Professor Tim A. Osswald, Director of SIMTEC Silicone Parts’ Technical Advisory Board will be one of the prestigious speakers presenting at this year’s Silicone Elastomers US 2011 event. Held at the Hyatt Rosemont Hotel in Rosemont, IL, Professor Osswald will be discussing the viscoelastic behavior of Liquid Silicone Rubber (LSR) at 11:45 CST, Wednesday, December 7th 2011.
The density or its reciprocal, the specific volume, is important for the shrinkage during processing and is greatly affected by temperature and pressure. The specific volume is often plotted as a function of pressure and temperature, in what is known as a pvT diagram (see image on the left below for an example of a pvT diagram). The measurement is defined in ISO 17744.
Semi-crystalline thermoplastic polymers show more order than amorphous thermoplastics. The molecules align in a structured crystalline form. The size of the crystals or spherulites is much larger than the wavelength of visible light, making semi-crystalline materials translucent, rather than transparent. Crystalline regions are small with molecular chains comprised of both crystalline and amorphous regions. The degree of crystallinity in a typical thermoplastic will vary from grade to grade, as for example in polyethylene, where the degree of crystallinity depends on the branching and the cooling rate.
Polycarbonate (PC), first introduced in 1958, is an amorphous engineering thermoplastic with exceptionally high impact strength, transparency, high temperature resistance, and dimensional stability. It has a high surface gloss and is available in many colors and color intensities. Additionally, it is impact resistant and maintains high strength and stiffness in a temperature range from -150 to +135˚C.
Thermoplastics are divided into two material classes (amorphous and semi-crystalline). Their classification is determined by both their transition temperatures and their structure in different states, which works great for molded silicone parts.