Preparation And Properties Of Modified Films Produced By Cupriavidus Necator

Polyhydroxybutyrate(PHB)is a kind of biodegradable thermoplastic polyester.It has broad market prospects,but it has high brittleness,poor toughness,and limited processing,which has a great impact on the PHB molding process.In order to overcome these shortcomings of PHB,Cupriavidus necator was selected as the fermentation strain to synthesize PHB by shake flask fermentation with low-cost sugar cane as the carbon source.Meanwhile,PBAT was selected as the base material to form a composite film with PHB,and modified with GTA to improve the mechanical properties of the film.This can not only make the utilization of molasses more comprehensive and reduce the producing cost of PHB,but also overcome the shortcomings of high brittleness and poor toughness of PHB,which is of great significance for promoting the development of fully degradable materials.The specific content and results are as follows:(1)In order to increase the content of PHB produced by Cupriavidus necator fermentation,with sugar cane molasses treated by concentrated sulfuric acid as the carbon source,the carbon source concentration,nitrogen source concentration,fermentation time,inoculation amount and initial pH of the fermentation broth were separately measured for single-factor experiment and Plackett-Burman design.Then according to the screening results of Plackett-Burman design,with PHB content as response value,the central combination experiment with Box-Behnken design was conducted to optimum the process for PHB production by shake flash fermentation.The results show that the optimal process parameters are:carbon source concentration 64.5 g/L,nitrogen source concentration 0.94 g/L,and fermentation time 46.47 h,and the PHB content under this condition is 1.58 g/L.(2)The composite film of PHB and PBAT was prepared by casting method,and then GTA was added to compatibilize modified PHB/PBAT composite film,and the mechanical properties,micro-morphology and thermal properties of PHB/PBAT composite film before and after modification were studied.The results show that when the ratio of PHB/PBAT is 50/50,the mechanical properties of the composite film are the best.When the amount of GTA added is 0.5 g,the best PHB/PBAT compatibilization modification can be obtained.SEM characterization shows that GTA promotes the compatibility of PHB and PBAT,making the film surface smoother.The cold crystallization temperature and melting temperature of GTA/PHB/PBAT composite film are lower than that of PHB/PBAT composite film,which shows that GTA improves the crystallization ability of PHB/PBAT blend system and the melting temperature range of materials processing.(3)By comparing the buffer solution treatment degradation method and the soil burial degradation method,the degradation appearance and degradation performance of PHB/PBAT composite film and PHB/PBAT composite film with GTA added were observed.The results show that when in the buffer solution,with the extension of the degradation time,the mass-loss rate of both composite films increases,and after the addition of GTA,the mass-loss rate of the composite film up to 51.06%is higher.Acidic and neutral environments are more conducive to the degradation of composite films.After 90 days of degradation in the soil,the structure and appearance of the two composite films are severely damaged,and the PHB/PBAT composite material with GTA added has a greater mass-loss rate and surface damage,and the degradation is more complete.