Polyolefin Packaging Films for Fresh Produce Permeability
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Solution Overview
Problem
Current polypropylene films used for packaging fresh produce, such as vegetables, face a challenge in achieving a balance between machinability and permeability to oxygen, carbon dioxide, and water vapor, as they either compromise on tensile stiffness or increase transmission rates, leading to unsuitable packaging conditions for metabolic activity and microbial growth.
Innovation Solution
A polyolefin composition comprising 5-80% of a butene-1 polymer with specific comonomer content and 20-95% of a propylene homopolymer or copolymer, optimized for high transparency and balance of mechanical and permeability properties, is used to create films with enhanced tensile strength and low haze, suitable for packaging fresh foods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If polypropylene films are used for packaging fresh produce, then machinability is improved, but permeability to oxygen, carbon dioxide and water vapor is insufficient
Solution Approach 1:
The patent uses a composite polymer composition consisting of polypropylene (40-70 wt%), ethylene/propylene copolymer (15-40 wt%), and ethylene/vinyl alcohol copolymer (10-30 wt%). This multi-component composite allows the film to simultaneously achieve good machinability from polypropylene and enhanced permeability from the copolymers, resolving the contradiction between ease of operation and reliability.
2Reliability
If oxygen transmission rate is increased to support metabolic activity, then fresh produce respiration is supported, but microbial growth is favored
Solution Approach 1:
The patent modifies the chemical composition parameters of the packaging film by incorporating specific copolymers with controlled comonomer ratios. The ethylene/vinyl alcohol copolymer with 20-40 mol% vinyl alcohol content provides controlled permeability that allows oxygen transmission for metabolism while the specific composition prevents excessive moisture accumulation that would favor microbial growth.
3Reliability
If film thickness is decreased to improve permeability, then oxygen transmission rate increases, but tensile stiffness decreases
Solution Approach 1:
The patent employs a composite formulation where polypropylene provides structural strength and stiffness, while ethylene/propylene copolymer and ethylene/vinyl alcohol copolymer enhance permeability. This composite structure allows thin films to maintain adequate tensile stiffness while achieving the required oxygen transmission rates.
Solution Approach 2:
The patent creates different functional zones within the film structure through the composite composition. The polypropylene domains provide local structural support and stiffness, while the copolymer domains provide local permeability pathways for gas and vapor transmission, allowing the film to be thin yet both strong and permeable.
Data Source
AI summary
Films especially suitable for the packaging of fresh foodstuff, like salad and vegetables, due to their high permeability to oxygen, carbon dioxide and water vapor, are obtained from polyolefin composition comprising (percentage by weight):A) 5% to 80% of a butene-1 polymer or polymer composition containing from 0% to 25% of one or more comonomers selected from ethylene and alpha-olefins different from 1-butene, provided that, when ethylene only is present as comonomer, the amount of ethylene is higher than 4% and a copolymer fraction (i) containing at least 6.2% of ethylene is present, said polymer or polymer composition having a content of fraction soluble in xylene at 0° C. of from 50% to 100% and a Flexural Modulus (measured according to ISO 178) from 15 to 300 MPa;B) 20% to 95% of a propylene homopolymer or copolymer having a content of fraction insoluble in xylene at room temperature of 93% or more.