| The hydrogenation of benzene ring is an effective way to remove the toxicity of phthalate plasticizers. The Di-iso-nonyl phthalate (DINP) plasticizer has been changed into Di(isononyl) cyclohexane-1,2-dicarboxylate (DINCH) overseas in this way. But in our country, the study of hydrogenation of widely used Di-2-ethylhexyl phthalate (DOP) plasticizer has just begun. In this article, we chose DOP and its hydrogenated products, Di(2-ethylhexyl) cyclohexane-1,2-dicarboxylate (DEHHP). We combined experiments, such as NMR, rheology, FTIR and DSC, and theoretical calculation, to study the structures, interactions and mobility of these two plasticized PVC systems. Furthermore, we also compared their curing conditions and mechanical performance, and confirmed the feasibility of DEHHP.By the red shift of carbonyl peak in FTIR spectra, the interactions between PVC and phthalate plasticizers were confirmed to be in form of electrostatic attraction. One end of this interaction is carbonyl oxygen. We also used theoretical calculation to simulate two possible initial states of interacted molecules. We compared the binding energies of two final states, and compared the calculated displacement with the real displacement of carbonyl peak in FTIR spectra, and confirmed that the interaction is in form of C-H...O=C hydrogen bond complex with a forcipate structure.On the basis of that, by combining experiment and theoretical calculation, we found that the intermolecular interaction in PVC/DEHHP system is much stronger than in PVC/DOP system. By Low-Field 1H NMR technology, we combined MSE and Hahn Echo pulse sequences, characterized the T2 relaxation times of different components and their distributions of two plasticized systems. Then we got the phase diagram of mobility, in which the most important difference was that a PVC chain could restrict much more DEHHP molecules than DOP. The displacement amplitude of carbonyl peak in FTIR spectra also showed that the hydrogen bond in PVC/DEHHP is stronger than that in PVC/DOP. Theoretical calculation results indicated that the number of pre-complexes in DEHHP, which could form hydrogen bond with PVC, is over twice as that in DOP. The binding energy of PVC/DEHHP complex is also larger than that of PVC/DOP one. The theoretical calculation results supported the experiments very well. They confirmed and elucidated the reason of stronger interaction resulting from hydrogenation.We studied the change of solute-solvate interaction in gel-sol transition of PVC/DEHHP and PVC/DOP systems. We determined the temperature gel points by study their rheology behavior. The temperature gel point of PVC/DEHHP is much higher than PVC/DOP, which showed that the interaction in PVC/DEHHP becomes smaller than PVC/DOP at high temperature. Low-Field 1H NMR results indicated that the number of hydrogen bonded complexes decreased as temperature increasing. And the number in PVC/DEHHP decreased much faster so that it was smaller than that in PVC/DOP. On the other side, we also determined the concentration gel points at room temperature. In consistent with temperature gel point, the concentration gel point of PVC/DEHHP is lower than that of PVC/DOP, which showed that at low PVC concentration, the interaction in PVC/DEHHP was weaker than that in PVC/DOP. Molecular dynamics results showed that when PVC concentration decreased from 30 wt% to2 wt%, the number of hydrogen bond also decreased rapidly. The experiment and simulation results confirmed each other, and showed that decreasing concentration and increasing temperature had the same influence on the interaction. They both made the molecular thermal motion more quickly, furthermore made the hydrogen bond destroyed. So the solute-solvate interaction was weaken in this way. And the hydrogen bonds in PVC/DEHHP gels were more easily influenced than that in PVC/DOP ones. The Low-Field 1H NMR technology and rheological method could be combined and be an effect way to characterize the gelling systems.We used DSC and FTIR to study the crystallization behaviors of i-PS freeze-extracted from semidilute solution in DEHHP, DOP and 1-chlorotetradecane. Because of the large molecular size of solvent, the chain entanglement of freeze-extracted i-PS was fewer, and the chains arranged in an ordered 31 helix conformation to form an metastable state. At the temperature about 10℃ higher than Tg, the ordered 31 helix structure could easily transferred to a highly homogeneous crystalline state. Also it could promote the homogeneous crystallization of amorphous i-PS. The homogeneous crystals would melt at 160℃ with an obvious endothermic peak on DSC curve. When all crystals melted completely above 240℃, the 31 helix with characteristic length m=10 would disappear quickly. But the amount of the 31 helix with characteristic length m=6 decreased slowly and still remained some at higher temperature. The short 31 helix structures would promote the ordered arrangements of i-PS chains upon cooling. Then the long 31 helix structures would be recovered and metastable state would be formed again.We simulated the real processing situation to study the curing conditions and mechanical performance of DEHHP and DOP, and confirmed the feasibility of DEHHP. We used DSC to determined the glass transition temperatures, and found that DEHHP plasticized PVC resins have lower Tg than DOP ones. It showed that the plasticizing efficiency of DEHHP is higher than that of DOP. Under the same curing conditions, we measured the situ torque values and the results showed that in melting state, DEHHP plasticized PVC resins has better flowability. DMTA was used to compare their mechanical performance and their breaking elongations were also measured. The results showed that DEHHP is more suitable to be used in soft materials. Its production showed better elasticity and tensile property. The differences between the two plasticizers in curing and mechanical performance could be well elucidated by the intermolecular interaction. |
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