We examine the simplest relevant molecular model for large-amplitude shear (LAOS) flow of a polymeric liquid: the suspension of rigid dumbbells in a Newtonian solvent. We find explicit analytical expressions for the shear rate amplitude and frequency dependences of the first and third harmonics of the alternating shear stress response. We include a detailed comparison of these predictions with the corresponding results for the simplest relevant continuum model: the corotational Maxwell model. We find that the responses of both models are qualitatively similar. The rigid dumbbell model relies entirely on the dumbbell orientation to explain the viscoelastic response of the polymeric liquid, including the higher harmonics in large-amplitude oscillatory shear flow. Our analysis employs the general method of Bird and Armstrong ["Time-dependent flows of dilute solutions of rodlike macromolecules," J. Chem. Phys. 56, 3680 (1972)] for analyzing the behavior of the rigid dumbbell model in any unsteady shear flow. We derive the first three terms of the deviation of the orientational distribution function from the equilibrium state. Then, after getting the "paren functions," we use these for evaluating the shear stress for LAOS flow. We find the shapes of the shear stress versus shear rate loops predicted to be reasonable.

The combination of high-density polyethylene (HDPE), low-density polyethylene (LDPE) and polypropylene (PP) is frequently found in polymer waste streams. Because of their similar density, they cannot be easily separated from each other in the recycling stream. Blending of PP/ polyethylenes (PEs) in different ratios possibly eliminate the sorting process used in the regular recycling process. PP has fascinating properties such as excellent processability and chemical resistance. However, insufficient flexibility limits its use for specific applications. Blending of PP with relative flexible PEs might improve its flexibility. This is a unique approach for recycling or upcycling, which aims to maintain or improve the properties of recycled materials. The effects of the branched-chain structures of PEs on the crystallization behavior and the related mechanical properties of such blends were investigated. The overall kinetics of crystallization of PP was significantly influenced by the presence of PEs with different branched-chain structures. The presence of LDPE was found to decrease the overall crystallization rate while the addition of HDPE accelerated the crystallization process of the blends. No negative effect on the mechanical performance and the related crystallinity was observed within the studied parameter range.

When measuring rheological properties in oscillatory shear flow, one worries about experimental error due to the temperature rise in the sample that is caused by viscous heating. For polymeric liquids, for example, this temperature rise causes the measured values of the components of the complex viscosity to be systematically low. For such linear viscoelastic property measurements, we use an analytical solution by Ding et al. [J. Non-Newtonian Fluid Mech. 86, 359 (1999)10.1016/S0377-0257(99)00004-X] to estimate the temperature rise. However, for large-amplitude oscillatory shear flow, no such analytical solution is available. Here we derive an analytical solution for the temperature rise in a corotational Maxwell fluid (a model with just two parameters: η0 and λ) subject to large-amplitude oscillatory shear flow. This result can then be generalized to a superposition of corotational Maxwell models for a quantitative estimate of the temperature rise. We chose the corotational Maxwell model because, when generalized for multiple relaxation times, it gives an accurate prediction for molten plastics in large-amplitude oscillatory shear flow. We identify three relevant pairs of thermal boundary conditions: (i) both plates isothermal, (ii) with heat loss by convection from both plates, and (iii) one plate isothermal, the other with heat loss by convection. We find that the time-averaged viscous heating increases as an even power series of the dimensionless shear rate amplitude (Weissenberg number), and that it decreases with the dimensionless imposed frequency (Deborah number). We distinguish between the dimensionless time-averaged temperature rise, $\bar \Theta $Θ¯, and the oscillating part, $\tilde \Theta $Θ̃, where $\Theta \equiv \bar \Theta + \tilde \Theta $Θ≡Θ¯+Θ̃. We solve analytically for the $\bar \Theta $Θ¯ profile through the sample thickness for all three pairs of thermal boundary conditions. For the worst case, two adiabatic walls, we derive an expression for the oscillating part of the temperature rise, $\tilde \Theta $Θ̃. We find this $\tilde \Theta $Θ̃ to be a Fourier series of even harmonics whose contribution to the temperature rise can be as important as $\bar \Theta $Θ¯. If both plates are adiabatic, then the sample temperature rises without bound. Otherwise, it does not.

Additive manufacturing, the so-called three-dimensional (3D) printing, is a revolutionary emerging technology. Fused filament fabrication (FFF) is the most used 3D printing technology in which the melted filament is extruded through the nozzle and builds up layer by layer onto the build platform. The layers are then fused together and solidified into final parts. Graphene-based materials have been positively incorporated into polymers for innovative applications, such as for the mechanical, thermal, and electrical enhancement. However, to reach optimum properties, the graphene fillers are necessary to be well dispersed in polymers matrix. This study aims to emphasise the interest of producing ABS/graphene oxide (GO) composites for 3D printing application. The ABS/GO composite filaments were produced using dry mixing and solvent mixing methods before further melt extruded to investigate the proper way to disperse GO into ABS matrix. The ABS/GO composite filament with 2 wt.% of GO, prepared from the solvent mixing method, was successfully printed into a 3D model. By adding GO, the tensile strength and Young’s modulus of ABS can be enhanced. However, the ABS/GO composite filament that was prepared via the dry mixing method failed to print. This could be attributed to the aggregation of GO, leading to the die clogging and failure of the printing process.

Kenaf cellulose fiber was extracted from kenaf locally grown in Thailand as a potential local renewable resource for the cellulose fiber. In this study, the biodegradable polymer composites, poly(butylene succinate) (PBS)/cellulose fiber composites with different types of cellulose were prepared. The kenaf fiber treated with hydrochloric acid (KTH), extracted cellulose fiber (EC), and commercial cellulose fiber (CC) were selected as alternative renewable fillers in the PBS (the biodegradable polymer). Regarding the fiber characteristics, the aspect ratio of the EC (11.5) was found to be higher than that of the CC (6.1). In a similar manner, the EC contained 65.9% crystallinity, which was higher than that of the CC (37.0%) and the KTH (58.9%). Moreover, the EC exhibited higher thermal stability (Td[Max] = 362.9°C) than the CC (Td[Max] = 302.0°C) and the KTH (Td[Max] = 353.8°C). For PBS/cellulose fiber composites, the rheological, tensile, and thermal properties were studied. The rheology results revealed that the addition of the fiber changed the PBS microstructure. The EC fiber dispersion in the PBS seemed to be better than the others; however, the KTH fiber dispersion was poor. The addition of the fiber raised the elastic moduli of the composites by 5‐26%; however, it reduced the tensile strengths (by 14‐53%) and the decomposition temperatures (by 1‐2%). Furthermore, the addition of the fiber slightly affected the crystallization temperatures and melting temperatures of the composites. The yellowness and whiteness of the composites were marginally reduced. The composite with the EC fiber showed a significant improvement in the elastic modulus as compared to the composite with the CC fiber, while the tensile strength and the strain at maximum stress were comparable. Thus, according to the rheological, thermal, and tensile properties of the composites, the EC fiber showed a possibility of using as an alternative reinforcement material from a local renewable resource.

3D printing has attracted a lot of attention over the past three decades. In particular the Fuse Filament Fabrication (FFF) technique, general materials require low shrinkage during cooling and viscous behavior during extrusion through a nozzle. Semi-crystalline thermoplastics and their composites are of the relevance of new materials for 3D printing. However, the crystalline structures, for instance, may have a favorable impact on their printability. In this study, polypropylene/organoclay nanocomposites were prepared by melt extrusion using a twin-screw extruder. The effects of organoclay on the thermal, rheological and morphological properties were studied to evaluate the possibility of using the polypropylene/organoclay nanocomposites as the FFF 3D printing feedstock. Dioctadecyl dimethyl ammonium chloride (D18) was successfully used to modify the clay surfaces, providing a good dispersity and wettability of organoclay in the PP matrix.

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To achieve a proper dispersion of nano-particles polymer matrix and to yield a better compatibility between the nano-particles and polymeric material, the use of different coupling agents for surface modification of nano-particle is recommended. In this research, surface of TiO2 was modified by hydrolytic condensation of titanium isopropoxide with three different silane coupling agents, hexadecyl trimethoxysilane (HTMS), triethoxyvinylsilane (TEVS) and aminopropyl trimethoxysilane (APS). The grafting of silane coupling agents on the TiO2 nano-particles surface was characterized using TGA and FTIR techniques. Mechanical properties of polyethylene composite films were evaluated via tensile strength measurement. Surface morphology of the particle was studied by SEM and TEM. The result showed that surface treatment TiO2 nano-particles with TEVS could improve dispersibility of TiO2 and showed the optimum mechanical properties.