Numerical simulation of reactive extrusion processes of PA6

To analyze the complicated relationships among the variables during the reactive extrusion process of polyamide 6 (PA6), and then control the chemical reaction and the material structures, the process of continuous polymerization of caprolactam into PA6 in a closely intermeshing co-rotating twin screw extruder was simulated by means of the finite volume method, and the influences of three key processing parameters on the reactive extrusion process were discussed. The simulated results of an example were in good agreement with the experimental results.

Free radical grafting of polyethylene with vinyl monomers by reactive extrusion

The free radical grafting of polyethylene with vinyl monomers by reactive extrusion was studied numerically. Numerical computation expressions of key variables, such as the concentrations of the initiator and polymer, grafting degree, average molecular weight and apparent viscosity, were deduced. The evolutions of the above variables were predicted by means of an uncoupled semi-implicit iterative algorithm. The monomer conversion monotonically increases with decreasing throughput or increasing initial initiator concentration; with increasing barrel temperature, the monomer conversion first increases then decreases. The simulated results are nearly in good agreement with the experimental results.

Preparation and chracaterization of novel graft copolymers of LLDPE

A series of novel fluorine surfactants, a, b, c, d, e and their acrylates, A, 13, C, D and E, were synthesized via poly( ethylene oxide) ( PEG) ( 200, 600, 1000, 2000, 5000) and perfluorooctane poly (ethylene oxide) ether as the main starting materials. Their chemical structures were characterized by means of FTIR and H-1 NMR. The surface activity and surface tension( y) of surfactants a, b, c, d and e were evaluated by maximum bubble pressure method. Surfactants A, 13, C, D and E were adopted as the grafting monomers of linear low density polyethere( LLDPE), and grafting reaction was carried out by melt reactive extrusion procedure. Their surface properties were characterized with measuring contact angle and XPS. It was found that the hydrophilic property of the graft copolymers was better than the palin LLDPE. Thermal properties of graft copolymers were studied by DSC. It was found that their crystalline temperatures of graft copolymers were faster than that of the plain LLDPE.

High-pressure sintering study of a novel hard material (W0.5Al0.5)C-0.5 without binder metal

A novel hard material of (W0.5Al0.5)C-0.5 has been successfully sintered under high-pressure (4.5 GPa). The influence of sintering time and temperature on the microstructure, Vickers microhardness and density of the as-prepared specimens are well described. Interestingly, sintering temperature has an amazing influence on the hardness, density and microstructure of the specimen while the sintering time does not. It is found that the most suitable sintering condition from our work is 1600 degrees C and 10 min under pressure of 4.5 GPa. The hardness and relative density of the as-prepared sample can reach 2340 kg mm(-2) and 98.62%, respectively. The cell parameters of the sintered specimen is found to be little smaller than that of the powder, which we propose is related to the high pressure.

Crystallization of mechanically alloyed amorphous W-Mg alloy under high pressure

Pure metal powder mixtures of W and Mg at the desired composition were milled in conventional high-energy ball mill, and amorphous alloy W50Mg50 was obtained after milling for 20 h. The structure evolution of elemental powder mixtures was studied following milling and subsequent high pressure and high temperature treatment. The amorphous alloy transform into a nanocrystalline material below 1050 degreesC at 4.0 GPa. On increasing the temperature, it transforms into a mixture of several new crystal phases under high-pressure condition. It also found that both mechanical alloying and high pressure treatment are the two necessary processes to form the nanocrystalline and the new phases.

Temperature and pressure dependence of phase separation of trans-decahydronaphthalene/polystyrene solution

The cloud-point temperatures (T-c1's) of ti-ans-decahydronaphthalene (TD)/polystyrene (PS, M-w = 270 kg/mol) solutions were determined by fight scattering measurements over a range of temperatures (1-16 degreesC), pressures (100-900 bar), and compositions (4.2-21.6 vol% polymer). The system phase separates upon cooling and the T-c1 was found to increase with the rising pressure for the constant composition. In the absence of special effects this finding indicates positive excess volumes. The special attention was paid to the demixing temperatures as a function of the pressure for the different polymer solutions and the plots in the T-volume fraction plane and P-volume fraction plane. The cloud-point curves of polymer solutions under changing pressures were observed for different compositions, demonstrates that the TD/PS system exhibits UCST (phase separation upon cooling) behavior. With this data the phase diagrams under pressure were calculated applying the Sanchez-Lacombe (SL) lattice fluid theory. Furthermore, the cause of phase separation, i.e., the influence of Flory-Huggins (FH) interaction parameter under pressure was investigated.

Kinetics study on melt grafting copolymerization of LLDPE with acid monomers using reactive extrusion method

Graft copolymerization in the molten state is of fundamental importance as a probe of chemical modification and reactive compatibilization. However, few grafting kinetics studies on reactive extrusion were carried out for the difficulties as expected. In this work, the macromolecular peroxide-induced grafting of acrylic acid and methyl methacrylate onto linear low density polyethylene by reactive extrusion was chosen as the model system for the kinetics study; the samples were taken out from the barrel at five ports along screw axis and analyzed by FTIR, H-1 NMR, and ESR. For the first time, the time-evolution of reaction rate, the reaction order, and the activation energy of graft copolymerization and homopolymerization in the twin screw extruder were directly obtained. On the basis of these results, the general reaction mechanism was tentatively proposed. It was demonstrated that an amount of chain propagation free radicals could keep alive for several minutes even the peroxides completely decomposed and the addition of monomer to polymeric radicals was the rate-controlled step for the graft copolymerization.

Neodymium oxide co-catalyzed melt free radical grafting of maleic anhydride onto co-polypropylene by reactive extrusion

Rare earth oxide, neodymium oxide (Nd2O3), CO-catalyzed melt grafting of maleic anhydride (MAH) onto co-polypropylene (co-PP) in the presence of dicumyl peroxide (DCP) was carried out by reactive extrusion. The experimental results reveal that the addition of Nd2O3 as a coagent leads to an enhancement in both MFR and the grafting degree of MAH, along with a simultaneous decrease in the gel content. When the Nd2O3 concentration is 6.0 mmol%, the increment of the grafting degree of MAH maximally is up to about 20% compared with the related system without adding Nd2O3, and the gel content decreases simultaneously to a very low level of about 3%. Attenuated total reflection FTIR (ATR-FTIR) indicates that the gel in the graft copolymers mainly arise from the cross-linking reaction between ethylene units of co-PP. A reasonable reaction mechanism has been put forward on the basis of our experimental results and other mechanisms reported in the literature. We also tentatively explain above results by means of synergistic effect between DCP and Nd2O3, which causes a higher concentration of the macroradical, in particular the tertiary macroradical.

Neodymium oxide-assisted melt free-radical grafting of maleic anhydride on isotactic-polypropylene by reactive extrusion

Rare earth oxide, neodymium oxide (Nd2O3), -assisted melt free-radical grafting of maleic anhydride (MAH) on isotactic-polypropylene (i-PP) was carried out by reactive extrusion. The experimental results reveal that the addition of Nd2O3 into reactive system leads to an enhancement of the grafting degree of MAH, along with an elevated degradation of i-PP matrix. When Nd2O3 content is 4.5 mmol %, the increment of the grafting degree of MAH (maximally) is up to about 30% compared with that of the related system without adding Nd2O3, while the severest degradation of i-PP matrix simultaneously occurs. On the basis of the reaction mechanism of PP-g-MAH proposed before, the sequence of beta-scission and grafting reaction is discussed in detail. It is found that, for the reactive system studied, most tertiary macroradicals first undergo beta-scission, and then, grafting reaction with MAH takes place at the new radical chain ends. The imported Nd2O3 has no effect on the aforementioned reaction mechanism, whereas it enhances the initiating efficiency of the initiator, dicumyl peroxide (DCP).

Pressure effects on the thermodynamics of trans-decahydronaphthalene/polystyrene polymer solutions: Application of the Sanchez-Lacombe lattice fluid theory

The cloud-point temperatures (T-cl's) of trans-decahydronaphthalene(TD)/polystyrene (PS, (M) over bar (w) = 270 000) solutions were determined by light scattering measurements over a range of temperatures (1-16degreesC), pressures (100-900 bar), and compositions (4.2-21.6 vol.-% polymer). The system phase separates upon cooling and T-cl was found to increase with rising pressure for constant composition. In the absence of special effects, this finding indicates positive excess volume for the mixing. Special attention was paid to the demixing temperatures as a function of pressure for different polymer solutions and the plots in the T-phi plane (where phi signifies volume fractions). The cloud-point curves of polymer solutions under different pressures were observed for different compositions, which demonstrated that pressure has a greater effect on the TD/PS solutions when far from the critical point as opposed to near the critical point. The Sanchez-Lacombe lattice fluid theory (SLLFT) was used to calculate the spinodals, the binodals, the Flory-Huggins (FH) interaction parameter, the enthalpy of mixing, and the volume changes of mixing. The calculated results show that modified PS scaling parameters can describe the thermodynamics of the TD/PS system well. Moreover the SLLFT describes the experimental results well.

Thermodynamical study on pressure-induced compatibility in UCST polymer-containing mixtures

The present calculations were performed on the basis of the Sanchez-Lacombe lattice fluid theory and the new combinatorial rules for block copolymer according to the experimental results on the pressure-induced compatibility in poly(ethylene oxide) (PEO) and poly(ethylene oxide-b-dimethylsiloxane) (P(EO-b-DMS)) mixtures with UCST behavior. The study on enthalpy, combinatorial entropy, vacancy entropy and Gibbs energy upon mixture shows that Sanchez-Lacombe fluid theory and the new combinatorial rules could describe the pressure-induced compatibility (PIC) of polymer mixtures with UCST behavior well.

Pressure-dependent glass-transition temperatures of poly(methyl methacrylate)/poly(styrene-co-acrylonitrile) blends

The pressure-dependent glass-transition temperatures (T-g's) of poly(methyl methacrylate) (PMMA)/poly(styrene-co-acrylonitrile) (SAN) blends were determined by pressure-volume-temperature (PVT) dilatometry via an isobaric cooling procedure. The Gordon-Taylor and Fox equations were used to evaluate the relationships between the T-g's and compositions of the PMMA/SAN system at different pressures. The relationships were well fitted by the Gordon-Taylor equation, and the experimental data for T-g positively deviated from the values calculated with the Fox equation. Also, the influence of the cooling rate (during the PVT measurements) on T-g was examined.

Abnormal pressure dependence of the phase boundaries in TL/PEO/P(EO-b-DMS) ternary mixtures

The cloud-point temperatures (T-cl's) of both binary poly(ethylene oxide) (PEO)-poly(ethylene oxide-b-dimethylsiloxane) [P(EO-b-DMS)] and ternary[toluene/PEO/P(EO-b-DMS)] systems were determined by light scattering measurements at atmospheric pressure. The phase separation behavior upon cooling in the ternary system has been investigated at atmospheric pressure and under high pressure and compared to the phase behavior in the binary system. The phase transition temperatures have been obtained for all of the samples. As a result, the pressure induces compatibility in the binary mixtures, but for the ternary system, pressure not only can induce mixing but also can induce phase separation.

Thermodynamics of phase behavior in PEO/P(EO-b-DMS) homopolymer and block co-oligomer mixtures under pressure

The cloud-point temperatures (T-cl's) of poly(ethylene oxide) (PEO) and poly(ethylene oxide)-block-polydimethylsiloxane (P(EO-b-DMS)) homopolymer and block-oligomer mixtures were determined by turbidity measurements over a range of temperatures (105 to 130degrees), pressures (1 to 800 bar), and compositions (10-40 wt.-% PEO). The system phase separates upon cooling and T-cl was found to decrease with an increase in pressure for a constant composition. In the absence of special effects, this finding indicates negative excess volumes. Special attention was paid to the demixing temperatures as a function of the pressure for the different polymer mixtures and the plots in the T-phi plane (where phi signifies volume fractions). The cloud-point curves of the polymer mixture under pressures were observed for different compositions. The Sanchez-Lacombe (SL) lattice fluid theory was used to calculate the spinodals, the binodals, the Flory-Huggins (FH) interaction parameter, the enthalphy of mixing, and the volume changes of mixing. The calculated results show that modified P(EO-b-DMS) scaling parameters with the new combining rules can describe the thermodynamics of the PEO/P(EO-b-DMS) system well with the SL theory.