Cross-thickness vibration welding of polycarbonate,polyetherimide, poly(butylene terephthalate), and modified polyphenylene oxide

In vibration welding of thermoplastics, frictional heat generated by vibrating two parts under pressure, along their common interface, is used to effect welds. In the normal, well-understood mode, the vibratory motion is along the weld seam, which is at right angles to the thickness direction for straight boundaries. But in many applications, such as in the welding of closed seams of box-like parts, this vibratory motion occurs in the part-thickness direction, so that a portion of the molten layer along the seam is exposed to the ambient air during each vibratory cycle. The resulting reduction in temperature can affect weld quality. The process phenomenology and the weld strengths of such cross-thickness vibration-welded butt joints are investigated for four neat resins. Weld amplitudes and weld pressures are shown to affect the strengths of 120-Hz welds differently. It is shown that strengths on the order of the strengths of the neat resins can be achieved in 250-Hz butt welds.     

The vibration welding of poly(methyl methacrylate) to itself and to polycarbonate,poly(butylene terephthalate), and modified poly(phenylene oxide)

The weldability of poly(methyl methacrylate) (PMMA) to itself and to polycarbonate (PC), poly(butylene terephthalate) (PBT), and modified poly(phenylene oxide) (M-PPO) is assessed through 120 and 250 Hz vibration welds. Weld strengths equal to those of the base resin have been demonstrated in welds of PMMA and M-PPO to themselves. In welds of PMMA to PC and to M-PPO, weld strengths equal to those of PC and M-PPO, respectively, have been demonstrated. PMMA does not weld well to PBT; the highest weld strength obtained was 21% of the strength of PBT resin.     

High-Temperature large-strain behavior of polycarbonate,polyetherimide and poly(butylene terephthalate)

A noncontacting experimental procedure has been used for characterizing the high-temperature large-strain uniaxial behavior of polycarbonate (PC), polyetherimide (PEI), and poly(butylene terephthalate) (PBT), through controlled tests on flat specimens cut from extruded sheet. While each of these polymers exhibits stable necking over a broad temperature range, the transition to the necked state is shown to be more gradual at higher temperatures, resulting in a less sharply defined neck transition region during the drawing process. These trends in necking behavior, and other phenomena such as double necking, which only occur at high temperatures, are illustrated through contour plots of the Cauchy-Green deformation tensor. Elevated temperature true-stress versus stretch data are given for each of these polymers.     

The vibration welding of poly(phenylene oxide)/poly(phenylene sulfide) blends

The weldability of three blends of poly(phenylene oxide) and poly(phenylene sulfide), each with a different level or type of impact modifier, is assessed through 120 and 240 Hz vibration welds. The type of impact modifier is shown to have a large effect on the strength and ductility of welds. Weld strength in these blends is shown to be sensitive to the weld frequency; higher weld strengths are attained at the higher weld frequency. In these three blends, maximum relative weld strengths of about 70%, 85%, and 87% have been demonstrated at a weld frequency of 240 Hz. The highest weld strength in each of these three blends is achieved at different weld pressures.     

Interpretation of intrinsic viscosity/temperature data for solutions of poly(phenyl acrylate) and poly(ethylene oxide)

Measured intrinsic viscosities ([η]) at several temperatures (T) within the interval 280–350 K have been found to increase with T for solutions of poly(phenyl acrylate) (PPA) in ethyl lactate. A decrease of [η] with T was observed for aqueous solutions of poly(ethylene oxide) (PEO) at several temperatures within the range 276–358 K. The results have been treated on the basis of eight excluded volume theories, among which the best consistency was afforded by those of Kurata-Stockmayer-Roig, Fixman, and Stockmayer (Padé). These yielded values of ?3.4 × 10^?3 to ?4.7 × 10^?3 deg^?1 and ?0.9 × 10^?3 to ?2.4 × 10^?3 deg^?1 for the temperatur coefficient of the unperturbed dimensions of PPA and PEO, respectively. The derived θ-temperatures were 287 K as the upper critical solution temperature for PPA in ethyl lactate and 365–382 K as the lower critical solution temperature for aqueous PEO.     

Modeling of poly(phenylene oxide) reactors

A simple model is presented for the polymerization of poly(phenylene oxide) (PPO) in the presence of mass-transfer limitations. The mass balance and moment equations for this system compose a hierarchy of infinite ordinary differential equations. Closure conditions similar to those used for nylon 6 are used to truncate the set of moment equations. The rate constants are adjusted to achieve a reasonable fit between model predictions and one set of available experimental data on the variation of the number-average chain length (μ_n) with time. The monomer conversion and the polydispersity index (PDI) are predicted. The PDI of the entire macromolecular species is found to very with time in an interesting manner (a decrease is predicted with time during certain periods). This is due to the effect of mixing of two sets of macromolecular species present in the reaction mass having different concentrations, as well as different individual values of μ_n and PDI. Sensitivity results are reported to identify the important parameters and operating conditions. It is found that the values of μ_n are very sensitive to even small changes in the operating conditions which decrease the mass-transfer rates. © 1995 John Wiley & Sons, Inc.     

Morphology,nonisothermal crystallization behavior,and kinetics of poly(phenylene sulfide)/polycarbonate blend

The morphology and nonisothermal crystallization behavior of blends made of poly(phenylene sulfide) (PPS), with a amorphous polycarbonate (PC) were studied. The blend is found to be partially miscible by the dynamic mechanical thermal analysis (DMTA) and melt rheological measurements. The nonisothermal crystallization behavior of blend was studied by differential scanning calorimetry (DSC). The results show clearly that the crystallization temperatures of PPS component in the blend decrease with increasing of PC contents. The crystallization kinetics was then analyzed by Avrami, Jeziorny, and Ozawa methods. It can be concluded that the addition of PC decreases the PPS overall crystallization rate because of the higher viscosity of PC and/or partial miscibility of blend, despite of small heterogeneous nucleation effect by the PC phase and/or phase interface. The results of the activation energy obtained by Kissinger method further confirm that the amorphous PC in the partial miscible PPS/PC blend may act as a crystallization inhibitor of PPS. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis and characterization of poly(phenylene sulfide), poly(2-methylphenylene sulfide), and poly(2,6-dimethylphenylene sulfide)

A facile synthesis of poly(phenylene sulfide) (PPS), poly(2-methylphenylene sulfide) (PMPS), and poly(2,6-dimethylphenylene sulfide) (PDMPS) from the respective copper (I) bromothiophenoxides is described. Polymerization was effected in a 10:1 quinoline:pyridine mixture at atmospheric pressure and conditions optimized for the preparation of high-molecular-weight materials. The preparation of PPS in pyridine under pressure at 250°C has been investigated for comparative purposes. Yields and the properties of materials produced by solution polymerization are comparable to or better than those produced in the autoclave reaction. Properties have been investigated as a function of reaction time and molecular weight, and the deficiencies of the molecular-weight assessment methods are discussed. PMPS and PDMPS have been similarly studied and their properties evaluated. The use of heat of crystallization determinations for molecular-weight studies on PPS are described and critically evaluated.     

Melt viscosity increase during rheological testing of poly(phenylene sulfide)

Poly(phenylene sulfide) (PPS) made via the melt polymerization of p-diiodobenzene and sulfur has previously been reported to increase in melt viscosity with time during rheological testing. Analysis of the oligomer from cleavage of PPS chains at the disulfide bonds via solution in 1-chloronaphthalene demonstrated that the disulfide content of the polymer decreased with rheological testing time. DSC of the polymer before and after rheological testing in combination with the T_cc and T_m of the chain fragments after the dissolution/cleavage in 1-chloronaphthalene showed that many samples exhibited primarily chain extension rather than chain branching, whereas for many others, some degree of chain branching occurred. This is currently only qualitatively understood. Chain branching as the exclusive mechanism of melt viscosity increase during rheological testing appears untenable in light of the T_m, in particular, of the chain fragments and also the polymer prior to chain cleavage. © 1993 John Wiley & Sons, Inc.     

Blends of thermotropic polyester with poly(phenylene oxide)

A thermotropic liquid crystalline polymer (LCP) based on wholly aromatic copolyesters based on hydroxynaphthoic and hydroxybenzoic acid was melt-blended with a thermoplastic poly(phenylene oxide) by corotating twin screw extruder. Rheological properties, temperature transitions, dynamic and mechanical properties, and electron microscopy study have been performed. Rheological study indicated significant viscosity reductions with increasing LCP content leading to ease of processing. From the differential scanning calorimeter (DSC) and dynamic mechanical thermal analyzer results, these blends showed incompatibility for the whole range of concentrations. Mechanical properties were found to be slightly improved at low LCP and dramatically improved at above 50% LCP contents. In addition, impact strength was significantly increased up to two times after adding 10% LCP into the matrix. The morphology of blends was affected by composition. Droplets and stubby fibrils structures caused lower tensile strength, whereas fibrillar structure improved this property.     

Molecular weight determination of poly(phenylene sulfide ether)

Poly(phenylene sulfide ether) and poly(phenylene sulfoxide ether sulfide ether) (PPSOESE) were successfully prepared and their structures were proved by several analytical techniques in the present work. The molecular weight (MW) of PPSOESE, a soluble polymer in common organic solvent at room temperature, was determined by gel permeation chromatography. Based on the conversion reaction of the two polymers, the MW of PPSE was calculated and correlated with its intrinsic viscosity. As a result, the Mark‐Houwink equation for PPSE was concluded. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Vibration welding of thermoplastics. Part IV: Strengths of poly(butylene terephthalate), polyetherimide,and modified polyphenylene oxide butt welds

In vibration welding of thermoplastics, frictional work done by vibrating two parts under pressure, along their common interface, is used to generate heat to effect a weld. The main process parameters are the weld frequency, the amplitude of the vibratory motion, the weld pressure, and the weld time or weld penetration.; The effects of these parameters on weld quality were systematically studied by first butt welding thermoplastic specimens under controlled conditions, over a wide range of process parameters, and by then determining the strengths and ductilities of these welds by tensile tests. The three thermoplastics investigated are poly (butylene terephthalate), polyetherimide, and modified polyphenylene oxide. Changes in the weld pressure are shown to have opposite effects on the strengths of polyetherimide and modified polyphenylene oxide welds; Also, the weld frequency is shown to have a significant effect on the weldability of polyetherimide. The weldability data for these three thermoplastics are compared with data for polycarbonate. Under the right conditions, the strengths of butt welds in these materials are shown to equal the strength of the virgin polymer.     

Gas transport and structural features of sulfonated poly(phenylene oxide)

The effect of ionomer structure on gas transport properties of membranes was investigated. For this purpose physical and transport properties of poly(phenylene oxide) (PPO) and its sulfonated derivative (SPPO) were compared. SPPO has a more rigid structure and a lower free volume, which determines low gas permeability and high permselectivity. Gas transport properties of two types of SPPO—PPO composite membranes with top layers prepared from solutions in methanol or N,N-dimethylacet-amide (DMA) were investigated. The use of SPPO solution in DMA leads to the formation of membranes with higher gas permeability. It was shown that DMA is a morphologically active solvent for SPPO. Strong complexes of SPPO with DMA are formed in solution and retained upon transition into the condensed state. The plasticizing effect of DMA on SPPO determines the high gas permeability of the membranes and is in agreement with their mechanical properties. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1439–1443, 1997     

Synthesis and microbial degradation of poly(2-methyl phenylene oxide)

The synthesis and biodegradation of poly(2-methyl phenylene oxide) was studied as an example of a synthetic polymer containing a biodegradable aromatic backbone. Polymer prepared with cuprous 2,2-isopropoxy ethyl pyridine catalyst demonstrated good blending properties with polystyrene. In soil experiments, the homopolymer degraded readily with over 50% reduction in 40 days. No. oligomeric intermediates were observed by gel permeation chromatography, suggesting degradation by cell-associated enzymes. © 1993 John Wiley & Sons, Inc.     

Synthesis of poly(phenylene acetylene) from poly(phenylene vinylene)

Summary The objective of this work was to prepare films of poly(phenylene acetylene) from films of a precursor polymer, namely poly(a, a-dibromoxylylene). This polymer was obtained by selective bromination of the vinylene groups of poly(phenylene vinylene) films in bromine/CHCl₃. Pyrolytic dehydrobromination of the brominated films under argon atmosphere gave dark yellow films which showed about 65 wt% of desired phenylene acetylene units.     

On the single-point determination of intrinsic viscosity

In the present paper we have analytically derived a single-point equation for determining the intrinsic viscosity of a polymer. It is observed that the proposed equation gives a much better agreement with the extrapolated value of [η] over a wide range of concentration for good as well as poor polymer–solvent systems.