Polylactic Acid Foam Composition with Block Copolymer
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Polylactic acid foams face challenges such as low expansion ratio, high density, poor heat resistance, and limited flexibility due to low melt tension and crystallization speed, as well as incompatibility with other resins, resulting in nonuniform mixtures and decreased closed cell content.
Innovation Solution
A foam composition combining polylactic acid with a thermoplastic resin like polyolefin or polystyrene, and a styrene-butadiene block copolymer, with specific ratios and modifications to enhance melt tension, Vicat softening point, and melt mass-flow rates, to achieve higher closed cell content, expansion ratio, and heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If polylactic acid is used as a raw material for foam, then environmental friendliness is improved, but closed cell content decreases due to low melt tension causing air bubble burst
Solution Approach 1:
A master batch containing a specific blend of polyolefin resin and polystyrene resin is introduced as an intermediary material. This master batch acts as a mediator between polylactic acid and the foaming agent, providing the necessary melt tension to prevent air bubble burst while maintaining environmental friendliness. The master batch is mixed with polylactic acid before foaming, ensuring stable foam structure with high closed cell content.
2Object-affected harmful factors
If polylactic acid is used for foam, then biodegradability is improved, but expansion ratio decreases due to air bubble burst
Solution Approach 1:
The master batch serves as an intermediary that transfers the foaming action efficiently. It contains a controlled blend of polyolefin and polystyrene resins that provide adequate melt tension to sustain air bubble growth, enabling the foam to achieve high expansion ratios (50-100 times) while maintaining biodegradability of the polylactic acid component.
3Temperature
If polylactic acid is used for foam, then heat resistance is worsened due to low allowable temperature limit, but if highly pure L-lactic acid or D-lactic acid is used to enhance crystallinity and heat resistance, then crystallization speed becomes exceedingly slow requiring high-temperature curing for a long time
Solution Approach 1:
The invention changes the compositional parameters by introducing a master batch with a specific ratio of polyolefin resin (40-80 parts) to polystyrene resin (20-60 parts). This parameter change allows the foam to achieve Vicat softening points of 80°C or higher without requiring long high-temperature curing, as the thermoplastic resins in the master batch provide the necessary heat resistance.
4Productivity
If polyolefin resin or polystyrene resin is blended with polylactic acid to improve foamability and heat resistance, then foamability and heat resistance are improved, but closed cell content decreases due to exfoliation at the interface between incompatible resins
Solution Approach 1:
The invention achieves homogeneity by pre-blending polyolefin resin and polystyrene resin in a master batch before mixing with polylactic acid. This ensures uniform distribution of the thermoplastic resins throughout the polylactic acid matrix, preventing interface exfoliation and maintaining high closed cell content while improving foamability and heat resistance.
Data Source
AI summary
The present invention provides a foam comprising (a) a polylactic acid resin, (b) at least one thermoplastic resin selected from a polyolefin resin and a polystyrene resin, and (c) a block copolymer of a vinyl aromatic compound and a conjugated diene, wherein a ratio of (a) to (b) by weight (a/b) is 80/20 to 20/80, and the foam comprises 0.5 to 20 parts by weight of (c) with respect to 100 parts by weight of (a) and (b) in total.