Crystals/crystallization thermoplastics

Advanced Thermoplastics Materials. Thermoplastics and linear plastics of finite molecular weight that can be fabricated into very complex stmctures by hot melt or injection mol ding are different from the thermoset materials that require cross-linking to build up infinite molecular weight to form network (cross-link) stmctures. Advances in thermoplastic engineering materials include amorphous thermoplastics, crystalline thermoplastics, Hquid crystal thermoplastics, and fluorinated thermoplastics (see Engineering plastics). 

Liquid crystal thermoplastics, 10 8 Liquid dessicants, 8 365-366 Liquid DGEBA resins, 10 460 Liquid diffusion, 9 109, 110-112 Liquid discharge treatment, ion-exchange, 14 422... 

LIQUID CRYSTALLINE MATERIALS] (Vol 15) liquid crystal thermoplastics... 

Thermally-Induced Phase Separation (TIPS). Thermally-induced phase separation (Tl PS) results from cooling a liquid crystal/ thermoplastic melt. The liquid crystal and thermoplastic are chosen to... 

Figure 6. Schematic phase diagram of a liquid crystal thermoplastic mixture.

Thermoplastic polymers are synthetic polymers that become plastic on heating and harden on cooling. PE, iPP, PET, and polyamides, among others, are typical examples of this type of polymers. Depending on the chemical and molecular structure and processing variables, they may or may not crystallize. Thermoplastic polymers that are able to crystallize have a significant amount of amorphous material, and therefore they are known as semicrystalline thermoplastic polymers. 

POLYMER COMPOSITES AND POLYMER LIQUID CRYSTAL + THERMOPLASTIC BLENDS... 

Such cements are applied to adherend and allowed to dry to the desired degree of tackiness before contacting the adherend coated surfaces. Or, as in the case of the crystallizing thermoplastic polyurethane resins, the adhesive coating may be allowed to fully dry and crystallize. Subsequent heat activation of the coated adherend surfaces, then in contact with each other, rapidly produces a strong bond. 

Dow Chemical developed liquid crystalline polymers (LCP) based on diglycidyl ether of 4-4 -dihydroxy-o -methylstilbene in the 1980s (62,63). Liquid crystal thermoplastics and thermosets based on this novel chemistry showed excellent combinations of thermal, mechanical, and chemical properties, imachievable with traditional epoxies. However, commercialization of these products has not materialized. 

Knlichikhin VG, Plate NA (1991) Blend composites based on liquid crystal thermoplast. Rev Polym Sci USSR 33(l) l-37... 

No polymer is ever 100% crystalline at best, patches of crystallinity are present in an otherwise amorphous matrix. In some ways, the presence of these domains of crystallinity is equivalent to cross-links, since different chains loop in and out of the same crystal. Although there are similarities in the mechanical behavior of chemically cross-linked and partially crystalline polymers, a significant difference is that the former are irreversibly bonded while the latter are reversible through changes of temperature. Materials in which chemical cross-linking is responsible for the mechanical properties are called thermosetting those in which this kind of physical cross-linking operates, thermoplastic. 

Polyester sheet products may be produced from amorphous poly(ethylene terephalate) (PET) or partiaHy crystallized PET. Acid-modified (PETA) and glycol modified (PETG) resins are used to make ultraclear sheet for packaging. Poly(butylene terephthalate) (PBT) has also been used in sheet form. Liquid-crystal polyester resins are recent entries into the market for specialty sheet. They exhibit great strength, dimensional stabHity, and inertness at temperatures above 250°C (see Polyesters,thermoplastic). 

Phase Materials. Phase holograms can be recorded in a large variety of materials, the most popular of which are dichromated gelatin, photopolymers, thermoplastic materials, and photorefractive crystals. Dichromated gelatin and some photopolymers require wet processing, and thermoplastic materials require heat processing. Photorefractive crystals are unique in that they are considered to be real-time materials and require no after-exposure processing. 

Materials. Beside inorganic materials (eg, barium chloride/fluoride crystals, doped with 0.05% samarium), transparent thermoplasts are preferred for the PHB technique, eg, poly (methyl methacrylate) (PMAIA), polycarbonate, and polybutyral doped with small amounts of suitable organic dyes, organic pigments like phthalocyanines, 9-arninoacridine, 1,4-dihydroxyanthraquinone [81-64-1] (quinizarin) (1), and 2,3-dihydroporphyrin (chlorin) (2). 

General-Purpose Polystyrene. Polystyrene is a high molecular weight M = 2 — 3 x 10 ), crystal-clear thermoplastic that is hard, rigid, and free of odor and taste. Its ease of heat fabrication, thermal stabiUty, low specific gravity, and low cost result in mol dings, extmsions, and films of very low unit cost. In addition, PS materials have excellent thermal and electrical properties that make them useful as low cost insulating materials (see Insulation, ELECTRIC Insulation, thermal). 

Crystallization and Melting Point. The abihty of PVA to crystallize is the single most important physical property of PVA as it controls water solubiUty, water sensitivity, tensile strength, oxygen barrier properties, and thermoplastic properties. Thus, this feature has been and continues to be a focal point of academic and industrial research (9—50). The degree of crystallinity as measured by x-ray diffraction can be directly correlated to the density of the material or the swelling characteristic of the insoluble part (Fig. 2). 

Polyarylether Ketones. The aromatic polyether ketones are tme thermoplastics. Although several are commercially available, two resins in particular, poly ether ether ketone [31694-16-3] (PEEK) from ICI and poly ether ketone ketone (PEKK) from Du Pont, have received most of the attention. PEEK was first synthesized in 1981 (20) and has been well studied it is the subject of numerous papers because of its potential use in high performance aircraft. Tough, semicrystalline PEEK is prepared by the condensation of bis(4-fiuorophenyl) ketone with the potassium salt of bis(4-hydroxyphenyl) ketone in a diaryl sulfone solvent, such as diphenyl sulfone. The choice of solvent is critical other solvents, such as Hquid HE, promote the reaction but lead to premature low molecular-weight crystals, which do not exhibit sufficient toughness (21). 

Substitution of chloropolymer is possible using a variety of nucleophiles. The most common are sodium salts of alcohols and phenols. Thermoplastics are obtained using a single substituent, whereas multiple substituents of sufficiently different size lead to elastomers (2). Liquid crystal behavior similar to polysHoxanes has been noted in most homopolymers. The homopolymer formed using trifluoroethanol as a substituent has received a fair amount of academic scmtiny (7). 

Some of the common types of plastics that ate used ate thermoplastics, such as poly(phenylene sulfide) (PPS) (see Polymers containing sulfur), nylons, Hquid crystal polymer (LCP), the polyesters (qv) such as polyesters that ate 30% glass-fiber reinforced, and poly(ethylene terephthalate) (PET), and polyetherimide (PEI) and thermosets such as diaHyl phthalate and phenoHc resins (qv). Because of the wide variety of manufacturing processes and usage requirements, these materials ate available in several variations which have a range of physical properties. 

Highly aromatic thermoplastic polyesters first beeame available in the 1960s but the original materials were somewhat difficult to process. These were followed in the 1970s by somewhat more processable materials, commonly referred to as polyarylates. More recently there has been considerable activity in liquid crystal polyesters, which are in interest as self-reinforeing heat-resisting engineering thermoplastics. 

Liquid crystal polyesters Polyester Thermoplastic Elastomers Poly(pivalolactone)... 

Crystalline polyesters are highly important as adhesive raw materials. They are normally crystalline waxes and are highly symmetrical in nature, which can aid the crystallization process [26]. Poly(hexamethylene adipate) and poly(caprolactone), shown in Table 2, are only two of the many crystallizable backbones. Poly(ethylene adipate) and poly(letramethylene adipate) are also commonly used in urethane adhesives. The crystalline polyesters are used in curing hot melts, waterborne polyurethanes, thermoplastic polyurethanes, and solvent-borne urethane adhesives. The adipates are available mostly as diols. The poly(caprolactones) are available as diols and triols. 

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