Study On The Preparation Of High-strength Poly (?-caprolactone) Materials

Extended-chain crystal(ECC)shows a high melting point and high crystallinity,and the crystal structure of ECC is the most stable structure in polymer thermodynamics.Traditionally,the ECC structure needs to be obtained by melting crystallization under high pressure and high temperature,the process conditions of which are so rigorous that it is difficult to be mass-produced.Our research group has managed to prepare powdery ECC materials under the normal pressure based on the method of the inclusion structure precursor.Taking poly(?-caprolactone)(PCL)as the research object,we have prepared PCL-ECC materials with the same processing method as introduced above,and have explored the technology of processing PCL-ECC powder into high-strength materials.The main findings are introduced as follows:Firstly,we prepared the ECC material of PCL by the clathrate method,whose melting point and melting enthalpy are 74 ? and 139.4 J/g respectively.Additionally,the effect of different temperatures on the mechanical properties of powder-molded splines under low pressure(100 MPa)conditions was explored,and a specimen with a tensile elastic modulus of 454.9 MPa was obtained,which is 2.6 times that of ordinary PCL splines.Thermodynamic and microscopic morphological characterizations showed that the melting of a small portion of ECC provided a blocking effect between ECC powders.However,the inter-particle pore defects remaining due to insufficient adhesion resulted in a much lower fracture elongation of the prepared material.Secondly,PCL-ECC splines were prepared under high-pressure conditions,and it was found that increasing the pressure was beneficial to improve the density and uniformity of the material to achieve the effect of improving the mechanical properties of PCL-ECC splines.Nevertheless,this method still could not avoid the pore defects in the elastic splines with the best elastic modulus measured in the experiment being 478.6MPa.Further,we tried secondary heat treatment to reduce pore defects,while the final mechanical properties were not be effectively improved because the ECC structure was easily transformed into a dispersed phase caused by the heat treatment process.Through our preliminary experimental exploration,it can be proved that ECC shows the characteristic of high elastic modulus,but due to its high crystallinity,it is difficult to avoid pore defects during the powder-processing process.Thus,the mechanical properties of the final shaped material obtained are not ideal,and further researches should be carried on.