Abstract
Advanced biocomposites reinforced by abundant biomass-derived fillers can add a revenue stream to enhance the economic viability of biofuel production chains and the energy efficiency of the composite industry. However, the low stiffness of biopolymers limits their use in structural applications. Poplar fibers (mesh size: <180 μm, Populus spp.), an abundant waste from the wood industry, were used as bio-filler to fabricate high-performance biocomposites based on polylactic acid (PLA), in which the poplar fibers were modified by an amino acid (L-lysine). As a benefit of the amino acid treatment, the tensile Young's moduli of the lysine/poplar/PLA composites increased by up to 68% with the addition of a small amount of lysine, compared with neat PLA. At the same time, the tensile strength, failure strain, and Young's modulus of the poplar/PLA composites all increased after adding only 0.1 wt % of lysine. It has been observed that the lysine content has a significant effect on the decomposition temperature, complex viscosity, storage modulus, crystallization temperature, and crystallinity of composites. The fracture surfaces of the composites with an optimum lysine content had fewer voids and were more compact compared with composites without any lysine. The pores on the surfaces of poplar fibers became more available for the penetration of PLA molecules as a result of lysine addition. Therefore, this study presents a facile method for reinforcing biocomposites with extremely low-cost and environmentally friendly biofillers.
| Original language | English |
|---|---|
| Article number | 108276 |
| Journal | Composites Part B: Engineering |
| Volume | 199 |
| DOIs | |
| State | Published - Oct 15 2020 |
Funding
This research is sponsored by the US Department of Energy (DOE) , FY 2019 BETO Project, under Contract 2.5.6.105 with UT-Battelle, LLC . This manuscript was authored by UT-Battelle LLC under contract DE-AC05-00OR22725 with DOE. The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ). The authors appreciate the valuable assistance from the members of Dr. Amit K. Naskar's Group (Carbon and Composites) of Chemical Sciences Division. Microscopy studies were completed at the Center for Nanophase Materials Sciences (CNMS), a DOE Office of Science User Facility. One possible explanation for the decrease in mechanical properties (e.g., tensile strength, Young's modulus, and failure strain) at high lysine contents is aggregation and phase separation of lysine from the PLA matrix in the composites. Two, an excessive amount of lysine with acidic carboxyl groups can cause degradation of composites to some extent. This reasoning is supported by the decreased complex viscosity of lysine/PLA composites due to the addition of lysine, shown in Fig. S2. Excessive amounts of lysine molecules also might act as a plasticizer, leading to property degradation. Shao et al. [27] reported that the addition of citric acid in amounts of less than 20% resulted in partial cross-linking of hemicellulose, thus slightly increasing the tensile strength of hemicellulose/sorbitol/citric acid/poly(vinyl alcohol) films. The tensile strength of the hemicellulose-based films increased further when a moderate content of citric acid was added (e.g., 20%). However, the addition of larger amounts of citric acid caused a decrease in the tensile strength of the hemicellulose-based films. The excessive citric acid was reported to act as a plasticizer and cause the molecular chains to be more prone to sliding [27].The cross-linking reaction between PLA, lysine and poplar fiber is supported by the below data analysis and discussion. The amide formation observed in FT-IR analysis (Fig. S11) indicates the reaction between lysine and PLA. Based on the PLA chain end structure, PLA is reactive under the melting condition, which has been confirmed by many previous studies [ 44?47]. For example, Wang et al. [44] found that PLA could react with a small amount of citric acid through a chain end reaction. From the chemistry structure, citric acid and lysine are both reactive to -OH and -COOH groups in PLA. Therefore, the reaction between lysine and PLA is possible and supported by our FT-IR results. From the SEM analysis, the phase separation occurred when directly mixing polar fibers and PLA because these two components are incompatible. With the appropriate addition of lysine, the interfacial adhesion between the PLA matrix and natural poplar fibers was enhanced. This phenomenon suggests the role of the lysine in the lysine/poplar/PLA composites (e.g., chemical bonding formation), which bridges the PLA matrix and natural poplar fibers. Furthermore, the cross-linking reaction in the lysine/poplar/PLA composites was reflected in the rheological behavior. When the lysine content increased, such as to 1.0 wt%, a plateau area of the storage moduli in the low frequency range appeared. This suggests an additional network structure built with the addition of lysine [44].This research is sponsored by the US Department of Energy (DOE), FY 2019 BETO Project, under Contract 2.5.6.105 with UT-Battelle, LLC. This manuscript was authored by UT-Battelle LLC under contract DE-AC05-00OR22725 with DOE. The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan). The authors appreciate the valuable assistance from the members of Dr. Amit K. Naskar's Group (Carbon and Composites) of Chemical Sciences Division. Microscopy studies were completed at the Center for Nanophase Materials Sciences (CNMS), a DOE Office of Science User Facility.
| Funders | Funder number |
|---|---|
| Center for Nanophase Materials Sciences | |
| DOE Office of Science | |
| DOE Public Access Plan | |
| US Department of Energy | |
| U.S. Department of Energy | DE-AC05-00OR22725, 2.5.6.105 |
Keywords
- Biocomposite
- Lysine
- Polylactic acid (PLA)
- Poplar
- Stiffness
