Session: 04-26-01: Nanoengineered, Nano Modified, Hierarchical, Multi-Scale Materials and Structures

Paper Number: 172898

Spray Coating as an Innovative Method for Enhanced Dispersion and Mechanical Strength of Lignin-Containing Cellulose Nanocrystal-Poly(lactic Acid) Composites 

Biobased materials are increasingly used in a wide range of applications due to concerns over environmental sustainability. Biopolymers and biobased composites are considered suitable alternatives to petroleum-based products and synthetic plastics due to their advantages, including biodegradability and biocompatibility. According to bio-composite market forecasts, the market is expected to grow by over $ 122 billion by 2031 at a compound annual growth rate (CAGR) of 18.26%. Polylactic acid (PLA) is one of the most widely used bio-based polymers in various applications, such as packaging, medicine, electronics, and electrical products, due to its excellent properties and eco-friendliness. However, some disadvantages, such as low tensile elongation and high brittleness of PLA, limit its large-scale application. Reinforcing PLA with nanomaterials, such as lignin-containing cellulose nanocrystals (L-CNCs), offers a promising solution to enhance its mechanical performance. However, challenges such as poor dispersion and weak interfacial adhesion, due to the hydrophilic nature of CNCs, often compromise the reinforcing efficiency. This study introduces spray coating as a novel and scalable approach for preparing highly concentrated PLA/L-CNCs masterbatch films, which enhances filler dispersion and matrix compatibility in PLA-based composites.

The primary objective of this work is to assess the viability of spray coating in enhancing the uniform distribution of L-CNCs in the PLA matrix and to compare its effectiveness with that of the conventional solvent casting method. The hypothesis was that rapid solvent evaporation and high surface area during spray coating limit nanoparticle self-assembly, resulting in better dispersion and interfacial interaction with the matrix. Highly concentrated masterbatch films of PLA with 33.3 wt.% L-CNCs were prepared using both spray coating and solvent casting. These films were then compounded with PLA pellets at different L-CNCs loadings (1, 3, and 5 wt.%) through melt extrusion, followed by injection molding to produce nanocomposite samples.

To evaluate material performance, a comprehensive set of characterization techniques were employed. Scanning electron microscopy (SEM) was used to assess filler dispersion and tensile-fractured surface morphology. Fourier-transform infrared spectroscopy (FTIR) confirmed the interactions and the successful incorporation of L-CNCs. Differential scanning calorimetry (DSC) was used to analyze crystallinity and thermal transitions, while dynamic mechanical analysis (DMA) and tensile testing evaluated mechanical and viscoelastic properties. Statistical analysis, including ANOVA and Fisher’s LSD tests, was used to validate the significance of results.

The findings reveal a clear advantage of the spray coating technique for masterbatch preparation. SEM analysis showed a more homogeneous L-CNC dispersion and reduced agglomeration in spray-coated samples, especially at 1% and 3% filler content. FTIR spectra confirmed the formation of new C–O bonds, which were more pronounced for spray-coated nanocomposites, suggesting improved interfacial bonding. DSC results demonstrated a significant increase in crystallinity (up to 62%) and a lower cold crystallization temperature, indicating the nucleating effect of well-dispersed L-CNCs. DMA results showed that the storage modulus of the 3 wt.% L-CNC spray-coated composite increased by 26% and 100% in the glassy and rubbery regions, respectively, compared to neat PLA. Additionally, the tan δ peak values were lower for spray-coated composites, indicating enhanced matrix-filler adhesion. In tensile tests, the Young’s modulus and ultimate tensile strength of spray-coated composites improved significantly, with the 3 wt.% sample showing a 54% increase in modulus compared to neat PLA.

The results validate the hypothesis that spray coating enhances filler dispersion and interfacial interactions, which results in improved thermal and mechanical performance of PLA composites. The scalability, material efficiency, and simplicity of spray coating make it a compelling alternative to solvent casting for industrial masterbatch production. Overall, this study provides a foundational framework for using spray coating in the fabrication of bio-nanocomposites, paving the way for more durable and sustainable materials in packaging, automotive, and consumer product applications.

Presenting Author: Dilpreet Bajwa Montana State University

Presenting Author Biography: Dr. Dilpreet Bajwa is a professor and the head of the Department of Mechanical and Industrial Engineering at Montana State University, USA. He is also Fellow of International Academy of Wood Science and Editor-in-Chief of Industrial Crops and Products Journal (Elsevier). Before joining the academia, he worked in the engineered composites industry (International Paper, Masonite Corp., Epoch Composites, Greenland Composites) for 12 years in R&D leadership roles. He served academia as an adjunct professor in the Department of Agriculture and Biological Engineering at the University of Arkansas, and as a professor at North Dakota State University. Bajwa graduated from the University of Illinois at Urbana-Champaign in 2000 with a doctorate in Wood Science and Engineering. Dr. Bajwa’s research focuses on developing novel, sustainable, and multifunctional materials from renewable feedstocks. Currently, his research includes the application of nanocellulosic materials for strengthening biobased polymers, engineered wood, synthesizing bio-based thermochemical energy storage materials, safe fire-retardant system for polymer composites, and processing and characterization of biopolymers. He has authored over 185 peer reviewed journal articles and technical papers.

Authors:

Dilpreet Bajwa Montana State University
Amirmohammad Raeisi Montana State University
Cecily Ryan Montana State Univeristy