Polyolefin treatment process for uniform crosslinking

Abstract

A process produces a block of polyolefin material with uniform crosslinking, which may be uniform between and within polymer chains in the polyolefin material. Steps include: providing an oven; placing the block into the oven; preheating the block to a uniform temperature above the melting point; further heating the block to a temperature at least 30 degrees Centigrade above the melting point; cooling the block to room temperature under an inert gas; and removing oxidized material from surface of the block. Optional steps include: subjecting the block to radiation before placing the block into the oven; removing the gases from the oven on a continuous or stepwise basis; controlling the purge gas flow out of the oven; and determining a heating time period for the block by subjecting control blocks to the same process and analyzing them after various heating times.

Description

TECHNICAL FIELD[0001]In the field of synthetic resins, a process of preparing a polyolefin using heat and / or wave energy to induce a physical and chemical reaction promoting uniform crosslinking in the polyolefin without changing the chemical composition of the polymer, without creating short polymer chains and enabling removal of oxidized polymer.BACKGROUND ART[0002]A polyolefin is a polymer produced from a simple olefin as a monomer. For example, polyethylene is the polyolefin produced by polymerizing the olefin ethylene. An olefin is also called an alkene with the general formula CnH2n and a polyolefin is also known as a polyalkene. Polypropylene is another common polyolefin which is made from the olefin propylene.[0003]By definition, cross-links are connecting points that link one polymer chain to another. There are two types of crosslinks: chemical crosslinks are covalent bonds that bridge the polymer chains; and physical crosslinks are hydrogen bonds or chain entanglements bet...

AI Technical Summary

Benefits of technology

[0013]Incomplete crosslinking, non-uniform crosslinking, chemically altered polymer and oxidized polymer have been shown to decrease wear resistance, increase creep, and degrade certain desirable mechanical or physical properties of polymers. Non-uniform crosslinking can cause early failure of material upon loading in industrial or medical applications.

[0016]Irradiated and oxidized polyolefin resulting from current treatment process to increase crosslinking, cause brittleness and reduced strength.

[0019]The present process provides a new polyolefin, which is a new polymeric material, with superior wear resistance, lower creep potential, less brittleness and enhanced strength. The process achieves this new polymeric material by producing a polyolefin with uniform chemical crosslinking, enhanced physical crosslinking, no chemical alteration by avoiding use of a crosslinking agent, a reduced amount of short chains, and removed oxidation.

[0022]High temperature treatment taught in the present process removes short chains in gamma irradiated and shelf aged polyolefin. As a result, melting characteristics and crystallinity are restored.

Problems solved by technology

These are deficient in that they either change the chemical composition of the polymer or create short polymer chains.

The major drawback of this method is that the resultant material often has a different chemical composition than that of the starting material due to the inclusion of the crosslinking agent.

The non-uniformity arises from the radiation dose distribution in the polymer.

The second major shortcoming is that irradiation penetration from the surface of the polymer may not be thorough.

For e-beam irradiation, the limited power of penetration results in a higher dose near the surface while lower or zero dose in the interior.

The third major shortcoming is that crosslinking reactions of free radicals are often incomplete; leaving residual free radicals in the material that can cause oxidation or other chemical changes during storage or field applications.

It is well known that material properties are deteriorated when a polymeric material is oxidized.

Short chain formation tends to weaken the material strength as the effective molecular weight is reduced.

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