Hydrophobicity Tuning by the Fast Evolution of Mold Temperature during Injection Molding

Hybrid Hemp Particles as Functional Fillers for the Manufacturing of Hydrophobic and Anti-icing Epoxy Composite Coatings

The development of hydrophobic composite coatings is of great interest for several applications in the aerospace industry. Functionalized microparticles can be obtained from waste fabrics and employed as fillers to prepare sustainable hydrophobic epoxy-based coatings. Following a waste-to-wealth approach, a novel hydrophobic epoxy-based composite including hemp microparticles (HMPs) functionalized with waterglass solution, 3-aminopropyl triethoxysilane, polypropylene-graft-maleic anhydride, and either hexadecyltrimethoxysilane or 1H,1H,2H,2H-perfluorooctyltriethoxysilane is presented. The resulting epoxy coatings based on hydrophobic HMPs were cast on aeronautical carbon fiber-reinforced panels to improve their anti-icing performance. Wettability and anti-icing behavior of the prepared composites were investigated at 25 °C and -30 °C (complete icing time), respectively. Samples cast with the composite coating can achieve up to 30 °C higher water contact angle and doubled icing time than aeronautical panels treated with unfilled epoxy resin. A low content (2 wt %) of tailored HMPs causes an increase of ∼26% in the glass transition temperature of the coatings compared to pristine resin, confirming the good interaction between the hemp filler and epoxy matrix at the interphase. Finally, atomic force microscopy reveals that the HMPs can induce the formation of a hierarchical structure on the surface of casted panels. This rough morphology, combined with the silane activity, allows the preparation of aeronautical substrates with enhanced hydrophobicity, anti-icing capability, and thermal stability.

Investigation of the Strength of Plastic Parts Improved with Selective Induction Heating

The use of selective induction heating of molding surfaces allows for better filling of molding cavities and has a positive effect on the properties of molded products. This is particularly important in the production of parts that include flexible hinges, which are thin plastic layers connecting two or more parts of the product. By using hinges, it is possible to expand the use of injection molding products and their capabilities. They are widely used in the production of parts for the electrical engineering industry and for packaging Fast Moving Consumer Goods (FMCG). The use of hinges also entails specific reductions in wall thickness. Increases in the shear rate can be expected, which can lead to the degradation of polymers and deterioration of mechanical properties of materials. This paper investigates injection molded flexible hinge parts manufactured with selective induction heating to improve their properties. To verify the efficiency of reduction of material degradation due to high shear rates, open/close tests of elastic hinges were performed. The linear relation between the number of cycles the hinges can withstand, mold temperature and injection time was identified, where mold temperature was the more significant factor.

Design and Simulation Study of the Induction Heated Injection Mold with Sliders

In order to increase the quality of the products manufactured by injection molding, RTC technology can be used to achieve higher mold temperatures. As a result, the path of the injected melt can be extended, allowing the production of parts with more complex shapes and greater length. Induction heating allows heating only selected forming surfaces of the mold which increases the speed and efficiency of the process. This paper presents the concept of a detachable inductor integrated with sliders to enable the application of this technology in an injection mold with sliders, along with the theoretical model used to perform the tests. First, the effect of the magnetic concentrator shape on the process was analyzed. This was followed by a simulation study of the influence of process parameters: heating time, frequency, and electric current. An extensive analysis of the test results of the temperature distribution on the insert allowed for the selection of parameter sets that would enable obtaining the desired surface temperature without a major increase in process time. The results of simulation studies confirm the possible applications and present the range of parameters for obtaining the optimal process.

Atomistic Investigation on the Wetting Behavior and Interfacial Joining of Polymer-Metal Interface

Polymer-metal hybrid structures can reduce the weight of components while ensuring the structural strength, which in turn save cost and subsequently fuel consumption. The interface strength of polymer-metal hybrid structure is mainly determined by the synergistic effects of interfacial interaction and mechanical interlocking. In this study, the wetting behavior of polypropylene (PP) melt on metal surface was studied by molecular dynamics simulation. Atomistic models with smooth surface and nano-column arrays on Al substrate were constructed. Influences of melt temperature, surface roughness and metal material on the wetting behavior and interfacial joining were analyzed. Afterwards the separation process of injection-molded PP-metal hybrid structure was simulated to analyze joining strength. Results show that the initially sphere-like PP model gradually collapses in the wetting simulation. With a higher temperature, it is easier for molecule chains to spread along the surface. For substrate with rough surface, high density is observed at the bottom or on the upper surface of the column. The contact state is transitioning from Wenzel state to Cassie–Baxter state with the decrease of void fraction. The inner force of injection-molded PP-Fe hybrid structure during the separation process is obviously higher, demonstrating a greater joining strength.

Three-Dimensionally-Printed Polyether-Ether-Ketone Implant with a Cross-Linked Structure and Acid-Etched Microporous Surface Promotes Integration with Soft Tissue

Polyether-ether-ketone (peek) is one of the most common materials used for load-bearing orthopedic devices owing to its radiolucency and favorable mechanical properties. However, current smooth-surfaced peek implants can lead to fibrous capsule formation. To overcome this issue, here, peek specimens with well-defined internal cross-linked structures (macropore diameters of 1.0–2.0 mm) were fabricated using a three-dimensional (3D) printer, and an acid-etched microporous surface was achieved using injection-molding technology. The cell adhesion properties of smooth and microporous peek specimens was compared in vitro through a scanning electron microscope (SEM), and the soft tissue responses to the both microporous and cross-linked structure of different groups were determined in vivo using a New Zealand white rabbit model, and examined through histologic staining and separating test. The results showed that the acid-etched microporous surface promoted human skin fibroblasts (HSF) adherence, while internal cross-linked structure improved the ability of the peek specimen to form a mechanical combination with soft tissue, especially with the 1.5 mm porous specimen. The peek specimens with both the internal cross-linked structure and external acid-etched microporous surface could effectively promote the close integration of soft tissue and prevent formation of fibrous capsules, demonstrating the potential for clinical application in surgical repair.

Replication of Micro- and Nanofeatures in Injection Molding of Two PLA Grades with Rapid Surface-Temperature Modulation

The production by injection molding of polymeric components having micro- and nanometrical surfaces is a complex task. Generally, the accurate replication of micro- and nanometrical features on the polymeric surface during the injection-molding process is prevented by of the low mold temperature adopted to reduce cooling time. In this work, we adopt a system that allows fast heating of the cavity surface during the time the melt reaches the cavity, and fast cooling after heater deactivation. A nickel insert with micro- and nanofeatures in relief is located on the cavity surface. Replication accuracy is analyzed by Atomic Force Microscopy under different injection-molding conditions. Two grades of polylactic acid with different viscosity have been adopted. The results indicate that the higher the cavity surface temperature is, the higher the replication accuracy is. The viscosity has a significant effect only in the replication of the microfeatures, whereas its effect results are negligible in the replication of nanofeatures, thus suggesting that the interfacial phenomena are more important for replication at a nanometric scale. The evolution of the crystallinity degree on the surface also results in a key factor on the replication of nanofeatures.