Functionalized Polymer Layer Scavenges Isocyanates in Polyurethane Adhesives
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Solution Overview
Problem
Existing food packaging using two-component polyurethane adhesives often contains appreciable amounts of monomeric isocyanate and primary aromatic amines, which are undesirable due to their toxicity and reactivity, leading to high primary aromatic amine (PAA) levels in food, requiring lengthy storage to reduce these levels.
Innovation Solution
A layered structure comprising a polyurethane layer and a functionalized polymer layer with specific functional groups such as acid, anhydride, or amine groups, which effectively scavenge PAAs by reacting with monomeric isocyanates, reducing PAA levels within a short period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If two-component polyurethane adhesive is used to bond substrates, then bonding strength is improved, but monomeric isocyanate compounds remain present causing high PAA levels in food
Solution Approach 1:
A functionalized polymer layer is introduced as an intermediary between the polyurethane adhesive and the food contact surface. This layer contains reactive functional groups that scavenge monomeric isocyanate compounds, preventing them from migrating into food and forming PAAs, thus resolving the contradiction between maintaining adhesive strength and reducing harmful PAA levels.
Solution Approach 2:
The invention creates a composite structure consisting of a polyurethane adhesive layer bonded to a functionalized polymer layer. This composite material combines the bonding properties of polyurethane with the PAA-scavenging properties of the functionalized polymer, allowing simultaneous achievement of strong bonding and low PAA levels in food contact applications.
2Object-affected harmful factors
If bonded assembly is stored for long periods, then PAA levels decrease, but storage time and productivity are reduced
Solution Approach 1:
The functionalized polymer layer is pre-applied or pre-bonded to the adhesive before the bonding assembly is ready for use. This preliminary action of incorporating the PAA-scavenging layer eliminates the need for lengthy post-bonding storage periods, as the scavenging function is immediately active, thus resolving the contradiction between reducing PAA levels and maintaining productivity.
3Object-affected harmful factors
If functionalized polymer layer is added to scavenge PAAs, then PAA levels in food are reduced, but device complexity increases
Solution Approach 1:
The functionalized polymer is applied as a thin film or coating layer on or near the adhesive. This thin-film approach provides effective PAA scavenging functionality while minimizing the increase in structural complexity and maintaining a relatively simple layered configuration that is easy to manufacture and integrate.
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
The layered structure significantly reduces PAA levels in food packaging within a short time, eliminating the need for long storage times and ensuring food safety by effectively scavenging PAAs, thereby enhancing the safety and efficiency of food packaging.
Implementation Method 1
monomeric isocyanate may react with water (for example, trapped water formed during the coating of the adhesive, or water from an atmosphere under high humidity) to form a primary amine
Implementation Method 2
These reactions result in formation of PAA which may further react with other 'isocyanate group-containing molecules' to form relatively innocuous urea-type compounds
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention provides a layered structure comprising at least two layers: A) a first layer A, formed from a composition A, comprising a polyurethane; and B) a second layer B, formed from a composition B, comprising at least one functionalized polymer B comprising the following: i) at least one polymerized monomeric unit comprising a functional group selected from the group consisting of the following: a) an acid group, b) an anhydride group, c) a primary or secondary amine group, and d) combinations thereof; or ii) at least one reacted functionalization agent comprising a functional group selected from the group consisting of the following: e) an acid group, f) an anhydride group, g) a primary or secondary amine group, and h) combinations thereof; or iii) combinations thereof; and wherein the functionalized polymer B has a number-average molecular weight greater than 1,000 g/mole, and/or a melt index (I2) less than, or equal to, 2500 g/10 min.