Cellulose-Based Expandable Microspheres for Low-Temperature Applications
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Solution Overview
Problem
There is a need for thermally expandable microspheres with low expansion temperatures and low density, derived from sustainable sources, that also possess improved storage stability, as existing thermoplastic polymers are often non-biodegradable and sourced from petrochemicals, making them environmentally unsustainable.
Innovation Solution
The development of thermally expandable microspheres with a polymeric shell comprising carboxylate-functionalised cellulose, which have a starting expansion temperature (TStart) between 80°C to less than 135°C, produced through a process involving mixing carboxylate-functionalised cellulose, an organic solvent, and a blowing agent, optionally with a polymer shell enhancer, and then spraying the mixture into a drying equipment to form microspheres with a hollow core.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional thermoplastic polymers are used for the microsphere shell, then acceptable expansion performance is achieved, but the material is non-biodegradable and derived from petrochemicals, causing environmental harm
Solution Approach 1:
The patent modifies the chemical composition parameters of the polymer shell by incorporating bio-based monomers (lactone, itaconate) alongside conventional monomers, adjusting the ratio to achieve both environmental sustainability and required expansion performance. The glass transition temperature and surface energy are tuned through compositional changes to maintain functional properties.
Solution Approach 2:
The patent creates a composite polymer shell combining bio-based polymers (cellulose acetate propionate, cellulose acetate butyrate) with conventional thermoplastics. This composite structure leverages the biodegradability and renewable sourcing of bio-polymers while maintaining the expansion characteristics of conventional materials through careful formulation.
2Object-affected harmful factors
If bio-based monomers are used to replace conventional monomers, then environmental sustainability is improved, but expansion performance deteriorates due to inadequate surface energy, gas barrier properties, and viscoelastic characteristics
Solution Approach 1:
The patent adjusts critical parameters including glass transition temperature (Tg), surface energy, and molecular weight of the polymer shell by modifying the bio-based monomer content and selecting specific cellulose derivatives. These parameter optimizations ensure the shell maintains adequate viscoelasticity for expansion while being environmentally sustainable.
Solution Approach 2:
The patent applies different functional requirements to different aspects of the polymer shell: the outer surface is optimized for blowing agent encapsulation through controlled surface energy, while the bulk material provides structural integrity and expansion capability. This localized optimization allows bio-based materials to meet diverse performance criteria.
3Strength
If the polymer shell has high glass transition temperature (Tg ≥ 125°C) for structural integrity, then expansion temperature is high (TStart ≥ 135°C), but low expansion temperature applications require TStart < 135°C
Solution Approach 1:
The patent systematically varies the glass transition temperature of the polymer shell by selecting different cellulose derivatives (acetate propionate, acetate butyrate) with distinct Tg ranges and adjusting the bio-based monomer content. This enables tuning of both structural integrity and expansion temperature to match specific application requirements.
Solution Approach 2:
The patent creates a dynamic relationship between shell stiffness and expansion temperature by using polymers whose viscoelastic properties change with temperature. The shell maintains structural integrity below Tg while becoming sufficiently compliant above Tg to allow expansion, with the transition temperature optimized for the intended application.
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 resulting microspheres exhibit desirable expansion characteristics, including low density and improved storage stability, while being sourced from renewable materials, addressing environmental concerns and maintaining performance.
Implementation Method 1
the blowing agent vapourises and expands, thus expanding the microsphere
Implementation Method 2
the thermoplastic polymeric shell softens, and the blowing agent vapourises
Data Source
AI summary
The present disclosure relates to thermally expandable microspheres comprising a polymeric shell surrounding a hollow core, wherein the hollow core comprises a blowing agent, and the polymeric shell comprises a carboxylate-functionalised cellulose, wherein the thermally expandable microspheres have a temperature at which expansion starts, TStart, of from 80° C. to less than 135° C. The present disclosure further relates to a process for preparing expandable microspheres as well as to thermally expandable microspheres obtained by such process, the process comprising mixing a carboxylate-functionalised cellulose, an organic solvent, a blowing agent and, optionally, a polymer shell enhancer and then spraying the thus obtained mixture into a drying equipment to produce the thermally expandable microspheres having a polymeric shell surrounding a hollow core, in which the polymeric shell comprises the carboxylate-functionalised cellulose, and the hollow core comprises the blowing agent.