Heat resilience

Saboo, A. K., Morari, M., and Colberg, R. D., RESHEX An Interactive Software Package for the Synthesis and Analysis of Resilient Heat Exchanger Networks II. Discussion of Area Targeting and Network Synthesis Algorithms, Computers Chem. Eng., 10 591, 1986. 

The property of polybutadiene of most interest to the mbber compounder is excellent abrasion resistance coupled with excellent resilience. The polymer has very high rebound and low heat generation. With a few exceptions, such as the core of soHd golf balls, the polymer is blended with other polymers to take advantage of its excellent abrasion and rebound. Uses in North America are as follows tires, 500,000 t (74%) plastic modification,... 

Processings and Properties. Polybutadiene is compounded similarly to SBR and vulcanised with sulfur. The high cis-1,4 type crystallizes poorly on stretching so it is not suitable as a "gum" stock but requires carbon black reinforcement. It is generally used for automotive tires in mixtures with SBR and natural mbber. Its low T (—OS " C) makes it an excellent choice for low temperature tire traction, and also leads to a high resilience (better than natural mbber) which ia turn results ia a lower heat build-up. Furthermore, the high i j -polybutadiene also has a high abrasion resistance, a plus for better tire tread wear. 

This lower has a number of ramifications on the properties of polybutadiene. For example, at room temperature polybutadiene compounds generally have a higher resilience than similar natural rubber compounds. In turn this means that the polybutadiene rubbers have a lower heat build-up and this is important in tyre applications. On the other hand, these rubbers have poor tear resistance, poor tack and poor tensile strength. For this reason, the polybutadiene rubbers are seldom used on their own but more commonly in conjunction with other materials. For example, they are blended with natural rubber in the manufacture of truck tyres and, widely, with SBR in the manufacture of passenger car tyres. The rubbers are also widely used in the manufacture of high-impact polystyrene. 

PTFE is a tough, flexible, non-resilient material of moderate tensile strength but with excellent resistance to heat, chemicals and to the passage of an electric current. It remains ductile in compression at temperatures as low as 4K... 

Vulcanisation can be effected by diamines, polyamines and lead compounds such as lead oxides and basic lead phosphite. The homopolymer vulcanisate is similar to butyl rubber in such characteristics as low air permeability, low resilience, excellent ozone resistance, good heat resistance and good weathering resistance. In addition the polyepichlorohydrins have good flame resistance. The copolymers have more resilience and lower brittle points but air impermeability and oil resistance are not so good. The inclusion of allyl glycidyl ether in the polymerisation recipe produces a sulphur-curable elastomer primarily of interest because of its better resistance to sour gas than conventional epichlorhydrin rubbers. 

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. 

If a branched polyol, usually either castor oil or a simple polyester, is heated with an isocyanate but without chain extenders soft and weak rubbery products are obtained with very low resilience. These materials are useful for encapsulation of electronic components and for printer rollers. 

There is also growing interest in multi-phase systems in which hard phase materials are dispersed in softer polyether diols. Such hard phase materials include polyureas, rigid polyurethanes and urea melamine formaldehyde condensates. Some of these materials yield high-resilience foams with load deflection characteristics claimed to be more satisfactory for cushioning as well as in some cases improving heat resistance and flame retardancy. 

The thermoplastic polyamide elastomers may be considered as premium grade materials available in a wide range of hardness values with, in some instances, very good heat resistance. Particular properties of interest are the flexibility and impact resistance at low temperatures and the good dynamic properties and related resilience, hysteresis and alternating flexural properties. 

Natural rubber was the only polymer for elastomer production until the advent of synthetics. Natural rubber, however, continues to maintain its competitive edge due mainly to the gain in properties such as high resilience, low hysteresis, low heat buildup, and excellent tack with mechanical properties achieved through the process of vulcanization [114-115]. The industry is said to be self-sufficient with a good technological base and is expected to compete successfully with synthetics because of the edge in properties mentioned above [116,117]. 

FIGURE 19.17 The gray cylinders in the small inset represent polyisoprene molecules, and the beaded yellow strings represent disulfide (—S—S—) links that are introduced when the rubber is vulcanized, or heated with sulfur. These cross-links increase the resilience of the rubber and make it more useful than natural rubber. Automobile tires are made of vulcanized rubber and a number of additives, including carbon. 

Richard D. Colberg and Manfred Moiari, Analysis and Synthesis of Resilient Heat Exchanger Networks... 

The study of the response of elastomers to forces which produce changes of motion in them. See Heat Build-up, Hysteresis and Resilience. 

When rubber is deformed the difference between the energy input and output is known as hysteresis. The loss of energy is consumed in internal friction and results in heat build-up. See Hysteresis Loop and Resilience. 

The ratio of the energy given up on recovery from deformation to the energy required to produce the deformation, expressed as a percentage. See Heat Build-Up, Hysteresis and Rebound Resilience. 

A product used in upholstery and as a resilient packaging material. It is made by spraying a loose mat of curled animal hair with latex and applying heat to vulcanise the rubber. The resilience of the product comes from the fibres, the junction points of which are anchored by the rubber. 

The choice of abradant should be made primarily to give the best correlation with service, but in practice is often chosen largely for reasons of convenience. In laboratory tests the most common are abrasive wheels (vitreous or resilient), abrasive papers or cloth and metal knives . The usual abrasive wheels and papers really only relate to situations where cutting abrasion predominates. Where plastics are used in some form of bearing the conditions will involve much smoother surfaces and materials such as smooth metal plates would be more appropriate. A problem with smooth materials is that they abrade relatively slowly and, if conditions are accelerated, give rise to excessive heat build up. 

To make cut pile carpets, two strands of BCF yarns are twisted together and heat-set with steam using a Superba heat setting machine at 135-145 °C or at 175-195 °C when heat-set with super-heated steam in a Suessen. An experimental design experiment [94] showed the higher the heat set temperature, then the lower is the bulk of the final carpet, but there is an increase in the tip definition and walk performance. The tufted carpets are then dyed with disperse dyes at atmospheric boil [95] in a continuous or a batch process. PTT carpets showed excellent resiliency in walk test experiments, equivalent to a nylon and much better than both PET and polypropylene, had lower static charge of <3.5 kV, and were resistant to coffee, mustard, betadine, red acid dyes and other stains [96],... 

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