Elisabeth E. C. Monteiro

Mechanical properties evaluation of PVC/plasticizers and PVC/thermoplastic polyurethane blends from extrusion processing

Abstract Mechanical and processing properties of blends of poly(vinyl chloride) (PVC) with di-isodecyl phthalate (DIDP) and thermoplastic polyurethane (TPU) were compared with di-2-ethylhexyl phthalate (DOP). The influence of processing conditions on the mechanical properties was studied by changing the content of the additives and using different twin screw speeds. The mechanical properties (tensile strength, modulus, and energy) of PVC/DIDP presented the same behaviour as PVC/DOP at all concentrations. The mechanical characteristics of PVC/DOP and PVC/DIDP show that these systems are probably affected by the speed of the twin screw. Polyurethane blends exhibit better structural properties compared to the other plasticizers. The twin screw speed exhibited no influence on the stress–strain property profile of the PVC/TPU blends. The results indicate a minor influence on the decrease of PVC properties when the plasticizer used is a TPU.

Study of the effect of gamma irradiation on polyolefins—low-density polyethylene

Many of the physical, chemical and utility properties of polymer materials can be altered by means of high energy radiation such as gamma-rays, neutrons and electron beams. In the present work the exposure to gamma radiation of a bulk virgin low density polyethylene (LDPE) was carried out at various doses up to 2000 kGy. The study of the irradiation effects on the material properties has been make by different methods in an integrated way. The experimental data indicate that the gel content, the hardness and the yellowing increase with gamma radiation dose and that the LDPE gamma irradiation process involves crosslinking at lower doses and chain scission at higher doses. The final results show the reliability of gamma radiation as a practical method for the control of long-term properties.

NMR study of plasticized PVC

Samples PVC plasticized by di-isobutylphthalate and di-2-ethylhexylphthalate, with plasti- cizer content varying up to 180 parts per hundred, have been examined using solid-state tH- and t3C-NMR. Proton spin-lattice relaxation times in both the laboratory and the rotating frames were measured, with analysis into multi-exponential components where necessary. Cross-polarisation magic- angle spinning ~3C spectra have also been obtained, including variation with contact time. The data are discussed in terms of the domain structure of the samples at the microscopic level and of the role of the plasticizer.

NMR studies of PVC molecular mobility

Abstract The molecular mobility of a polymer in the solid state can be determined by NMR relaxation measurements. The analysis of proton spin-lattice relaxation time (T 1 H) and proton spin-lattice relaxation time in the rotating frame (T 1 H ϱ ), allow information to be obtained about the behaviour of homogeneous samples. The response of this behaviour can be extracted by NMR solid state techniques such as: magic-angle spinning (MAS), variable contact time, inversion-recovery, spin-locking, delayed contact time and cross polarization-MAS.

Phase segregation and viscoelastic behavior of poly(ether urethane urea)s

Two poly(ether urethane urea)s were synthesized, one based on poly(pro- pylene glycol) and another one on poly(tetramethylene glycol). Hydrogenated MDI was used as the diisocyanate and propylenediamine as the chain extender. The diisocya- nate : polyol : diamine molar ratio was 2 : 1 : 1 for both copolymers. Data from stress- relaxation tests were adjusted to a power law and to the Kohlraush-William-Watts equation. Phase separation and viscoelastic behavior were correlated through the calcu- lation of the time-relaxation spectrum, the steady-state tensile compliance, and the tensile viscosity. The results indicated that the material based on poly(tetramethylene glycol) was the more effectively phase-segregated block copolymer. q 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2227-2236, 1997

Analysis of natural cis- and trans-polyisoprene mixtures by near-infrared spectrophotometry

Natural trans- and cis-polyisoprenes and mixtures of these polymers were analysed by near-infrared spectrophotometry. The relative absorptivity data versus the amount of isomers in synthetic mixtures showed a non-linear behaviour. The results are compared with literature data from polyisoprenes extracted from other vegetal species.

Miscibility of PVA/EVA systems by viscometry

Viscometric data were applied to characterize the miscibility of poly(vinyl chloride) (PVC)/poly(ethylene-co-vinyl acetate) (EVA) mixtures using six samples of EVAs with different vinyl acetate content in the copolymer. Relative viscosity vs composition plots showed the imiscibility of PVC/EVA 31 and PVC/EVA 41 blends. The variation of the reduced viscosity, ηsp/C with the concentration, C, has been studied for 50:50 by weight blends of PVC/EVA 45, PVC/EVA 45A, PVC/EVA 50 and PVC/EVA 70 in tetrahydrofuran at 25°C. The presence of a sharp crossover and a consequent reduction of slope in ηsp/C vs C plots showed that these systems are miscible for a concentration range which corresponds to the regime of dilute solution.

Surface phenomena and polymer miscibility of PVC/EVA blends

Abstract The study of the interface in polymer blends gives a user full information about the thermodynamical miscibility of the system. The surface tension studies of the pure copolymers have shown that the acetate content plays the major role and this is also reflected in the interfacial tension of the PVC blends. The results show a direct relationship between the interface thickness and the vinyl acetate content in the EVA copolymer. Interaction parameter values show an inversely related correlation. Calculated values obtained from the appropriate equations have shown small discrepancies from experimental data. The Flory-Huggins parameters, theoretically calculated by using recent theories which suppose that the vitreous transition is a true transition, are in good agreement with the values obtained from calorimetric measurements. Thermal stability and the degradation process were also studied. The experimental data showed a relationship between the thermogravimetric curves and the degree of interaction in the mixtures as compared to pure polymers that are consistent with microscopy analysis. Kinetic parameters and life time data of the mixtures were also calculated.

Stress relaxation of thermoplastic polyurethanes monitored by FTIR spectroscopy

Abstract Stress relaxation of two poly(ether-urethane-urea)s was monitored using FTIR spectroscopy. Structurally, these block copolymers were the result of the reaction of 1 mol of a polyol [poly(propylene glycol) or poly(tetramethylene glycol)], 2 mol of 4-4′-dihexylmethane diisocyanate, and 1 mol of propylenediamine. FTIR spectra during relaxation showed that the copolymer based on poly(tetramethylene glycol) is more phase-segregated then the one based on poly(propylene glycol).

Thermal analysis and NMR studies of methyl methacrylate (MMA)–methacrylic acid copolymers synthesized by an unusual polymerization of MMA

Methyl methacrylate-methacrylic acid (MMA-MAA) copolymers were pre- pared from the polymerization reaction of the methyl methacrylate (MMA) monomer with concentrated nitric acid (65% HNO3) at different reaction times in the absence of other reagents in the reaction mixture. The hydrolysis degrees of the MMA-MAA (sodium salts) copolymers estimated by thermogravimetry (TG) corroborated the data obtained by chemical titration. By calorimetry (DSC), a relationship between the glass transition temperature (Tg) and the hydrolysis degree was obtained. The results pre- sented a deviation from linear behavior and it was related to the strength of the interactions involved in the copolymer chains. The equation that relates the glass transition temperature to the interaction parameter, x, for miscible binary polymer blends was applied for the MMA-MAA copolymers and demonstrated the composition dependence of x. The molecular mobility was determined by nuclear magnetic reso- nance (NMR) in the solid state and through the proton spin-lattice relaxation time in the rotating frame. The NMR data were in a good agreement with the results obtained by calorimetry.