Ultrafine Dispersion Of Composite Organic Nucleating Agents In Polypropylene Matrices

In this thesis, the organic nucleating agents and the corresponding compositenucleating agents were innovatively prepared via micoremulsions to modify polypropylene.Furthermore, spray drying technique was investigated thoroughly, and the compositenucleating agents obtained by this method were also used to modify polypropylene. Fourdifferent series of microemulsions and spray drying technique were designed to control thenucleating agents’ size and their dispersion in PP matrix. The relationship betweenmorphology and properties in the composite was studied in detail.The main results of the thesis were as follows:1. Sodium benzoate (SB) was solubilized by adding predetermined amount of water,mineral oil,1-hexanol and Tween60dropwise to obtain a single-phase microemulsion withthe desired composition. Both SB microemulsion and SB powder were used for PPmodification through melt compounding. The mechanical properties, small angle X-rayscattering (SAXS), polarized optical microscopy(POM) and differential scanningcalorimetry(DSC) results show that the microemulsion method can improve the dispersionof nucleating agent and the orientation of PP. The flexural strength and moduli of PPmodified with SB microemulsion are much higher than those of PP modified with SBpowder using conventional mixing method. More nuclei can be formed during thecrystallization of PP and the crystallinity of PP can be further increased when SB wasloaded by using microemulsion method compared with using in powder form.2. The microemulsion method was used to ultra-finely disperse and compound twowidely used commercial melt-insensitive PP nucleators, sodium2,2’-methylenebis-(4,6-di-tert-butylphenyl) phosphate (NA11) and sodium benzoate (SB), for the first time.The NA11and/or SB microemulsions were successfully prepared by choosing themicroemulstion system composed of ethyl butyrate, tween80, ethanol and water withNA11and SB dissolved in ethanol and water respectively. An ultrafine or even nanoscaledispersion of NA11nucleator was achieved by using the microemulsion method. The NA11dissolved in ethanol phase was dispersed on the interface of droplets, whose size is c.a. tensof nanometers as characterized by dynamic light scattering(DLS) and cryo-TEM(cryo-transmission electron microscopy). The composite NA11/SB compositenucleator microemulsion possesses even smaller dispersed phase.The investigation of crystallization behavior of nucleator modified PP samples viaPOM and DSC showed that NA11microemulsion can disperse better in PP matrix andimprove the nucleation efficiency compared to its powder. The mechanical properties of PP,especially the stiffness, can be further improved when using NA11microemulsion at aloading of250ppm. However the oil and surfactant components within the microemulsioncan be incorporated into the final PP matrix and adversely affect the stiffness as well as thecrystallization ability of PP. Therefore a higher loading of nulceator microemulsion is notpreferred. The NA11/SB composite microemulsion shows the best performance inpromoting PP’s crystallization and improving its mechanical properties. The smallestdroplet size of microemulsion as well as a composite structure of nucleator crystallites maycause this synergistic effect between the two nucleators.3. To alleviate the adverse influences of the residual components of themicroemulsions composed of ethyl butyrate, tween80, ethanol and water in the PP matrixon the crystallization and the mechanical properties of PP, we innovatively replaced the oilcomponent of the microemulsion, ethyl butyrate, with other functional liquid processingadditives, i.e. liquid antioxidants, to achieve the ultrafine dispersion of nucleating agentswith the micoremulsion method. Two liquid antioxidants1135and1520were used tosuccessfully prepare the NA11and/or SB microemulsions with antioxidant function. Theantioxidant-containing NA11/SB composite nucleator microemulsions also showedsynergistic modification effect when used in PP, i.e. improved nucleation efficiency as wellas better improvements of the mechanical properties of PP. The oxidation induction timeexperimental results of PP samples showed the antioxidant-containing nucleatormicroemulsions can provide anti-oxidation properties for PP.4. By replacing oil component of the microemulsions composed of ethyl butyrate,tween80, ethanol and water with the liquid light stabilizer, a series of microemulsionsbased on liquid light stabilizer (oil phase), ethanol (cosurfactant), Tween80(surfactant) andwater were formed. The NA11/SB composite microemulsion shows the best performance inpromoting PP’s crystallization and improving its mechanical properties. The stability of PP increased insignificantly as ethyl butyrate was replaced by light stabilizer.5. A series of composite nucleating agents based on inorganic nano-particles(attapulgite and/or silica) and NA11were prepared via spray drying technique. The researchresults suggested that the mechanical properties of PP had been improved substantially withaddition of composite nucleating agents into the system. The stiffness of PP was increasedsignificantly with increasing the loading of composite nucleating agents. The ternarycomposite nucleating agents showed significant effect on improving the stiffness of PP atthe loading of0.2%, which is similar as using pure NA11at such loading. The observationon microscopic morphology showed that three components in the ternary compositenucleating agent were inter-partitioned with each other, resulting in the improved dispersionof NA11and the inorganic nano-particles in PP matrix.