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New extensional mixing elements (EME) for twin-screw extrusion were applied to compound glass fibers (GF), carbon fibers (CF) or polyethylene terephthalate fibers (PETF) reinforced polymer composites with polymer matrix of polypropylene (PP) or polyethylene oxide (PEO) and the resulting fiber degradation upon processing was evaluated and compared with compounding via shear flow-dominated kneading blocks (KB). Composites structures were characterized in terms of fiber length and distribution, and cumulative length ratio, at five locations along the mixing zone. Although significant fiber breakage was achieved for both configurations, it was markedly lower in composites processed using the EME, because whereas the high shear stress kneading motion in the KB degrades fibers significantly, fiber breakup is significantly minimized by the alignment induced by the EME prior to flow in the high-stress regions.

Poly(ethylene terephthalate) (PET) and polyamide (PA) are immiscible polymers, which requires the use of compatibilizers to stabilize the morphology and achieve acceptable property levels. Therefore, controlling the degree of dispersion, especially the size of the disperse PA droplets in the PET matrix is of paramount importance. This study aims to improve the mixing, i.e., minimize PA droplet size, in immiscible and compatibilized PET/PA and PET/Nylon-MXD6 (MXD6) blends by resorting to extension-dominated mixing in twin-screw extrusion (TSE). MXD6 is an aromatic polyamide similar in polarity to PET, so it is expected that it will blend more effectively than is the case with aliphatic nylon-6 and PET. Two screw configurations are used, a benchmark shear-dominated screw with kneading blocks (KBs) in an aggressive configuration, and an extension-dominated screw configuration with static mixers with hyperbolic C–D channels, recently developed by our group, in place of the KBs. The results show that the use of extensional mixing elements (EMEs) in place of KBs results in a significant decrease of both average and maximum droplet size for all blends, and up to more than one order of magnitude between the most extreme cases of the KB-processed immiscible blend and EME-processed compatibilized blends.

Surface roughness and sharkskin of extruded polymers, including blends are affected by the morphology and processing conditions. In this study, different effects on the roughness of the polymer blend extrudates were investigated. Co-continuous poly(ethylene) oxide/ethylene-vinyl acetate (PEO/EVA) blends with three different molecular weight (Mw) PEOs were compounded successfully. It was found that the better co-continuity of the structure and smoother surface were achieved for lower Mw PEO/EVA blend because of more effective stress transfer in the PEO phase. The effect of processing temperature was also studied with decreasing processing temperature reducing the surface roughness of the high Mw PEO/EVA blend, which was also achieved as a result of improved co-continuous morphology by adjusting the viscosity and elasticity ratio with shifting temperatures.

Sodium hydroxide was used as a base catalyst to reduce the flammability of poly(vinyl alcohol) (PVA) aerogels. The base-modified aerogels exhibited significantly enhanced compressive moduli, likely resulting in decreased gallery spacing and increased numbers of “struts” in their structures. The onset of decomposition temperature decreased for the PVA aerogels in the presence of the base, which appears to hinder the polymer pyrolysis process, leading instead to the facile formation of dense char. Cone calorimetry testing showed a dramatic decrease in heat release when the base was added. The results indicate that an unexpected base-catalyzed dehydration occurs at fire temperatures, which is the opposite of the chemistry normally observed under typical synthesis conditions.

Dense nanolipid fluid (DNLF) dispersions are highly concentrated aqueous dispersions of lipid nanocarriers (LNCs) with more than 1015 lipid particles per cubic centimeter. Descriptions of dense nanolipid fluid dispersions in the scientific literature are rare, and they have not been used to encapsulate drugs. In this paper we describe the synthesis of DNLF dispersions comprising ibuprofen using a recently described twin-screw extrusion process. We report that such dispersions are stable, bind ibuprofen tightly and yet provide high transdermal drug permeation. Ibuprofen DNLF dispersions prepared according to the present study provide up to five times greater flux of the pharmacologically active S-ibuprofen isomer through human skin than a commercially available racemic ibuprofen emulsion product. We demonstrate scaling up the twin-screw extrusion method to pilot production for a stable, highly permeating ibuprofen DNLF composition based on excipients approved by the US FDA for use in topical products as a key step towards development of a commercially viable, FDA approvable topical ibuprofen medicine to treat osteoarthritis, which has never before been accomplished.

Double-percolated thermally conductive polymer composites comprising of polypropylene (PP), poly (methyl methacrylate) (PMMA), and boron nitride (BN) were successfully produced by melt compounding. The effects of BN platelets sizes on morphology and thermal conductivity (TC) were investigated by mixing three different sizes BN, namely 16, 30 and 180 μm with PP and PMMA. The obtained results demonstrate that for all the sizes, BN platelets were either in the PMMA phase or at the interface, and the ternary composites with high filler loadings showed enhanced TC compared to the corresponding binary systems. It is shown that smaller BN platelets led to finer morphology, which caused more interfaces and consequently more phonon scattering and lower TC of the system. Finally, we show for the first time that there is a direct scaling between particle size, mechanical properties and TC. This work proved the advantage of using double-percolated structure to improve TC of polymer composites and provided a better understanding of the filler size effects on the morphology and TC of ternary systems.

A dimensionless mixing number is developed to quantify dispersive mixing in a simple and immediate way. This takes into account number-average diameter, volume-average diameter and interfacial area simultaneously. It is an experimentally determined number, meaning the calculations are performed using microscopy images. This parameter was validated using various polymer blends (droplet morphology) and composite systems and can be used to compare various technologies on the basis of dispersive mixing efficiency.

Double percolation threshold method was used in this work to fabricate conductive polymer blend composites comprising of high density polyethylene (HDPE), poly (methyl methacrylate) (PMMA), and carbon nanofibers (CNFs). Distribution of fillers and their consequent effect on electrical conductivity (EC) and thermal conductivity (TC) is a function of many parameters including viscosity ratio (VR) of polymeric components, which varies with processing temperatures. Here, the effect of VR on the ultimate TC and EC of this polymer blend composite was investigated by blending the components at two processing temperatures of 150 and 230 °C with VR of 3.5 and 0.9, respectively. The obtained results demonstrated more homogeneous distribution of CNFs in the blend with VR of 0.9 while it was mostly aggregated in the blend with VR of 3.5 leading to different TC and EC properties at the same loading of CNFs. This means that the composite with higher EC showed lower TC and vice-versa. These phenomena can be explained due to passage of electrons through the filler-matrix interface with tunneling effect, whereas phonons will be scattered at the interfaces. Therefore, although more homogenous distribution of fillers results in improved EC, it is accompanied with formation of more interfacial area and phonon scattering, and less enhancement of TC. This study provides a better understanding of the TC and EC mechanisms, and also the importance of VR in optimization of these properties, which can be applied for fabrication of the desired composites based on their targeted applications.

The alternating multilayered damping composites, chlorinated butyl rubber (CIIR) as damping layer and polymethyl methacrylate (PMMA) as constraining layer, were first prepared through novel multilayered co-extrusion. The damping properties of the CIIR/PMMA multilayered damping composites were investigated by dynamic mechanical analysis (DMA). The results showed that the damping peak moved to high temperature and the efficient damping temperature range was broaden with the layer number increasing. The shift of the loss peak was ascribed to the move of Rouse mode of CIIR, which was attributed to the motion of longer chain segment, but the local segmental motion was not changed. Finite element analysis (FEA) was used to simulate the distribution of shear strain in the multilayered damping composites. The FEA results exhibited that, in the temperature range between Tg-CIIR and Tg-PMMA, the shear strain occurred in the CIIR layer under vibration field, since the storage modulus (E′) of PMMA was much higher than that of CIIR. Furthermore, the average shear strain was increased with the layer number increasing.