Preparation And Properties Of Nanodiamond/biodegradable Composites

The application of polymer materials not only brings convenience to people,but also brings the problems of energy waste and environmental pollution.In order to achieve sustainable development,the research and development of biodegradable materials has attracted social attention.Polyvinyl alcohol（PVA）and polylactic acid（PLA）are both synthesized by non-petroleum route.They are highly biocompatible polymer materials with the advantages of biodegradation,high transparency and easy processing.However,these two polymers also have similar shortcomings,such as low thermal decomposition temperature,poor mechanical properties,low thermal conductivity,which limits the application of polymers to a certain extent.Therefore,in scientific research,they are usually modified in different ways.Nanodiamond（ND）is a kind of inorganic carbon nanomaterial with good biocompatibility,which has excellent parameters such as Young’s modulus and thermal conductivity.It is a nano reinforced filler with excellent performance.However,because of its high specific surface area and van der Waals force between particles and other factors,the agglomeration of particles is serious,which affects the properties of the composites.In this paper,different reagents were used to modify the surface of nanodiamond to reduce its agglomeration,and at the same time,hydrophilic and hydrophobic modified particles were prepared respectively,which expands the application range of nanodiamond as reinforcing filler.The main research contents are as follows:（1）In order to make nanodiamond as reinforcing filler evenly dispersed in water-soluble polyvinyl alcohol matrix.Firstly,polydopamine was used to modify the surface of nanodiamond,and then polyethyleneimine was grafted onto the surface of the polydopamine layer through Michael addition and Schiff base reaction.The change of grafting rate of particles with different proportion of polyethyleneimine was investigated.Through modification,nanodiamond is evenly dispersed in water and the agglomeration is weakened.The particles before and after modification were added into polyvinyl alcohol matrix to prepare a series of composites.The results show that the heat resistance,mechanical properties and thermal conductivity of polymer are improved by adding nano filler.When the addition amount of modified particles is 1.00%,the thermal conductivity of the composite film is 0.2544 W·m^-1·K^-1,which is 148.20%higher than that of pure PVA film.The tensile strength reached the maximum（73.00 MPa）and increased by 113.45%.（2）In order to make hydrophilic nanodiamond particles can be used in hydrophobic polymers,hydrophobic modification was carried out in this paper.After coated with polydopamine,ε-caprolactone was grafted onto the surface of nanodiamond by ring-opening reaction ofε-caprolactone initiated by hydroxyl group on the surface.The nanodiamond particles grafted with biological polyester chain have good hydrophobicity and can be evenly dispersed in polylactic acid matrix.A series of composites were prepared by using the particles before and after modification.The results show that the properties of the composites with filler are improved,especially the modified particles.When the amount of filler is 1.50%,the thermal conductivity of the composites can reach 0.6035W·m^-1·K^-1,which is 159.10%higher than that of pure PLA film.At this time,the tensile strength of the composite film reaches the peak 52.36 MPa,which is 39.63%higher than that of pure PLA film.