Influence Of New Nucleating Agent On Crystallization Property Of Polypropylene

PP （Polypropylene） becomes one of the fast growing classes of commoditythermoplastics, with the rapid growth of6-7%/year which owing to moderate cost andfavorable properties. Due to the low toughness in low temperature, which limits itsfurther application, the toughening modification of PP has become a hot spot in thestudy of both at home and abroad recently. Moreover, PP is of polymorphiccomposition, mainly having three modification: α、β and γ, endowing β-PPwith excellent impact toughness. Controlling the crystal structure is the direct、simpleand effective method to enhance impact toughness. By the addition of β nucleatingagent can effectively obtain PP with higher level of β crystal form. At the sametime, the processing technique about the formation β crystal of PP is especiallyimportant.The difference of thermal performance was examined between propylenehomopolymer and propylene copolymer and selected two types of PP withoutstanding properties. A new kind of nucleating agent （β-NA） was added into theT30S and EPC30R, also investigated the influence of β-NA on the crystallizationbehavior and impact toughness of PP. The difference of mechanical properties ofsamples before and after being annealed at different temperature（70-110℃） anddifferent time（0.5-8h） have been discussed. The T30/β-NA/GF, T30S/β-NA/CaCO₃and T30S/β-NA/Talc ternary compounds were prepared and the fillers whether affectthe nucleating agent was tested. Thermal properties and crystallization propertieswere studied by Different Scanning Calorimeter （DSC）, Polarizing OpticalMicroscope（POM）、Wide Angle X-ray diffraction（WXRD）、Thermogravimetry （TG）and Scanning Electron Microscope （SEM）. The main results are listed as follows:1. The melting behavior of propylene homopolymer and propylene copolymerwas investigated by DSC, founding that heat treatment didn’t chang the crystalstructure of PP and only had a significant effect on melting behavior. The crystallinityof PP first increases and than reduces as increase of the heat treatment temperature.The crystalline peak absorption frequency (1167cm^-1) shifted towards low frequencywith the change of temperature. The heat shrinkage rate of PP increased firstly andwas stable when the heating temperature reached110℃. 2. The effect of β-NA on crystallization properties of propylene homopolymerand propylene copolymer was discussed by DSC、POM、SEM、XRD. The researchshowed that adding a small amount of β-NA, the crystal structure of T30S andEPC30R produced a lot of β-PP. There were two double melting peaks on the DSCcurves and the β melting peak appeared in155℃. There was a strong representativeof crystal diffraction peak in the diffraction angel of15.9°and crystal face index300. Etching the amorphous phase of PP, the crystalline morphology presented redialin the SEM photos of adding β-NA. Its was spherulite crystal forms in the POMpictures of pure PP, which was a typical black cross extinction phenomenon.Otherwise, the samples ofβ-NAadding appeared the acicular crystal morphology.3. To join the β-NA and use heat treatment process can effectively improve thetoughness. The tensile and bending properties of all kinds of PP increased firstly andthen decreased with rising the heating temperature. The impact strength of propylenehomopolymer reduced with elevation of Tr, but the impact strength of propylenecopolymer increased. Also adding a small amount of β-NA, the tensile properties ofthe two kinds of PP would be reduced. Otherwise, the impact strength of T30S/β-NAwas increased by9.5kJ/m²to18.5kJ/m²and EPC30R/β-NA was increased by13.9kJ/m²to19.9kJ/m², elongation at break was increased exponentially. When weadopted the optimal thermal heat temperature （110℃） and time （1h）, the mechanicalproperties was better than others.4. When the fillers and β-NA were mixed into PP, they were two oppositeeffect on PP. Fillers and β-NA was existed a competition relationship. The resultshowed that when the content of fillers was lower than15%, the role of β-NA wasmore obvious than fillers. When the content of the filler was over15%, the role offilers was dominant. When the content of fillers was5-10%, mechanical properties ofPP were better than others.