Volume 29, Issue 2

In our study, liquid tin (Sn) was mixed with molten polyethylene using an internal mixer; the interfacial tension between the liquid Sn and molten polyethylene was measured using the deformed drop retraction method. The results showed that liquid Sn separated when the Sn content was higher than approximately 2 % by volume because of the interfacial tension of up to 167 mN/m and the 10 6 -fold viscosity difference between the liquid Sn and the molten polyethylene. When Sn separation did not occur, the effects of the mixing time and rotary speed on the degree of mixing and the Sn particle size were analyzed using thermogravimetric analysis and scanning electron microscopy. The results showed that the effects of mixing time and rotary speed on the degree of mixing and Sn particle size can be combined as the impact of specific energy input. With increasing specific energy input, the degree of mixing initially increased and subsequently remained constant, while the Sn particle size initially decreased and subsequently remained constant. The refinement of the dispersed phase was completed with a low specific energy input, but the homogenization of the dispersed phase required a higher specific energy input to achieve completion, revealing the relationship between distributive mixing and dispersive mixing.

Packing phase control during injection molding process plays a crucial role in ensuring the product quality. As one of the hot topics in the field of polymer precise injection molding, quality control of injection molded parts has always been of concern. In this present study, a part weight control method based on the cavity pressure-temperature during the packing phase was proposed. Experimental results illustrated that the proposed method, which used cavity pressure and Pressure-Temperature (P-T) control as filling-to-packing switchover mode and packing method respectively, was an effective approach for the part weight control. Typical crystalline material (polypropylene) and amorphous material (ABS) were chosen to further verify the feasibility of the control method, and experiments had shown to yield consistent conclusions. The experimental results and conclusions presented in this paper will be useful for proper setting of injection molding process.

In this study, a novel phosphorus-containing flame retardant (IFR) of spirocyclic pentaerythritol diphosphonate dinitroguanidine (SPDD) was successfully synthesized, which was characterized by 1 H NMR, 31 P NMR and FTIR spectra. At the same time, the SPDD was used in LLDPE to prepare flame-retardant materials whose flammability and thermal behavior were studied by thermogravimetric analysis (TGA), limiting oxygen index (LOI) and scanning electron microscopy (SEM). The TGA data showed that SPDD could effectively enhance the thermal stability and char residue of LLDPE/IFR composite. And with the increase of SPDD, the LOI value of LLDPE/IFR increases obviously. When SPDD reached 30 wt%, the LOI value of LLDPE/IFR reaches 31 %. The SEM also shows the surface of intumescent chars of LLDPE/IFR (30 %) has many sphere-like swollen bubbles.

In this study, the non-isothermal viscoelastic simulation of the film casting process was carried out. Low-density polyethylene polymerized by a high-pressure process (LDPE) was used for the simulation. The LDPE exhibited strain hardening in elongational viscosity since it has long chain branching. The Phan-Thien/Tanner model, as a constitutive equation of the viscoelastic fluid, and temperature dependence of the Arrhenius law were employed for the simulation to investigate the effect of viscoelasticity on extrusion drawing, so-called neck-in phenomenon. We developed the theoretical model on the basis of deformation type and force balance of a film to recognize the mechanism of the neck-in phenomenon. It was confirmed from a combination of the simulation results and the theoretical model that neck-in was determined by the ratio of planar to uniaxial elongational viscosity rather than the strain hardening nature of a uniaxial elongational viscosity.

The melt blends of recycled polycarbonate and recycled poly(acrylonitrile-butadiene-styrene) were performed by using a novel vane extruder. The morphology, mechanical, and thermal properties of the RPC/RABS blends in the whole composition range were investigated. When the concentration of RABS was 20 wt%, the blend presented the best comprehensive mechanical properties, especially for the impact strength which was significantly improved compared with RPC and RABS individuals. The blend with 90 wt% RABS also presents better mechanical properties compared with the adjacent blending ratio. With the increase of RABS concentration in blends, T g of the RABS phase decreases slightly, but T g of the RPC phase increases. The DSC and SEM results indicate that RPC are partial miscible with RABS.

We prepared polypropylene (PP) filled with boron nitride (BN) particles by melt compounding. The effects of filler content, particle size, and combined filler on the thermal conductivity of PP/BN composites were investigated. The results indicated that the thermal conductivities depend on the content and BN particle size. The good dispersion of BN particles of intermediate size in PP matrices led to a higher thermal conductivity than that of PP matrices containing small and large BN particles in which the agglomeration of BN particles was observed. The incorporation of BN particles of two different sizes could enhance the thermal conductivities of PP composites relative to those of composites containing BN particles of a single size at the same total content. A PP composite containing 50 wt% combined fillers with a mixture of BN particles measuring 45 μm and 10 μm at a weight ratio 1 : 4 showed the highest thermal conductivity in this experiment. Furthermore, several models for predicting the thermal conductivity of the composites were studied.

Biodegradation is the degradation process of organic substances via catabolic reactions that usually takes place in the presence of microorganisms and enzymes. In the present study, the enzymatic degradation of PLA was investigated by protease DSM and candida rugosa lipase enzymes. When the molecular weight loss in the degradation processes using protease DSM and candida rugosa lipase was examined, there was a 23 % reduction after 90 days for protease DSM, and 28 % reduction after 50 days for candida rugosa lipase. In addition, FT-IR, TGA, XRD and SEM analyses demonstrated significant changes in the characteristic, morphological and thermal structures of PLA during the enzymatic degradation processes.

In the present research die swell phenomenon is investigated for the viscoelastic polymer melts both experimentally and by developing a mathematical model in a circular die for high impact polystyrenes (HIPS), high density polyethylene (HDPE), low density polyethylene (LDPE) and linear low density polyethylene (LLDPE). Die swell is generally attributed to the fluid stress field when the fluid flows in a die. The Leonov-like equations as a conformational model are solved simultaneously with dynamic equation of momentum transfer to predict the stress field for a viscoelastic fluid in a circular die. The average molecular weight, the polymer relaxation time and the polymer mobility tensors are determined using the experimental measurements of shear viscosity. Then, based on those data, a model is developed. The results predicted by the model for flow stress field are then used to calculate die swell ratio by Tanner’s analytical model. Die swell ratio is also found out experimentally using a capillary rheometer for the samples. Comparison of the die swell results predicted by the model and measured experimentally show very good agreement for the polymers.

This paper analyses and reports on processing and solid particle erosion wear response of a new class of hybrid composites prepared by reinforcement of short glass fibers (SGF) in blast furnace slag (BFS) filled polypropylene (PP) matrix. In this investigation, composites with different BFS content (0, 10, 20 and 30 wt%) in a polypropylene matrix base, with and without 20 wt% SGF reinforcement, are prepared by injection molding route. To study the erosion wear response of these BFS filled composites, a plan of experiments based on the Taguchi technique is followed to acquire the wear data in a controlled way. This systematic experimentation has led to identification of significant process parameters and material variables that predominantly influence the erosion rate and also enables us to determine optimal parameter settings that lead to minimization of the erosion rate. An artificial neural network (ANN) approach is also implemented to predict the wear rate of the composites. The morphology of eroded surfaces is then examined by scanning electron microscopy (SEM) and possible erosion mechanisms are discussed. This study reveals that addition of blast furnace slag improves the erosion resistance of glass-polypropylene composites significantly and thus makes them suitable for tribological applications.

Microchannel deformation is a problem which often occurs in the thermal bonding of polymer microfluidic chip, and which is significantly determined by bonding parameters. In this paper, numerical analysis of the microchannel deformation in the process of in-mold bonding polymer chip was conducted, using Young's modulus and shear relaxation modulus of polymethylmethacrylate (PMMA) obtained in creep tests. Adhesion between the top and two lateral walls of microchannel was observed in the results, which can be attributed mainly to the viscoelastic deformation of PMMA. It was also revealed that the maximum percent deformation of microchannel is in height, and that bonding temperature had greater effect on the deformation of microchannel than bonding pressure and bonding time. The deformation of microchannel in simulation were consistent with those of experiment under the optimized parameters of 105 °C, 2 MPa and 240 s.

Starch-based superabsorbent polymers (SAPs) were produced by graft copolymerization of starch-g-acrylamide using a twin-roll mixer as reactor. This work focused on the effect of starch microstructure (amylose/amylopectin contents) from the same source (corn starch) on the graft ratio (GR), graft efficiency (GE) and Add-on (AO), as well as water absorption capability (WAC) of the SAPs, which were investigated by FTIR, NMR, gravimetric and TGA. The torque variation represented all the processing in the reactor, including compress, gelatinization, graft reaction and crosslinking. Results showed that all the starches were successfully grafted with acrylamide then crosslinked by N.N′-methylene-bisacrylamide through this technology. Both AO and GR increased with increasing amylose content. But the GE decreased with increasing amylose content, which is different from the results in the solution reaction. The higher WAC of high amylose starch-based SAP corresponds with higher AO and GR, while the higher WAC of waxy-based SAP corresponds with higher GE.

The alignment of polymer chains is a well known microstructural evolution effect due to straining of polymers. This has a drastic influence on the macroscopic properties of the initially isotropic material. In this work, cold forming is performed at room temperature on a tensile testing machine. Polycarbonate films are examined in two loading phases. In the first phase, the specimen is loaded to induce anisotropy, and in the second, it is re-loaded, while the material direction is varied. The investigations are supported by an optical measurement system to gain knowledge about the inhomogeneous material behavior in the initial loading phase and about the anisotropic homogeneous behavior during the re-loading phase. Two dimensional strain contours are obtained from the test data. Additionally, we propose a method for approximation of the macroscopic true stress and compare the results with a common approach based on volume consistency. In the future, the test data will set a basis for parameter identification of constitutive equations taking into account a combination of inhomogenous and homogenous material behavior, exhibiting strain induced anisotropy.

Searching for new and cost-effective methods of waste rubber recycling is a subject of research in many scientific centers in the world. In this paper there are presented results of the research of the extrusion process of cheap and environmentally friendly thermoplastic compositions containing 50% wt. of masses of ground tire rubber (GTR). The aim of this study was to determine the relationship between the mixing conditions and properties of obtained products, which is important from a technological point of view. The mixing conditions were determined by using two variables: the screw configuration (co-rotating and counter-rotating) and the type of polyethylene. In the case of both variables, thermoplastic compositions were treated with various shear forces induced by screw speed changes. The influence of mixing conditions on the extrusion process was determined (screw torque, melt flow rate) as well as static and dynamic mechanical properties of obtained materials.

In this work, thermoplastic elastomers based on polypropylene (PP) and recycled ethylene-propylene-diene monomer (r-EPDM) blends with polypropylene-graft-maleic anhydride (PP-g-MA) as modifier (0 to 8 wt.%) were prepared by melt compounding via twin-screw extrusion followed by injection molding. In particular, the effects of material composition and feeding strategies were studied. The morphological and mechanical properties of the blends were investigated by using scanning electron microscopy (SEM), tensile, flexural, impact, density and hardness tests. The results indicate that good dispersion and compatibility between PP and r-EPDM particles was obtained and that incorporation of r-EPDM leads to significant increase in PP impact strength. Finally, the feeding order of each component in the extruder was found to modify substantially the final morphology of the blend, thus having a direct influence on their mechanical properties.

Chitosan & L-alanine and chitosan & L-leucine superabsorbent hydrogels were prepared by crosslinking chitosan with glutaraldehyde. L-alanine and L-leucine were used as amino acid structures in different loading degrees and the optimum amount of amino acid was determined for both types of hydrogel. The swelling behaviors of neat chitosan, chitosan & L-alanine and chitosan & L-leucine hydrogels were investigated by gravimetric measurements with different pH values and at different intervals of time. The neat chitosan, chitosan & L-alanine and chitosan & L-leucine hydrogels were characterized by Fourier transform infrared spectroscopy (FT-IR). Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) were used to find the thermal stability of the hydrogels. Also, surface morphological studies of all the hydrogels were carried out by using a Scanning Electron Microscope (SEM). In addition, XRD analysis demonstrated significant changes in the characteristic and morphological structures of the hydrogels.

In the technical literature, some authors have reported calculation of negative pressures in simulations of twin screw extrusion and other types of processing, without giving any explanations. In the majority publications there is no mention of such meaningless results, even though theoretical considerations indicate that negative pressures could be obtained in the expansion region of drag flows through narrow non-parallel surfaces. The meaningless negative pressures are due to the application of single fluid theory to flow regions where bubbles would form, when the pressure drops below the vapor pressure of the liquid. This has been known for a long time from the study of lubrication bearings and related cavitation phenomena. It is argued that the boundary conditions should be carefully chosen for avoiding results in numerical simulations, which can never be reconciled with experimental pressure data.