Study On The Influence Of ZnO Crystal Plane On Polymer Crystallization And Mechanical Properties

The surface is very important for solid materials.Different crystal planes have different polarities and surface energies caused by different geometric and electronic structures in crystalline materials,showing different physical and chemical properties.However,there is currently no report on the effect of crystal plane on polymer properties in polymer nanocomposites.Zinc Oxide was an important inorganic semiconductor material with special electrical,optical properties and antibacterial properties,and has been widely introduced into the polymer matrix to give the polymer new functions.In this work,ZnO nanocrystals with different crystal planes were used to modify isotactic polypropylene(iPP),poly(L-lactic acid)(PLLA)and poly(ethylene 2,6-naphthalate)(PEN).The effects of nanocrystalline ZnO with different crystal planes on the crystal morphology,thermal stability and mechanical properties of iPP(non-polar),PLLA(weak polar)and PEN(polar)polymers were investigated by differential scanning calorimetry(DSC),polarizing optical microscope(POM),wide-angle X-ray diffraction(WAXD),scanning electron microscopy(SEM),thermogravimetry(TG)and mechanical properties test.Firstly,two kinds of ZnO exposed(1010)and(0002)crystal plane were obtained by controlling reaction conditions and purchased,respectivey.They were recorded as H-ZnOc/(1010)and and T-ZnOw/(0002)in this thesis.The analysis of HRTEM and contact angle test proved that(1010)crystal plane was non-polar and low surface energy(88.65mN/m2);(0002)crystal plane was polar and high surface energy(349.24mN/m2).The effects of crystal planes(1010)and(0002)for ZnO on the crystallization and thermal oxygen stability of non-polar iPP were investigated.The research results showed that(1010)and(0002)crystal planes for ZnO had different effects on crystallization and thermal stability of iPP.The(1010)crystal plane with non-polarity and low surface energy played a heterogeneous nucleation effect on iPP,the crystallization temperature increased by 11?,the size of spherulites decreased,the number of spherulites increased,the nucleation efficiency and crystallization rate up to 57.81%and 1.27 min-1,the thermal and thermal oxidation stability(TG,OIT,OOT)of iPP improved by 6?,6 min and 12?.On the contrary,the(0002)crystal plane with polarity and high surface energy had a weaker effect on the properties of iPP.Secondly,the effects of crystal planes(1010)and(0002)for ZnO on the crystallization,thermal stability and mechanical properties of the weakly polar PLLA were investigated.The results showed that(1010)and(0002)crystal planes had different effects on the PLLA crystallization and mechanical properties.The(1010)planes with no-polar and low surface energy increased the chain mobility of PLLA chain,and showed a plasticizing effect;accompanied by the glass transition temperature,melt temperature and cold crystallization temperature decreased by 12?,10? and 12?,respectively.The size of spherulites increased,the number of spherulites decreased,the crystal form of PLLA changed from mixed crystal form ?,?' to unique a crystal form.However,the(0002)planes with polar and high surface energy had highly nucleating effective for PLLA,especially the appearance of crystallization peak and the crystallization temperature significantly increased to 106.41?,and the cold crystallization peak disappeared.The size of spherulites decreased and the number of spherulites increased,while the crystal form of PLLA did not change.Moreover,the(0002)planes increased the elongation at break of PLLA to 20.34%.On the contrary,the(1010)planes reduced the elongation at break of PLLA to 7.49%.Their thermo-gravimetric analysis(TGA)results also showed the similar trend.Finally,the effects of two crystal planes(1010)and(0002)for ZnO on the crystallization nucleation,thermal stability and mechanical properties of polar PEN crystals were investigated.The experimental results showed that the two crystal planes(1010)and(0002)had the same rules for the crystallization nucleation of PEN.It is mainly reflected in that the crystallization temperature was increased by 23? compared with neat PEN,and the nucleation efficiency was increased to 52.86%and 52.17%,respectively.With the increase of the content of the two kinds of ZnO with different crystal planes,the size of spherulites decreased and the number of spherulites increased.The thermal stability and mechanical properties tests further showed that the thermal stability and impact properties of PEN/H-ZnOc/(1010)were stronger than PEN/T-ZnOw/(0002),and the impact strength was increased to 2.7 kJ/m2 and 2.4 kJ/m2,respectively.It was observed through SEM that the impact section was very rough,accompanied by obvious plastic deformation and shear bands.In the process of isothermal crystallization kinetics,H-ZnOc/(1010)can effectively promote the crystallization of PEN,increase the crystallization rate of PEN/H-ZnOc/(1010)composites,and reduce the half crystallization time by one time.