Plasticizing Modification Of PVC And Study Of Miscibility Of Relative Polymer Blends

Polyvinylchloride (PVC) is one of the most important plastic materialsthroughout the world. Due to its inherent fragileness, low toughness and high meltviscosity, plasticization has been a great task for decades. Generally, traditionalplasticizers (phthalates, phosphates, etc.) are small molecules, which could easilyleave the plastic surface into atmosphere or organic bodies by means of migration,extraction or evaporation. The loss of plasticizers results in the decrease in toughnessand shortening of the life time of the material. Meanwhile, environmental pollutionand harm to human bodies have increasingly become a hot issue.In the light of such problems of traditional plasticizers, we have prepared a newpolymeric plasticizer for PVC, polyepichlorohydrin (PECH). Compared with traditionalplasticizers, polymeric plasticizers have long chains which can form great amounts ofentanglements and physical association by dipole interactions of C-Cl bonds. Thesetwo points can inhibit the migration and extraction of plasticizers to a large extent.Furthermore, high molecular weight could help to reduce its evaporation.In the current thesis, the cationic polymerization was employed to synthesize aseries of PECH. We also used gel permeation chromatogram (GPC) and differentialscanning calorimetry (DSC) to determine the molecular weight (1000to4000g/mol)and glass transition temperature (-50℃to-40℃) of PECH. PVC/PECH blends wereprepared by industrial blending methods and pressed into plastic sheets. Thermalgravity analysis (TGA), tensile tests and dynamic mechanical analysis (DMA) wereutilized to investigate the thermal stability, stress-strain relationship, glass transitiontemperatures of blending materials, and so forth. Since there is some structuralsimilarities between PECH and PVC, the degradation processes are also alike (the1stdegradation process for PVC), both dehydrochloronation. Sharing similardecomposition temperatures, PECH can not harm the thermal stability of PVC. PECHis a kind of viscous fluid and can lead to the reduction in modulus and promotion in ductibility. As PECH content increases, there is a great enhance in elongation, anddepress in yield and break strength. DMA results show that the blends arehomogeneous when weight percent of PECH is below20%, while phase separationtakes place when above20%(PVC-rich phase and PECH-rich phase). Thisphenomenon is interpreted as the differences in viscosity and chain softness of thetwo polymers. There are large quantities of chlorine atoms on the main chain of PVC,which offer strong dipole interactions between macromolecules, so PVC exhibits arelatively strong toughness. On the contrary, for PECH molecules chlorine atoms lieon side chains which can not provide enough interactions. Moreover, there is anoxygen atom in each PECH unit which makes molecules much softer. Therefore, thetwo polymers are only partially compatible.For PVC/PECH system, viscometric measurements were performed to evaluatethe miscibility. Solvent is introduced into the system, which is the most markedcharacteristic of this method. There have been quite a lot reports before on thesolvent effect on polymer interactions. In our experiments, three solvents,tetrahydrofuran (THF), dimethylformamide (DMF) and methyl ethyl ketone (MEK),were chosen and viscosity of PVC/PECH/solvents system was studied. Some theoriesusing viscometric means on miscibility investigation were introduced and a finalconclusion of miscibility sequence was put forward as: THF>DMF>MEK. Thephenomenon is essentially an issue of solubility parameters, and we employedHansen Theory to explain it. Also, the total and partial solubility parameters of PECHwere calculated through viscometric method and Hansen Theory.To promote the miscibility of PVC/PECH, the third component, polycaprolactone(PCL), was added to the blends as the compatibilizer. The three polymers were mixedfrom THF by different ratios, and DSC was used to characterize the thermalproperties. According to the number of Tg, homogeneity was speculated and thethree-phase diagram was drawn. Since PCL strongly crystallizes, the crystallizationkinetics of the blends was also studied, including crystallinity, crystallizing speed anddimension, equilibrium melt temperature, etc.