Preparation, Micro-structures And Properties Of Nano Silica/PLA Composites

The preparation of silica nanoparticles using a biomineralization method, the crystallization behavior of silica/PDLA nanoconposites, and the mechanical properties of silica/PLA nanocomposites were studied in the article.Compare with nanosphere or nanotube, silica nanoplates have unique advantages on preparation of nanocomposites and nanomedicine materials for its distinctive nature. In this paper, we designed and synthesized several block coplymers, and obtained different polymer grafted silica nanoplates via those polymers’ templating and modification function. The main results are as follows:The synthesis of hydrophilic silica nanoplates via biomineralization of polyethylene glycol-block-poly-L-lysine (PEG-b-PLL) diblock copolymer. The PEG-PLL diblock polymer was prepared using the ring-opening polymerization of Lys-NCA initiated by PEG-NH2. The structure of the polymer was characterized using GPC and 1H NMR. The results showed that the diblock polymer had high purity and narrow molecular distribution. And we prepared the silica nanoparticles using a biomineralization method. The diblock polymer was used as a template in the process. We studied the influence of reactant ratio on the morphology of silica nanoparticles using a systematic synthetic method. The SEM images indicated the the surface of silica nanoparticles was smooth, and the shape was regular. we came up with a plausible mechanism for the biosilicification of PEG-b-PLL diblock copolymer.The crystallization behavior of silica/PDLA nanoconposites was studied. The the bare silica nanocomposites and PEG grafted silica nanoparticles were prepared, the their influence on the crystallization behavior of silica/PDLA nanocomposites was studied. The PEG grafted silica/PDLA nanocomposites was very interesting. It contained plasticizer, hydrogen bondings and nucleating agent, which could affect the Crystallization behavior PDLA. The FT-IR and TGA results showed that the PEG covered on the surface of silica nanoparticles was removed after been heated to 550 ℃. The SEM images showed that the silica nanoparticles had favorable dispersibility in the PDLA matrix. The DSC results showed that the PEG grafted silica nanoparticles could peed the crystallizing rate of silica/PDLA nanocomposites at a lower temperature, inhibited the crystallizing at middle temperature, and promoted crystallization behavior at high temperature. The POM images showed that the crystal growth rate of PDLA filled with PEG grafted silica was lower at 120 ℃, and the quantity was smaller at 130 ℃. The WAXS results showed that the PDLA filled with bare silica was a’-form crystal at 80 ℃, which was unstable. We conclude that the crystallization behavior was affected by plasticizer, hydrogen bonding, and nucleating agent. The plasticizer could speed the crystallizing rate at a lower temperature, the hydrogen bonding may inhibit the crystallizing at middle temperature, and the nucleating agent could promot crystallization behavior at high temperature.The mechanical properties of silica/PLA nanocomposites was studied. The influence of silica nanopalte and nanosphere were studied. The TEM and SEM images showed that silica nanoparticles had favorable dispersibility in the PLA matrix. Tensile test results showed that the elongation at break of silica/PLA nanocomposites containing 2.4 vol% silica nanoplated increased 278.3% comparing with neat PLA, while that of matrix containing 2.4 vol% silica nanospheres increased 185%. More interesting, the tensile modulus and tensile strength didn’t decrease. The DMA results showed that the strain recovery of nanopalte/PLA was 5.4% higher than that of nanosphere/PLA, and was 91.3% higher than that of neat PLA. Nanoplate/PLA had better creep resistance and strain recovery properties. Because of the large aspect ratio of silica nanoplate, more surface microcracks were formed in PLA matrix, which leaded to laeger energy dissipation. Besides, the silica nanopalte could affect the formation and growth mechanism, increased the elongation at break and improved the creep property, which attributed the energy dissipation.