Citric acid grafted polyvinyl alcohol (PVA) Preparation and characterization of thin films
|School||University of North|
|Course||Polymer Chemistry and Physics|
|Keywords||Polyvinyl alcohol Citric acid Biodegradation In vitro degradation|
Polyvinyl alcohol (PVA) is a fully biodegradable polymers, biodegradable alternative to hard polyvinyl chloride, polystyrene, plastic products, plastic film become excellent. But the pure polyvinyl alcohol film is too long degradation time, limiting the application of the polyvinyl alcohol. This paper by the method of blending the graft-modified polyvinyl alcohol, thereby obtaining a faster degradation rate, the complete degradation of the modified polyvinyl alcohol film. In this thesis, the use of esterification of citric acid and a graft copolymer of polyvinyl alcohol (CA-PVA). The use of polyvinyl alcohol molecule hydroxyl citric acid reacts with carboxyl groups on the PVA molecular chain introduced a more readily biodegradable ester group and its microstructure by IR spectroscopy. Discussed by orthogonal experiments of polyvinyl alcohol with citric acid mass ratio (feed ratio), reaction temperature and reaction time on the degree of esterification (key and amount), and identifies the graft-modified polyvinyl alcohol, citric acid preferred conditions are: feed ratio m (citric acid): m (PVA) is 4:1, the reaction temperature was 60 ℃, reaction for 3 hours, the yield of the resulting product up to 47.12%. By TG, DSC investigated CA-PVA showed the thermal properties: CA-PVA thermal degradation process into two phases, the first phase mainly esterified pyrolysis CA-PVA, and the second stage is mainly the thermal degradation of PVA . From the DSC curve that: the introduction of citric acid reduces the thermal decomposition temperature of PVA. Respectively plasticizer starch and polyvinyl pyrrolidone, polyvinyl alcohol and modified blended in water, cast film, investigated the modified PVA film the mechanical properties and transparency, and the use of electron microscopy of the films morphological characterization. The results showed that: Starch / CA-PVA film tensile strength and elongation at break increases with the amount of starch filled first increases and then decreases, the transmittance showed a downward trend, and when the starch filling reaches 50 %, the mechanical properties of the film transmittance and have undergone a sharp decline finalize the optimum filling amount of starch was 50%, then the best mechanical properties of the film, the tensile strength and elongation at break, respectively, the 7.7 MPa and 32.20%, transmittance of 70% or more. PVP / CA-PVA film tensile strength with an increase in the amount of PVP first increases and then decreases, elongation at break showed a downward trend, the transmittance gradually decreases, and when the filler content of 50% PVP so, the mechanical properties of the film transmittance and have undergone a dramatic decline in finalizing the optimum filling amount of PVP was 50%, the tensile strength of the film at this time 5.3 MPa, the elongation at break 13.6%, through the light rate more than 95%. Respectively, through in vitro degradation and soil degradation buried Investigation of methods of the modified film degradation. The results showed that: Starch / CA-PVA membrane degradation in vitro weight loss after 24 hours 85%; buried in the soil degradation experiments in: Starch / CA-PVA film weight loss rate after six months of 30% pure PVA film degradation in vitro weight loss after 24 hours only 70% buried in the soil degradation weight loss after 6 months was 12%. The degradation of Starch / CA-PVA film mechanical properties that: the tensile strength of the film was gradually decreasing trend, the elongation at break increased at first, after a sharp decrease trend.