From 04/16/2015 through 7/5/2012
Crosslinking: Patent Titles
Crosslinking: Patent Abstracts
“Cross-links can be formed by chemical reactions that are initiated by heat, pressure, change in pH, or radiation. For example, mixing of an unpolymerized or partially polymerized resin with specific chemicals called crosslinking reagents results in a chemical reaction that forms cross-links. Cross-linking can also be induced in materials that are normally thermoplastic through exposure to a radiation source, such as electron beam exposure, gamma-radiation, or UV light. For example, electron beam processing is used to cross-link the C type of cross-linked polyethylene. Other types of cross-linked polyethylene are made by addition of peroxide during extruding (type A) or by addition of a cross-linking agent (e.g. vinylsilane) and a catalyst during extruding and then performing a post-extrusion curing.
The chemical process of vulcanization is a type of cross-linking and it changes the property of rubber to the hard, durable material we associate with car and bike tires. This process is often called sulfur curing, and the term vulcanization comes from Vulcan, the Roman god of fire. However, this is a slow process taking around 8 hours. A typical car tire is cured for 15 minutes at 150°C. However, the time can be reduced by the addition of accelerators such as 2-benzothiazolethiol or tetramethylthiuram disulfide. Both of these contain a sulfur atom in the molecule that initiates the reaction of the sulfur chains with the rubber. Accelerators increase the rate of cure by catalysing the addition of sulfur chains to the rubber molecules.
Cross-links are the characteristic property of thermosetting plastic materials. In most cases, cross-linking is irreversible, and the resulting thermosetting material will degrade or burn if heated, without melting. Especially in the case of commercially used plastics, once a substance is cross-linked, the product is very hard or impossible to recycle. In some cases, though, if the cross-link bonds are sufficiently different, chemically, from the bonds forming the polymers, the process can be reversed. Permanent wave solutions, for example, break and re-form naturally occurring cross-links (disulfide bonds) between protein chains in hair.”
(Wikipedia, Crosslinking, 7/5/2012
Direct conversion of solar energy to electrical energy can provide a virtually unlimited source of clean energy. Conventional photovoltaic modules typically include a stack of materials encapsulated in a transparent polymer such as ethylene vinyl acetate (EVA) copolymers. During lamination, EVA is applied to a photovoltaic module and cured to prevent long term creep due to temperature and stress. Crosslinking is critical to long term performance and must be monitored. Conventional crosslinking measurements are the “gel fraction” test and "creep" test requiring destruction of the tested material. An automated, nondestructive test is badly needed.
Dobble et al measured cross-linking by localized deformation without damage to the module. A polymer sample is indented and the relaxation or a recovery recorded. This recovery is then compared to a reference material. An automated test for crosslinking could be a major step in quality control as well as monitoring long term performance.
US Patent 8,950,267 (February 10, 2015), “ Methods and Apparatus for Detecting Cross-Linking in a Polymer,” Dan Doble, Rafal Mickiewicz, John Lloyd, Marco Jaeger, and William F. Hartman (Fraunhofer USA, Inc., Plymouth, Michigan, USA).
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Roger D. Corneliussen
Maro Polymer Links
Tel: 610 363 9920
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Copyright 2012 by Roger D. Corneliussen.
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* Date of latest addition; date of first entry is 7/5/2012.