EP-4735515-A1 - METHODS OF CROSSLINKING A MOISTURE CURABLE POLYMERIC COMPOSITION

Abstract

A method of crosslinking a moisture curable polymeric composition includes the steps of: creating a moisture curable polymeric composition of a silane functionalized polyolefin and an intumescent flame-retardant mixture, wherein the intumescent flame-retardant mixture includes piperazine pyrophosphate and from 15 wt% to 55 wt% of a phosphoric acid compound based on the total weight of the intumescent flame-retardant mixture. The method also includes a step of catalyzing a moisture-induced crosslinking reaction of the silane functionalized polyolefin using the intumescent flame-retardant mixture to form a moisture cured polymeric composition.

Inventors

• CHAUDHARY, BHARAT I.
• TAPPER, Richard I.

Assignees

• Dow Global Technologies LLC

Dates

Publication Date

20260506

Application Date

20240626

Claims (10)

1. 1. A method of crosslinking a moisture curable polymeric composition, the method comprising the steps of: creating a moisture curable polymeric composition of a silane functionalized polyolefin and an intumescent flame-retardant mixture, wherein the intumescent flame-retardant mixture comprises piperazine pyrophosphate and from 15 wt% to 55 wt% of a phosphoric acid compound based on the total weight of the intumescent flame-retardant mixture; and catalyzing a moisture-induced crosslinking reaction of the silane functionalized polyolefin using the intumescent flame-retardant mixture to form a moisture cured polymeric composition.
2. 2. The method of claim 1, wherein the step of catalyzing the moisture-induced crosslinking reaction is carried out in one of a water bath at a temperature greater than 50°C or in a gaseous atmosphere having a temperature of 15°C or greater and a relative humidity of 10% or greater as measured according to ASTM E337.
3. 3. The method of any one of claims 1 and 2, wherein the moisture curable polymeric composition comprises 10 wt% to 99 wt% of the silane functionalized polyolefin based on a total weight of the moisture curable polymeric composition and the silane functionalized polyolefin is a silane functionalized ethylene-based polymer.
4. 4. The method of claim 3, wherein the silane functionalized ethylene-based polymer comprises from 0.1 wt% to 5.0 wt% of silane based on the total weight of the silane functionalized ethylene-based polymer.
5. 5. The method of claim 4, wherein the silane is vinyltrimethoxy silane.
6. 6. The method of any one of claims 1 -5, wherein the moisture curable polymeric composition comprises 1 wt% to 90 wt% of the intumescent flamc-rctardant mixture based on a total weight of the moisture curable polymeric composition.
7. 7. The method of claim 5, wherein the polymeric composition comprises 1 wt% to 30 wt% of the intumescent flame-retardant mixture based on a total weight of the moisture curable polymeric composition.
8. 8. The method of any one of claims 1-7, wherein the intumescent flame-retardant mixture comprises from 25 wt% to 45 wt% of the phosphoric acid compound based on the total weight of the intumescent flame-retardant mixture.
9. 9. The method of any one of claims 1-8, wherein the phosphoric acid compound is selected from the group consisting of melamine polyphosphate, ammonium polyphosphate, or combinations thereof.
10. 10. The method of any one of claims 1-9, wherein the moisture curable polymeric composition is free of dibutyltin dilaurate and sulfonic acid.

Description

METHODS OF CROSSLINKING A MOISTURE CURABLE POLYMERIC COMPOSITION BACKGROUND Field of the disclosure The present disclosure relates to moisture curable polymeric compositions, and more specifically to methods of crosslinking such moisture curable polymeric compositions. Introduction Crosslinked polyolefin compositions are used in a variety of applications where heat resistance and good mechanical properties are desired. The crosslinking of a polyolefin transforms a thermoplastic composition into a thermoset composition which increases its resistance to deformation and flow at elevated temperatures because the polymer chains are linked together unlike in the case of a thermoplastic composition. There are a variety of industrially practiced physical and chemical methods to crosslink polymeric compositions including vulcanization for peroxide-induced crosslinking, electron beam irradiation based crosslinking and moisture-induced crosslinking through the use of silane functionalization. Silane crosslinking of polymeric compositions utilizing silane functionalization of the polymers typically requires use of silanol condensation catalysts such as tin-based dibutyltin dilaurate and/or strong acids such as sulfonic acids. The presence of moisture in such formulations is undesirable, and therefore to be avoided, as it can lead to premature crosslinking during melt extrusion and negatively impact the final material properties. Moisture-induced crosslinking of the formulations occurs in a subsequent step after fabrication of the article, through the diffusion of water into the article. Polymeric compositions are typically considered to be crosslinked if they exhibit a gel content of 10 wt% or greater as measured according to ASTM D2765. Intumescent compounds can be used as halogen-free flame retardant (“HFFR”) fillers in polymeric applications. For example, United States Patent Application Publication number 2003/0088000A1 discloses the use of intumescent compounds with polymeric systems such as polypropylene. Intumescent compounds have not been used in silane crosslinked systems before possibly because they often contain pentaerythritol (as a charring agent) which can undergo dehydration in the presence of an acid or acid source (such as ammonium polyphosphate, which is a typical component of intumescent compounds) to yield water that in turn would yield premature crosslinking during melt extrusion of compositions containing silane functionalized polymers. Equation 1 of Applied Catalysis A: General 253 (2003) 29-32 depicts the generation of water from acid-catalyzed dehydration of pentaerythritol. Furthermore, intumescent compounds have not been shown to possess catalytic activity for moisture-induced crosslinking of silane-functionalized polyolefins . In view of the forgoing, it would be surprising to discover a method of crosslinking a silane functionalized polyolefin using an intumescent flame-retardant mixture where premature crosslinking during melt extrusion does not occur. Additionally surprising would be any evidence of catalytic activity for moisture-induced crosslinking of the formulation after melt extrusion. SUMMARY OF THE DISCLOSURE The present disclosure provides a moisture-curable polymeric composition as well as method of crosslinking a silane functionalized polyolefin using an intumescent flame -retardant mixture. The silane functionalized polyolefin is preferably a silane functionalized ethylene-based polymer. The inventors of the present disclosure have discovered that certain intumescent compounds can function as a catalyst to crosslink silane functionalized polyolefin without the need for additional or conventional catalysts. Specifically, it has been discovered that intumescent flame-retardant mixtures comprising piperazine pyrophosphate and a phosphoric acid compound can catalyze moisture-induced silane crosslinking reactions thereby producing crosslinked polymeric compositions having a gel content of 10 wt% or greater as measured according to ASTM D2765. Without being bound by theory, it is believed that an acid moisture cure catalyst may be generated upon thermal dissociation of the phosphoric acid compound. According to a feature of the disclosure, a method of crosslinking a moisture curable polymeric composition, the method comprising the steps of: creating a moisture curable polymeric composition of a silane functionalized polyolefin and an intumescent flame-retardant mixture, wherein the intumescent flame-retardant mixture comprises piperazine pyrophosphate and from 15 wt% to 55 wt% of a phosphoric acid compound based on the total weight of the intumescent flame-retardant mixture; and catalyzing a moisture-induced crosslinking reaction of the silane functionalized polyolefin using the intumescent flame-retardant mixture to form a moisture cured polymeric composition. According to another feature of the disclosure, the step of catalyzing the moisture-induced crosslinking reaction is ca