Preparation Of Polycarbonate-based TPU Compatibilizers And Their Application In PC/PP Blending System

The polycarbonate/polypropylene(PC/PP)blending system is a typical thermodynamic incompatible system because of the large difference in solubility parameters and polarity between PC and PP,which can lead to obvious phase separation phenomenon.Therefore,the design and synthesis of new compatibilizers to reduce the interface tension and improve the compatibility between PC and PP plays an important role in preparing PC/PP blends with low price and excellent performance,which is not only of scientific research value,but also of great industrial application value.At present,compatibilizers used in PC/PP blending system are graft copolymers and block copolymers,such as maleic anhydride polypropylene graft copolymer,acrylic ester polypropylene graft copolymer,SEBS block copolymer,ethylene-methyl acrylate block copolymer(EMA),etc.Because these compatibilizers have non-polar backbone structures,when used in PC/PP blends with PC as continuous phase,the curvature of the interface will be biased toward the continuous phase PC,which is not conducive to the refinement of the dispersed phase PP particle size,limiting its compatibility effect.Thermoplastic polyurethane elastomer(TPU)is a kind of block copolymer with polar backbone structure,which can be processed as thermoplastic plastics structure.Through the change of type and proportion of raw materials during the synthesis process,TPU with preset structure and performance can be prepared as compatibilizer used in PC/PP blending system with PC as continuous phase.In this paper,polycarbonate-based thermoplastic polyurethane elastomer compatibilizer with octadecyl side chains(TPU-Gx)was synthesized,and the polarity of its backbone structure was similar to that of continuous phase PC,and its branch chain structure was similar and compatible with the dispersed phase PP.TPU-Gx was used as a C-D type compatibilizer in PC/PP blending system.Specific research contents and results were listed as below:(1)A novel aromatic polycarbonate diol(PCDL)was prepared from bis-hydroxyethyl ether of bisphenol A(BHE-BPA)and diphenyl carbonate(DPC)by using transesterification polycondensation method.Then,a series of aromatic polycarbonate-based thermoplastic polyurethane elastomers(TPU-Gx)with octadecyl side chains and different PCDL/GMS contents were synthesized by using PCDL,polycaprolactone diol(PCL),1-octadecylglyceryl diol(GMS)and isophorone diisocyanate(IPDI)as raw materials,of which the polarity of backbone structure was similar to that of continuous phase PC,and branch chain structure was similar and compatible with the dispersed phase PP.The structures of the synthesized products were confirmed by FT-IR and ~1H-NMR.The molecular weight,thermal properties,mechanical properties,and microphase separation of TPU-Gx were characterized by gel penetration chromatography,thermogravimetry,differential scanning calorimetry(DSC),tensile property test,and scanning electron microscopy(SEM).Thermogravimetry results showed that TPU-Gx had good thermal stability and could meet the processing condition of PC/PP blends as a compatibilizer.(2)The effects of the types and contents of compatibilizers TPU-Gx on the structure and properties of PC/PP blends were investigated.Mechanical properties test results showed that the addition of TPU-Gx could increase the tensile strength and bending strength of PC/PP blends.When the content of TPU-Gx was fixed at 5 wt%,with the increasing of PCDL and GMS content in TPU-Gx,the impact strength of PC/PP/TPU-Gx blends showed a trend of increasing at first and then decreasing,but all of them were higher than that of PC/PP blends without TPU-Gx.Among them,the impact strength of PC/PP/TPU-G1.5 blends was 31.8 k J/m~2,which was 54.1%higher than that of pure PC/PP blends.After changing the content of TPU-G1.5,the impact strength increased at first and then decreased with the increasing of the content of TPU-G1.5.PC/PP blends with 4 wt%of TPU-G1.5 had the highest impact strength as 38.7k J/m~2,which was 87.9%higher than that of pure PC/PP blends.The SEM results showed that the addition of TPU-Gx could make the PC/PP blends achieve a more uniform two-phase structure with reduced particle size of dispersed PP.The dynamic mechanical property test(DMA)results showed that the addition of TPU-Gx made the T_g peaks of PC and PP become close to each other.DSC results showed that the addition of TPU-Gx reduced the crystallinity of the dispersed phase PP and changed the crystalline morphology from homogeneous nucleation to heterogeneous nucleation.The melt flow rate(MFR)test showed that the MFR of PC/PP blends was increased after adding TPU-Gx,and the processing fluidity became better.In conclusion,TPU-Gx had a significant capacity increasing effect on PC/PP blends,and PC/PP blends prepared by adding 4 wt%of TPU-G1.5 had the optimal performance.(3)The effects of TPU-Gx and EMA on the structure and properties of PC/PP blends were investigated.When the total amount of TPU-G1.5 and EMA was fixed at 4 wt%,the tensile strength and bending strength of PC/PP blends decreased gradually with the increasing of EMA content,while the impact strength increased gradually.The SEM results showed that TPU-G1.5and EMA had completely different ways to improve the interface between PC and PP.After adding 2 wt%of TPU-G1.5 and 2 wt%of the EMA,the particle size of dispersed PP and fuzziness of two phase interface were between those of using TPU-G1.5 or EMA along.The impact strength of PC/PP blends was higher than that of PC/PP/TPU-G1.5(4 wt%)blends,tensile and bending properties of PC/PP blends were not lower than that of pure PC/PP blends,and the melting flow index was higher than that of pure PC/PP blends.The process fluidity of the above PC/PP blends was improved while ensuring excellent mechanical properties,which had the best comprehensive properties.