Rubber resilience

Both side groups and carbon-carbon double bonds can be incorporated into the polymer structure to produce highly resilient rubbers. Two typical examples are polyisoprene and polychloroprene rubbers. On the other hand, the incorporation of polar side groups into the rubber structure imparts a dipolar nature which provides oil resistance to these rubbers. Oil resistance is not found in rubber containing only carbon and hydrogen atoms (e.g. natural rubber). Increasing the number of polar substituents in the rubber usually increases density, reduces gas permeability, increases oil resistance and gives poorer low-temperature properties. 

This property depends on filler particle size and filler loading. Higher filler loading gives lower resilience. Rubber type plays a great role here in that no synthetic rubber can match the characteristic of high resilience of natural rubber. 

Chemical compatibility is another important factor to reckon with in material selection as in the case of butterfly valves which are frequently used in industrial fluid flow systems where the valves are operated to load and unload different kinds of fluids for shipment or storage. These applications include tank trailers for transportation of fluids from one location to another as well as fluid flow pipelines. A typical butterfly valve usually incorporates a resilient rubber seal component which the valve pivots to seal off the flow lines and when opened allows the fluid to be conveyed to the flow line. The chemicals transported in tanks using butterfly valves are often caustic or acidic. These chemicals corrode the pivot area of the valve making its function ineffective. The rubber gasket material prevents leakage while the valve chamber is protected by a chemically resistant rubber material. 

Staggered conformations require sufficient energy for the chain to overcome the high barrier represented by crowded eclipsed forms, and polyisobutene does not retain its elastic character at temperatures as low as those at which more resilient rubbers can be used. 

This is a relief printing process in which the image areas are raised above the level of the non-image areas and transferred from the inked printing plate to the metal surface by means of an intermediate resilient rubber surface. 

S-B-S and S-I-S. Much of our discussion will refer directly to data for S-B-S and S-I-S block polymers. We justify this on several counts. These block polymers can be clearly defined as to structures, molecular weights, and compositions. They have served as model systems for much of the recent work in block polymers. They also comprise the largest volume of commercial block polymers. Finally, we believe that the discovery (20) of the S-B-S and S-I-S thermoplastic rubbers which are strong, resilient rubbers without vulcanization, and the concomitant, readily understood theory (21). provided a paradigm (terminology of T. S. Kuhn (2 2)) that significantly accelerated the scientific work on these polymers in recent years. 

For cooling tower water lines butterfly valves with a resilient rubber lining which serves as both the seat and the flange gasket have proved to be very economical. These valves will fit between a standard 125-poimd or 150-pound flange. They are limited to 180° F and 150 psi applications but give good service in 8-inch and 10-inch valve sizes. 

The chemistry just outlined produces silicone sealants which cure to a fairly tough, resilient rubber. Generally, sealants made by the above route are the higher modulus, strong silicone sealants used in products like silicone glazing sealants, silicone adhesives and silicone bath tub caulk. 

The time constants for this response will vary with the specific characteristics of a type plastic and processing technique. In the rigid section of a plastic the response time is usually on the order of microseconds to milliseconds. With resilient, rubber sections of the structure the response time can be long such as from tenths of a second... 

Another form of positive-acting rotary pump is the single-screw extruder pump typified by the Mono-piunp, illustrated in Figures 3.32 and 3.33. A specially shaped metal helical-rotor revolves eccentrically within a resilient rubber or plastic double-helix, thus creating a continuous forming cavity which progresses towards the discharge of the piunp. A continuous seal is created... 

Maleination of soybean oil is interesting as it has been shown to produce two wildly different polymer structures. Maleic anhydride-modified soybean oil was polymerized with styrene to give a hard, rigid polymer modification improved modulus, strength and glass transition values when compared to the unmodified polymerized oil [45], These also showed comparable strengths to commercial unsaturated polyester resins. In contrast, by using diols as the comonomer, maleinated soybean oil was used to form soft, resilient rubbers at room temperature [46]. 

The basic forms are effective and very simple to use. The more complex vulcanised versions offer one of the few methods by which resiliant rubber may be bonded securely to metal... 

In this kind of seal, wider tolerances are possible between the OD of the seal and the seal housing. Irregularities of the housing surface can be taken up by the resilient rubber layer on the outside of the seal. However, the rubber covered seal can be blown out under high pressure in a reciprocating application whereas, with a metal case, there is no such danger. 

FIGURE 10.7 Typical stress-strain diagrams for brittle glass (A), resilient rubber (B), and ductile plastic (C). 

---