Polybutylene terephthalate (PBAT) is a new type of fully biodegradable aliphatic-aromatic copolyester with chain segments that combine the flexibility of long-chain aliphatic hydrocarbons with the rigidity of aromatic rings, giving it excellent flexibility. As a result, PBAT has become one of the most active degradable materials in biodegradable plastics research and good market applications. However, the presence of aromatic PBT chain segments in the molecular chain results in a relatively slow degradation rate. It also has a low crystallinity and high viscosity, which makes it highly susceptible to adhesion. In addition, the material is relatively expensive, further limiting its market development and application. Therefore, in order to reduce the cost and obtain high performance degradable plastics, the modification of PBAT needs to be studied. Blending PBAT with biodegradable polymers is a proven method of modification, which can improve other properties without affecting the degradability of PBAT, and some biodegradable polymers can also enhance the degradation rate of PBAT.
-PBAT blended with PLA-
Polylactic acid (PLA), one of the most researched and commercially successful biodegradable materials, has excellent gloss and barrier properties, but also has the disadvantages of being hard and less tough, lacking flexibility and elasticity. Therefore, the blending of high toughness PBAT with PLA can not only improve the toughness of PLA, but also accelerate the decomposition rate of PBAT.
It has been found that the addition of PLA significantly improves the tensile strength of the blend without affecting the crystalline properties of PBAT; and that the increased melt viscosity improves the stability of PBAT films during processing and forming.
Since PBAT and PLA are incompatible systems, more research is currently based on improving the compatibility between the two, resulting in blends with better mechanical properties. For example, the incorporation of glycidyl methacrylate (GMA) at a mass fraction of 3% to 5% can increase the impact strength of PLA/PBAT blends to 26.5% and 51.7%, while improving the dispersion of PBAT in PLA. In addition, the addition of chain extender can significantly reduce the interfacial tension between the two, which greatly improves the ductility of PBAT/PLA films; the addition of multifunctional group plasticizer and capacitor can produce a good capacitance and plasticizing effect on PBAT/PLA blends, while improving the processing properties.
-PBAT blended with PPC-
Polypropylene carbonate (PPC) is anenvironmentally friendly plasticmade by alternating copolymerization of industrial waste carbon dioxide and propylene oxide, which has degradability and excellent resistance to permeability. However, it is an amorphous material, the glass transition temperature is only 30-40°C, and there is low-temperature toughness, high-temperature dimensional stability is poor, film formation difficulties and other disadvantages. The blending of PPC with PBAT not only improves the process ability of PPC, but also provides PBAT with more excellent overall performance, and the resulting composite material will have great development space in disposable food packaging, medical materials, etc.
As the PPC fraction is amorphous in the blended system, the microcrystalline size of the PBAT/PPC composite film is reduced; the incorporation of PPC greatly improves the tensile strength and gas barrier properties of the composite film while ensuring the biodegradability of the matrix. In addition, the presence of PPC and PBAT effectively improves the thermal stability, crystallinity and mechanical properties of the blends; when only 10% PPC by mass is present, the crystallization temperature of the blends increases from 37.5°C to 66.8°C, which facilitates the blown film forming process.
Since PBAT is a crystalline polymer and has a large polar molecular chain, it also has compatibility problems with PPC. The introduction of the chain extender triphenylmethane triisocyanate resulted in a significant increase in the tensile and tears strength of the PBAT/PPC film in both the longitudinal and transverse directions; the introduction of the opening agent monoglyceride stearate also improved the stability of the film during blowing. In addition, the addition of the bulking agent ethylene methyl acrylate – glycidyl methacrylate (EMA-GMA) to the blend of PPC and PBAT not only improves the processing stability and quality of the blown film, but also effectively improves its mechanical properties, oxygen barrier and UV shielding properties.
-PBAT co-mingled with PBS-
Polybutylene succinate (PBS) has the best processing performance among existing biodegradable plastics, with excellent mechanical properties; however, its low viscosity leads to poor melt strength, which is not conducive to processing by blow moulding or cast, and the products have certain brittleness. Therefore, by using PBAT and PBS modified blends, the advantages of both can be combined to make up for the defects, and the products made can be used in packaging, tableware, agricultural films, biomedical materials and other fields.
In general, the content of PBS in PBAT/PBS blends should not be too high, to about 25% is appropriate. It has been found that PBAT/PBS blends exhibit high tensile modulus and high elongation at break when the mass fraction of PBS is 25%; once the PBS content is too high, the products exhibit strong brittleness.
-PBAT co-mingled with PHBV-
Poly(pentyl hydroxybutyrate) (PHBV) is a biomaterial made from natural renewable materials, synthesized by fermentation with carbon source and energy stored in microorganisms, which has good biodegradability and biocompatibility; however, it also has disadvantages such as poor thermal stability and poor crystallization properties. Therefore, blending it with PBAT can improve the crystalline properties of PHBV and enhance the processing and application properties of the material.
The blend of PHBV and PBAT exhibits better processability and film properties; and the mechanical properties of the film are in line with those of commercial food packaging films, with strains up to 750% at break.
-PBAT blended with PGA-
Polyglycolic acid (PGA) has a similar molecular structure and performance characteristics to PLA, but it has more excellent degradation and barrier properties; not only is the raw material cost low, but it also has the advantages of high tensile strength and high heat deflection temperature. Therefore, the choice of PGA for PBAT blending modification has great potential for application in the field of disposable products such as heat-resistant tableware, biodegradable film bags and barrier packaging.
It has been found that PBAT/PGA composites with a PGA mass fraction of 20% have a tensile strength of 25 MPa and an elongation at break of over 600%, which can be used to make film products; PBAT/PGA composites with a PGA mass fraction of 80% have a heat deflection temperature of 120°C while improving toughness, which can be used to make disposable tableware; meanwhile, the addition of PGA The addition of PGA can significantly improve the water vapour barrier performance of PBAT/PGA composite films.
Similar to PLA, the compatibility between PGA and PBAT is poor, so suitable compatibilisers need to be selected to improve the dispersion of the system. For example, 4,4′-ylidenebis(isocyanatophenyl) (MDI) can be used to in situ capacitate PBAT/PGA composites. The successful reaction with MDI resulted in a significant increase in the interfacial adhesion of the blends and a significant increase in impact strength from 9.0 kJ/m2 to 22.2 kJ/m2; and a reduction in crystallinity and spherical crystal size, which contributed to the enhanced toughness of the composites and their thermal stability.
-PBAT blended with PVB-
Polyvinyl butyral (PVB) is the product of the acid-catalyzed condensation of polyvinyl alcohol and n-butyraldehyde, with a certain amount of plasticizer in its recycled trimmings. Due to its molecular structure, PVB is endowed with a combination of high tensile strength, impact resistance, high transparency, flexibility and degradability. As an edge recycled material PVB is available in large quantities and at low prices, so its selection as a modified material has great development advantages. The low concentration of PVB increases the crystallization temperature of PBAT; the compatibility and mechanical properties of PBAT/PVB are improved by the joint action of the capacitor ionomer and PVB.