Hubei University of Technology: Progress of talc powder strengthening and toughening polylactic acid biodegradable materials
Abstract: Because of its excellent mechanical properties and good biodegradability, the bio-based polylactic acid (PLA) material is one of the most promising biodegradable materials at present. However, its brittleness is large, which limits the application range of polylactic acid materials. Therefore, the progress of physical modification of polylactic acid (PLA) by Talc was introduced, and the enhancement and nucleation effect of TALC on polylactic acid (PLA) by refining the particle size of TALC and surface functionalization were summarized.
The research progress of Talc and its toughening modification of PLA material with plasticizer, elastomer, biodegradable material, plant fiber and other materials was described in detail. The enhancement and nucleation effect of Talc and toughening effect of ductile polymer are used to give full play to the synergistic effect between multiple components, which is the main way and research direction to prepare high-performance polylactic acid materials in the future.
Polylactic acid (PLA), commonly known as polylactide, is a biodegradable polyester that is polymerized from starch fermented lactic acid as a monomer, and its environmental load is much lower than petroleum-based materials. At the same time, it has good mechanical properties, biodegradability, biocompatibility and processing properties, and is widely used in clothing, biology, tissue engineering, packaging materials and other fields. However, PLA is brittle and has low impact performance, which limits its scope of use. Therefore, PLA needs to be modified to achieve the purpose of toughening and strengthening, which has become the focus and hot spot of polylactic acid material research.
Comprehensive PLA modification research reports, plasticizer as a common method to improve the toughness of PLA, the use of plasticizer can penetrate into the molecular chain of the matrix, so that the force between the PLA molecular chain is reduced, improve the plasticity of the material. Among them, the plasticizer with good plasticizing effect includes polyethylene glycol (PEG) tributyl citrate (TBC), epoxy soybean oil (ESO), acetyl butyl citrate (ATBC) and so on.
However, the compatibility of plasticizer with PLA is poor, which is due to the easy migration of small molecular chains; Its blend with flexible polymers such as natural rubber (NR), epoxidized natural rubber (ENR), nitrile butadiene rubber (NBR), polyurethane elastomer (TPU), polyester elastomer (TPEE), etc., can improve the toughness of PLA, thus significantly improving the toughness of the material, but at the same time destroying the biodegradability of PLA; In order to strengthen and toughen without changing the biodegradability of PLA, the use of polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polycaprolactone (PCL) and other biodegradable materials for modification, can greatly improve the toughness of the material; Inorganic rigid particles such as montmorillonite (MMT), silicon dioxide (SiO2), Talc (Talc) and calcium carbonate (CaCO3) can improve the crystallinity of PLA material, play a role in making up for the defects of polylactic acid modified by toughening agents, and improve the toughness and strength of the material at the same time.
Aiming at TALC toughening modified polylactic acid system, the influencing factors of physical modification of PLA material by TALC were introduced. The properties of PLA/Talc composite were modified by compounding the third component. The modification of PLA/Talc composite by blending of plasticizer and elastomer with the third component is introduced, and the strength of the composite is enhanced by improving the regularity of PLA molecular arrangement. Using the flexibility and toughness of its own molecular chain to improve the brittleness of PLA material, emphasizing the compatibilizing effect of compatibilizers, improving the compatibility of the third component and PLA matrix, enhancing the interface viscosity of multi-component system, and improving the toughness of PLA/Talc material.
Polylactic acid intermolecular force is strong, the movement ability of the chain is weak, adding small molecule additives such as plasticizer can improve the movement volume and movement ability of polylactic acid chain, and the plasticity of polylactic acid is increased. Is conducive to the dispersion of talc powder. The synergistic effect between inorganic particles and plasticizer is beneficial to the regular arrangement of polylactic acid, improve the crystallization behavior of polylactic acid, and make the composite material have high strength and high toughness at the same time.
2, PLA/talc powder/elastomer blend system
Elastomer is a kind of elastic material at room temperature, divided into degradable elastomer and non-degradable elastomer, both of which have high toughness, and with inorganic particles blending can reduce the surface activation energy of inorganic particles, to achieve good dispersion. When it is subjected to greater external force, it becomes a stress concentration, hollowing occurs inside the elastomer, causing silver lines, talc in the matrix to hinder the development of silver lines into destructive cracks, while absorbing energy, improving the mechanical properties of the material.
3, PLA/talc powder/degradable material
Degradable material is environmentally friendly, does not affect the degradation performance of PLA, its flexible molecular chain and PLA chain blend, can increase the PLA chain of the remote space, enhance the flexibility of polymer molecular chain, so that the composite material shows good toughness. Talc powder and degradable materials can promote the dispersion of each other, so that the compatibility of the matrix and the filler is enhanced, when the external force is impacted, the talc deadhesions occur, and the purpose of toughening is reached.
4, PLA/talc/plant fiber composite system
fiber and PLA blend can increase the stiffness of polylactic acid, its good toughness can also significantly improve the defect of polylactic acid brittleness. The coexistence of plant fiber and talc can reduce the aggregation of talc powder and further improve the mechanical properties of the composite. Compared with synthetic biodegradable materials, plant fiber has the advantages of easy access to raw materials, rich types, economic and environmental protection, and reduces the cost of materials while solving the problem of poor toughness of talc/polylactic acid system, and has a positive effect on the wide application of composite materials.
Talc powder is easy to disperse in polylactic acid matrix, a small amount of talc powder in PLA crystallization can be adsorbed on the surface, play a nucleation role, accelerate the crystallization rate of polylactic acid, improve the
regularity of the chain segment arrangement of polylactic acid, It has important research value and application potential in PLA modification.
The use of talc powder alone has limited effect on toughening PLA. The surface treatment of talc powder and its compounding with plasticizers, elastomers and other materials can significantly improve the toughness of PLA material and maintain high strength and modulus.
Talc particle size refinement and surface functionalization treatment are important methods to further improve the function of TALC. At the same time, studying the synergistic system of Talc with other components such as plasticizer flexible polymer, giving full play to the strengthening effect of inorganic particles and nucleation effect, and improving the synergistic effect by using the toughening effect of ductile polymer of plasticizer system is an important way to prepare high-performance PLA, which still needs further research.
Source: Hubei University of Technology, Key Laboratory of Green Light Industrial Materials in Hubei Province, New materials and Green Manufacturing Innovation Demonstration Base in Hubei Province, Hubei Longzhong Laboratory
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