Study On The Toughening And 3D Printing Properties Of Polylactic Acid Modified By Biodegradable Poly (4-Hydroxybutyrate)

Poly（4-hydroxybutyrate）（P4HB）is a new generation of biodegradable semi crystalline polymers.Currently,it is mainly produced in small quantities through microbial fermentation.However,the high production cost and difficult quality control of biological fermentation method limit its application in traditional bulk materials.Our team achieved mass production of P4HB using chemical synthesis method,and the obtained P4HB has similar performance to biological fermentation method,lower cost,more stable quality,and has a wider application prospect.Polylactic acid（PLA）has become a research hotspot in recent years due to its biodegradability and high strength.This article first studies the crystallization performance and 3D printing performance of pure P4HB.The low crystallization temperature and slow crystallization rate of P4HB can lead to problems such as insufficient cooling and product collapse during 3D printing,greatly limiting its application.P4HB was modified by adding zinc salt of D-phenylalanine（Zn（D-Phe）₂）and cyanuric acid（CA）as nucleating agents,respectively.Systematically study the effects of two nucleating agents on the crystallization behavior of P4HB.Obtain bone tissue engineering scaffolds using 3D printing,and study the mechanical properties,biocompatibility,and biological activity of the scaffolds.In addition,P4HB not only has high strength but also good toughness,making it a high-strength and flexible molecular chain degradable polyester with the potential to modify PLA.In previous studies,it was found that poor two-phase compatibility resulted in P4HB not effectively improving the performance of PLA.In this study,the compatibility of PLA/P4HB blends was further improved through crosslinking modification and the addition of compatibilizers,enabling P4HB to more effectively improve the performance of PLA and further expand the application fields of P4HB and PLA.The main research content is as follows:（1）By using zinc salt of D-phenylalanine（Zn（D-Phe）₂）and cyanuric acid（CA）as nucleating agents to modify P4HB,the problems of low crystallization temperature and slow crystallization rate of P4HB,resulting in insufficient cooling of the product and collapse of the product during the molding process,have been solved.The modified and rapidly crystallized P4HB was used to prepare bone tissue engineering scaffolds through3D printing for mechanical and biological performance analysis.The results are as follows:Adding 0.6%CA and 2%Zn（D-Phe）₂ can effectively improve the crystallization temperature and rate of P4HB,successfully solving the problems of low crystallization temperature and slow crystallization rate of P4HB.The tensile strength of P4HB/Zn（D-Phe）₂ and P4HB/CA samples prepared by 3D printing were 27.2 MPa and 33.4 MPa,respectively,and the elongation at break was 370%and 449%,respectively,fully meeting the requirements of bone tissue engineering for the mechanical properties of the scaffold.The biological performance test results show that the stent has no biological toxicity,good biological activity and biocompatibility,and is an ideal scaffold material.（2）By adding BIBP and TAIC to compatibilize and modify PLA/P4HB blends,the goal of promoting two-phase compatibility and effectively improving the performance of PLA is achieved.The effects of the content of crosslinking agent and co crosslinking agent on the compatibility of PLA/P4HB system were studied by adjusting the content of BIBP and TAIC.The results are as follows:the higher the BIBP/TAIC content is,the higher the degree of crosslinking of the blend system is.When the BIBP/TAIC content is 0.5%,the gel content of the blend system is as high as 56.1%;The addition of crosslinking agent can promote the crystallization of PLA phase,and with the increase of crosslinking agent content,the crystallinity of PLA phase presents a trend of first increasing and then decreasing;The tensile breaking strength,yield strength,and elongation at break of the blends all showed a trend of increasing first and then decreasing.The results of SEM and DMA tests showed that the cross-linked structure promoted the compatibility of PLA and P4HB,but when the degree of cross-linking was too large,the cross-linked network structure would also limit the movement of large sub chains.In addition,the impact strength of the blends modified by crosslinking also increased;the rheological test results showed that the melt strength of the blends was improved.（3）P4HB-g-GMA was prepared by melt grafting method as a compatibilizer,and the effect of compatibilizer content on the compatibility of PLA/P4HB system was studied.The results are as follows:After adding P4HB-g-GMA as a compatibilizer to the PLA/P4HB blend,the impact strength of the PLA/P4HB blend was improved from7.1 k J/m² to 18.8 k J/m².At the same time,both tensile strength and yield strength showed a trend of increasing first,then decreasing and increasing,but the overall change was not significant.The SEM results verified that the compatibility of PLA/P4HB blend system is not good,and there is an obvious phase interface between the two phases.The addition of compatibilizers can improve the compatibility of the two phases,making P4HB more effective in toughening PLA.The same conclusion was also reached through dynamic mechanical property testing.In addition,the 3D printing spline test results show that the PLA/P4HB/P4HB-g-GMA blend has good toughness and higher yield strength compared to PLA and P4HB,indicating that the compatibilizer modified PLA/P4HB blend is an excellent 3D printing material,which greatly widens the application field of PLA and P4HB materials.