Preparation And Properties Study Of Poly(Ethylene Terephthalate)/lnorganic Nanocomposites

Polyester nanocomposites research has become a hot spot, with the shortage offossil resources and the development of high technology to improve the materialperformance requirements. The inorganic nanoparticles are added to PET, in order toimprove the performance of PET, save costs, and slow the rate of consumption offossil resources. Although the positive effect of nano-fillers is well known, a uniqueand consistent method of dispersing the nanoparticles into the polymer matrix is stilllacking, due to the particle agglomeration and immiscibility between the inorganicparticles and the polymer matrix.In this article, two fronts were treated. On the one hand, a novel surfactant wasdesigned, synthesized and selected in order to treat the surface of inorganicnanoparticles. On the other hand, a dispersant was designed and synthesized toparticipate in a polyester esterification, polycondensation reaction. The uniformdispersion of inorganic nanoparticles in the polyester was achieved by these twoefforts, obtaining the excellent performance of the PET/inorganic nanocomposites.Firstly, polyethylene glycol phosphate1000, a non-ionic surfactant, was preparedby polyethylene glycol1000and polyphosphoric acid, in order to treat the surface ofCaCO₃nanoparticles. The chemical bond was formed between the one end ofsurfactant and the surface of CaCO₃nanoparticles, and the other end of surfactant canparticipate in the in situ esterification, polycondensation reaction, forming a strongchemical bond at the molecular scale between PET and surfactant, achieve a uniformdispersion on a molecular scale.Hydrophobic BaSO₄nanoparticles and hydrophobic ZnO nanoparticles wereprepared with stearic acid （SA） as the modifying agent. The presence of SA induced achange on BaSO₄and ZnO surface from hydrophilic to hydrophobic. Furthermore,PET was also hydrophobic. The polymer/particle adhesion was lowered by themodifier resulting in a reduction of the constraint effect of BaSO₄and ZnO nanoparticles on the PET molecular chains. The results also indicated that there wasno distinct phase-separated structure for PET and the modified BaSO₄and ZnO in thenanocomposites.Secondly, bis（2-hydroxyethyl） maleate （BHEM） was prepared by esterificationreaction between maleic anhydride and ethylene glycol with p-toluenesulfonic acid ascatalyst. BHEM, as a dispersant, can block or graft on the PET molecular chain,forming a kind of unsaturated copolymer, reducing the interfacial tension. A newunsaturated copolymer （PET-co-BHEM） was formed by the reaction of the preformedpolymer of PET （BHET） and BHEM in the polycondensation process. The freerotational and vibrational motions were more easily occurred in the carbon-carbondouble bond of BHEM than the benzene ring of PET chains. It was assumed that freerotational and vibrational motions in the chains allowed different conformations andpromoted the tendency to crystallize. However, the presence of BHEM changed thecrystalline state of PET by destroying structural regularity of PET chains, resulting inestablishment of unidentity periods, forming the interspace in the polymer chains.Thus, nano-CaCO₃could fill in the polymer chains, resulting in the prevention of theiragglomeration and breaking up of large aggregates into smaller ones. The presence ofBHEM promoted the uniform dispersion of inorganic nanoparticles in the PET matrix,especially, the surface-treated inorganic nanoparticles.Finally, well-dispersed PET/inorganic nanocomposites were synthesized by in situpolymerization method, and the effect of inorganic nanoparticles on PET propertieswas studied. The results showed that the presence of inorganic nanoparticlesimproved the thermal stability and crystallization properties of PET matrix, thesurface modified inorganic nanoparticles were the heterogeneous nucleating agentsfor the process of PET crystallization. The addition of the surface treated inorganicnanoparticles induced crystallization to start at high temperatures. The presence ofsurfactant, promoting good adhesion between the filler and the polyester matrix,facilitated the role of the nanoparticles as effective nucleating agents for PET.Conversely, inorganic nanoparticles alone can not promote nucleation of PET. Thecrystallization exotherms of the PET/modified inorganic nanocomposites result much narrower. For this sample, crystallization occured at higher temperatures, wheregrowth rates were lower. The high number of nuclei provided by the nanoparticlesinduced a large amount of crystallites to grow simultaneously, overweighing theeffect of lower growth rates. The large quantity of preformed nuclei in PET/modifiedinorganic nanocomposite produced a steep beginning of the exothermic peak, andcrystallization was completed in a relatively short time, slowing only whencrystallization closed to completion, due to termination of growth by impingement.Conversely, in the pure PET and PET/blank inorganic nanocomposites a much lowernumber of effective heterogeneous nuclei, with a relatively broad distribution ofinduction times, were present, resulting in a more gradual beginning of thecrystallization exotherm. The overall effect was much a sharper crystallization peakfor the PET/modified inorganic sample, which supported the hypothesis ofeffectiveness of modified inorganic nanoparticles as nucleating agent for PET.In addition, thermal degradation kinetics of PET/inorganic nanocomposites wasinvestigated, and compared the effect of different inorganic nanoparticles on thethermal stability of PET. The pure PET and the samples with different nanoparticlespresented a good thermal stability. No remarkable weight loss occurred up until360oC （<0.5%）. The main difference among them was the different residue content above500oC, where the residue content of nanocomposites was always larger than that ofthe pure PET. However, T2%and Tmaxof nanocomposites shifted to highertemperatures compared with the pure PET, which meant that the incorporation ofinorganic nanoparticles into PET matrix increased the thermal decompositiontemperatures, indicating that the addition of inorganic nanoparticles improved thethermal stability of PET matrix. In PET/inorganic nanocomposites, inorganicnanoparticles as protective barriers against thermal decomposition may retard thethermal decomposition of PET, resulting from the effective function of inorganicnanoparticles acting as physical barriers to hinder the transport of volatiledecomposed products out of PET nanocomposites during the thermal decomposition.In this paper, Friedman method was used to investigate E of nanocomposites duringthermal decomposition. The different CaCO₃content was used to study the thermal degradation kinetics of PET/CaCO₃nanocomposites. The average of activationenergies at different reaction degree （from α=0.1to α=0.9） for PET nanocompositescontaining0,1,3,5,8wt.%CaCO₃nanoparticles were200.58,212.64,219.50,223.47,223.81kJ/mol, respectively. The activation energy of nanocompositesincreased with addition of CaCO₃from0to5wt.%. It seemed that decomposition innanocomposites was more difficult than that in the pure PET under same experimentalconditions. It was evident that the addition of CaCO₃nanoparticles led to theincrement of the activation energy of decomposition and there existed a maximumvalue of E. It was concluded that the addition of nanosized CaCO₃in PET efficientlyimproved the thermal stability of PET by increasing the activation energy of thenanocomposites during thermal decomposition. However, the value of activationenergy had no significant variation when increasing CaCO₃content from5to8wt.%.It was probably due to the fact that CaCO₃nanoparticles came to agglomeration inPET nanocomposite containing8wt.%CaCO₃. The improvement of properties wasdependent on the dispersion state of inorganic nanoparticles in the polymer matrix. Atthe same time, the thermal degradation kinetics of PET/2wt.%CaCO₃, PET/2wt.%BaSO₄, PET/2wt.%ZnO nanocomposites were studied, the results showed theaverage of activation energies for PET/2wt.%CaCO₃, PET/2wt.%BaSO₄, PET/2wt.%ZnO nanocomposites were215.22,209.97and212.86kJ/mol.In summary, in order to improve the dispersion of inorganic nanoparticles in thePET matrix, two fronts were treated. On the one hand, a novel surfactant wasdesigned, synthesized and selected in order to treat the surface of inorganicnanoparticles. On the other hand, a dispersant was designed and synthesized toparticipate in a polyester esterification, polycondensation reaction. The results showedthe dispersion of nanoparticles into the PET matrix was homogeneous, resulting inexcellent performance of PET/inorganic nanocomposites.