Volume 31, Issue 2

Rotational molding, which is widely used in furnishing, entertainment facilities, automotive and boats, military industry and other fields, is a forming method used to produce hollow thermoplastic products. Temperature is the most important process parameter in the rotational molding process, so accurate temperature modulation and control are undoubtedly the main way to ensure product quality. During the rotational molding process, temperature in the oven is very high. Current temperature measuring device cannot make real-time measurement and cannot provide the necessary reference for accurate temperature modulation and control. This article provides an analysis of a wireless temperature measurement device which is used in high temperature enclosed environment, researches the structure, the barrier principle of the temperature measurement device. Finally, tests have been done to verify the working performance. Accurate monitoring and control of the temperature parameter during the rotational molding process can not only improve the working efficiency and energy efficiency of the rotational molding machine, but also provide the reference to design the rotational molding device and molds.

The production of functional optical parts made of plastics is a growing market and the associated production processes have to be developed to fulfil the increasing quality requirements. In this paper an alternative injection compression molding process using the pvT-behavior of the plastics material is compared to the conventional processing method using an isobaric process path. For both control strategies a cavity pressure loop-control is implemented and used. According to measurements of the mold surface reproduction accuracy and internal properties of the molded part the processing method using the pvT-behavior results in a higher optical part quality in the same cycle time compared to the isobaric processing method.

Plug temperature is a key parameter affecting the thickness distribution of thermoplastic components made by plug assist thermoforming. For a specified pair of plug and plastic sheet, the variation in plug temperature can alter the coefficient of friction (COF) between the pair. We show here how the temperature dependence of COF influences the nature and extent of biaxial stretching of the sheet and consequently the thickness distribution of the thermoformed component. In the present study, high impact polystyrene (HIPS) sheets were thermoformed into axisymmetric cups using a plug-assist process in which the aluminum plug temperature (T plug ) was varied from ambient to above the glass transition temperature of HIPS (∼100 °C). Biaxial strain maps on the surfaces of the formed cups were measured and quantified using Grid Strain Analysis (GSA). Thickness distributions of the cups were also measured. Temperature dependent COF between HIPS and aluminum was determined independently using a rotational rheometer. The measured COF was low for T < 100 °C, whereas it increased appreciably at and above 100 °C. We conclude that when T plug < 100 °C the HIPS sheet slips on the plug during forming, and this results in biaxial stretching of the base and walls of the formed cup. In contrast for T plug > 100 °C, a significant reduction in the magnitude of slip is expected. Here the sheet is gripped at the clamp and by the plug during forming which causes reduced biaxial stretching of the base and increased uniaxial stretching of the walls of the cup. Simulations of plug-assist thermoforming using a temperature dependent COF showed qualitative agreement with the GSA data thereby supporting our inferences.

The effects of the addition of different functionalized compatibilizers on toughness, morphology and rheological properties of a polypropylene (PP) – poly(ethylene terephthalate) (PET) (85–15 wt%) blend were studied. The three compatibilizers compared were: (Styrene Ethylene Butylene Styrene)-grafted-(glycidyl methacrylate); (Styrene Ethylene Butylene Styrene) – grafted – (maleic anhydryde); (polyolefin) – grafted – (glycidyl methacrylate), abbreviated to: SEBS-g-GMA, SEBS-g-MA and POE-g-GMA respectively. The effective grafting content was the same for all three compatibilizers. Before the comparison of the different compatibilizers was done, first the effects of three different processing temperatures and three different compatibilizer contents were investigated, based on the addition of SEBS-g-GMA. The compatibilization effect was significantly improved with an increase in processing temperature from 250 to 300 °C. The toughness was increased with almost a factor two and a decrease in the average domain size of the dispersed phase was observed. An increase in compatibilizer content from 0.25 to 2.5 wt% resulted in a finer dispersity as well as in a steep increase in toughness, which was noted to approach the brittle-to-ductile transition. The comparison of the three compatibilizers was subsequently done at the most promising processing temperature and content: 300 °C and 2.5 wt%. The results showed that the addition of SEBS-g-MA and POE-g-GMA had a less significant positive effect on the compatibilization compared to SEBS-g-GMA. The difference is attributed to a higher reactivity for GMA compared to MA and a higher possibility for migration towards the PP-PET interface for the SEBS chain compared to the POE chain.

The present work was done to improve the impact property of isotactic polypropylene (PP), especially at low temperatures, by incorporating ethylene propylene diene monomers (EPDM). This was done by ensuring compatibility between the two polymers with phase modifiers polyethylene grafted with maleic anhydride (PE-g-MA) and initiator dicumyl peroxide (DCP). In addition, attempts were also made to understand the fundamentals of impact toughening as well as fracture toughness, and to correlate the results with that of morphological evidences obtained from scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods. Varying the ratios of all blend composition, mechanical properties were studied. It was observed that as the rubber fraction increased, the impact property as well as fracture toughness increased. All these tests also showed promising results when PE-g-MA was added, leading to more improvement in all the mechanical properties including increase in crystallite size. It had shown plasticization effect on the compositions, which could be further confirmed by differential scanning calorimetry (DSC) compared to the uncompatibilized ones. But when DCP was added, it behaved like an initiator which directly reacted with the PP matrix, decreasing the molecular weight of the blend with decreasing size of the crystallites.

Composites based on thermoplastic matrix and glass or carbon fibre fabrics, like the so called organic sheets, show high potential for structural parts, e. g. in automotive applications. In this study renewable organic sheets based on bio-polyamides with a melting point above 200 °C and polypropylene for reference purposes were prepared. High energy absorption for these composites were expected regarding the high elongation at break (> 10 %) of the man-made cellulose fibres. In comparison to the cellulose reinforced composites, glass fibre composites were prepared. The complete or partly bio-based composites, with a thickness of approx. 2 mm, were manufactured by a high precision hot-press using the film-stacking-process considering less fibre degradation at high processing temperatures. Besides dart drop tests (penetration mode and impact mode) and optical microscopy were done to characterize the composites. The bio-based composites show lower density, higher energy absorption rates and lower damping values as a consequence of the cellulose fibres properties and the fibre-matrix-adhesion.

Inspired by the hydration capability of hydrogel materials, cross-linked poly(N-acryloylmorpholine) (PACMO) chains were designed into poly(vinylidene fluoride) (PVDF) backbones to synthesize the copolymers (PVDF-g-PACMO) using the radical polymerization method. These copolymers were then cast into the porous membranes via immersion phase inversion. The effects of N,N′-methylenebisacrylamide (MBAA) in the reaction solution on the structure and performance of as-prepared copolymer membranes were evaluated by elemental analysis, X-ray photoelectronic spectroscopy, field emission scanning electron microscopy, water contact angle measurement, protein adsorption and filtration experiment. The grafting degree of PACMO increases with the increase of MBAA amount in the reaction solution, which endows the copolymer membrane with a good hydrophilicity. The protein adsorption and irreversible membrane fouling decrease and then further increase with the elevated grafting degree of PACMO. This result indicates that the anti-fouling property of membrane not only depends on the surface hydrophilicity and but also associates with the grafting structures of PACMO. This work provides a fundamental understanding of various grafting structures governing the performance of anti-fouling properties.

Formation behavior of fine fibers of polymethylpentene (PMP) and polypropylene (PP) in the melt blowing process was investigated through the observation of the spin-line near the spinning nozzle using a high speed camera. Reduction of the polymer throughput rate and increase of the air flow rate were necessary to achieve fine diameter fibers, however these conditions generally cause the instability in the spinning process. Observation of the spin-line at the melt blowing die revealed the periodic accumulation of polymer flow near the spinning nozzle followed by the quick pulling down of the accumulated polymer by the air flow. This behavior caused the periodic fluctuation of fiber diameter as well as the intermittent breakage of the spin-line under extreme conditions. Because of high extrusion viscosity, PMP showed more stable spinning behavior than PP. Frequency of diameter fluctuation became higher with the increases of air flow rate and throughput rate, and the maximum frequency of about 60 Hz was observed for PP spinning with the throughput rate of 0.18 g/min. Diameter distribution of the fibers in the prepared web was also analyzed to compare with the spinning behavior. Fiber diameter distributions were narrow and symmetric under stable spinning conditions, whereas skewed diameter profiles with a maximum at low value and a long tail to the larger diameter region were observed under unstable conditions. Intermittent spin-line breakage caused flaws of “shot” and/or “fly”, and the skewed fiber diameter distribution with the presence of a small amount of fiber of extremely large diameter was confirmed.

The influence of the distribution of the inorganic particles on the toughness of the PP/EPDM/nano-ternary composites was investigated. Four morphologies for PP/EPDM/nano-ternary composites were obtained by means of adjusting the surface tension of inorganic particles (nano-CaCO 3 , hydrophobic nano-SiO 2 and hydrophilic nano-SiO 2 ) and the compounding sequence (one-step extrusion and two-step extrusion). Morphological observation revealed that the segregated dispersion morphology was formed in the PP/EPDM/CaCO 3 composite. For the PP/EPDM/R974 (hydrophobic nano-SiO 2 ) composite, R974 particles were dispersed at the interface between the PP matrix and EPDM dispersed phase. A200 particles (hydrophilic nano-SiO 2 ) continuously dispersed between PP and EPDM phase for PP/EPDM/A200 composites prepared by one-step, while were present in EPDM dispersed phase for the two-step PP/EPDM/A200 composites. The dependence of the toughness on the phase morphology of the components, especially the distribution of nanoparticles, was studied systematically. The impact strength of one-step PP/EPDM/A200 composites was pronouncedly enhanced, increasing 552 % compared to pure PP. Compared with the other three composites, the one-step PP/EPDM/A200 composites exhibits better effect of preventing crack propagation and far higher fracture energies. It is attributed to the A200 particles continuously dispersed between EPDM phase and matrix, which makes EPDM particles have better compatibility with the PP matrix and the overlapping of the stress field with A200 particles.

This paper reports a simple and rapid method for fabrication of microfluidic chips on polymethylmethacrylate (PMMA) substrate using a flexible and low-cost CO 2 laser system. The CO 2 laser employed has a wavelength of 10.6 μm. The laser power used for channel fabrication ranged from 3 and 12 W, the beam travel speeds ranged from 5 to 50 mm/s and the passes were varied in the range of 1 to 3 times. Typical channel depths were between 100 and 900 μm, while the width of fabricated channels ranged from 100 to 300 μm. The effects of the process parameters (the laser power, the beam travel speed of the laser beam and the number of passes) on the dimensional quality (the depth, the width and their aspect ratio) of the microchannel manufactured from PMMA were experimentally investigated. The change law of the channel geometry depending on process parameters was obtained. A high reproducibility of micro-channel geometry was attained. At last, a CO 2 laser output power of 5.5 W and a laser beam travel speed of 35 mm/s combining a hot press bonding technique were chosen to fabricate a microfluidic chip within half hour. The pattern qualities and experimental results confirm that the CO 2 laser micromachining technology has a great potential for application in flexible, rapid and economic production of polymeric microfluidic chips.

A micro chain length and temperature (MCLT) wall slip model of polymer was developed on the basis of chain length and temperature. The effectiveness and accuracy of the MCLT slip model were verified through a micro-square-column filling rate experiment for Polypropylene (PP) material and a micro-square-column pressure difference experiment for Polystyrene (PS) material. The difference between the simulated data of the MCLT slip model and the experimental data decreased with decreasing feature size. The accuracy of the MCLT slip model was enhanced by decreasing the feature size. When the feature size was decreased to 200 μm, the maximum deviation between the simulated filling rate by the MCLT slip model and the experimental result was 8.67 %. Moreover, under different shearing rates, the simulated pressure drop by the MCLT slip model was closer to the experimental result than that by the conventional slip model. The micro-scale flow characteristics of the melt were also explored using the MCLT slip model. Melt flow velocity decreased from the center of the micro-channel to the wall, and the wall slip phenomenon was beneficial to the melt flow.

Antistatic poly(vinyl chloride) (PVC) composites filled with silver plated hollow glass microspheres (Ag-HGMs) were prepared using the melt-mixing method. Electrical resistivity and mechanical properties of the Ag-HGMs/PVC composites were subsequently investigated. The results show that the HGMs were successfully coated with a uniform and compact silver layer. With increasing Ag-HGMs content, the volume resistivity of Ag-HGMs/PVC composites decreases nonlinearly. With an Ag-HGMs content of about 120 phr, reaching the percolation concentration, the composites meet the antistatic requirements for commercial antistatic PVC materials. Furthermore, the tensile strength of Ag-HGMs/PVC composites decreases with increasing content of Ag-HGMs, while the impact strength increases with increasing content of Ag-HGMs from 0 phr to 150 phr. We especially found that, with a Ag-HGMs content of 20 phr, Ag-HGMs/PVC composites exhibit great impact strength.

In several thermoplastic extrusion based processes the melt flow has to be divided into independent streams that are merged before the flow channel outlet. This promotes the formation of weld lines, usually related to mechanical weak zones and aesthetic imperfections. There is a large amount of scientific publications related to weld lines formed in other processing techniques, e. g. injection molding. However, studies related to extrusion are scarce. This work presents the conception of a new prototype system that allows performing systematic studies aiming a better understanding of the effect of weld lines in extrusion. A case study illustrates the employment of the developed device to study the effect of several process parameters (e. g. spider leg location, processing temperature and flow rate) on the mechanical performance of the extruded profiles.

Extrudate swell of industrial-grade high-molecular mass high-density polyethylenes (HDPEs) in flat/slit dies is studied using both experiments and simulations. The experimental set-up consists of an optical micrometer to measure the extrudate dimensions and a pair of radiation heaters to control the extrudate temperature outside the die attached to the capillary rheometer. The simulation of extrudate swell phenomenon is carried out by using a well-known integral K-BKZ model. The effects of several rheological characteristics, die characteristics, and processing conditions on swell measurements are studied systematically, and the corresponding two-dimensional, steady-state numerical predictions are presented in this paper. This study includes the effects of polymer molecular characteristics, apparent shear rate, die geometrical characteristics (length to die gap (L/H) and width to die gap (W/H)), and distance from the die exit. It is found that the integral K-BKZ model predicts well both the width and thickness extrudate swells. Extrudate swell measurements demonstrate that the thickness swell is predominant in comparison with width swell.