Volume 33, Issue 4

Ultrasonic micro-molding technology can dispense, melt and inject as small an amount of polymer as is required for one cycle, an advantage which makes the process highly desirable for low-volume and customized production of micro parts made from sensitive and very expensive polymers, especially in the medical sector. In this study, the feasibility of processing the polyetheretherketone (PEEK) polymer was investigated. The experiments conducted determined the parameters of a process that would allow parts with specific mechanical properties to be produced and verified as not degraded. The development of the process used three amplitude values as well as varying plunger velocity and vibration times. The three amplitude values and four speed values were tested to determine appropriate parameters for the ultrasonic process. Completely filled samples without any visual signs of degradation were analysed using FTIR-ATR, crystallinity percentage and tensile strength tests. Results show that the amplitude parameter is an important factor in the ultrasonic process and the higher its value is, the better the mechanical properties of complete parts are. Moreover, the tensile strength value of the specimens fabricated by ultrasonic micro-molding is comparable to that of conventional injection molding technology.

Internal heat exchangers are often employed in solar thermal applications as well as in many other applications that involve heat, and, for the most part, consist of metallic materials (copper, stainless steel). Corrugated stainless steel tubes are easy to assemble, and are commonly used in various storage geometries. In order to significantly reduce costs, alternative materials, such as plastics, can function as excellent substitutes. Alternative heat exchangers for the following examinations using various materials and an extrusion process were produced. Subsequently, the heat exchangers were examined in regards to the heat they transfer. The heat transfer coefficient and the thermal conductivity of all materials were determined.

To improve the performances of waste rubber powder filled polypropylene (PP/WRP) blends, WRP was modified by γ-aminopropyltriethoxysilane (APTES) via mechano-chemical method, and then maleic anhydride (MAH) grafted PP (mPP) and MAH grafted ethylene-α-octene copolymer (mEOC) were chosen as the interfacial compatibilizers. The PP/WRP blends were prepared by melt-compounding and compression, and their morphological structures, tensile properties and thermal behavior were investigated carefully. Results showed that modification of APTES decreased the surface energy of WRP and facilitated its compatibility to PP. Both mPP and mEOC could further enhance their interfacial bonding and mPP was superior to mEOC in increasing the tensile strength and elastic modulus. Thermal analysis revealed relative lower melting temperature and crystallinity but higher activation energy for PLA/WRP blends in comparison to pristine PP.

The morphology of nanoporous nickel phosphate (NP) has a close relationship with its properties, so in this work NP with needle-like and mushroom-like shape was synthesized. Then NP with needle-like and mushroom-like shape was applied in intumescent flame retardant polypropylene (PP) composites. With the addition of suitable content of NP, both mushroom-like and needle-like NP can improve the combustion and thermal properties of intumescent flame retardant PP composites. Needle-like NP shows a better thermal ant flame retardant synergist effect with intumescent flame retardants compared to mushroom-like NP. However, mushroom-like NP shows a better effect on smoke suppression. With the addition of suitable content of needle-like NP, the peak heat release rate of flame retardant PP composite decreases by 68.2 % comparing with that of the pure PP, and decreases by 23.8 % comparing with that of flame retardant PP composite without NP. The maximum weight loss temperature of PP composites can be increased from 408 °C to 485 °C with the addition of needle-like NP. Furthermore, the pyrolysis products of flame retardant PP composite with needle-like NP were investigated. From the research, it provides a further understanding of the influence on synergic effects in intumescent flame retardant systems.

The sulfonated cardo poly(aryl ether sulfone) with zwitterionic side groups (PES-DS-70) was electrospun to bead-free nanofibers. The PES-DS-70 nanoporous mat was successfully filled with Nafion solution. Scanning electron microscopy observed that the PES-DS-70/Nafion composite membrane has bilayer morphology and good interfacial compatibility. Compared with the neat PES-DS-70, the PES-DS-70/Nafion bilayer membranes showed improved swelling resistance and proton conductivity. Moreover, methanol crossover of the composite film was suppressed due to incorporation of the PES-DS-70 nanofibers. The tensile strength and Young's modulus for the PES-DS-70/Nafion composite membranes were higher than Nafion117. Therefore, the composite membrane with superior combined properties has potential applications for polymer electrolyte membrane fuel cells.

The task of the solid conveying section is to collect the entering material and transfer it to the melt dominated sections. Therefore, its upstream interface is the hopper and its downstream interface is the section in which the first melting occurs. Beneath the hopper opening, the screw rotation collects and conveys the material forward. It is hereby assumed that the friction forces among the particles are higher than the transferring forces on the screw and barrel. For that reason commonly known models for describing the solid conveying in single screw extruders assume that the screw channel is always completely filled so that a plug flow occurs. At high screw speeds, however, these assumptions are no longer valid. To analyze and mathematically describe the solid conveying behavior at screw speeds up to 2000 rpm, simulations based on the Discrete Element Method have been executed in previous investigations. Based on this, a model for describing the solid conveying behavior was developed which enables a variation of general screw and hopper geometry parameters but neglects the backpressure that inhibits the solid movement. For that reason, further investigations based on the Discrete Element Method are presented in this paper, which enable a consideration of the backpressure and pressure build-up in the feeding zone. Astonishingly, at high screw speeds a low filling degree in the screw channel was observed which did not fulfill the expectations of an always fully filled channel due to a backpressure forced particle backlog. Based on the investigations, a mathematical model has been developed which now fully comprehends the effects occurring in the solid conveying section. The conducted simulations were subsequently validated by experimental investigations. Therefore, a test bench was designed which enables solid conveying analysis with adjustable backpressures. The results indicate a good agreement with the formulated model which now enables the calculation of solid conveying zones with consideration of the pressure build-up and filling degrees.

Thermoplastic elastomer (TPE) and thermoplastic vulcanizate (TPV) polyvinylchloride/acrylonitrile butadiene rubber (PVC/NBR) (70/30) blends containing 0, 0.5, 1, 1.5 and 2 phr graphene nanoplatelets (GnP) were prepared by melt mixing. The morphology and properties of resulting samples were investigated. Scanning electron microscopy (SEM) and transmission electron microcopy (TEM) techniques were employed for morphology studies. The progressive incorporation of GnP into PVC/NBR blends led to a gradual decrease in the size of NBR domains. TEM revealed fine distribution of GnP nanoplatelets in the blends. DMTA results showed a monotonic increase in storage modulus along with a steady decrease in damping factor with the GnP content in TPE and TPV nanocomposites. Mechanical properties revealed enhanced elastic modulus and ultimate strength at the cost of a fall in the elongation at break for TPE and TPV nanocomposites as a function of GnP loading. The swelling index of the samples declined with GnP content up to 1 phr after which the swelling index was not considerably affected by GnP up to 2 phr. A substantial increase in the electrical conductivity of the resulting nanocomposites was observed at GnP loadings higher than 1 phr. TPV samples demonstrated higher stiffness and strength along with lower extensibility, swelling indexes and electrical conductivity than their TPE counterparts.

This study aims at exploring composite materials based on polymer matrix for microelectronics application. Materials used for such applications need to have added multifunctional properties. Up to now, a sole polymer or single filler-filled polymer composites is tough to satisfy the demand for more multifunctional properties, particularly to acquire high effective thermal conductivity and low-dielectric constant simultaneously. In this study, hybrid filler systems i.e. aluminum nitride of average particle size 60 to 70 micron and solid glass microspheres of 90 to 100 micron were incorporated into epoxy matrix in an attempt to reach a composite with such desired properties. By varying the volume fraction of fillers (5 to 25 % for aluminum nitride and 5 to 10 % for solid glass microspheres), a new kind of epoxy-matrix composite is fabricated on a laboratory scale by simple hand lay-up technique keeping in mind the fact that the future electronic packaging materials would possess high heat dissipation capability, high glass transition temperature, low coefficient of thermal expansion and low dielectric constant for appropriate functioning of the electronic substrate. In addition, the measured thermal conductivity is compared with calculated values obtained from the proposed mathematical model and found that they are in better agreement with the values obtained from the proposed correlation.

A series of polypropylene/multi-walled carbon nanotubes (PP/CNT) nanocomposites were prepared by masterbatch dilution, then followed by microinjection molding under a defined set of processing conditions. A micropart (μ-part) which has a three-step decrease in thickness along the flow direction was fabricated to study the effect of abrupt geometrical changes in mold cavities on the distribution of CNT in PP. To facilitate characterization, the μ-parts were divided into three sections based on thickness. The distribution of CNT within each section of subsequent μ-parts was evaluated by morphological observations and electrical resistivity measurements. In addition, the thermal properties of pure PP and PP/CNT nanocomposites as well as each section of subsequent μ-parts, were assessed by differential scanning calorimetry and thermogravimetric analysis.

Constant growth of waste polymers around the world leads to several environmental problems. This is why solutions to reuse these high amounts of materials available must be developed. In this work, highly filled (up to 90 wt.%) recycled polyethylene (R-PE)/ground tire rubber (GTR) thermoplastic elastomers were prepared by extrusion compounding and injection molding. To improve on processability and overall properties, two copolymers (Engage 8180 and Vestenamer 8012) were added as compatibilizers for comparison. SEM results showed that compatibilizer addition changed the blend morphology. In all cases, the mechanical properties in tension and flexion decreased with GTR addition. It was also observed that the addition of a copolymer improved on some properties (such as elongation at break), but Engage 8180 showed better compatibilization effect than Vestenamer 8012 which was confirmed from SEM analysis, while other properties (tensile strength, Young's and flexural modulus) were reduced due to lower GTR and compatibilizer moduli. For impact strength, negligible variation was observed below 40 wt.% GTR. However, the samples did not break for GTR contents above 60 wt.%. Density increased with GTR content, while Shore A and D hardness decreased. Overall, the addition of a compatibilizer mostly enabled to produce compounds at higher GTR contents (above 70 wt.%). From the result obtained, it can be concluded that recycled materials can be used to produce blends with reasonable quality for automotive, packaging and construction applications since the mechanical properties can be optimized via formulation over a very wide range of GTR (0–90 wt.%).

In this work, the combustion, thermal, and mechanical performances of long-glass-fiber-reinforced polypropylene/intumescent flame retardant (LGFPP/IFR) composites with different contents of polyamide 6 (PA6) as a charring agent were investigated by limiting oxygen index (LOI), UL-94 test, cone calorimetry, thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), and mechanical property test. The results showed that LGFPP/IFR/PA6 composites exhibited much better flame retardancy due to the dense char layer structure, as proved by SEM. When 15 wt% PA6 was added, the LGFPP/IFR composites had the best flame retardancy, and LOI increased by 55.1 %, and the UL-94 reached V-0 rating. The cone calorimeter tests indicated that PA6 could prevent the transmission of heat and the volatilization of flammable substances, thereby reducing the heat release of “second burning”. According to TGA analysis, the carbon layer began to form at a lower temperature due to the synergistic effect between IFR and PA6. Moreover, the calculation of apparent active energy (E a ) revealed that PA6 effectively increased the E a values of the composites, resulting in a better thermal stability and flame retardancy. In addition, PA6 enhanced the mechanical properties of the composites effectively.

Understanding the effect of fiber orientation on mechanical properties is a primary consideration for long fiber-reinforced thermoplastics in automotive applications. In injection-molded parts, the classical Folgar-Tucker model has been used to predict the shell-core structure of short fiber orientation patterns. However, this model results in a thinner core region for long fiber composites. Recently, the RSC (Reduced Strain Closure), ARD (Anisotropic Rotary Diffusion), and iARD-RPR (improved ARD and Retarding Principal Rate) models are potential models developed in relation to suspension rheology. In addition to improving the inaccurate predictions, a so-called inlet condition of fiber orientation set at the gate is examined in the RSC. In this approach, a significant requirement is to numerically investigate the nature of the shell-core structure, while validating a predictive difference between the orientation models via related experimental data. Dramatic changes in the orientation distribution at various filling times and mold temperatures are discussed herein.

The relaxation behavior of PMMA-PS core-shell particles in PP matrix was studied. The effects of composition and viscosity ratio of core and shell forming components on relaxation processes of PP/(PMMA+PS) 80/20 ternary blends were evaluated at three different temperatures (200, 225 and 250°C) and discussed. For the ternary blends containing low-viscosity PMMA (PP/L-PMMA/PS), the shape relaxation time, λ, sharply reduced at first with PS content and then increased after passing through a minimum with further increase in the PS content. The corresponding relaxation strength, λ.H(λ), increased suddenly at first and then monotonically decreased upon further incorporation of PS. The changes of λ and λ.H(λ) with PS content were attributed to a change in the interfacial energy (shell formation) and average viscosity of the dispersed composite droplets upon progressive addition of PS into PP/L-PMMA blend so that the minimum λ corresponding to the maximum λ.H(λ) was observed at shell completion composition with finest core-shell- particles (12 wt% of PS phase). The core-shell particles of all the ternary blends containing L-PMMA exhibited a shape relaxation at 200°C, while at the same temperature for the blends containing high-viscosity PMMA (H-PMMA) no shape relaxation peak was detected when the PS shell content was lower than 62 wt%. This was attributed to restriction effect of non-deformable H-PMMA core droplets, which led to no droplet relaxation. At higher PS contents, appearance of the shape relaxation peak was related to the relaxation of PS shell, suggesting that there is a critical shell thickness above which the relaxation behavior of core-shell droplets is dominated by the low-viscous PS shell. Increase in temperature from 200 to 250°C reduced the PS shell content corresponding to onset of deformation and accelerated the relaxation of composite droplets.

The mechanical properties of polyethylene (PE)/polypropylene (PP)/styrene-ethylene/butylene-styrene (SEBS)/mica composites were investigated as a model composition. Four types of mica with different particle sizes and different aspect ratios were used. These composites were extruded by a twin-screw extruder and subsequently injection molded, and their mechanical properties, including their tensile, bending, and impact properties were evaluated. The addition of mica to PE/PP/SEBS effectively improved its mechanical properties; the addition of SEBS as a compatibilizer likewise enhanced the mechanical properties compared with those of PE/PP composites without SEBS. The use of larger average particle size and higher aspect ratio mica, such as M-35, M-27, and P-33, effectively increased the tensile and bending properties of the PE/PP/SEBS/mica composites. The morphologies of the composites with an added mica as observed by scanning electron microscopy, showed good dispersion between the matrix polymer and the mica.

Filled polymer compounds can present processing challenges, including poor dispersive mixing, high screw shaft torque and energy consumption, flow instabilities, and significant increases in melt pressures and temperatures. Previous theoretical development and experimental evaluations of polymer melts filled with particulate solids showed that the viscosity can be described with a model based on percolation theory concepts. This paper describes a batch mixer characterization method developed to measure the effects of filler concentration and operating conditions on the melt viscosity and process response. Experimental results are compared with capillary rheometer measurements using several low-density polyethylene resins, calcium carbonate and titanium dioxide. The theoretical treatment of the viscosity as a particulate percolating system with power-law behavior was used to analyze and compare rheometer and batch mixer data. The effects of resin molecular weight, filler type and size on viscosity and melt processing were examined and there was good agreement between rheometer and mixer viscosity trends, and percolation model predictions. The laboratory experiments and model estimates provide quantitative information that can be used to develop and troubleshoot extrusion compounding, single screw extrusion and low-shear forming processes.