HTV silione rubber
Methylvinylsilicone gum- POLIMER MV
In 2002 Zakład Chemiczny “Silikony Polskie” Sp. z o.o. (Chemical Plant “Polish Silicones” Ltd.) started producing polimers under the trade name of POLIMER MV which are used for production of HTV rubbers. MV polymer is a methyl vinyl silicone polymer (VMQ) which has a molecular weight within the range from 500 000 to 720 000. It is produced in two basic forms which differ with regard to vinyl group content:MV 0.07 polymer contains about 0.07 % of vinyl groups and MV 1.0 polymer about 1.0% of vinyl groups in gram-molecular weight.
The presence of vinyl groups in the polymer chains, also at their ends, facilitates crosslinking process and allows to obtain rubbers which are characterized by small permanent deformation after compression. In order to guarantee satisfactory mechanical properties of silicon rubber, filling material should be added to Polimer MV. Pyrogenic silica, hydrophobic silica or hydrophilic silica are the most suitable in this case. However, hydrophilic silica requires softening agents (reactive polysiloxane) to be added which modify the surface of silica and reduce its susceptibility to connecting (through hydrogen bonds) with polymer chains. These agents, when added in a proper amount, not only facilitate the mixture processing but also improve physical properties of rubber. Also other substances are usually added which make the rubber resistant to ageing, heat, oil etc.
Organic peroxides are used as crosslinking agents during vulcanisation of mixtures made of Polimer MV. Their molecules disintegrate when heated into free radicals which react with methyl or vinyl groups and cause crosslinking of polymer chains. Vulcanisation temperature depends on the type of peroxide used and is usually within the following temperature ranges: 100–140ºC or 150 – 190ºC. After vulcanisation which lasts for about 10 minutes the rubber is additionally hold at a temperature of approximately 200ºC for about 4 hours. This process, so-called additional crosslinking, enables removal of volatile matter and products of organic peroxide disintegration from the rubber. Additionally, the process stabilizes the internal structure of the rubber. Rubbers made of Polimer MV, depending on the mixture composition and vulcanisation conditions, have the following properties:
Hardness (Shore) 40 – 70
Tensile strength 8 -11 N/mm2
Elongation at break 360 – 620%
Tearing strength 18 – 25 N/mm
Based on Polimer MV the Company produces silicone mastrbatches to be processed into HTV silicone rubber.