WEATHERPROOF AND WEAR RESISTANT – SEMI-CRYSTALLINE THERMOPLASTICS
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.
Because of the existence of both amorphous and crystalline regions, a semi-crystalline polymer has two distinct transition temperatures: the glass transition temperature, Tg, and the melting temperature, Tm. The dynamic shear modulus of a semi-crystalline thermoplastic shows these two distinct transitions. Above the melting temperature, the shear modulus is negligible and the material will flow. Crystalline arrangement begins to develop as the temperature decreases below the melting point. Between the melting and glass transition temperatures, the material behaves as a leathery solid, and in tensile testing it shows an increase in toughness in that range. Below the glass transition temperature, which is close to or below room temperature for many semi-crystalline thermoplastics, the material is brittle.
When compared to amorphous thermoplastics, semi-crystalline thermoplastics are softer, more ductile, and they are translucent or opaque rather than transparent, excellent for silicone rubber parts. Semi-crystalline thermoplastics also show a higher resistance to fatigue, wear, abrasion, and chemicals – this makes most of them ideal for tribological silicone rubber parts applications like gears. They are also well suited for silicone rubber parts applications like packaging for food contact. In addition, it works great for silicone rubber parts that need to be weatherproof components and devices.
SIMTEC Silicone Parts has ample experience manufacturing Two Shot solutions for food contact components, as well as parts that are exposed to extreme temperature changes and need to be weatherproof.
[1] Osswald, T. A.; Baur, E.; Brinkmann, S.; Oberbach, K.; Schmachtenberg, E.: International Plastics Handbook; 4th edition, Hanser Gardner Pubilcations, Cincinatti, 2006
[2] Ehrenstein, G. W.: Polymeric Materials: Structure, Properties, Applications; Hanser Gardner Publications, Cincinatti, 2001
[3] Campo, E. A.: Industrial Polymers; Hanser Gardner Publications, Cincinatti
At SIMTEC Silicone Parts, a leading company in manufacturing high precision parts and components, we are exclusively focused and specialized in the production of LSR and LSR/Thermoplastic (Two-Shot) components.
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