Volume 43, Issue 6

When selecting a polymer or a reinforced polymer material for a specific drive technology, it is crucial to have a comprehensive understanding of the component’s operating characteristics, including the mechanics of tribological contact and the fatigue life of the materials used in gears. The choice of material plays a pivotal role in the gear running process, as it induces heat generation in the meshing zone and triggers flank wear progression along the high points of the teeth, which directly impacts the gear’s lifetime. This paper presents the results of durability testing conducted on steel/polymer gear pairs. The tested polymer materials were based on polyacetal and polyamide 66 chemical bases, reinforced with aramid, carbon fibers, and internally lubricated with polytetrafluoroethylene. The aim of the study was to evaluate the durability and thermal response of the materials and determine their correlation with flank wear rate progression. The results indicate that gears produced from polyacetal, and carbon-reinforced polyamide 66 materials exhibit the longest durability. Notably, the generated meshing temperatures are closely connected with flank wear propagation. The lowest wear coefficients were observed in gears produced from polyacetal and polyamide 66 materials reinforced with carbon fibers.

Capacitor films from biaxially oriented polypropylene (BOPP) involve intensive external stress field, resulting in special crystallization and orientation characters. However, it still remains ambiguous on the relationship between crystallized morphology in BOPP bulk film and electric properties. In this work, two stretching modes, simultaneously biaxial stretching and sequentially biaxial stretching, were chosen to adjust film thickness, extended chain crystal content, fibrillar morphology, and orientation texture. Meanwhile, the working rules of these structural issues on electrical insulating properties were inspected. It reveals that extended chain crystals with thermal stability and isotropous fibrillated network favor to improved breakdown strength and lowered dielectric loss. These results offer good understanding on the processing-structure-property relation of polymer film dielectrics.

Fluorine free analogues of three commercially available rigid contact lens materials were prepared by replacing the fluorinated component, hexafluoroisopropyl methacrylate (HFPM), with the widely used, non-fluorinated monomers methyl methacrylate (MMA) and 3-methacryloxypropyltris-(trimethylsiloxy)silane (TRIS). The properties of the commercial materials and analogues were measured and compared. The oxygen permeabilities of the MMA analogues were found to be significantly lower than those of the commercial materials, decreasing by 87 % on average, while the TRIS analogues lacked sufficient hardness, dimensional stability and lipid deposit resistance to be viable for use in rigid contact lenses. Analogues prepared using a 1:1 mixture of MMA and TRIS had the best overall combination of properties, but were still on average 47 % less permeable to oxygen and also significantly less resistant to lipid deposition. The analogues prepared in this study did not adequately replicate the performance of marketed, fluorine containing rigid contact lens materials. These observations give an indication of the challenges that would face contact lens material manufacturers in preparing rigid lens polymers without the use of fluorinated species. A reduction in effectiveness would be almost inevitable, and would be expected to have a negative impact on the safety and eye health of rigid contact lens patients.

This work describes the successful tunable production of polycaprolactone (PCL) microspheres using very low-concentration solutions. The PCL solutions (1, 3, and 5 w/v%) were prepared with different solvents (dichloromethane (DCM) and chloroform (CHL)) and electrosprayed at different distances (5, 10, and 15 cm). The solubility and viscosity of PCL solutions were in accordance with the polymer concentrations, demonstrating PCL-DCM gave a higher solubility of PCL, but PCL-CHL solutions had a higher viscosity. Optical microscopy (OM) and field emission-scanning electron microscopy (FE-SEM) revealed that the PCL-DCM preparations produced a smaller and more uniform microsphere size and pore size compared to PCL-CHL microspheres. The linear regression analysis showed that the solubility and viscosity of PCL concentration influence the size of microspheres more greatly than the pore size. The toxicity results indicated that PCL-CHL and PCL-DCM are well-tolerated by zebrafish embryos that were able to follow a normal growth pathway and can thus be deemed safe.

The linear and star polyethylene during static crystallization and stretch-induced crystallization has been investigated by molecular dynamics simulations. The findings demonstrate that the branching point of the star polymer system does not participate in crystallization, and the crystallization ability of the segments near the branching point and at the end of the chains is inferior. Due to the existence of branching points, the mobility and conformational extension of chain segments are weak, and the entanglement degree is higher than that of linear systems. For stretch-induced crystallization, stretching promotes the extension of molecular chains and arranges them along the stretching direction. The crystal nucleation and growth in linear and star polymer systems are significantly faster than in static crystallization. The mobility of the chain segments close to the branching point is partially enhanced by stretching, while the branching point still substantially affects the chain conformation and segment orientation. It is worth mentioning that we have verified some crucial results that cannot be observed in the experiments at the microscopic scale.

Additive manufacturing represents a powerful tool for the fabrication of parts with complex shapes by the deposition and the consolidation of materials as opposed to subtractive manufacturing methodology. Selective laser sintering (SLS), one of the most popular powder bed fusion (PBF) technologies for thermoplastic part production, has demonstrated extensive applications in various industrial sectors. The process involves the deposition of homogeneous powder layers and employs a laser source to selectively melt a powder bed according to a CAD model. Due to its layer-by-layer nature, voids and pores are inevitably introduced in the fabricated thermoplastic parts. Porosity represents one of the major limitations of this technology being one of the main causes of the variation of the mechanical properties. With the intention of providing support for reducing the porosity and thus increasing the quality and performance of the final product, in this paper, a brief review was carried out focusing on the SLS process parameters and their interaction with the porosity of the product. In addition, an in-depth look was given to the mechanisms of formation and consolidation of pores within parts made of polymeric material.

It is challenging to effectively purge wastewater containing heavy metal ions at low concentration. In order to remove trace Cr (VI) from wastewater efficiently, a positively charged microporous membrane was prepared by firstly non-solvent induced phase separation (NIPS) of amphiphilic polymer and secondly surface quaternization modification. The morphologies, surface roughness, surface charge, hydrophilicity, and pore size of membranes were characterized. Based on the dual action of micellar adsorption and charge repulsion, when surfactant is 4 mM and Cr (VI) is 60 ppm, the surface quaternization membrane (Q-MPVD) achieves 99.8 % Cr (VI) rejection simultaneously accompanied by a permeability of 100 LMH/bar. Meanwhile, the effects of STAC concentration, Cr (VI) concentration, pH as well as inorganic salt concentration on the composite micellar size, and Cr (VI) rejection performance were investigated, respectively. Moreover, the Q-MPVD membrane shows an excellent separation stability over a wide pH range, indicating its application perspective in engineering process. In summary, this work provided a positively charged membrane with high-efficiency performance for treating practical trace Cr (VI)-containing industrial wastewater.