Study On Melt Grafting Of Polypropylene Induced By Low Temperature Plasma

Low temperature plasma technology is a green,clean and pollution-free technology.Low temperature plasma induces the melt graft modification of polypropylene,which is a greener and more efficient polypropylene bulk grafting modification method.It has good feasibility in developing polypropylene materials with superior performance,low price and environmental protection.In this thesis,the surface modification of isotactic polypropylene(iPP)by dielectric barrier discharge(DBD)of air plasma is studied.The melt grafting of pentaerythritol triacrylate(PETA)onto polypropylene is induced by air plasma.The effects of different experimental conditions on grafting degree and the long chain structure are studied.Moreover,the crystallization behavior of the grafts is investigated.The peroxides on the surface of plasma treatment polypropylene(PiPP)are detected by the 2,2-diphenyl-1-picrylhydrazyl(DPPH)method,indicating that the concentration of the peroxides is up to 3.38-3.69×10^-7 mol/cm².FTIR-ATR and XPS measurement are used to analyze the surface activity.The results show that an amount of-OH,C=O and COOH groups are introduced onto the PiPP surface.The characterization of surface morphology of PiPP by scanning electron microscopy(SEM)reveal that the plasma can etch the polymer surface,and the etching degree gradually increased with the increase of discharge voltage and treatment time.The air plasma can induce the melt grafting of PETA onto iPP.For the iPP and PETA grafting systems,the effects of treatment voltage,mixing time,mixing temperature and monomer concentration on the experimental results are studied by FTIR and rheological methods.When the reaction temperature is 180°C,the treatment voltage is 70 V,the reaction time is 15 min,the PETA monomer is 5%,the grafting degree is up to 1.29%,and the long chain weight percentage is up to about 0.03.The linear viscoelastic behavior of long-chain branched polypropylene is studied.The introduction of long chain branches changes the relaxation mechanism of the polypropylene,causing the material to undergo a transition from viscous to elastic.The structure and crystallization behavior of iPP,PiPP and grafts are investigated.X-ray diffraction(XRD)and differential scanning calorimetry(DSC)results indicate that plasma treatment and grafting do not change the crystalline form of the polypropylene.Compared with PiPP,the equilibrium melting point of grafts has a significant increase.The effect of plasma grafting on the crystallization kinetics of isothermal and non-isothermal crystallization of polypropylene is investigated.For the isothermal crystallization process,the crystallization rate of the iPP-g-PETA is higher than that of the iPP due to the nucleation of the long-chain branch in the grafts.For the non-isothermal crystallization process,the iPP-g-PETA crystallization rate is slower than iPP due to the slower molecular mobility of the iPP-g-PETA graft chain.