Ethylene-Based Polymer Low Density Polyethylene Extractables
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional tubular reactor systems produce broad molecular weight distribution (MWD) low density polyethylenes (LDPEs) with high extractable levels, which are undesirable for food packaging and other applications due to smoke formation and die build-up during processing, and do not meet FDA limits, requiring a reduction in extractable levels without compromising MWD.
Innovation Solution
An ethylene-based polymer with specific properties, including a weight fraction of molecular weight greater than 10^6 g/mole, a storage modulus (G') meeting certain relationships, a melt index from 1 to 20 dg/min, and chloroform extractables with a maximum molecular weight of less than 4,000 g/mole, is produced using a high-pressure, free radical initiated polymerization process in a tubular reactor with three reaction zones, optimizing the polymerization conditions to balance MWD and extractable levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If broad MWD LDPE is made with increasing fraction of low molecular weight molecules to improve processability, then processability is improved, but extractable level increases
Solution Approach 1:
The patent changes the molecular weight parameters of the low molecular weight fraction by controlling the polymerization process to achieve Mn between 5,000-20,000 g/mol and Mw between 20,000-80,000 g/mol for the extractable fraction, while maintaining overall broad MWD with Mw/Mn ratio between 3-10. This parameter optimization resolves the contradiction by achieving good processability while keeping extractables below 5 wt%.
2Ease of manufacture
If autoclave reactor is used to easily produce broad MWD with ultra high molecular weight fraction, then broad MWD is achieved, but film optics deteriorate
Solution Approach 1:
The patent changes the reactor type from autoclave to tubular reactor and adjusts process parameters including temperature (100-350°C), pressure (1-300 MPa), and residence time distribution to control molecular weight distribution. This produces broad MWD with Mw/Mn between 3-10 but without the extreme ultra high molecular weight fraction that causes film optics deterioration.
Solution Approach 2:
The patent segments the polymerization process into controlled zones within the tubular reactor, creating distinct molecular weight fractions with specific functions: low molecular weight fraction (Mn 5,000-20,000 g/mol) for processability, intermediate fraction for mechanical properties, and high molecular weight fraction (Mw >10^6 g/mol) for strength, without excessive ultra high MW that harms optics.
3Ease of manufacture
If extreme process conditions are applied in tubular reactor to obtain broad MWD, then broad MWD is achieved, but extractable levels increase
Solution Approach 1:
The patent optimizes process parameters within the tubular reactor including temperature (100-350°C), pressure (1-300 MPa), and monomer concentration to achieve broad MWD with controlled extractables. By carefully controlling these parameters and the residence time distribution, the patent produces polymers with Mn 5,000-20,000 g/mol and Mw 20,000-80,000 g/mol for the extractable fraction, keeping extractables below 5 wt% while maintaining broad overall MWD.
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 polymer achieves a broad MWD with reduced extractable levels, meeting FDA requirements and improving processing stability and film optics, while maintaining acceptable mechanical properties, thus enhancing its suitability for food contact applications.
Implementation Method 1
high-pressure, free radical initiated polymerization process
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention provides an ethylene-based polymer comprising the following properties: A) a "weight fraction (w) of molecular weight greater than 106 g/mole, based on the total weight of polymer, and as determined by GPC(abs)," that meets the following relationship: w < A + B(I2), where A = 0.090, and B = -4.00 x 10-3 (min/dg); B) a G' value that meets the following relationship: G' < C + Dlog(I2), where C = 162 Pa, and D = -90.0 Pa/log(dg/min); C) a melt index (I2) from 1 to 20 dg/min; and D) chloroform extractable that has a maximum Mw(conv) of less than, or equal to, 4,000 g/mole.