Polyethylene Pipe Composition Balancing Creep Strength and Moldability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing ethylene-based polymer compositions for pipes do not meet the requirements for higher pressure resistance, particularly in applications where internal fluid pressure is sustained for long periods, and there is a demand for improved moldability and reduced sagging properties.
Innovation Solution
A composition comprising 40 to 60% ethylene homopolymer and 60 to 40% ethylene/α-olefin copolymer, with specific density, molecular weight distribution, and intrinsic viscosity ranges, optimized using a Ziegler-Natta-based catalyst, to achieve enhanced creep strength and moldability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional ethylene-based polymers are used, then basic pipe performance is achieved, but higher pressure resistance and improved moldability are not satisfied
Solution Approach 1:
The patent applies parameter changes by precisely controlling the molecular weight distribution (Mw/Mn ratio of 30-70), density (940-960 kg/m³), and compositional ratios of homopolymer and copolymer components. These parameter optimizations enable the material to simultaneously achieve high pressure resistance (MRS ≥11.2 MPa) and good moldability, resolving the technical contradiction between strength and ease of manufacture
Solution Approach 2:
The patent uses composite materials by creating a blended composition of ethylene homopolymer (A) and ethylene/α-olefin copolymer (B) in specific ratios (40-60 mass% and 60-40 mass% respectively). This composite structure combines the high strength characteristics of homopolymer with the good processability of copolymer, achieving both high pressure resistance and improved moldability simultaneously
2Strength
If higher strength polymers are used to improve pressure resistance, then MRS increases, but moldability and sagging properties deteriorate
Solution Approach 1:
The patent resolves this contradiction through parameter changes by controlling the MFR5 value (0.03-0.3 g/10min) and molecular weight distribution (Mw/Mn of 30-70). The specific parameter range ensures that the material has sufficient viscosity for maintaining shape (reducing sagging) while retaining enough flowability for good moldability, all while achieving MRS ≥11.2 MPa
Solution Approach 2:
The patent applies local quality by creating a bimodal molecular weight distribution with specific amounts of high molecular weight components (log M≥7: 0.35-0.80%) and low molecular weight components (log M≤3: 1.85% or less). The high MW components provide strength and sag resistance, while the low MW components improve flow and moldability, allowing both properties to coexist
Data Source
AI summary
An object of the present invention is to obtain an ethylene-based polymer composition suitable for polyethylene pipes that satisfy the performance of PE112 (having MRS of 11.2 MPa or higher) requiring higher creep strength, as well as excellent moldability and low sagging properties. The present invention relates to an ethylene-based polymer composition containing: 40 to 60 mass % of an ethylene homopolymer (A) having MFR measured at a temperature of 190° C. under a load of 2.16 kg (MFR2) within a range of 100 to 600 g/10 min; and 60 to 40 mass % of a copolymer (B) of ethylene and an α-olefin having four or more carbon atoms [ethylene/α-olefin copolymer (B)] [provided that a total amount of (A)+(B) is 100 mass %], in which the following requirements (i) to (iii) are satisfied.(i) A density is within a range of 940 to 960 kg/m3.(ii) An amount of a component with GPC-measured log M≥7 is within a range of 0.35 to 0.80%.(iii) An amount of a component with GPC-measured log M≤3 is 1.85% or less.