Surfactants used to reduce hydrophilicity of protein-based materials
A Memmert HPP110 constant climate chamber with Advanced Peltier Technology has been used in research into a new technique for turning proteins into plastic. A US study looked into the copolymerization of proteins and monomers and came up with a new approach for reducing the hydrophilicity of protein-based materials by using surfactants as plasticizers and compatibilizers.
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The ACS American Chemical Society research was published in 2019.
Proteins are abundant in biomass sources such as agricultural and forestry feedstocks, plant and animal-based agricultural by-products and municipal wastes. Their ability to form continuous matrixes and the high amount of reactive functional groups amenable to chemical modification make them suitable for a wide variety of potential uses in plastic applications. However, without modification or plasticizers, proteins are known to be too brittle to handle and form. Plasticization, a commonly employed strategy that increases the processability of protein-based materials and enables them to be thermoformed, is used to reduce glass transitions or softening temperatures of proteins by disrupting polymer-polymer interactions and increasing the free volume of protein chains.
This work explores an approach to reduce the hydrophilicity of protein-based materials by covalently attaching proteins to hydrophobic polymer chains using whey protein isolate (WPI) as the model protein. The material synthesis requires mixing between the incompatible protein and water-insoluble vinyl monomers, achieved using an ionic surfactant as a compatibilizer. The surfactant of choice, benzalkonium chloride (BAC), has a low melting point and is able to plasticize the protein. The dual role of surfactant as both compatibilizer and plasticizer critically enables solvent-free melt polymerization of the protein-based copolymers and the preparation of mouldable thermosets. This synthetic strategy enables partially renewable materials containing protein reinforcing domains to be prepared using industrially relevant processes and can potentially be expanded in the future to incorporate vinyl monomers or rubbery polymer segments derived from biomass to produce fully biobased plastics.
The research paper discusses the use of various chemical compounds in the manufacturing process. n-Butyl acrylate, poly(ethylene glycol) methyl ether acrylate, azobis (isobutyronitrile), butanediol diacrylate, methacrylic anhydride, tert-Butyl peroxyacetate, and benzalkonium chloride were all sourced from reputable suppliers.
The process involved a number of different steps. We were delighted to read in the study that one of our top-quality constant climate chambers played a vital role in the process. The Memmert HPP110 was utilised in the copolymerization of proteins and monomers.
A Memmert constant climate chamber HPP110 with Advanced Peltier Technology was implemented for equilibrating samples at various relative humidity conditions for at least 72 h prior to mechanical characterization. Hydrophobic and hydrophilic copolymers were prepared by adding n-butyl acrylate or poly(ethylene glycol) methyl ether acrylate to protein-surfactant complexes, polymerizing the mixture under pressure and cooling it to room temperature. A cross-linked poly(butyl acrylate) control was also prepared.
The paper describes a technique for making protein copolymers using surfactants as plasticizers and compatibilizers. The surfactants enable mixing proteins with monomers of different polarities and expand the range of material properties for protein-based copolymers. These copolymers can be thermoformed and melt polymerized, which is useful for industrial processes like injection and blow moulding. Materials were prepared by first combining whey protein with a cationic surfactant and then mixing it with the hydrophobic monomer n-butyl acrylate. Copolymers have lower stiffness but higher elongation at break, ultimate tensile strength and a higher level of robustness than uncross-linked blends.
The presence of both the stiff protein and the flexible polyacrylate domains are crucial for mechanical properties. Copolymers may be microphase separated, but they do not have ordered microstructures. Copolymers made with hydrophilic monomers have similar moisture absorption when desiccated but absorb more water at higher humidities. Protein-surfactant complexes represent an important technology for solvent-free processing of protein biomass into hydrophobic polymers, but challenges remain with managing humidity effects on the protein domains.
Memmert's constant climate chamber HPPeco with Advanced Peltier Technology is designed to provide a stable and controlled environment for a wide range of applications including material testing, research and quality control. The chamber features precise temperature and humidity controls, large interior volume and easy-to-use digital controls. It also includes a built-in light and data logger to ensure accurate and consistent results. Memmert's Peltier constant climate chamber also offers a variety of options including automatic door opening and multiple shelves for placing samples on. The chamber is made of high-quality materials to ensure long-lasting performance and durability. It is available in different sizes and temperature ranges.
