Stretch Blow-Molded PET Preform Suppressing Spherulite Formation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Recycled PET materials used in stretch blow molding often have reduced molecular weight, leading to increased crystallization and spherulite formation, which results in preform rupture during the molding process, and the energy-intensive solid phase polymerization method further exacerbates this issue, limiting the use of recycled PET in bottle molding.
Innovation Solution
A method involving a blend of two polyesters, where the first polyester has an intrinsic viscosity of 0.60 to 0.74 dL/g and the second polyester has a structure corresponding to terephthalic acid and bisphenol A, is used to suppress spherulite formation and stabilize the blow molding process, allowing for the use of recycled PET with reduced molecular weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If recycled PET with reduced molecular weight is used for stretch blow molding, then material recycling efficiency is improved, but preform rupture occurs due to increased crystallization and spherulite formation
Solution Approach 1:
The patent changes the chemical composition parameters of the polyester material by incorporating a specific type of copolymer (PETG or PETD) with defined structural characteristics into the recycled PET blend. This parameter change modifies the crystallization behavior and molecular weight characteristics of the material, allowing it to maintain molding stability while using recycled content. The specific structural parameters of the copolymer (such as glycol content and molecular weight distribution) are controlled to achieve the desired balance between recyclability and process reliability.
Solution Approach 2:
The patent creates a composite material system by blending recycled PET with a specific copolymer (PETG or PETD) that has different molecular and structural characteristics. This composite approach allows the material to combine the recyclability benefits of post-consumer PET with the processing stability provided by the copolymer component, effectively resolving the contradiction between using recycled material and maintaining molding reliability.
2Reliability
If solid phase polymerization is used to raise molecular weight of recycled PET, then molding stability is improved, but energy consumption increases significantly
Solution Approach 1:
Instead of using energy-intensive solid phase polymerization to extend the life of polymer chains, the patent introduces a copolymer component that inherently provides the necessary molecular characteristics for stable molding. This approach accepts the shorter effective chain length of recycled PET but compensates through compositional modification, avoiding the high energy input required for repolymerization while achieving similar molding stability.
Solution Approach 2:
The patent changes the compositional parameters of the polyester blend by adding copolymer components with specific structural features that provide the necessary molecular weight and crystallization characteristics without requiring energy-intensive post-recycling treatment processes. This parameter change allows the material to achieve molding stability through composition rather than through energy-consuming molecular weight restoration.
3Stability of the object's composition
If PET with lower molecular weight is used, then spherulite formation increases leading to preform rupture, but raising molecular weight through repolymerization increases process complexity and environmental impact
Solution Approach 1:
The patent merges recycled PET material with a copolymer component (PETG or PETD) in a blended composition. This merging approach combines the benefits of recycled content with the structural stability provided by the copolymer, achieving the necessary molecular weight and crystallization characteristics without requiring complex multi-stage repolymerization processes or additional decomposition equipment.
Solution Approach 2:
The patent modifies the compositional parameters of the polyester material by incorporating copolymers with specific structural characteristics (such as glycol content and molecular weight distribution) into the recycled PET blend. This parameter change directly addresses the molecular weight and crystallization issues without requiring complex process changes or additional equipment for repolymerization.
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
This approach enables stable and high-quality stretch blow molding of PET bottles by inhibiting crystallization and spherulite formation, reducing the risk of preform rupture and minimizing energy consumption, thus enhancing the recycling efficiency of PET materials.
Implementation Method 1
PET resins exhibit a characteristic in that the crystallization time of the resin shortens as the molecular weight thereof decreases. When such low-molecular-weight PET is used, preforms crystallize readily during stretch blow molding on account of the lower molecular weight, and thus blow molding defects are prone to occur.
Implementation Method 2
Studies by the inventors reveal that PET as a material resulting from recycling of recovered blow bottles exhibits a lowered molecular weight. Such PET resins with shorter molecular chains tend to exhibit a folded structure, which is one of crystalline states, and form spherulites easily.
Data Source
AI summary
A stretch blow-molded article comprising: a first polyester; and a second polyester having a structure different from a structure of the first polyester, wherein an intrinsic viscosity value of the first polyester is 0.60 to 0.74 dL/g, and the second polyester has a structure corresponding to terephthalic acid and a structure corresponding to bisphenol A.