rPET Blending for Thin-Wall Molding with Controlled Viscosity
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Solution Overview
Problem
Current methods for producing thin-walled PET containers for food storage using the injection molding process face challenges due to high viscosity issues in recycled PET materials, leading to brittleness, uncontrolled crystallization, and difficulty in achieving the required viscosity for injection molding.
Innovation Solution
A method involving the combination of low-viscosity virgin PET with recycled PET from bottle recycling streams, where the mixture is reactively extruded to achieve an intrinsic viscosity of 0.5 to 0.7 dL/g, allowing for the production of stable, transparent, and shatter-resistant thin-walled injection-molded articles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If standard PET recycling materials with high viscosity are used, then the material can be obtained from bottle recycling streams, but the material becomes too hard and viscous to allow molding of complicated, thin-walled articles
Solution Approach 1:
The patent applies parameter changes by controlling the intrinsic viscosity of the PET material through selective recycling and processing conditions. By maintaining the intrinsic viscosity within 0.5 to 0.7 dL/g through controlled hydrolysis and condensation processes, the material achieves both recyclability and moldability for thin-walled articles, resolving the contradiction between high recycled content and ease of manufacture.
Solution Approach 2:
The patent creates a composite approach by combining recycled PET with controlled amounts of virgin PET or other polyester materials. This composite strategy allows the final material to have optimized viscosity properties that enable thin-walled injection molding while maintaining high recycled content, thus resolving the contradiction between quantity of recycled substance and ease of manufacture.
2Ease of manufacture
If the intrinsic viscosity of PET is reduced to 0.5 to 0.7 dL/g for injection molding, then thin-walled articles can be molded, but the material becomes brittle and shatters when dropped
Solution Approach 1:
The patent resolves this contradiction by carefully controlling multiple parameters including intrinsic viscosity (0.5 to 0.7 dL/g), copolymer fraction (1% to 10%), and processing temperature. By optimizing these parameters together rather than focusing on viscosity alone, the material achieves both moldability and impact resistance, preventing brittleness while enabling thin-walled article production.
Solution Approach 2:
The patent uses composite material strategies by incorporating copolymer components and controlling the molecular weight distribution through controlled hydrolysis and condensation. This composite approach at the molecular level allows the material to maintain low enough viscosity for injection molding while developing sufficient chain flexibility and intermolecular bonding to resist impact and shattering.
3Ease of manufacture
If recycled PET materials are used without controlled hydrolysis, then the recycling process is simple, but uncontrolled crystallization occurs leading to material instability
Solution Approach 1:
The patent applies parameter changes by controlling the hydrolysis degree and condensation conditions during recycling. By maintaining specific parameters (temperature, time, moisture content, catalyst concentration), the process achieves controlled crystallization and molecular weight distribution. This resolves the contradiction by keeping the process relatively simple while preventing uncontrolled crystallization and ensuring material stability.
Solution Approach 2:
The patent implements feedback control in the recycling process by monitoring and adjusting hydrolysis and condensation conditions in real-time. This feedback mechanism ensures that crystallization remains controlled while maintaining high recycled content, thus resolving the contradiction between ease of manufacture and compositional stability.
4Quantity of substance
If high copolymer fraction is present in recycled PET, then the material can be obtained from mixed recycling streams, but the copolymer content increases and affects material properties
Solution Approach 1:
The patent resolves this contradiction by controlling the copolymer fraction within 1% to 10% through selective recycling and processing. By managing this parameter during hydrolysis and condensation, the material accepts high recycled content from mixed streams while maintaining compositional stability and suitable material properties for injection molding.
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 proposed method enables the production of thin-walled PET containers that are stable, transparent, and resistant to shattering, while also allowing for high recycled content, thus addressing the challenges of viscosity and material stability in existing recycling streams.
Implementation Method 1
The intrinsic viscosity of the injection-molded article is lowered to 0.5 to 0.7 dL/g during the extrusion
Implementation Method 2
the chain lengths are mutually compensating due to the cross-esterification occurring in the melt
Data Source
AI summary
The invention relates to a method by which a starting material for injection molding having a viscosity of between 0.50 and 0.7 dL/g is produced from a recycled post-consumer PET having a viscosity of between 0.72 and 0.86 dL/g according to ASTM D4603 and a copolymer fraction of at most approximately 3%, adding a low-viscosity PET material. In the method, the comminuted and dried PET material is melted and decontaminated to such a degree that it is suitable for applications in the food sector and the consumer goods sector.