CRAZE RESISTANCE

Plastic Sheet. Poly(methyl methacrylate) plastic sheet is manufactured in a wide variety of types, including cleat and colored transparent, cleat and colored translucent, and colored semiopaque. Various surface textures ate also produced. Additionally, grades with improved weatherabiUty (added uv absorbers), mat resistance, crazing resistance, impact resistance, and flame resistance ate available. Selected physical properties of poly(methyl methacrylate) sheet ate Hsted in Table 12 (102). 

Isophthalic acid (m.p. 347°C), made by oxidation of /w-xylene, has also been introduced for resins. The resins have higher heat distortion temperatures and flexural moduli and better craze resistance. They are also useful in the preparation of resilient gel coats. 

Solvent crazing resistance Enhances Enhances Initially remains unchanged then deteriorates Enhances Deteriorates... 

Good stress-crack and craze resistance, brittle Good processibility, no stress whitening Higher-heat styrenic, brittle... 

EP 323142 (European) 1989 Ternary polyether ketone blend wire insulations Pirelli General PLC, UK CK Alesbury, RJ Murphy Formulation shows excellent stress craze resistance, flexibility and flame resistance Blends of polyarylene ether ketones, polyether imides and polyfimide siloxanes) were coated onto wire for solvent resistance, O index and abrasion resistance. Blends without siloxane-imide copolymer did not meet these properties... 

Two families of transparent polycarbonate-silicone multiblock polymers based on the polycarbonates of bisphenol acetone (BPA) and bisphenol fluorenone (BPF) were synthesized. Incorporation of a 25% silicone block in BPA polycarbonate lowers by 100°C the ductile-brittle transition temperature of notched specimens at all strain rates silicone block incorporation also converts BPF polycarbonate into a ductile plastic. At the ductile-brittle transition two competing failure modes are balanced—shear yielding and craze fracture. The yield stress in each family decreases with silicone content. The ability of rubber to sustain hydrostatic stress appears responsible for the fact that craze resistance is not lowered in proportion to shear resistance. Thus, the shear biasing effects of rubber domains should be a general toughening mechanism applicable to many plastics. 

Surface oxyfluorination was also performed on poly(methyl methacrylate) by Jolet [4] as a method for manufacturing the outer panel of craze-resistant windows. 

The low viscosity of silicone resins can encourage settling. However, more often than not, remixing of the soft settled mass yields a smooth uniform enamel. Because low viscosity accompanies the use of silicones, the formulator may be tempted to over pigment, and this should be avoided if poor craze resistance is to be avoided and gloss retention is to be maintained. 

PS or copolymers are used extensively in injection blow molding. Tough and craze-resistant PS containers have been made by multiaxially oriented injection-molded parisons (238). This process permits the design of blow-molded objects with a high degree of controlled orientation, independent of blow ratio or shape. 

Formations with enhanced resistance to craze formation have been described. Increasing the molecular weight has little influence on suppressing varnish-induced crazing in PAI Aims. However, craze resistance is associated with curing and crosslinking. The ratio of imide to amide and the surface tension of the film coatings influence the tendency to craze formation. 

General purpose Rigid moldings, craze resistant... 

Only a small percent of styrene copolymers reported in the literature achieved industrial importance. Some of the interesting copolymers of styrene that were reported but not utilized commercially are copolymers with various unsaturated nitriles. This includes vinvlidine cyanide, fumaronitrile, malononitrile, methacrylonitrile, acrylonitrile, and cinnamonitrile. Often, copolymerization of styrene with nitriles yields copolymers with higher heat distortion temperature, higher tensiles, better craze resistance, and higher percent elongation. 

Furane adhesives are suitable for gap-filhng applications because their strength is maintained with thick glue lines. For this reason, the resins are used as modifiers for urea-formaldehyde adhesive to improve gap-filling and craze resistance. As furanes are compatible with a variety of other resins, they are used in mixtures with silicates and carbonaceous materials for chemically resistant grouting compositions. ... 

Besides the fundamental strength of the plastic part, important properties that must be considered when using mechanical fasteners are creep, relaxation, craze resistance, notch sensitivity, and stiffness. When these properties are disregarded, premature failure of the assembly is possible. 

---