an aqueous solution with selected ions and is exposed to a high-energy radiation. Then, the cellulose molecule cracks and radicals are formed. Afterwards, the radical sites of the cellulose are treated with a suitable solution (compatible with the polymer matrix), for example vinyl monomer [35] acrylonitrile [34], methyl methacrylate [47], polystyrene [41]. The resulting copolymer possesses properties characteristic of both fibrous cellulose and grafted polymer. 

When used as substitutes for asbestos fibers, plant fibers and manmade cellulose fibers show comparable characteristic values in a cement matrix, but at lower costs. As with plastic composites, these values are essentially dependent on the properties of the fiber and the adhesion between fiber and matrix. Distinctly higher values for strength and. stiffness of the composites can be achieved by a chemical modification of the fiber surface (acrylic and polystyrene treatment [74]), usually produced by the Hatschek-process 75-77J. Tests by Coutts et al. [76] and Coutts [77,78] on wood fiber cement (soft-, and hardwood fibers) show that already at a fiber content of 8-10 wt%, a maximum of strengthening is achieved (Fig. 22). 

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