| Polylactic acid (PLA) is a kind of natural biodegradable polymer biomaterials, due to its good biocompatibility and processing performance are widely used in biomedicine, etc.But Unmodified PLA has poor toughness and low crystallization rate which limit the scope of its application. Nanocellulose or Microfiber cellulose (MFC) is a kind of natural mesh plant fiber, with the diameter of the nanometer level and strong rigidity and toughness. In order to improve the toughness and stiffness of PLA and enlarge its application scope, MFC were selected to composite with the PLA, and it is expected to the preparation of high performance nano modification of biodegradable materials.But the MFC molecule contains a lot of hydroxyl groups (OH) which have strong hydrophilicity,and the PLA material belongs to the typical lipophilicity material.It is very difficult to evenly dispersed the compound. This article prepared the MFC/PLA composite materials via emulsion blending method. The water tolerance , dispersion, fracture morphology, spherulitic morphology, the non-isothermal crystallization and mechanical properties of the MFC/PLA bio-composites were characterized by laser particle size instrument, scanning electron microscope (SEM), polarized optical microscopy (POM),DSC and Electro-mechanical Universal Testing Machines, The ball indentation hardness tester, etc.Results show that:(1)The moderate MFC can be homodispersed in PLA matrix to prepare MFC/PLA bio-composites via emulsion blend method. When the mass fraction of MFC is less than 0.6%, it can be evenly dispersed in the PLA matrix. And the excessive MFC is easy to form together.(2)SEM images of MFC/PLA composite show that MFC can be evenly dispersed in the PLA matrix, when the mass fraction of MFC is less than 0.6%. And the composites have coarser cross section, fuzzy interface and pulling out the traces of MFC. MFC and PLA can form the good interface bonding which can present a typical ductile fracture characteristic.(3)The moderate MFC as the heterogeneous nucleating agent can significantly decrease the spherulite size of PLA. When the mass fraction of MFC is 0.6%, the spherulite size of PLA is the minimum. When the mass fraction of MFC is more than 0.6%, the spherulite size of PLA gradually increases via the reunion.(4)Mechanical performance of MFC/PLA composites with the increase of the content of MFC showed a trend of decrease after the first increase. Comparing with pure PLA,the tensile strength, elastic modulus, bending strength, notched impact strength and hardness of the composites at 0.6% mass fraction of MFC increased by 15.6%, 21.1%, 30.6% ,53.6% and 39.3% respectively.(5)After testing water resistance and absorption of the composite material, it can find that the MFC itself has a lot of hydroxyl groups which can produce hydrogen bond with the water and increase the water absorption of the PL A. So, joining MFC can reduce the water resistance of the composite, and the bibulous rate is increased with the increase of MFC content increase. When the MFC content was 0.6%, the impact on the bibulous rate of composite materials is the minimum.(6)In the non-isothermal crystallization, with the increase of cooling rate, the crystallization temperature, melting temperature and crystallinity of the MFC/PLA composite showed a trend of decline. When the MFC/PLA composite materials begin to crystallize at the same temperature crystallization, it can be found that the composite material which has 0.6% MFC has the highest degree of crystallinity and fastest crystallization rate. When the mass fraction of MFC is less than or greater than 0.6%, the crystallinity and crystal rate are presented decreasing state. At the same time the Mo's method could describe the non-isothermal crystallization of PLA /MFC composites very well.(7)MFC/PLA composite can be better applied to FDM model in the 3D printer, and its mechanical properties were very excellent. |
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