Volume 29, Issue 4

The Pressure-Volume-Temperature (PVT) property of polymer nanocomposite (PNC)/gas solutions is an important fundamental property in the foaming of PNC. However, accurate data have not yet been reported. We examined the PVT behaviors of polypropylene (PP) and PP/organoclay polymer nanocomposite (PP-PNC) by monitoring the swelling changes of the polymer melt in supercritical carbon dioxide (scCO 2 ). A model was adopted that describes the PVT behaviors of PP-PNC with and without dissolved gas. Based on the model, a PNC consists of two sections: a hard section (a nanoparticle surrounded by solidified polymer) and a soft section (neat polymer). It was observed that an infusion of nanoparticles decreased the swelling. It seems that the hard section had a minimal free volume in which to dissolve the blowing agents, and that the number of hard sections increased with the infusion of nanoparticles. As a result, the total gas absorption capacity of the system decreased, and consequently, the swelling also decreased.

Injection molded composites are becoming more widespread in recent years because of their high quality and low cost. However, compared to synthetic fiber composites, it is difficult to maintain a constant fiber volume fraction and uniform distribution for natural fiber composites during the direct injection process. This is mainly because natural fibers are more easily twisted during feeding into the injection machine, owing to their rough surfaces. These feeding difficulties are particularly due to the low bulk densities of natural fibers, especially natural fillers. Additional challenges to the injection process include the concentration and, especially for natural filler reinforced composite. To address these problems, the current study investigates the mechanical properties and morphologies of polypropylene (PP) reinforced by wood powder. Two pre-molding processes, dry-blending and compounding, were compared, and the effects of an additive (crystalline polyalpha olefin (CPAO)) on the mechanical properties of the wood/PP composites were investigated. This investigation is based on tensile, three point bending, and Izod impact tests, and scanning electron microscope (SEM) observation of the fracture surfaces. Results indicated that the composites molded through compounding exhibited better mechanical properties than the samples molded through the direct dry-blending process. In addition, the tensile and bending properties of the composites produced through compounding were found to increase with the addition of CPAO content, because of improved wood powder distribution in the PP matrix.

Non-halogen flame retarded polyethylene (PE) can be prepared by filling metallic hydroxides magnesium hydroxide (MH) or aluminium hydroxide (ATH), the mechanical properties of polymer composites will decline greatly when filling much more inorganic particles. Selecting microencapsulating particles, suitable synergistic agents or compatibilizers are good methods for improving the combination performance of composites. In this study, microencapsulated red phosphorous (MRP) was synthesized by using melamine-formaldehyde resin through in-situ polymerization, and used as a synergistic agent of MH and ATH, and the best proportion of three flame retardants was studied in detail. Results showed that flame retarded PE had a better combination performance when filling with 45 wt% compound flame retardants of MRP, MH and ATH under the weight ratio of 46/46/8. In order to improve the mechanical performance of composite, two polymeric compatibilizers POE-g-MAH and EPDM-g-MAH were selected to toughen the flame retarded PE composite. Results showed the flame resistance and mechanical properties of composites improved greatly with an increase of compatibilizer content, under the same condition, POE-g-MAH has a better contribution on the flame resistance and EPDM-g-MAH has a better toughening effect. The best flame retarded PE composite can be obtained by filling with 45 wt% compound flame retardants and 10 wt% EPDM-g-MAH.

Hydroxyapatite/polyamide-66 (HA/PA66) composite scaffolds were prepared using injection-molding technique, and also analyzed by means of scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), Fourier transform infrared spectroscopy (FTIR) and mechanical testing. Compared with common methods including solvent casting/particulate leaching, phase separation and so forth to fabricate scaffolds, this process is of a rapid and convenient manner. The increase of HA content can increase the stiffness of composite scaffolds accompanied by the reduction of impact strength, pore size and porosity. The storage modulus of composite scaffolds increases with increasing HA content and with decreasing porosity. The damping (tan δ) of PA66 decreases with the increase of HA content, and the α and β relaxation peaks of PA66 for the foamed HA/PA66 composites slightly shift to lower value, indicating that both HA and gas in the foamed HA/PA66 composites have an effect on the chain mobility of the polymer and the interaction between the polymer chains. The microstructure of the 30 wt% and 40 wt% HA/PA66 composite scaffolds with porosity more than 59 % and pore size ranging from 100 to 500 μm is similar to that of dry human trabecular bone. The obtained composite scaffolds with 30 wt% and 40 wt% HA have a compressive modulus of 232 to 443 MPa, and a compressive strength of 9.3 to 9.8 MPa, similar to or a little higher than those of trabecular bone, and close to those of the cancellous bone.

We report on a gas-sensor-based measurement setup for the detection of volatile degradation products directly in the extrusion process. In contrast to available measurement tools, the system is located in the air flow and works independently of the polymer melt flow. Therefore, the sensor can be used also for non-transparent melts with different colors and filler contents. For process validation, the measurement setup was tested offline using selected organic solvents, as well as directly in the extrusion process using talc-filled polypropylene compounds. We show that the amount of lubricants, the shear load, as well as the temperature and the back pressure influence the level of low molecular weight volatile compounds (LMWVOC) and finally the gas-sensor value.

A biodegradable alternative material to synthetic plastics was explored in this study through the extrusion of soy protein isolate (SPI) composite films containing soy cellulose microfibers (SMF). SMF were isolated from soy pods and stems using a chemo-mechanical method. The fibers produced through successive treatments were characterized by microscopy, x-ray diffraction, and Fourier transform infrared analysis. SMF/SPI composite films (0.08 to 0.3 mm thick), containing different concentrations of cellulose fibers, were produced using a single-screw extruder (0.625″ screw; 24 : 1 L/D ratio; 100 – 120 min −1 ; 120 to 150 °C barrel temperature) and characterized. Homogenous films with uniform distribution of SMF were obtained with the highest concentration of 0.5 % w/w SMF/SPI. Increasing fiber content resulted in the formation of aggregates. As with other protein films, mechanical properties of the extruded pristine SPI and composite films were negatively affected by humidity. At the optimal concentration of 0.25 % w/w SMF/SPI, films exhibited improved mechanical performance at elevated relative humidity (84 %) when compared to the pristine SPI films.

Considering the growing interest in the development of new materials based on renewable materials, this paper presents the results of experiments carried out with high content (80 to 95 %) of coconut endocarp particles in phenol formaldehyde resin for the development of composite material by compression molding. The morphology of the particles and chemical composition and thermal stability of both the particles and the resin were evaluated. Tensile and flexural properties of the composites exhibited significant improvements with increasing resin content, attributed to good bonding between the resin and the particles and the presence of fewer voids in the composites as well as to the microstructural homogeneity, as corroborated by the fractographic studies. The thermal stability of the composites is influenced by the proportion of particles, while the swelling characteristics are affected by the amount of resin. The results taken together suggest that the developed composite can be used for various applications.

Flash known as burr is defined as additional resin filling a gap between parted surfaces. It is caused by mold deformation from excessive cavity pressure. In our previous research, there had been attempts to detect the occurrence of the flash using the contact-pressure-sensor which was developed. Although the sensor showed a reliable response of mold deformation, the sensor alone could not tell us the exact occurrence of flash. In order to understand response of the sensor, a structural analysis in conjunction with a molding analysis was carried out. In the analysis, the platens of an injection molding machine were included in the model to accurately implement deformation of the mold. We found that the trend of strain predicted by the CAE analysis was similar to the measured one although the strain value was not comparable. We examined the stress at the parting edge and found that the most probable moment for the flash occurrence appeared when the z-axis stress was closed to zero value.

One of the most commonly used vegetable oil plasticizer in polyvinyl chloride (PVC) is epoxidized soybean oil (ESBO). On the contrary, epoxidized palm oil is among the least used, because of its low compatibility with PVC. This work reports that epoxidized and esterified palm kernel oil (EEPKO) has the potential to be used as a plasticizer for PVC. In this study, it was found that a maximum of 65 phr of EEPKO could be incorporated within the PVC resin. In addition, subjecting this EEPKO plasticized PVC (p-PVC) at a processing temperature of 200 °C resulted in much reduced plasticizer loss. EEPKO lowers the glass transition temperature of PVC from 79 °C to −23 °C. The optimum mechanical properties, namely tensile strength, elongation at break and hardness, were obtained for p-PVC processed at 200 °C.

The influence of processing parameters on injection-molded bottle caps consisting of 20 wt% of cellulose fibers and an ethylene-acrylic acid copolymer was studied. The study included three cylinder barrel temperatures and three mold temperatures. For each combination of temperatures, the holding pressure time was varied and the mold sealing time was determined. High density polyethylene caps were also produced as reference material, and injection-molded tensile test bars were also produced in order to assess the tensile mechanical properties. The results showed no major differences in sealing time for the caps containing cellulose fibers, except for the highest melt and mold temperatures where a slightly longer time was observed. The viscosity of the composite material was higher than that of the polymeric matrix. For the highest temperature and high shear rates, the viscosity of the composite material was close to the viscosity of the matrix material. The moisture content of the injection-molded bars was less than 1 %, showing that almost no water was absorbed during the compounding or after several months. The crystallinity decreased when the fibers were included but was not influenced by the mold temperature. Enhanced mechanical properties were obtained by using the fibers compared to the pure ethylene-acrylic acid copolymer, both in the tensile test bars and in the caps. The reference high density polyethylene had, however, a higher mechanical performance than the composite.

A vane extruder consists of a group of vane plasticization units that can together be considered a vane pump. During extrusion, materials in the extruder are plasticized and conveyed by positive conveying and suppressed by normal stress. A mathematical model of the pumping capacity of polymer solids in the vane extruder is established based on its structure and conveying mechanism. The minimum bulk density under atmospheric pressure and leakage coefficient in this model are obtained experimentally. Four general polymer materials are chosen to investigate the pumping conveying capacity of polymer solids in the vane extruder. The experimental results of the first vane plasticization unit show that the pumping conveying capacity increases almost linearly with the rotor velocity and is only slightly influenced by the material properties. Furthermore, the leakage coefficient increases when the temperature and velocity in the vane extrusion process are set inappropriately; this reduces the pumping conveying capacity of polymer solids in the vane extruder.

In the current study, 70/30 (w/w) polypropylene (PP)/polyamide 6 (PA6)/organoclay ternary blends were prepared by melt mixing in three different blending sequences, i. e., organoclay premixed with PA6 and then mixed with PP (S1 blending sequence), organoclay premixed with PP and then mixed with PA6 (S2 blending sequence), and organoclay, PA6 and PP mixed simultaneously (S3 blending sequence). The effects of organoclay on the phase morphologies, rheological properties and mechanical properties of the blends are examined to reveal the role of organoclay in these immiscible blends. First of all, the dispersion and distribution of organoclay is investigated using XRD and TEM techniques. The organoclay is exfoliated and distributed in the dispersed PA6 phase as well as at the interface between PA6 and PP. Interestingly, more organoclay sheets are observed at the interface when the S2 or S3 blending sequences are utilized. From the SEM images, it is clear that the domain size of the PA6 phase decreases remarkably after introducing organoclay into the PP/PA6 blends. Two different rheological protocols are applied to probe the effect of organoclay on the morphology of the blend by in-situ monitoring the morphological evolution. The rheological results reveal that the phase morphology of the PP/PA6 blends remains relatively stable during shear for a wide range of shear rates when 1.0 wt% organoclay has been added. For the blends with a relatively high clay loading (5.0 wt%), a characteristic and pronounced “plateau” is observed in the low frequency range of the G′-ω curves, which indicates the presence of a percolating network of clay nanosheets. From the mechanical measurements, we find that the tensile strength of the blends increases slightly first and then declines dramatically with increasing organoclay content. Moreover, the elongation at break drops sharply as the organoclay content increases. In summary, it is clear that the organoclay can effectively reduce the domain size of the dispersed PA6 phase and stabilize the phase morphology in shear flow. However, the mechanical properties of the blends are not really improved by clay addition, even though a cocontinuous morphology with a percolated clay network was generated.

Studies to improve the machining of engineering materials have great importance for mechanical systems. Abrasive water-jet turning (AWJT) is a new and effective process for increasing machinability of engineering materials by providing temperature free cutting conditions, high surface quality and having no tool wear problem. In this study, AWJT of low density polyethylene (LDPE) material were investigated in terms of average surface roughness (ASR) and material removal rate (MRR) values and process parameters were optimized by experimental design method. The primary objectives of the study are to investigate AWJT process and system parameters to enhance machinability of LDPE material and to determine optimal processing parameters. Nozzle feed rate (5, 25 and 45 mm/min), abrasive flow rate (50, 200 and 350 g/min) and spindle speed (1 000, 1 500 and 2 500 min −1 ) were analyzed as process parameters. Taguchi L 27 orthogonal full factorial design, optimization box and analysis of variance (Anova) were used for the experimentation and results analysis. Experimental results show that, AWJT process is more efficient in the machining of LPDE material than the conventional machining methods by increasing surface quality and MRR parameters. Minimum ASR and maximum MRR were obtained 1.67 μm and 14 072.02 mm 3 /min respectively; at optimum parameters of 5 mm/min nozzle feed rate, 350 g/min abrasive flow rate and 2 500 min −1 spindle speed.