Polylactic Acid Composition for Stretch-Molded Bottles
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Solution Overview
Problem
Polylactic acid is weak in alkali resistance and has low resistance to environmental stress crack (ESCR) due to internal pressure, limiting its use in pressure-resistant bottles, especially for carbonated beverages.
Innovation Solution
A polylactic acid composition incorporating a small amount of ethylene resin with specific melt flow characteristics, such as high density polyethylene, to enhance alkali resistance and ESCR, along with a hydrocarbon deposited film on the inner surface for improved barrier properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polylactic acid is used alone in molding bottles, then biodegradability and environmental benefits are maintained, but alkali resistance and environmental stress crack resistance are insufficient
Solution Approach 1:
The invention uses a composite resin composition consisting of polylactic acid (70-95 mass%) and polyethylene (5-30 mass%). This composite structure combines the biodegradability and environmental benefits of polylactic acid with the excellent alkali resistance and environmental stress crack resistance of polyethylene, thereby resolving the contradiction between reliability and environmental benefits.
2Reliability
If polyethylene is blended with polylactic acid to improve ESCR, then environmental stress crack resistance is enhanced, but the resistance to internal pressure remains insufficient
Solution Approach 1:
The invention optimizes the composition ratios of polylactic acid (70-95 mass%) and polyethylene (5-30 mass%), and controls the melt flow rate of polyethylene within 0.3-10 g/10min. These parameter changes ensure that the composite maintains sufficient resistance to internal pressure while achieving improved ESCR through the polyethylene component.
3Reliability
If a hydrocarbon deposited film is formed on the inner surface, then barrier properties are improved, but manufacturing complexity increases
Solution Approach 1:
The hydrocarbon deposited film acts as an intermediary layer on the inner surface of the bottle, providing enhanced barrier properties against gas and moisture penetration. Although this adds a manufacturing step, the film thickness is controlled at 1-100 nm, and the process uses existing plasma deposition technology, thereby limiting the increase in manufacturing complexity while achieving significant improvement in barrier properties.
Data Source
AI summary
A polylactic acid composition including polylactic acid and an ethylene resin, characterized in that the ethylene resin is selected so that a melt flow rate ratio (RMF), defined by the following equation (1): RMF=APLA/BPE (1) where APLA represents the melt flow rate of the polylactic acid measured at 210° C. and 2.16 kg, and BPE represents the melt flow rate of the ethylene resin measured at 190° C. and 2.16 kg, in a range of 0.5 to 10 is satisfied. Also disclosed is a stretch-molded bottle formed using the polylactic acid composition. The polylactic acid composition is preferably used in molding a container particularly improved in alkali resistance and environmental stress crack resistance.