Abstract
BackgroundPolylactic acid (PLA) is considered to be a sustainable alternative to petroleum-based polymers for many applications. Using cellulose fiber to reinforce PLA is of great interest recently due to its complete biodegradability and potential improvement of the mechanical performance. However, the dispersion of hydrophilic cellulose fibers in the hydrophobic polymer matrix is usually poor without using hazardous surfactants. The goal of this study was to develop homogenously dispersed cellulose nanowhisker (CNW) reinforced PLA composites using whole milk casein protein, which is an environmentally compatible dispersant.ResultsIn this study, whole milk casein was chosen as a dispersant in the PLA-CNW system because of its potential to interact with the PLA matrix and cellulose. The affinity of casein to PLA was studied by surface plasmon resonance (SPR) imaging. CNWs were functionalized with casein and used as reinforcements to make PLA composites. Fluorescent staining of CNWs in the PLA matrix was implemented as a novel and simple way to analyze the dispersion of the reinforcements. The dispersion of CNWs in PLA was improved when casein was present. The mechanical properties of the composites were studied experimentally. Compared to pure PLA, the PLA composites had higher Young’s modulus. Casein (CS) functionalized CNW reinforced PLA (PLA-CS-CNW) at 2 wt% filler content maintained higher strain at break compared to normal CNW reinforced PLA (PLA-CNW). The Young’s modulus of PLA-CS-CNW composites was also higher than that of PLA-CNW composites at higher filler content. However, all composites exhibited lower strain at break and tensile strength at high filler content.ConclusionsThe presence of whole milk casein improved the dispersion of CNWs in the PLA matrix. The improved dispersion of CNWs provided higher modulus of the PLA composites at higher reinforcement loading and maintained the strain and stress at break of the composites at relatively low reinforcement loading. The affinity of the dispersant to PLA is important for the ultimate strength and stiffness of the composites.
Highlights
The development of biodegradable polymer composites, especially composites combining biodegradable matrices and structural biodegradable reinforcements, is of great importance currently
In this study, amphiphilic whole milk casein was explored as a dispersant in Polylactic acid (PLA)-cellulose nanowhisker (CNW) composites
The dispersion of CNWs in PLA was studied by Calcofluor staining
Summary
The development of biodegradable polymer composites, especially composites combining biodegradable matrices and structural biodegradable reinforcements, is of great importance currently. It is a commercially available polyester polymerized from lactic acid, which is produced from biorenewable sugar based sources, such as corn starch and sugarcane Nature fiber such as lignocellulose or purified cellulose derived from a variety of nature feedstocks (e.g. woods, cotton, and bacterial cellulose) has great potential to replace synthetic reinforcements such as glass fiber or fiber produced using petroleum derived polymers used in composite materials. To this end, various forms of cellulose including microcrystalline cellulose (MCC) or nanodimensional cellulose such as cellulose nanowhiskers (CNWs) and cellulose nanofibrils (CNFs) have been explored as reinforcements for different composite materials [2]. The goal of this study was to develop homogenously dispersed cellulose nanowhisker (CNW) reinforced PLA composites using whole milk casein protein, which is an environmentally compatible dispersant
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