Polyurethane Sole Moulding with Steam Baking
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Solution Overview
Problem
Current methods for reusing polyurethane waste in footwear sole production, such as glycolysis and agglomeration, face limitations including low recovery rates, high energy consumption, and geometric simplicity of recovered products, with previous techniques achieving at most 50% recycled content and limited shape complexity.
Innovation Solution
A moulding method involving the use of polyurethane scraps with a selected breaking load and density, wetted with a polyurethane binding agent, then baked with steam in a mould to create a high-density, complex-shaped product with over 75% recycled content, allowing for efficient and high-recycled-content polyurethane sole production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If glycolysis is used to recover polyurethane waste, then the waste can be chemically broken down and reused, but the process requires high temperature reaction for many hours and achieves at most 50% recovered content
Solution Approach 1:
The invention changes the fundamental parameters of the recovery process by replacing chemical glycolysis with physical steam baking. This shifts the process from high-temperature chemical reaction to lower-temperature physical treatment, dramatically reducing processing time from many hours to a fraction of that time while achieving over 75% recovery rate
Solution Approach 2:
The invention replaces the chemical system (glycolysis reaction) with a physical system (steam baking). Instead of using chemical reagents and prolonged thermal chemical reaction, the process uses steam heating to activate the binding agent and fuse granules, achieving faster processing and higher recovery
2Loss of substance
If agglomeration with raw polyurethane is used, then waste granules can be mixed and moulded, but the granules hinder material flow and limit recovered content to 20-30%
Solution Approach 1:
The invention introduces a binding agent as an intermediary substance that coats the waste granules. This binding agent acts as a mediator that enables granules to adhere to each other during steam baking, allowing high granule concentration (over 75% recovery) without hindering the moulding process or material flow
Solution Approach 2:
The invention changes the state and properties of the granules through steam baking treatment. The steam activates the binding agent and facilitates granule fusion, transforming the material from a state where granules hinder flow to a state where they are effectively bonded and integrated
3Loss of substance
If binder agglomeration is used to achieve high recovered material percentage, then granules can be glued together, but the products obtained have very geometrically simple shapes
Solution Approach 1:
The invention moves from simple block moulding to complex three-dimensional shape formation. By using specifically designed moulds with multiple cavities and intricate geometries, the process can produce geometrically complex products such as footwear soles with detailed patterns, channels, and varying thicknesses, rather than simple geometric shapes
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 method enables the production of polyurethane footwear soles with over 75% recycled content and complex shapes, overcoming previous limitations by achieving higher recovery rates and reducing processing time, while maintaining product quality and ecological impact.
Implementation Method 1
baked with steam in a mould
Implementation Method 2
wetted with a polyurethane binding agent
Data Source
Figure 1
AI summary
A method of moulding an object in polyurethane, in particular a sole for footwear, comprising the steps of: - preparing polyurethane scraps, in granular form, said scraps having a breaking load greater than 20 kg/cm2, and a density greater than 200 g/l, - wetting said scraps with a polyurethane binding agent in order to obtain an agglomerate of scrap material and binding agent, - inserting the agglomerate in a mould (4), so that the percentage by weight of the binding agent is at least equal to 10% of the total weight of the agglomerate inserted in the mould (4), - closing the mould (4) and baking the agglomerate with steam blown inside the mould (4), so as to obtain an increase in the molecular weight of the binding agent and the incorporation of the scraps inside a binding agent matrix, - cooling the mould (4) and removing the moulded part.