Poly(aliphatic ester)-polycarbonate blend for PLA impact strength
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Solution Overview
Problem
Polylactic acid (PLA) based polymers lack formability, mechanical strength, and heat resistance, and when blended with petroleum-based thermoplastics like polycarbonate, they make articles brittle and have low impact strength.
Innovation Solution
A blended composition of polycarbonates, including a poly(aliphatic ester)-polycarbonate with sebacic acid units, combined with a polylactide polymer, which enhances impact strength and ductility while maintaining a high biocontent, eliminating the need for impact modifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If polylactic acid (PLA) is blended with petroleum-based thermoplastics like polycarbonate, then mechanical strength and formability are improved, but the articles become brittle and have low impact strength
Solution Approach 1:
The invention changes the chemical composition parameters of the polycarbonate by incorporating specific aliphatic ester units (sebacic acid, adipic acid, succinic acid) in controlled amounts (0.1-10 mole%). This compositional parameter change modifies the polymer chain flexibility and intermolecular forces, resulting in improved impact strength and ductility while maintaining mechanical strength, thus resolving the brittleness issue in conventional PLA/polycarbonate blends
Solution Approach 2:
The invention creates a composite polycarbonate material combining aromatic polycarbonate units (for strength) with aliphatic ester units (for flexibility and impact resistance). This composite structure at the molecular level allows the material to exhibit both high mechanical strength and high impact strength, eliminating the brittleness problem when blended with PLA
2Reliability
If polylactic acid (PLA) based polymers are used, then biocontent and decomposition characteristics are improved, but heat resistance and formability are poor
Solution Approach 1:
The invention modifies the thermal parameters of PLA by blending it with a specially designed polycarbonate containing aliphatic ester units. The polycarbonate component has a higher glass transition temperature and melting point than PLA, which raises the overall processing temperature range of the blend. This parameter change enables the material to maintain structural integrity at higher temperatures during molding while preserving the biocontent and decomposition benefits of PLA
3Reliability
If polylactic acid (PLA) is used, then biocontent is improved, but mechanical strength and heat resistance are insufficient
Solution Approach 1:
The invention creates a composite blend system where PLA (providing biocontent) is combined with a modified polycarbonate containing aliphatic ester units (providing mechanical strength). The polycarbonate component acts as a reinforcing phase that compensates for PLA's inherent weakness, while the aliphatic ester units in the polycarbonate ensure good interfacial adhesion and stress transfer, maintaining high impact strength in the composite
Data Source
AI summary
The present invention is directed to a blended composition comprising one or more polycarbonates wherein at least one of the polycarbonates is a polyesterpolycarbonate having at least one unit derived from a soft block ester unit, e.g., sebacic acid, and at least one unit derived from bisphenol A, and a polylactic polymer wherein the composition has an overall biocontent of at least 10% according to ASTMD6866.