| Nanometer zinc oxide?ZnO?is a new kind of inorganic filler with various functions.Polypropylene incorporated it can obtain many excellent properties.According to the structure,polypropylene can be classified into three types,namely,homogeneous polypropylene?PPH?,block copolymer polypropylene?PPB?and random copolymer polypropylene?PPR?.In this paper,the effect of different types of PP on the migration of nano-ZnO was studied from experimental and theoretical aspects,and their results were compared.The performances of 9 different kinds of films?b-PPH,b-PPB,b-PPR,ZnO-PPH,ZnO-PPB,ZnO-PPR,ZnO-PPH#,ZnO-PPB#,ZnO-PPR#?were tested.DSC analysis showed that the crystallinity of PP was changed by nano-ZnO,the crystallinity of PPH decreased from 88.6%to 74.7%,and the crystallinity of PPB and PPR increased slightly.The FTIR spectra showed that a new chemical bond could be formed between nano-ZnO and titanate coupling agent?HY13B?,and they both were dispersed as a physical form in the PP polymer.The content of nano-ZnO in the composite membrane was detected by ICP-OES combined with microwave digestion pretreatment,and the migration behavior was studied by reference to EU 10/2011 and GB 31604.The effects of temperature and time on the migration of nano-ZnO were consistent with the regular migration.There were differences in the migration rate between PP composite films with different types.The migration rate in PPH was much higher than that in PPB and PPR,while the migration rate in PPR was the lowest.Titanate coupling agent could not only reduce the loss of nano-ZnO in the preparation process of PP composite film,but also significantly inhibit the migration of nano-ZnO.The higher the concentration of acetic acid,the larger the migration of nano-ZnO.The linear relationship was good?R between 0.97910.9959?in the lower concentration interval.The migration of nano-ZnO was found to decrease rapidly with the increase of the number of cycles.It mainly concentrated in the first contact with the acetic acid solution,which accounted for more than 62.4%.The migration mechanism of Zn from different types of PP to 3%acetic acid solution is surface detachment and chemical dissolution,and the nanoparticles within the matrix are not easily moved out.Two phase molecular dynamics model was established based on the Material Studio system to simulate the diffusion movement of nano-ZnO clusters in three different types of PP.The simulation value(Dsim)of diffusion coefficients was1.147.15×10-7.The results demonstrate that the diffusion coefficient of the PR-Ac system was the smallest,and the diffusion coefficient of the PH-Ac and PB-Ac system were slightly larger.The diffusion coefficient of nano-ZnO was elevated with the increase of temperature.The high temperature could enhance the activity of polymer chain segment,enlarge the free volume,widen the fluctuation amplitude,and increase the space and opportunity that the cluster was able to access.The trajectories showed that nano-ZnO was moving from one space to the next and wriggling in the small area.The structure of the polymer chain affected the motion range of the nanocluster.At the same temperature,the range of motion trajectories was the widest in the PH-Ac system,the second in the PB-Ac system,and the smallest in the PR-Ac system.However,the model needs further improvement.By using Fick's second law to fit the experimental data,the experimental values of the diffusion coefficient(Dexp)were obtained.The determination coefficient of fitting curve by Matlab was 0.80530.9897,and the linear relationship was good.The established migration equation could be utilized to fit the experimental value,and Dexpxp was 1.94×10-145.39×10-10.The simulation value(Dsim)based on the molecular dynamics was far greater than the fitting value(Dexp)based on the experimental.The molecular dynamics model was not suitable for predicting the diffusion of nano-ZnO in PP,which grossly overestimated the diffusion coefficient.The reason might be that there were some defects in the force field or simulation system was too small scale to be near the real situation,but the simulation was feasible on qualitative and showed that the diffusion coefficient of nano-ZnO in the PPR was the minimum.At the same time,the distribution coefficient was predicted by the statistical thermodynamic model of Scatchard-Hildebrand,and it was found that the distribution coefficient of prediction was higher than the distribution coefficient of experimental measurement.Therefore,more factors need to be introduced to modify the model. |
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