Processing Effects on the Through-Plane Electrical Conductivities and Tensile Strengths of Microcellular-Injection-Molded Polypropylene Composites with Carbon Fibers.

Polymers reinforced with conducting fibers to achieve electrical conductivity have attracted remarkable attention in several engineering applications, and injection molding provides a cost-effective way for mass production. However, the electrical performance usually varies with the molding conditions. Moreover, high added content of conducting fibers usually results in molding difficulties. In this study, we propose using microcellular (MuCell) injection molding for polypropylene (PP)/carbon fiber (CF, 20, and 30 wt%) composites and hope that the MuCell injection molding process can improve both electrical and mechanical performance as compared with conventional injection molded (CIM) parts under the same CF content. Both molding techniques were also employed with and without gas counter pressure (GCP), and the overall fiber orientation, through-plane electrical conductivity (TPEC), and tensile strength (TS) of the composites were characterized. Based on the various processing technologies, the results can be described in four aspects: (1) Compared with CIM, microcellular foaming significantly influenced the fiber orientation, and the TPECs of the samples with 20 and 30 wt% CF were 18-78 and 5-8 times higher than those of the corresponding samples molded by CIM, respectively; (2) when GCP was employed in the CIM process, the TPEC of the samples with 20 and 30 wt% CF increased by 3 and 2 times, respectively. Similar results were obtained in the case of microcellular injection molding-the TPEC of the 20 and 30 wt% composites increased by 7-74 and 18-32 times, respectively; (3) although microcellular injection molding alone (i.e., without GCP) showed the greatest influence on the randomness of the fiber orientation and the TPEC, the TS of the samples was the lowest due to the uncontrollable foaming cell size and cell size uniformity; (4) in contrast, when GCP was employed in the microcellular foaming process, high TS was obtained, and the TPEC was significantly enhanced. The high foaming quality owing to the GCP implementation improved the randomness of fiber orientation, as well as the electrical and mechanical properties of the composites. Generally speaking, microcellular injection combined with gas counter pressure does provide a promising way to achieve high electrical and mechanical performance for carbon-fiber-added polypropylene composites.

The Investigation of Novel Dynamic Packing Technology for Injection Molded Part Quality Control and Its Production Stability by Using Real-Time PVT Control Method.

Injection molding is an effective mass production process for plastic, partly due to a number of advantages such as complex shape moldability, material selectivity, and a rapid process cycle. However, highly labor-based conventional production restrains the development of the industry. Experience-driven molding setups are used to trial the mold process, and also for quality checking the molded part for mass production. There is no effective solution for maintaining the production stability and defect-free adjustment. This study aimed to establish scientific packing pressure setup technology to optimize the molded part quality and the stability of consecutive production. The dynamic packing pressure setup technology for molded part quality and the process stability were investigated. This not only achieves the optimization of the packing pressure setup, but the stabilization of quality in mass production. Four major qualities were discussed in this study including tensile strength, regional deviation on shrinkage, total shrinkage, and warpage. The qualities improved by up to 3.9%, 92.9%, 41.9%, and 9.2%, respectively. A series of pilot runs of 300 cycles for two packing pressure control methods were tested to investigate the stability of the qualities. Dynamic packing pressure control improved the weight replication by 54%, reduced total shrinkage by 23%, and improved the warpage by 12%.

Using Gas Counter Pressure and Combined Technologies for Microcellular Injection Molding of Thermoplastic Polyurethane to Achieve High Foaming Qualities and Weight Reduction.

Microcellular injection molding technology (MuCell®) using supercritical fluid (SCF) as a foaming agent offers many advantages, such as material and energy savings, low cycle time, cost-effectiveness, and the dimensional stability of products. MuCell® has attracted great attention for applications in the automotive, packaging, sporting goods, and electrical parts industries. In view of the environmental issues, the shoe industry, particularly for midsole parts, is also seriously considering using physical foaming to replace the chemical foaming process. MuCell® is thus becoming one potential processing candidate. Thermoplastic polyurethane (TPU) is a common material for molding the outsole of shoes because of its outstanding properties such as hardness, abrasion resistance, and elasticity. Although many shoe manufacturers have tried applying Mucell® processes to TPU midsoles, the main problem remaining to be overcome is the non-uniformity of the foaming cell size in the molded midsole. In this study, the MuCell® process combined with gas counter pressure (GCP) technology and dynamic mold temperature control (DMTC) were carried out for TPU molding. The influence of various molding parameters including SCF dosage, injection speed, mold temperature, gas counter pressure, and gas holding time on the foaming cell size and the associated size distribution under a target weight reduction of 60% were investigated in detail. Compared with the conventional MuCell® process, the implementation of GCP technology or DMTC led to significant improvement in foaming cell size reduction and size uniformity. Further improvement could be achieved by the simultaneous combination of GCP with DMT, and the resulting cell density was about fifty times higher. The successful possibility for the microcellular injection molding of TPU shoe midsoles is greatly enhanced.

Transfer Learning Applied to Characteristic Prediction of Injection Molded Products.

This study addresses some issues regarding the problems of applying CAE to the injection molding production process where quite complex factors inhibit its effective utilization. In this study, an artificial neural network, namely a backpropagation neural network (BPNN), is utilized to render results predictions for the injection molding process. By inputting the plastic temperature, mold temperature, injection speed, holding pressure, and holding time in the molding parameters, these five results are more accurately predicted: EOF pressure, maximum cooling time, warpage along the Z-axis, shrinkage along the X-axis, and shrinkage along the Y-axis. This study first uses CAE analysis data as training data and reduces the error value to less than 5% through the Taguchi method and the random shuffle method, which we introduce herein, and then successfully transfers the network, which CAE data analysis has predicted to the actual machine for verification with the use of transfer learning. This study uses a backpropagation neural network (BPNN) to train a dedicated prediction network using different, large amounts of data for training the network, which has proved fast and can predict results accurately using our optimized model.

A Methodology to Predict and Optimize Ease of Assembly for Injected Parts in a Family-Mold System.

In this study, the assembly behavior for two injected components made by a family mold system were investigated. Specifically, a feasible method was proposed to evaluate the characteristic length of two components within a family mold system using numerical simulation and experimental validation. Results show that as the packing pressure increases, the product index (characteristic length) becomes worse. This tendency was consistent for both the simulation prediction and experimental observation. However, for the same operation condition setting through a basic test, there were some differences in the product index between the simulation prediction and experimental observation. Specifically, the product index difference of the experimental observation was 1.65 times over that of the simulation prediction. To realize that difference between simulation and experiment, a driving force index (DFI) based on the injection pressure history curve was proposed. Through the DFI investigation, the internal driving force of the experimental system was shown to be 1.59 times over that of the simulation. The DFI was further used as the basis for machine calibration. Furthermore, after finishing machine calibration, the integrated CAE and DOE (called CAE-DOE) strategy can optimize the ease of assembly up to 20%. The result was validated by experimental observation.

Effects of Injection Molding Process Parameters on the Chemical Foaming Behavior of Polypropylene and Polystyrene.

In the present study, semi-crystalline polypropylene (PP) and amorphous polystyrene (PS) were adopted as matrix materials. After the exothermic foaming agent azodicarbonamide was added, injection molding was implemented to create samples. The mold flow analysis program Moldex3D was then applied to verify the short-shot results. Three process parameters were adopted, namely injection speed, melt temperature, and mold temperature; three levels were set for each factor in the one-factor-at-a-time experimental design. The macroscopic effects of the factors on the weight, specific weight, and expansion ratios of the samples were investigated to determine foaming efficiency, and their microscopic effects on cell density and diameter were examined using a scanning electron microscope. The process parameters for the exothermic foaming agent were optimized accordingly. Finally, the expansion ratios of the two matrix materials in the optimal process parameter settings were compared. After the experimental database was created, the foaming module of the chemical blowing agents was established by Moldex3D Company. The results indicated that semi-crystalline materials foamed less due to their crystallinity. PP exhibits the highest expansion ratio at low injection speed, a high melt temperature, and a low mold temperature, whereas PS exhibits the highest expansion ratio at high injection speed, a moderate melt temperature, and a low mold temperature.

Using P(Pressure)-T(Temperature) Path to Control the Foaming Cell Sizes in Microcellular Injection Molding Process.

Microcellular injection molding technology (MuCell) using supercritical fluid (SCF) as a foaming agent is one of the important green molding solutions for reducing the part weight, saving cycle time, and molding energy, and improving dimensional stability. In view of the environmental issues, the successful application of MuCell is becoming increasingly important. However, the molding process encounters difficulties including the sliver flow marks on the surface and unstable mechanical properties that are caused by the uneven foaming cell sizes within the part. In our previous studies, gas counter-pressure combined with dynamic molding temperature control was observed to be an effective and promising way of improving product quality. In this study, we extend this concept by incorporating additional parameters, such as gas pressure holding time and release time, and taking the mold cooling speed into account to form a P(pressure)-T(temperature) path in the SCF PT diagram. This study demonstrates the successful control of foaming cell size and uniformity in size distribution in microcellular injection molding of polystyrene (PS). A preliminary study in the molding of elastomer thermoplastic polyurethanes (TPU) using the P-T path also shows promising results.

An Automatic Lab-on-Disc System for Blood Typing.

A blood-typing assay is a critical test to ensure the serological compatibility of a donor and an intended recipient prior to a blood transfusion. This article presents a lab-on-disc blood-typing system to conduct a total of eight assays for a patient, including forward-typing tests, reverse-typing tests, and irregular-antibody tests. These assays are carried out in a microfluidic disc simultaneously. A blood-typing apparatus was designed to automatically manipulate the disc. The blood type can be determined by integrating the results of red blood cell (RBC) agglutination in the microchannels. The experimental results of our current 40 blood samples show that the results agree with those examined in the hospital. The accuracy reaches 97.5%.

Biomimetic composite scaffolds based on surface modification of polydopamine on electrospun poly(lactic acid)/cellulose nanofibrils.

An appropriate surface chemical property is crucial in tissue engineering scaffolds, which promotes cell attachment and proliferation. A biomimetic composite scaffold with a polydopamine (PDA) coating layer on electrospun poly(lactic acid) (PLA)/cellulose nanofibrils (CNF) composite nanofiber was developed in this study. PLA/CNF composite nanofibers were fabricated and then coated via treatment with a dopamine solution. The PDA coating layer was successfully formed on the surface of the PLA/CNF composite nanofiber by using a simple, environment-friendly, and effective procedure. Results indicated that the addition of CNF into the PLA matrix can effectively improve the deposition rate of the PDA coating layer on the surface of the composite nanofiber during the initial stage of coating because of hydrogen bonding between the CNF and PDA molecular chains. The hydrophilicity and mechanical properties of the PLA/CNF-PDA scaffold were higher than those of the PLA/CNF scaffold. In addition, the cell culture test showed that the adhesion, proliferation, and growth of human mesenchymal stem cells (hMSCs) cultured on the PLA/CNF-PDA scaffold were significantly enhanced relative to those cultured on the PLA/CNF scaffold because of the introduction of the PDA coating. This finding suggested that surface biofunctionalization via the PDA coating layer could simply and effectively enhance cell biocompatibility for polymer-based scaffolds.

Chemical absorption of carbon dioxide with asymmetrically heated polytetrafluoroethylene membranes.

In this study, the absorption of carbon dioxide using an absorbent composed of 2-amino-2-methyl-L-propanol (AMP) + monoethanolamine (MEA) + piperazine (PZ) in asymmetric and symmetric polytetrafluoroethylene (PTFE) membrane contactors was investigated. Experiments were conducted using various gas flow rates, liquid flow rates, and absorbent blends. CO(2) recovery increased with increasing liquid flow rates. The mean pore size of PTFE membrane reduced via heating treatment. An asymmetric membrane had a better CO(2) recovery than a symmetric membrane. For the asymmetric membrane, placing the smaller pore-size side of the membrane in contact with the liquid phase, reduced the level of wetting of the membrane. The membrane mass transfer coefficient and durability of the PTFE membrane were enhanced by asymmetrically heating.

Patterning nanowire and micro-nanoparticle array on micropillar-structured surface: Experiment and modeling.

DNA molecules in a solution can be immobilized and stretched into a highly ordered array on a solid surface containing micropillars by molecular combing technique. However, the mechanism of this process is not well understood. In this study, we demonstrated the generation of DNA nanostrand array with linear, zigzag, and fork-zigzag patterns and the microfluidic processes are modeled based on a deforming body-fitted grid approach. The simulation results provide insights for explaining the stretching, immobilizing, and patterning of DNA molecules observed in the experiments.

Effects of shape, porosity, and operating parameters on carbon dioxide recovery in polytetrafluoroethylene membranes.

In this study, the recovery of carbon dioxide using an absorbent composed of 2-amino-2-methyl-l-propanol (AMP)+monoethanolamine (MEA)+piperazine (PZ) in polytetrafluoroethylene (PTFE) membrane contactors was investigated. Experiments were conducted using various gas flow rates, liquid flow rates, absorbent blends, and pore size membranes. CO(2) recovery increased with increasing liquid flow rates. The blended amine absorbent had a synergistic effect on CO(2) recovery. CO(2) recovery increased as the pore size of the PTFE membrane decreased. An asymmetric membrane had a better CO(2) recovery than that of symmetric membrane. Besides, membrane mass transfer coefficient and operational stability of asymmetric membrane were enhanced. For an asymmetric membrane, the smaller pore-size side of the membrane surface contacting the liquid phase can reduce the level of wetting of the membrane.

The application of fuzzy theory for the control of weld line positions in injection-molded part.

This research proposes the fuzzy theory for the control of weld lines in plastic injection molding. The weld line occurs as a result of geometrical changes in molded parts in the injection molding process. The weld line is one of the defects present in plastic injection-molded parts; the line affects the quality of parts as well as the strength of the products. In the present study, fuzzy theory was applied in the design of injection molding. First, expert experiences were transformed into IF approximately THEN approximately rules to establish the knowledge base for developing fuzzy inference rules. The rules were then used to adjust the molding parameters, which in turn were applied to control the weld line position in the injection molding process. The results indicate that fuzzy theory exhibited favorable applicability in the control of the weld line as well as decreased the simulation time, thereby accelerating the design process of injection molding.