Volume 37, Issue 3

Microneedles are sharp microscopic features, which can be used for drug or vaccine delivery in a minimally invasive way. Recently, we developed a method to produce polymer microneedles using laser ablated molds in an injection molding process. At this moment, extensive injection molding experiments are needed to investigate the replication fidelity. Accurate predictions of the injection molding process would eliminate these costly and time expensive experiments. In this study, we evaluated the replication fidelity of solid polymer microneedles using numerical simulations and compared the results to injection molding experiments. This study was performed for different sizes of microneedles, different thermoplastics (polypropylene and polycarbonate) and different mold materials (tool steel, copper alloy and aluminium alloy). Moreover, different processing conditions and different locations of the microneedles on the macroscopic part were considered. A good correlation with experimental findings was achieved by optimizing the heat transfer coefficient between the polymer and the mold, while using a multiscale mesh with a sufficient number of mesh elements. Optimal heat transfer coefficients between 10,000 and 55,000 W/m 2  K were found for the different combinations of polymer and mold materials, which resulted in an accuracy of the simulated microneedle replication fidelity between 94.5 and 97.0%.

Additive manufacturing (AM) is a versatile and promising method for rapid prototyping and advanced design applications. Owing to its unique potential for fast production rates, and capacity of creating complex shapes, the number of researches on AM techniques have increased day by day in the technical literature. In this work, contrary to common literature efforts focused on mechanical properties, friction and wear behaviors of additively manufactured PETG samples were analyzed experimentally. As a methodology, fused filament fabrication (FFF) was selected. In order to explore the influence of manufacturing factors on wear properties, layer thickness (0.1, 0.2, and 0.3 mm), infill rate (40, 60, 80, and 100%), and building direction (vertical and horizontal) were changed. Before the friction tests, dimensional accuracy, hardness, and surface roughness measurements were conducted to interpret better the wear results. In addition, macroscopic and microscopic inspections were performed to determine the correct reason behind the deformation. From the data collected during the tests, there was a positive interaction between volume loss and layer thickness. Besides, there was no direct interaction between infill rate/building direction and coefficient of friction. In comparison with vertically built samples, horizontally built samples were subjected to more plastic deformation, and their worn surfaces were severely damaged.

To study the influence of expansion temperature on the properties of expanded graphite (EBG), EBG 300 , EBG 600 , and EBG 900 were prepared by heating expandable graphite (EG) at 300, 600, and 900 °C, respectively. Furthermore, the influence of these EBGs on the combustion performance and physical-mechanical properties of linear low density polyethylene (LLDPE) were investigated. The expansion volumes of EBG 300 , EBG 600 , and EBG 900 increase with the rise of temperature, and a four-stage ordered structure of “graphite worm” gradually forms. The thermal stability increases gradually for EBG 300 , EBG 600 , and EBG 900 . On the contrary, the thermal conductivity decreases in sequence. However, the incorporation of EBG 900 promotes the formation of a continuous network structure and makes the modified LLDPE to present the best heat transmission. The addition of 30 wt% of these EBGs significantly improves LLDPE’s flame retardancy and high-temperature thermal stability. The total heat release, the peak value of heat release rate, and the fire growth index of 70LLDPE/30EBG 300 reduce by 69, 91, and 87% respectively, while the effective fire performance index improves seven times. The addition of these additives reduces the tensile strength and elongation at break, the larger the EBG size, the more obvious the effect.

This study aims at determining the mechanical deformation behavior of recycled poly (ethylene terephthalate) (r-PET) with digital image correlation (DIC) and finite element method (FEM), and to investigate the morphological, thermal, and rheological properties of r-PETs. Waste bottles were collected in trash bins and granulated with a cutter. Neat PET (n-PET) was also was used to determine accurately the changes in the properties of r-PET. PET test samples were obtained by injection molding at 260, 265, 270, and 275 °C. DIC and FEM were conducted to detect the deformation behavior of the PETs under mechanical loading. The data showed that the behavior of n-PETs and r-PETs were similar, and the stress distribution was found to densify in various areas for both PETs. The mechanical properties generally increased with increasing processing temperature, the best mechanical properties being obtained for thPETs processed at 275 °C. Scanning electron microscopy (SEM) analysis showed that the morphology of all the PETs were similar. Thermal stability was also found to be similar. The rheological moduli of n-PET processed at 260 °C were the highest, while processing r-PET at 275 °C improved its rheological properties.

Biodegradable films based on mung bean protein (1, 3 and 5%) incorporated with cumin essential oil (EO) (0, 0.25 and 0.5 ml/g protein) were developed. Adding cumin oil and increasing the protein content enhanced the thickness, tensile strength and yellowness. Films incorporated with EO exhibited less water vapor permeability and water solubility, as compared to the control films. A higher antioxidant activity was also obtained by increasing the EO and protein ratios. Films with higher levels of protein displayed lower thermal stability with a lower degradation temperature, as suggested by thermo-gravimetric analyses. In addition, the incorporation of EO reduced thermal stability, as confirmed by the higher weight loss and lower degradation temperature. Furthermore, mung bean protein films containing 0.5 ml cumin oil/g protein had suitable physical characteristics, antioxidant activities, water barrier properties and thermal stability; thus, they can be used as appropriate biodegradable packaging materials for food preservation.

In order to improve the flame retardancy and smoke suppression of polyvinyl chloride (PVC), ammonium octamolybdate (AOM)/nano-antimony trioxide (nano-Sb 2 O 3 )/dioctyl Phthalate (DOP)/PVC composites were prepared by high energy ball milling and melt blending methods using AOM as the smoke suppressant. The effects of AOM on the flame retardancy and smoke suppression of the PVC composites were studied by means of vertical burning tests (UL-94), limiting oxygen index (LOI), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and cone calorimetry (CCT). The results showed that the flame retardancy of PVC composites containing AOM was improved, namely the UL-94 grade of the composites reached the V-0 grade and the LOI increased from 22.3% to 30.6%, whilst the heat release rate (HRR), total heat release (THR), smoke production rate (SPR), total smoke production (TSR) and smoke factor (SF) decreased significantly. In addition, AOM could promote the dehydrochlorination reaction of the PVC composites at lower temperature, resulting in more compact and continuous char residues. Therefore, AOM is an effective smoke suppressant and has a good synergistic flame retardant effect with nano-Sb 2 O 3 in flame retardant PVC matrix composites.

The poor adhesion of TPU films limits their extensive application in lightweight laminated glass (LLG). A simple and effective method is reported in this paper to obtain modified TPU films by silane coupling agent (SCA) treatment. The polar groups (such as urethane groups, carboxyl groups, etc.) on the surface of TPU films reacted chemically with the reactive groups of SCA. Meanwhile, hydrogen bonds were formed between the silicon hydroxyl groups generated by the hydrolysis of SCA. Therefore, the adhesivity and thermal stability of TPU films were improved. Moreover, the surface of TPU films became rough after modification, hence the interfacial bonding area between TPU film and glass increased, which furthered the bonding effect of TPU film with glass plate. Compared with unmodified TPU films, the tensile shear bond strength (TSBS) of modified TPU films increased by nearly 28%, and the initial decomposition temperature increased from 277 °C to a maximum of 295.3 °C. The impact resistance of LLG was significantly improved due to the improvement of the adhesivity of TPU film.