Technology and mechanism of enhanced compatibilization of polylactic acid-grafted glycidyl methacrylate

Highlights

• Strengthening of polylactic acid obtained from bagasse cellulose is explored

• Polylactic acid is combined with glycidyl methacrylate to obtain a composite and modified via reinforcements

• Chemical grafting and physical blending modifications are performed

• Glycidyl methacrylate content has the highest influence on grafting rate.

• The materials may be used in the household aspects of 3D printing materials, such as vases, and packaging materials such as wood-plastic boxes.

Abstract

A PLA-based bagasse cellulose composite material with excellent performance and low cost was prepared. As one of the most commonly used thermoplastic materials in fused deposition modeling (FDM), PLA is currently the most widely used three-dimensional (3D) printing technology. It has the natural advantage of being biodegradable. However, due to its poor toughness, it cannot meet the requirements for 3D printing consumables in some areas. Therefore, polylactic acid (PLA) is used as the matrix, tert-butyl peroxybenzoate (TBPB) are used as the free radical initiator, and glycidyl methacrylate (GMA) is used as the reaction monomer to prepare the PLA-GMA graft product, which realizes the toughening of PLA, and the PLA/PLA-GMA/BC (bagasse cellulose) composite material is prepared by the physical blending method, which realizes the reinforcement of PLA; it was proved by fourier transform infrared spectroscopy (FTIR) and ¹H NMR that GMA was successfully grafted onto the PLA molecular chain, and the influence of the grafting rate on the toughness of PLA-GMA was explored. It was concluded that the grafting rate of PLA-GMA with the best toughness was 10.33%. The strength is 15.94 MPa, the modulus of elasticity is 969.01 MPa, and the elongation at break is 278.17%, which is about 44 times the elongation at break of pure PLA. The PLA/PLA-GMA/BC composite material with high cellulose loading was prepared by physical blending. The effect of PLA-GMA content, BC particle size and BC content on the properties of composite materials was explored. The results showed that PLA-GMA when the addition amount is 25%, the capacity enhancement effect is the best; when the additional amount of BC is as high as 40%, the PLA/PLA-GMA/BC composite still has good mechanical properties, and the addition of BC can promote the crystallization of PLA; DSC results show that BC can promote the crystallization of PLA, and the addition of PLA-GMA is not conducive to the composite material the formation of PLA crystalline regions; the temperature at the maximum decomposition rate of 40% BCB/25% PLA-GMA/PLA composite material is 355.44 ℃, and the thermal stability is improved. This study proves that the functional group properties of GMA realize the toughening and enhanced dual modification of polylactic acid, which expands the choice and application range of FDM 3D printing materials.

Introduction

Fused deposition modeling (FDM) is the original developed 3D printing technology with minimal equipment requirements (Jia et al., 2017). FDM material prints exhibit high strength, with facile industrial production. Currently, polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), polycarbonate (PC), and other polymers and composite materials are available for FDM 3D printing. Among them, PLA exhibits adequate biodegradability (Gonzalez-Bautista et al., 2020; Guo et al., 2016; Stoikov et al., 2019), low shrinkage, and suitable warping resistance (Fernandez-Cervantes et al., 2019; Haneef et al., 2019; Morao and de Bie., 2019).

China is largely an agricultural country that produces 1.4 billion tons of agricultural and forestry waste annually, with a utilization rate of less than 10% (Wang et al., 2012), wherein the yield and concentration of bagasse are high. However, the traditional high-value utilization of bagasse (Khonngam and Salakkam., 2019; Seabra and Macedo., 2011; Zhao et al., 2012; Zhao et al., 2011) reveals low benefits and high energy consumption, which is not ideal. Therefore, the high-value utilization of cellulose is a major problem (Hong et al., 2020) that may be addressed using FDM 3D printing technology, as the printing is not limited to thermoplastic materials. Cellulose FDM 3D printing materials may increase the types of 3D printing materials and ensure viable utilization of cellulose. Blending and extruding cellulose and PLA to prepare FDM 3D printing composite materials, specifically wood-plastic composites, should be explored for the use of cellulose materials in 3D printing (Wang et al., 2018). Liu Hao et al. (2019) prepared sugarcane bagasse (SCB)/PLA composite materials and studied their mechanical properties, crystallization characteristics, and thermal stabilities. The highest tensile strength of the 3D printed sample of approximately 53 MPa was observed at an SCB content of 6 wt.%. However, the elastic modulus continued to decrease from 49 MPa to 34 MPa with the increasing SCB content, suggesting that SCB promotes the crystallization of PLA (Liu et al., 2019). Yang et al. (2016) thermoformed wood flour and PLA into a composite material, with the wood flour improving the crystallinity of PLA despite negatively affecting its rheology negatively (Yang et al., 2016). Chun et al. (2013) added coconut shell powder (CSP) to PLA, which reduced the tensile strength of PLA/CSP composites from 54 (PLA) to 24 MPa (PLA/CSP composites). Conversely, the tensile strength of the same material decreased from 54 MPa to 28 MPa after the maleic acid treatment, which was an improvement in comparison with the untreated tensile strength. Moreover, the thermal stabilities of the composites increased with increasing CSP content (Chun et al., 2013). Zander et al. (2019) used cellulose waste to enhance the work of recycled polypropylene, producing green composite raw materials for extrusion-based polymer additive manufacturing. After cellulose waste addition, the storage modulus increased by 20–30%. However, after adding 10 wt.% cellulose, the tensile strength did not increase significantly, but the elastic modulus increased by 38% relative to that of the original polypropylene (Zander et al., 2019). Thus, composite materials exhibit the high strength and elasticity of natural plant fibers, along with the high elasticity and fatigue resistance of plastics (Liu et al., 2015). However, although the mechanical strength of PLA and wood-plastic composites has improved, it remains low, and the cellulose loading can only reach 10%. Despite wood-plastic composites have the high mechanical strength and easy processing, the natural fibers and polymer matrix easily agglomerate during the process, resulting in low dispersibility of cellulose within the polymer matrix and degrading the mechanical properties of the composite. Therefore, increasing the interface compatibilities of wood-plastic composites is necessary.

Owing to poor toughness (Qiang et al., 2012), poor heat resistance, slow degradation (Rogovina et al., 2018), and lack of reactive side chains within PLA, its practical applications are limited. Therefore, toughening and modifying PLA is necessary to expand its application in the fields of biomedicine (Li et al., 2020), packaging materials (Spiridon et al., 2015), and 3D printing (Teixeira et al., 2019). Although wood-plastic composites can combine the advantages of polymer materials and cellulose to reduce the amount of PLA used and minimize costs, compatibility is a major problem. This is because the direct mixing of the hydrophobic ester and hydroxyl groups of PLA and the fiber, respectively, causes severe phase separation. To reduce the interaction between the two interfaces and increase the compatibility, we explored the toughening and strengthening of PLA in terms of two aspects, chemical grafting and physical blending modifications. Additionally, a PLA-based structural FDM 3D printing material was prepared to analyze the relationship between the structure and performance of the synthesized product. The bifunctional properties of GMA were fully utilized for the first time to toughen and enhance PLA, expanding the selection and application range of FDM 3D printing materials. PLA is toughened and reinforced using a simple melt polymerization, which is appropriate for industrial production, while reducing the use of chemical solvents, and is therefore green. The reinforced PLA-based bagasse cellulose composite exhibits a high cellulose load, which reduces the amount of PLA used, realizes the high-value utilization of bagasse resources, and saves production costs. This study may provide certain experimental and theoretical guidance in the field of 3D printing materials and PLA-based packaging materials.