Study On Preparation, Structure And Properties Of PP/PA6/TiO₂ Nanocomposites

Incorporation of titanium dioxide(TiO₂) nanoparticles into polypropylene/polyamide 6(PP/PA6) blends may give the matrix materials excellent mechanical properties and strong antibacterial and sterilization function.In order to improve the compatibility of TiO₂ nanoparticle and polymer and to hinder them aggregate together,silane coupling agents with different function groups and toluene-2,4-diisocyanate(TDI) were used to functionalize TiO₂ nanoparticle.It was found that TDI was the best modifier to functionalize TiO₂ nanoparticles.The main effecting factors on the reaction of TDI with the hydroxyl at the surface of TiO₂ nanoparticles had been investigated by determining the reaction extent of hydroxyl group.It was found that the reaction maintained at 95℃for 6 hours with the fixed mole ratio of[TDI]/[—OH]of 6:1,the reaction extent of hydroxyl reached 92.31 mol%.Fourier transform infrared spectrum(FTIR) spectroscopy and thermogravimetric analysis(TGA) were employed to characterize the TDI-functionalized TiO₂ and the results show the TDI molecules were covalently bonded at the nanoparticle surface.In addition,transmission electron microscope(TEM) images showed that the functionalized-TiO₂ can be well dispersed in toluene with the pristine size.PP/PA6 based nanocomposites were prepared via melt blending.The mechanical properties were analyzed by static mechanical test and dynamic mechanical thermal analyzer(DMTA) and the results indicated that the mechanic properties can be significantly increased with the addition of functionalized-TiO₂.The comprehensive properties of the PP/PA6/TiO₂ nanocomposites will achieve their maximum with 3 phr functionalized-TiO₂ and 5 phr compatibilizer of PP-g-MAH.Compared with the uncompatibilized PP/PA6 blends,the tensile strength,notched impact strength and flexural strength of the PP-g-MAH compatibilized PP/PA6 blends with 3 phr of TDI-functionalized TiO₂ have increased 50.55%,71.84%and 52.58%,respectively.Scanning electron microscopy (SEM) and TEM were used to assess fracture surface morphology and dispersion of the TDI-functionalized TiO₂,respectively.Owing to the isocyanate(—NCO) at the TDI-functionalized TiO₂ surface can react with the—NH₂ or carboxyl groups of PA6 during melting blend,i.e.there are portions of PA6 will be grafted onto the nanoparticle surface,SEM and TEM micrographs showing that PA6 particles are uniformly distributed in the continuous PP phase and the functionalized-TiO₂ are preferentially located in the PA6 phase and the interface of PP and PA6 phase.In addition,it was found that the PA6 domain size would decrease with the incorporation of functionalized-TiO₂ and PP-g-MAH,which indicated they have strong compatibilizing effect on the immiscible PP/PA6 blends.In the presence of PP-g-MAH,the mechanical properties of PP/PA6 based nanocomposites filled with functionalized-TiO₂ will be further improved.The isothermal and non-isothermal crystallization and melting behavior of PP/PA6 based nanocomposites were investigated by differential scanning calorimetry(DSC).The Avrami equation was used to describe the isothermal crystallization kinetics.It was found the TiO₂ nanoparticles act as effective nucleating agents,the crystallization rate of PP and PA6 in the uncompatibilized PP/PA6 based nanocomposites is increased.The TiO₂ nanoparticles have less influence on the isothermal crystallization of PP phase in PP-g-MAH compatibilized nanocomposites. However the TiO₂ nanoparticles play an important role in the isothermal crystallization behavior of PA6 phase.Owing to portions of PA6 chains were grafted at the TiO₂ surface,which hinder the motion of PA6 chains, incorporation of TiO₂ nanoparticles result in higher isothermal crystallization activation energies phase and lower crystallization rate of PA6.All PP phases exhibit single melting endotherms in the as-prepared nanocomposites isothermally crystallized,however PA6 phases exhibit double melting endotherms at higher crystallization temperature and triple melting endotherms at lower crystallization temperature.The increased melting temperatures forâ… andâ…¡peaks of PA6 phase can be attributed to the nucleation of TiO₂,which resulted in perfect PA6 crystal. Melting temperature forâ…¢peak did not change with the variable isothermal crystallization temperature,which can be attributed to melting of the more stable crystal of PA6.The multiple melting endotherms are mainly caused by the recrystallization of PA6 spherulites with different crystal sizes and perfection during heating.The non-isothermal crystallization and melting behavior of PP and PA6 phase were investigated by DSC.The results show the Avrami index is higher than two,which indicated the non-isothermal crystallization process is complex.Owing to heterogeneous nucleation of TiO₂,non-isothermal crystallization of PP and PA6 phase began at higher temperature. However,the TiO₂ nanoparticles hinder the growth of PP and PA6 crystals and then lead to low crystallization rate.The crystallization activation energies of PP and PA6 phase decrease in the presence of low TiO₂ content.However,the crystallization activation energies of PA6 in the PP-g-MAH compatibilized nanocomposites increased with the incorporation of TiO₂.Crystallinity of PP and PA6 is increased with the incorporation of TiO₂ nanoparticles;however,they increased at first and then decreased with increase of cooling rate.This phenomenon can be explained as follows:the TiO₂ nanoparticles have two effects on the PP and PA6 phase,i.e.they act as effective nucleating agents for PP and PA6 phase,on the other hand the existence of the TiO₂ and the interaction between the nanoparticle and blends hinder the motion of the polymer chains.The two effects lead to the observed change of crystallinity with the increase of cooling rate.The PA6 phase in the non-isothermally crystallized sample exhibits multiple melting endotherms,which can be attributed to the different crystalline structures.The additions of small amount of TiO₂ nanoparticles make melt viscosity of PP/PA6 based nanocomposites decrease and also make non-newtonian index(n) of the PP-g-MAH compatibilized nanocomposites increase,however the n will decrease with increase of TiO₂ content,which favors the enhancement of pseudoplastic property. Flow activation energy of the PP-g-MAH compatibilized nanocomposites decrease with the incorporation of small amount of TiO₂ nanoparticles and the sensitivity of melt viscosity to temperature decreases.Owing to the homogeneous dispersion of TiO₂ nanoparticles in polymer blends,the TiO₂ nanoparticles have lubricating effect on the matrix polymer,which was the reason of the observed phenomenon.The storage(G') and loss moduli(G") and complex viscosity(η^*) are resulted from the dynamic frequency.All parameters increased monotonically in the entire frequency range with the addition of TiO₂ nanoparticles into the PP/PA6 blend,which indicated that the TiO₂ nanoparticles give the matrix polymer good elastic and viscous.The as-prepared PP/PA6 based nanocomposites have strong antimicrobial abilities against bacillus subtilis,staphylococcus aureu and escherichia coli.The average efficiency of antibacterial properties is over 90%within 2.0 h.Thermal stability of the PP/PA6 based nanocomposites was investigated by TGA and the result showed the TiO₂ nanoparticles favor the enhancement of thermal stability.In addition,the theoretical weight loss rate of the PP/PA6 based nanocomposites is equal to the actual weight loss rate at the range of error,which indicated that the nanoparticles are uniformly dispersed in the polymer matrix.