LDPE Elongational Hardening via Oxygen Radical Initiation
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Solution Overview
Problem
Low density polyethylene (LDPE) products face challenges in achieving high elongational hardening and broad molecular weight distribution without using organic peroxides, which are necessary for better processability in applications like extrusion coating, while maintaining desirable organoleptic properties.
Innovation Solution
A low density polyethylene (LDPE) is produced with a density of 0.910 to 0.924 g/cm3, elongational hardening of at least 4.2 at 150°C, and a weight average to number average molecular weight ratio of at least 18, using oxygen as the sole radical initiating agent in the polymerization process, and without solvents, to achieve the desired properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If autoclave process with organic peroxides is used, then high concentration of long chain branches and broad molecular weight distribution are achieved, but organoleptic properties such as odor are harmed due to degradation products
Solution Approach 1:
The patent changes the chemical parameter of the radical initiating agent from organic peroxides to oxygen, and adjusts polymerization conditions (pressure 100-3000 atm, temperature 50-300°C, oxygen concentration 0.01-50% by weight) to achieve the desired molecular weight distribution (Mw/Mn ≥ 18) and elongational hardening (≥4.2) without compromising organoleptic properties
Solution Approach 2:
The patent converts the typically harmful role of oxygen (which can cause degradation) into a beneficial radical initiating agent that produces the desired long chain branches and molecular weight distribution without generating harmful degradation products, thereby improving both processing properties and organoleptic quality
2Object-generated harmful factors
If tubular process with oxygen alone is used, then organoleptic properties are improved, but concentration of long chain branches and molecular weight distribution are reduced
Solution Approach 1:
The patent systematically varies polymerization parameters including increasing pressure up to 3000 atm, adjusting temperature range 50-300°C, and optimizing oxygen concentration (0.01-50% by weight) to achieve sufficient long chain branching (gpcBR ≥ 1.5) and broad molecular weight distribution (Mw/Mn ≥ 18) while maintaining good organoleptic properties
3Strength
If high molecular weight is achieved, then elongational hardening is improved, but processability in extrusion coating is reduced
Solution Approach 1:
The patent optimizes the molecular weight distribution by controlling polymerization conditions to achieve Mw ≥ 230,000 g/mol with broad distribution (Mw/Mn ≥ 18), which provides sufficient elongational hardening while maintaining processability through the broad distribution that includes lower molecular weight fractions
Solution Approach 2:
The patent creates a composite molecular weight distribution within the polymer, combining high molecular weight chains (for elongational hardening) with lower molecular weight chains (for processability), achieved through controlled radical polymerization with oxygen initiating agent under optimized conditions
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 resulting LDPE exhibits enhanced elongational hardening and molecular weight distribution, suitable for high-speed extrusion coating and other applications, while maintaining improved organoleptic properties by avoiding organic peroxide degradation products.
Implementation Method 1
free-radical polymerization of ethylene in the presence of oxygen as a radical initiating agent
Implementation Method 2
in the presence of oxygen as the only radical initiating agent
Data Source
AI summary
The present disclosure provides a low density polyethylene (LDPE) having (A) a density from 0.910 to 0.924 g/cm3, determined according to ISO 1183 at 23° C.; (B) an elongational hardening of at least 4.2, at 150° C. at an elongational rate of 1 s−1; (C) a ratio Mw/Mn of at least 18, where (i) Mw is the weight average molar mass, measured by a MALLS detector coupled to a GPC, and (ii) Mn is the number average molar mass, measured by GPC (Gel Permeation Chromatography); and (D) a Mw of at least 230,000 g/mol. The present disclosure also provides an article of manufacture made from or containing (A) a substrate and (B) a coating layer made from or containing the disclosed LDPE. The present disclosure further provides a polymerization process occurring (A) in the presence of oxygen as the only radical initiating agent and (B) in the absence of solvents.