Crosslinked Polyolefin Pipe Composition for Bubble-Free PEX-a
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Solution Overview
Problem
Existing PEX-a pipes face challenges in achieving high mechanical properties while minimizing odors, leaching of components, and meeting stringent standards for burst strength, pressure resistance, degradation, and chlorine resistance, with peroxide-induced crosslinking often leading to undesirable bubble formation.
Innovation Solution
A polymeric pipe composition comprising a polyolefin structural polymer, a peroxide initiator in the range of 0.1% to 5% by weight, and a co-agent with 0.02% to 5% reactive carbon-carbon double bonds, which minimizes bubble formation and enhances crosslinking efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If relatively high levels of peroxide are used to increase crosslinking and provide good mechanical properties, then mechanical strength and crosslinking degree are improved, but odour and undesirable leaching of components from the pipe increase
Solution Approach 1:
The patent introduces a specific peroxide initiator system with controlled decomposition characteristics as an intermediary to mediate between the need for high crosslinking (for mechanical strength) and the need to minimize harmful byproducts (odour and leaching). The peroxide is selected and dosed to provide sufficient crosslinking while its decomposition products are less harmful, thus resolving the contradiction between strength improvement and harmful factor reduction.
Solution Approach 2:
The patent changes critical parameters including peroxide concentration (optimized range rather than maximum), crosslinking temperature, and processing time to achieve a balance where adequate crosslinking (70-90% CCL) is obtained without excessive peroxide that would cause odour and leaching. By adjusting these parameters, the system achieves mechanical properties while minimizing harmful effects.
2Strength
If peroxide crosslinking is performed to achieve high crosslinking levels (70-90% CCL), then mechanical properties and stability are improved, but bubble formation increases
Solution Approach 1:
The patent applies preliminary action by pre-drying the polyolefin material and controlling moisture content before crosslinking. It also pre-heats the material uniformly and controls the heating rate during crosslinking to prevent rapid gas expansion that would cause bubbles. These preliminary measures ensure high crosslinking levels are achieved without bubble formation compromising manufacturing quality.
Solution Approach 2:
The crosslinking process uses periodic or staged heating rather than single-step rapid heating. The patent employs controlled temperature ramps and holding periods that allow gradual crosslinking progression, preventing sudden gas evolution and bubble formation while still achieving the required 70-90% crosslinking density for mechanical properties.
3Reliability
If crosslinking is performed to meet standards for burst strength and pressure resistance, then long term stability is improved, but compliance with hygiene standards for leaching becomes more difficult to achieve
Solution Approach 1:
The patent converts the potential harm of peroxide residues into a benefit by carefully selecting peroxide initiators whose decomposition products are less harmful and more easily degraded. The controlled crosslinking process ensures complete peroxide consumption, turning what could be a source of leaching into a benefit where the crosslinked structure itself prevents future degradation and leaching, thus meeting both mechanical reliability and hygiene standards.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution results in pipes with improved long-term mechanical properties, reduced odors, and compliance with standards such as NSF 61 for leaching and chlorine resistance, while maintaining high crosslinking levels.
Implementation Method 1
The primary reaction is the formation of free radicals upon decomposition of the peroxide, which has to be present by definition for PEX-a
Implementation Method 2
The primary reaction is the formation of free radicals upon decomposition of the peroxide
Implementation Method 3
the free radical abstracts hydrogens from the PE polymer chains
Implementation Method 4
The latter gives new carbon radicals, which next combines with neighboring PE chains to form stable carbon-carbon bonds, i.e., crosslinks
Implementation Method 5
cross-linking a polyolefin structural polymer by heating the extruded pipe
Data Source
AI summary
This invention relates to a polymeric pipe obtained by a peroxide crosslinking process. The pipe is formed from a composition comprising a polyolefin structural polymer, a peroxide initiator in an amount of from about 0.2% to about 5% by weight, and a co-agent in an amount of from about 0.02% to about 5% by weight. The co-agent comprises at least two reactive carbon-carbon double bonds. The invention also relates to methods of forming said pipes. The invention also relates to the use of a co-agent in a composition to reduce bubble formation in a peroxide crosslinking process. The invention also relates to the use of such polymeric pipes for the transport of water.