Preparation And Characterization Of P(LA-HPro) /HA Composites

Poly(lactic acid)(PLA) is biodegradable and its degradation products is environmental friendly and the source of lactic acid(LA) as monomer is abundant. PLA is studied deeply by many researchers because of its many advantages. But its disadvantages limit its usage in many ranges. For example, hydrophobicity leads to low bio-compatibility, high degree of crystallinity results in PLA fragility. So it is necessary to modified PLA to meet the clinical application. In this paper, PLA was modified through co-polymerzation and physical blending to improve its hydrophilicity and mechanical strength.PLA was synthesized in Lab. by lactide ring opening polymerization. The polymerization conditions were optimized in the experiment. The optimum conditions were: polymerization temperature 130 ℃, polymerization time 13 h, polymerization vacuum degree 80 Pa and the usage of catalyst was 0.3 wt%. At the best conditions, the PLA viscosity reach at 0.97 g/dL. Polymer molecular weight was measured by gel permeation chromatographic(GPC). Results were: z-average molecular weight(Mz) 6.3×104, weight-average molecular weight(Mw) 5.4×104, number-average molecular weight(Mn) 4.7×104 and the dispersion index 1.15. PLA was characterized by infrared spectroscopy(IR) and nuclear magnetic resonance spectrum(NMR). Through thermogravimetry(TG) and differential scanning calorimetry(DSC) analysis, this paper got PLA’s glass transition temperature(Tg) was 55 ℃, melting temperature(Tm) was 160 ℃and thermal decomposition temperature(Tf) was 200 ℃. The measured dates were accordance with the reported on the whole. PLA was synthesized successfully in Lab..This paper synthesized Poly(L-lactic acid-hydroxyproline)(P(LA-HPro)), by solution-melting polymerization with hydroxyproline(HPro) as modification monomer.The polymerization conditions were selected in this paper and the best conditions were: polymerization temperature 130 ℃, polymerization time 12 h, polymerization vacuum degree 70 Pa and the usage of catalyst 3% wt. The P(LA-HPro) Mw was 5.6×104 and Mn was 6.1×104 measured by GPC. The dispersion index was 1.08. The co-polymer was characterized by IR、TG and DSC. The result was Tg 45 ℃, Tm 155 ℃, Tf 173 ℃. Its thermal stability was lower than unmodified PLA. Through contact angle testing, material’s contact angle lowered to 32° and its hydrophily was improved. Degradation test indicated the material’s weigh loss reached at 10% after 8 weeks, degradation spreed was higher than PLA.P(LA-HPro)/HA composites were prepared with P(LA-HPro) as matrix and hydroxyapatite as reinforcement. Both of the matrix and reinforcement keep them chemical structure and the composites were physical bonded in the mixing process. Through TG and DSC analysis, Tg and Tf of the materials became higher, but Tm was lower than PLA/HA. The HA particle at micron order didn’t agglomerate in materials observed in SEM photos. And them interfacial compatibility was very well. Mechanics performance testing indicated the materials’ strength was best at 9% wt HA. Its tensile strength reached at 45.7 MPa, bending strength 127.7 MPa and bending modulus 2.34 GPa. The adding of HA could slow down the spreed of degradation velocity dramatically by the degradation testing. The material would meet the basic requirement for repairing human’s bone tissue.The composites: P(LA-HPro)/HA would be applied in repairing bone and teeth for human because of its high strength and good bio-compatibility.