X-alt Highly Crosslinked Polyethylene Processing Steps
Step 1: UHMWPE before crosslinking
Ultra-high molecular weight polyethylene (UHMWPE) is a network of molecular chains composed of carbon and hydrogen, connected by molecular bonds.
Step 2: Crosslinking
The chains are energized by 7.5Mrad gamma radiation. As a result, some of the molecular bonds are broken, creating open bonding sites or free radicals. Many of the free radicals bond with free radicals on adjacent chains, creating crosslinks between the chains.
Step 3: Elimination of Free Radicals
When the material is heated above melt, the chains become mobile and able to slide past one another. The remaining open bonding sites connect, eliminating all free radicals and creating additional crosslinks.
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| 1. GUR 1020 polyethylene powder resin. | 2. Powder consolidated into sheets by compression molding. | 3. Long, circular bars cut from sheets. |
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| 4. Bars in an aluminum canister, submitted to 7.5 Mrad of gamma radiation at room temperature. | 5. Bars in an oven, heated to about 168°C (above melt). | 6. Bars machined into final liner geometry. |
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| 7. Liners packaged and gas-plasma sterilized. |
Note: Gamma sterilization at this step would re-introduce free radicals.