Glass transition temperature rubber materials

Other theories proposed dissipation of energy through crack interaction localised heating causing the material to be raised to above the glass transition temperature in the layers of resin between the rubber droplets and a proposal that extension causes dilation so that the free volume is increased and the glass transition temperature drops to below the temperature of the polyblend. 

There are several ways in which the impact properties of plastics can be improved if the material selected does not have sufficient impact strength. One method is by altering the composition of the material so that it is no longer a glassy plastic at the operating temperature of the product (Chapter 6). In the case of PVC this is done by the addition of an impact modifier which can be a compatible plastic such as an acrylic or a nitrile rubber. The addition of such a material lowers the glass transition temperature and the material becomes a rubbery viscoelastic plastic with much improved impact properties. This is one of the methods in which PVC materials are made to exhibit superior impact properties. 

Most PHAs are partially crystalline polymers and therefore their thermal and mechanical properties are usually represented in terms of the glass-to-rubber transition temperature (Tg) of the amorphous phase and the melting temperature (Tm) of the crystalline phase of the material [55]. The melting temperature and glass transition temperature of several saturated and unsaturated PHAs have been summarized in Table 2. 

This is very useful for generating modulus versus temperature data on rubber compounds. The effects of temperature on this important material property can be obtained over a wide temperature range (typically -150 to +200 °C), along with the glass transition temperature and information on thermal stability. 

Also termed glass temperature or Tg. The temperature at which the stiffness of an elastomer subjected to low temperatures changes most rapidly. If the glass temperature is close to the operational temperature the material will be leathery in its behaviour rather than rubber-like. Approximate glass transition temperatures for different polymers are NR -70 °C SBR -52 °C HR -75 °C PCP -40 °C and silicone rubber -85 °C. 

Subsequently, Devia came to the U.S. to continue the research. A SIN type synthesis was selected because it offered two advantages ease in processing and a lower glass transition temperature, Tg, of the rubber product. As shall be seen from the following, the IPN and SIN synthesis yield quite different materials, even if the chemistry is nominally the same. However, since the earlier work has already been described, the following will emphasize the SIN synthesis (19-22). 

Physical and Mechanical Behavior of the Oils and SIN s. One of the most important properties of any polymer is its glass transition temperature. This defines its range of use, as well as a host of fundamental properties. This holds for IPN s and SIN s. In particular, for multiphase materials, the rubber phase must have a T below about -40°C if significant impact resistance is to be obtlined. 

When different elastomers are being described, a fundamental property which is often quoted is the glass transition temperature, Tg, which differs from one elastomer to another. For example, for natural rubber Tg is -70°C (-95°F). Broadly this means that above -70°C the material behaves as a rubber, but below -70°C the material behaves more like a glass. When glassy, natural rubber is about one thousand times as stiff as it is when rubbery. When glassy, a hammer blow on natural rubber will cause it to shatter like a glass when rubbery the hammer is likely just to bounce off. 

At normal temperatures, the rubber molecular chains are in a constant state of thermal motion, they are constantly changing their configuration, and their flexibility makes them reasonably easy to stretch. It is to be noted that as the temperature is lowered the chains become less flexible and the amount of thermal motion decreases. Eventually, a low temperature, the glass transition temperature, is reached, where all major motion of the chains ceases. The material no longer has the properties which make it a rubber, and it behaves as a glass. 

RESINS (Acrylonitrile-Butadiene-Styrene). Commonly referred to as ABS resins, these materials are thermoplastic resins which are produced by grafting styrene and acrylonitrile onto a diene-rubber backbone. The usually preferred substrate is polybutadiene because of its low glass-transition temperature (approximately —80°C). Where ABS resin is prepared by suspension or mass polymerization methods, stereospedfic diene rubber made by solution polymerization is the preferred diene. Otherwise, the diene used is a high-gel or cross-linked latex made by a hot emulsion process. 

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