CPVC Pipe Fitting Compound for Stress Cracking Resistance
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Solution Overview
Problem
CPVC resin-based articles face challenges with environmental stress cracking (ESC) and low impact strength, particularly when exposed to certain liquids, necessitating improved resistance and processing ease while maintaining or enhancing physical properties.
Innovation Solution
A CPVC compound comprising a high molecular weight CPVC resin with a chlorine content between 63 to 66.75 wt% and optionally including standard molecular weight CPVC resin, along with additives like stabilizers and impact modifiers, to enhance resistance to ESC and impact strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If CPVC resin is chlorinated to increase chlorine content to improve high temperature performance and chemical inertness, then heat deflection temperature and flame resistance are improved, but the material becomes more brittle and impact strength decreases
Solution Approach 1:
The patent optimizes the chlorine content parameter to a specific range (63-66.75 wt%) rather than maximizing it, and controls the inherent viscosity of the vinyl chloride resin (0.79-1.02 dL/g) to achieve the right balance between heat deflection temperature and impact strength, eliminating the need for impact modifiers
Solution Approach 2:
The patent creates a compound with non-uniform molecular weight distribution by combining high molecular weight CPVC resin (providing heat resistance) with standard molecular weight CPVC resin (providing processability and impact strength), where each component performs its specific function
2Stability of the object's composition
If CPVC resin is chlorinated to increase chlorine content to improve chemical inertness, then flame resistance and chemical stability are improved, but resistance to environmental stress cracking decreases
Solution Approach 1:
The patent identifies and controls multiple parameters simultaneously: chlorine content (63-66.75 wt%), inherent viscosity of vinyl chloride resin (0.79-1.02 dL/g), and molecular weight distribution, to achieve the optimal balance between chemical inertness and environmental stress cracking resistance
Solution Approach 2:
The patent creates a composite CPVC compound combining high molecular weight CPVC resin (providing chemical stability) with standard molecular weight CPVC resin (providing ESC resistance), achieving superior overall performance
3Temperature
If CPVC resin is chlorinated to increase chlorine content to improve high temperature performance, then heat deflection temperature is improved, but processing difficulty increases
Solution Approach 1:
The patent introduces molecular weight distribution heterogeneity into the CPVC compound, combining high molecular weight fractions (for heat resistance) with standard molecular weight fractions (for easy processing), allowing each fraction to perform its specialized function
Solution Approach 2:
The patent formulates a composite material system using two different CPVC resin types with distinct molecular weight characteristics, enabling the compound to simultaneously exhibit high temperature performance and good processability
4Strength
If impact modifiers are added to improve impact strength of CPVC, then impact properties are improved, but resistance to environmental stress cracking may be compromised
Solution Approach 1:
The patent extracts and eliminates the need for impact modifiers by discovering that high molecular weight CPVC resin itself provides sufficient impact strength, thereby avoiding the potential ESC problems associated with conventional impact modifiers
Solution Approach 2:
The patent enables the CPVC resin to self-provide impact strength through its high molecular weight characteristics and optimized molecular weight distribution, without requiring external impact modifier additives
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 CPVC compound exhibits improved resistance to environmental stress cracking and maintains or exceeds impact strength compared to traditional CPVC compounds, meeting ASTM D1784 cell class 23447 and providing enhanced chemical stability.
Implementation Method 1
CPVC homopolymer resins prepared by chlorinating a vinyl chloride resin having an inherent viscosity of 0.79 to 1.02 have improved resistance to environmental stress cracking when such homopolymer resins are chlorinated to a chlorine content of between 63 to 66.75 wt%
Data Source
AI summary
The disclosed technology relates to a plastic compound suitable for preparing articles, such as pipe fittings and valves, with good physical properties, such as impact strength, and resistance to environmental stress cracking (ESC). In particular, the technology relates to a vinyl chloride resin, which includes chlorinated polyvinyl chloride ("CPVC") homopolymer. Furthermore, the invention relates to vinyl chloride homopolymer compounds containing the vinyl chloride homopolymer resin, and articles made from such compounds, which compounds meet 23447 cell classifications under ASTM D1784.