Study On Structure And Properties Of Poly(propylene Carbonate)/poly-3-hydroxybutyrate Composite And Its Barrier Mechanism

Poly(propylene carbonate)(PPC)is an aliphatic polycarbonate synthesized from carbon dioxide and propylene oxide.It has full biodegradability and good gas barrier properties.However,the poor thermodynamic properties and oxygen barrier is still lower than traditional barrier material like EVOH,which limits its application.Poly-3-hydroxybutyrate(PHB)is a type of thermoplastic polyester produced by biological fermentation.It has complete biodegradability and excellent barrier properties.The brittle mechanical properties and high modulus is similar to that of polypropylene,while the narrow processing window limits its application.The blending of PHB and PPC can effectively enhance the mechanical properties and barrier properties of PPC.It can provide new methods and theoretical guidance for the further application of PPC and PHB in packaging materials.Firstly,PPC/PHB blends were prepared by melt blending with Haake Rheomixer.Infrared spectrogram analysis was used to analyze the interaction between PPC and PHB.Differential scanning calorimetry(DSC)and polarizing microscope(POM)were used to analyze the crystallization properties of composites.The results show that there is a strong hydrogen bond between PPC and PHB,which can improve the tensile strength and oxygen barrier properties of the composites.Based on the intermolecular hydrogen bonding,the interaction between the resin matrix and the filler can be strengthened.In this paper,nanocrystalline cellulose(CNC)was selected as the reinforcing filler.Then,a PEG/CNC masterbatch was prepared by using water-soluble polyethylene glycol(PEG-10000)as the CNC carrier to solve the dispersion problem of CNC,and then the PEG/CNC masterbatch was melt-blended with PPC to prepare PPC/PEG/CNC composites.The dispersion effect of CNC in composites,the influence of CNC content on the mechanical properties and barrier properties of composites were studied.Results show that PEG can promote the dispersion of CNC.With the increase of CNC content,the tensile strength and oxygen barrier performance of composites are continuously improved.The oxygen barrier performance of PPC/PEG/0.7CNC composites is higher than that of pure PPC(nearly 20 times).For PPC-PEG-CNC-PHB composites,the results show that the tensile strength,impact strength,and oxygen barrier properties of the composites increased with the increase of the CNC content.When the CNC content is 1 wt%,the oxygen barrier performance increases nearly 18 times,owing to that CNC is impermeable to gas molecules,and also has a large ratio of diameter to thickness.When it is dispersed in a polymer matrix,it will hinder the diffusion of gas permeation molecules into the matrix and prolong the diffusion path of gas permeation molecules in the vertical direction.Based on the consideration of PPC/PHB blending system structure and industrial application,PPC/PHB composites were prepared by continuous extrusion.The phase morphology and rheological properties of the blends were mainly studied by scanning electron microscope(SEM)and dynamic rheological measurement,which showed that when the PHB content was 10wt% and 20wt%,the compatibility of PPC and PHB was good.As the PHB content increased to 30wt%,the compatibility of the two phases became poor.On this basis,Ax8900(ethylene-methyl acrylate-glycidyl methacrylate random terpolymer)was used as a compatibilizer for the reaction compatibilization of PPC/PHB blends.The effects of compatibilizer content on rheological behavior,phase morphology and mechanical properties of the system were studied.SEM results show that the compatibilizer plays a role in compatibilizing the PPC/PHB blend system.The tensile strength of PPC/PHB blends increases first and then decreases with the increase of the compatibilizer content.When the content of the compatibilizer is 2wt%,the tensile strength of the composite reaches a maximum of 20.7MPa.The elongation at break and fracture energy of composites gradually increase as the content of compatibilizer increases.Based on the effective enhancement of the mechanical properties and barrier properties of composites by the PHB,Ax8900 can further improve the compatibility of the two phases.The PPC/PHB/Ax8900 composite films were prepared by extrusion blow molding.Themorphology,optical properties,mechanical properties and barrier properties of the films were studied.It was observed by SEM that the prepared film had a certain orientation along the stretching direction.The mechanical test results show that the tensile strength of PPC/PHB/Ax8900 composite films increases with the increase of PHB content.The longitudinal tensile strength of the film is larger than that of the transverse direction The transverse right-angle tear strength is slightly higher than that of the longitudinal direction.This is due to the fact that the film undergoes a greater amount of drawing force in the longitudinal direction during the blow molding process.Both the water vapor permeability coefficient and the oxygen permeability coefficient of the film continuously decrease with increasing PHB content,indicating that the water blocking and oxygen barrier properties are improved.Compared with the PPC-2Ax8900 without PHB,the 70PPC-30PHB-2Ax8900 improves oxygen barrier performance by about 5 times.Based on the basic model of polymer gas barrier,the corresponding model values were compared with the actual values to explore the barrier mechanism and provide theoretical guidance for future high barrier performance PPC/PHB composites.For the PPC/PHB system,the Maxwell two-phase the “series” model is more suitable for predicting oxygen barrier property of the blends.For the PPC/PHB/Ax8900 blend film system,due to the different content of the dispersed phase,its morphology in the matrix will also be different.When the dispersed phase morphology is droplet-shaped,a theoretical prediction model proposed by Rodriguez can be used.When the dispersed phase morphology is flake-like,the theoretical prediction model proposed by Carmabi and Kaman can be used.For the PPC/PEG/CNC composite system,the distribution and morphological characteristic of CNC play a major role in the barrier performance.When the volume fraction of CNC is small,the theoretical prediction value of the Nielsen model and the Cussler(random array)model are in good agreement with the experimental value.When the CNC volume fraction is large,Cussler(random array)model is more applicable.