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The decision to recycle polymers is by no means straightforward. In some instances, recycling polymers can lead to more energy usage and more pollution than merely disposing of them in [...]

Improvements in Young's modulus and strength (tenacity) of poly(ethylene terephthalate) (PET) fibers were obtained by drawing unoriented nanocomposite filaments containing low concentrations (< 3 wt%) of various organically modified montmorillonites (MMTs) in a second step at temperatures above the glass transition. Prior to melt spinning, solid-state polymerization was used to rebuild lost molecular weight, due to MMT-induced degradation, to a level suitable for producing high strength fibers. Greater improvements in mechanical properties occurred when the MMT stacks were intercalated with PET. A nominal 1 wt% loading of dimethyl-dehydrogenated tallow quaternary ammonium surface modified MMT in drawn PET fiber showed a 28% and 63% increase in Young's modulus and strength, respectively. Relative to an unfilled PET fiber, these results surpassed the upper bound of the rule of mixtures estimate and suggested that both the type of surface modification and concentration of MMT affect the degree of PET orientation and crystallinity. Furthermore, drawability above [T.sub.g] and elongation at break increased upon the addition of organically modified MMT to unoriented PET fibers, which was a key distinction of this work from others examining similar systems. POLYM. ENG. SCI., 50:2205-2215, 2010. [C] 2010 Society of Plastics Engineers, INTRODUCTION Over a decade of research has shown the potential of polymer nanocomposites to become one of the most significant engineering materials with a number of immediate applications (1), (2). [...]

The effect of sparse long chain branching, LCB, on the shear step-strain relaxation modulus is analyzed using a series of eight high-density polyethylene (HDPE) resins. Strains of 1 to 1250% are imposed on materials with LCB content ranging from zero to 3.33 LCB per 10,000 carbon atoms. All materials are observed to obey time-strain separation beyond some characteristic time, [τ.sub.k]. The presence of LCB is observed to increase the value of [τ.sub.k] relative to the linear resin. The behavior of the relaxation modulus at times shorter than [τ.sub.k] is investigated by an analysis of the enhancement seen in the linear relaxation modulus, G°(t), as a function of strain and LCB content. This enhancement is seen to (1) increase with increasing strain in all resins, (2) be significantly larger in the sparsely branched HDPE resins relative to the linear HDPE resin, and (3) increase in magnitude with increasing LCB content. The shape and smoothness of the damping function is also investigated. The finite rise time to impose the desired strain is compared to the Rouse relaxation time of linear HDPE resins studied. Sparse LCB is found to increase the magnitude of the relaxation modulus at short times relative to the linear resin. POLYM. ENG. SCI., 50:1424-1432, 2010. [C] 2010 Society of Plastics Engineers, INTRODUCTION Step-strain tests are used to determine the strain dependence of the relaxation modulus. These tests are defined by a sudden shearing displacement of a fluid at rest to some [...]

The purpose of this study is to determine under what conditions it is possible to use [CO.sub.2] to plasticize and, thereby, reduce the viscosity of an acrylonitrile (AN) copolymer in an extrusion process and render it melt processable. To assess whether it was possible to absorb adequate amounts of [CO.sub.2] in short residence times by injection into a single screw extruder, a slit-die rheometer was attached to the end of the extrusion system for the purpose of directly assessing the viscosity reduction. A chemorheological analysis was performed on 65 and 85% AN copolymers to establish the temperature at which the 85% material would be as stable as the melt-processable 65% material at its recommended extrusion temperature. This, coupled with studies correlating the degree of [T.sub.g] and viscosity reduction with the amount of absorbed [CO.sub.2], and comparison to previous data obtained in batch processes allowed one to predict conditions for melt extrusion of the 85% AN. Preliminary studies using a pressurized chamber attached to the exit of the die allowed one to assess the conditions under which suppression of foaming is possible. POLYM. ENG. SCI., 49:1990-2004, 2009. © 2009 Society of Plastics Engineers, INTRODUCTION Fibers based on acrylonitrile (AN) copolymers having AN content of 85 mol% or greater are typically spun via a solution spinning process to avoid the intramolecular cyclization and intermolecular [...]

In this study, a benign process was used to successfully produce low density foam from poly(arylene ether sulfone) (PAES). Both carbon dioxide ([CO.sub.2]) and water as well as nitrogen and water were used as physical blowing agents in a one-step batch process. A large amount of blowing agents (up to 7.5%) was able to diffuse into the PAES resin in a 2-h saturation time. Utilizing water and [CO.sub.2] as the blowing agents yielded foam with better properties than nitrogen and water because both the water and [CO.sub.2] are plasticizers for the PAES resin. PAES foam produced from [CO.sub.2] and water had a large reduction in foam density (~80%) and a cell size of ~50 µm, while maintaining a primarily closed cell structure. The small cell size and closed cell structure enhanced the mechanical properties of the foam when compared with the PAES foam produced from nitrogen and water. The tensile, compressive, and notched izod impavt properties of the PAES foams were examined, and the compressive properties were compared to commercially available structural foams. With reduced compression strength of 39 MPa and reduced compression modulus of 913 MPa, the PAES foam is comparable to polyetherimide and poly(vinylchloride) structural foams. POLYM. ENG. SCL., 49:44-51. 2009. [C] 2008 Society of Plastics Engineers, INTRODUCTION Polymeric foams are one important class of lightweight materials under investigation because of their high strength to weight ratio. Polymeric foams can also posses other attractive features such as [...]

The semi-hyperbolic (SHPB) die with and possibly without wall lubrication has been proposed as a device for measuring the elongational viscosity of polymeric fluids. Using numerical simulation under the condition of complete wall slip, it was found for two polyethylenes (LDPE and LLDPE) that the calculated elongational viscosity values agreed well with strain-averaged values, , obtained from independent measurements in stretching type rheometers. This is in agreement with the original hypothesis of Everage and Ballman (E-B). Numerical simulations showed that the Baird and Huang (B-H) approach for calculating , which accounts for the shear stress due to geometric considerations in the presence of complete slip, agreed with data better than did the E-B approach. Numerical simulations using varying degrees of wall slip indicated that reasonable values of could be obtained using the B-H approach with wall slip levels which could be most likely reached using a coating such as a flouroelastomer. The numerical simulations provided an explanation as to why the elongational viscosity values determined in the SHPB die for resins such as LDPE, which are extensional-strain hardening, are less sensitive to wall slip than non-strain-hardening resins such as LLDPE.

The Materials Institute and the Department of Chemical Engineering Virginia Tech, Blacksburg, Virginia The concept of the fuel cell in which electricity and water are generated from the oxidation/reduction of [...]