Preparation Of Poly-Lactic Acid Compound Functionally Graded Membrane Material And Its Properties

There are kinds of the materials in nature with the gradient structure such as the nonuniform gradient structure of the bones and teeth and the thin shell structure of shells.,etc. They have excellent physical and chemical properties, which can better adapt to the changes in the environment. The PLA, PCL and NR material are presently several baiodegrading and polymer materials which are used in medical and food packaging fields.PLA has great biocompatibility and excellent mechanical properties and easy processing performance. But the degradation rate of poly(lactic acid)(PLA) is slower and the degradation cycle is difficult to control. The polylactic acid material is qualitative hard and brittle and lacks flexibility and elasticity and processing performance is poor. Polycaprolactone(PCL) has excellent biocompatibility and flexibility and its degradation rate is moderate. However, the application of PCL material is limited due to its low melting point. Natural rubber has high molecular compound with gather isoprene as the main component and has the very good mechanical strength at room temperature with high elasticity and plasticity. But the multiple deformation heat production and the flexing resistance is low. Therefore, the concept of gradient function is introduced to the complex system of poly(lactic acid)(PLA) using the complementary performance of both. The PLA/PCL and PLA/NR asymmetric or symmetric gradient material are prepared through the special structure design and suitable technology. This kind of material is no doubt more adapting to the working environment than the pure blend homogeneous polylactic acid material and better meets the actual needs.The polymer dissolving and melting processing methods are used to prepare the PLA compouent membrane material, with the aid of the composite distributted and the designed and controlled graded construre of the PLA component system. Basing the PLA and complementary property polymers as main materials, the PLA material is modified gradiently to prepare PLA component membrane material to improve the comprehensive property of functional graded material. The effect of the polymer content and ratio tud different graded constitution are discussed to the kinds of properties.The FTIR, the Raman spectroscopy and optical microscope(SEM) are characterized to show the the transverse graded structure. The thermal degrade, the mechanical property and biodegradation are ultimately tested to determine the applied value.The experimental results show that the wettability, biodegradadibility and mechanical properties of the component gradient membrane are relatively improved than the pure polylactic acid material with the certain thickness. The FTIR and Raman spectrum results shows that he PCL and the PLA have the excellent bio-compatibility because there is strong correlation between the two kinds of molecular forces. The phase of the PLA/PCL, PLA/rubber, PLA/rubber/PLA and PLA/PCL/PLA gradient membrane are prepared when the polylactic acid content is 4%. SEM images show that the cross section of the PLA complex gradient membrane is good gradient structure. The gradient structure between the components have the good biocompatibility. with the increase of polylactic acid content and within a certain range in keeping the polycaprolactone or rubber content. The tensile strength of different proportion of PLA/PCL or rubber gradient film is increased but the elongation at break is lowered due to the increase of the ratio of the PLA content. The mechanical properties of different proportion of PLA/PCL and PLA/rubber gradient membrane are compared. And the breaking strength of the gradient membrane is decreased with the increase of ratio of polylactic acid firstly, and then the elongation is increased. Comprehensive performance of the gradient PLA/PCL membrane is excellent, and when the polylactic acid content is 4%. The comprehensive performance of the PLA/rubber gradient film is the best when the polylactic acid content is 3%. The tensile strength of gradient membrane was improved than the pure polylactic acid membrane, however, the breaking elongation is slightly damaged with the increase of proportion of PLA. In practice, the brittleness and flexibility of gradient membrane are improved by adjusting the ratio of the content of various kinds of high polymer. The kind of the gradient structure will have broad application prospects in the biomedical field such as the wound dressing and artificial skin.