Maintenance Of Mechanical Properties Research Articles

Polymer Binder-Free aqueous spinning of biomimetic CNT based hierarchical hollow fiber for structural and energy storage application

Assembly of functional nanomaterials into structural–functional integrated materials, such as structural-energy storage materials, are highly desirable for lightweight, high-performance wearable electronics, automobiles, and aviation/aerospace vehicles, yet extremely challenging due to the paradox between functional properties and the maintenance of mechanical properties. Herein, inspired by wheat-straw structures, we reported a polymer binder-free aqueous spinning strategy to manufacture biomimetic hollow carbon nanotube-based fibers (H-CNTF), where two-dimensional graphene oxide (GO) nanosheets are employed as an alternative to polymer binder for assisting the formation of hollow structures by rapid interaction with cations in coagulation, forming strong interaction with CNTs and tunning rheological property of spinning dope. The hierarchical hollow structure consisting of micron-scale hollow tubular space and porous walls endows H-CNTF with large surface area and abundant loading sites for guest materials, and the good CNT orientation and the absence of polymer binder enable H-CNTF excellent electrical and mechanical properties. As a proof of concept, the resulting H-CNTF supercapacitor electrodes exhibit high electrochemical energy storage performance with a specific capacity of 163 F/cm3 and high tensile strength of 0.35 N/tex. In addition, the polymer composite based on H-CNTF is about 100 % stronger than that based on solid fiber owing to the more uniform composite structure. The combination of outstanding electrochemical and mechanical properties makes this hollow fiber a promising material for future structural and energy storage applications.

Facile strategy for low dielectric constant polyimide/silsesquioxane composite films: structural design inspired from nature

It is important for the development of high-performance dielectric materials to reduce the dielectric constant and water uptake simultaneously, with the maintenance of mechanical properties. Herein, sandwich-type composite film was prepared through coating the both sides of flat polyimide (PI) film with polyhedral oligomeric silsesquioxanes (POSS) contained hierarchical porous structure using the microemulsion method, in which water droplets were used as the template for patterned pores. Due to the introduction of two layers of hierarchical porous structure with patterned pores and POSS, the dielectric constant of PI film was significantly reduced, accompanied by the low dielectric loss. In addition, the water uptake was also greatly reduced, thus contributing to its excellent durability under high humidity. More importantly, even with the introduction of porous structure, the mechanical properties of PI film can still be maintained, or even improved by optimizing POSS content. Through varying the POSS content from 10 to 50%, low dielectric constant of 2.28–2.42, dielectric loss of 0.005–0.009, water uptake of 0.56–0.62%, increment of dielectric constant under high humidity of 1.19–2.35%, with 26–32%, 43–69%, 77–80% and 31–37% of reduction, respectively, compare to flat PI film were achieved. These results indicate the potential of our sandwich-type composite film as low dielectric material in microelectronics.

Effect of clay amount and reprocessing cycles on thermal, morphological, and mechanical properties of polypropylene/organovermiculite nanocomposites

Nanocomposites of polypropylene (PP) and PP‐grafted‐maleic anhydride (PP‐g‐MA) with and without organophilic vermiculite (OVMT) (5–8%w/w) were evaluated. The nanocomposites and neat PP were submitted to extrusion reprocessing cycles. It was found that the presence of OVMT in PP/PP‐g‐MA was critical for maintaining thermal stability during reprocessing. The exfoliation/intercalation was confirmed, mainly, in the nanocomposite submitted to reprocessing cycles, by X‐ray diffraction. The melt flow index (MFI) values for the 3× and 5× reprocessed PP increased by 40% and 70%, respectively, as compared to the neat PP. The MFI for the 3× and 5× reprocessed PP/PP‐g‐MA/OVMT decreased 26% and 17%, respectively, as compared to the decrease occurred in the 3× and 5× reprocessed PP, indicating that the presence of 5% (w/w) OVMT was sufficient to allow an increase in viscosity. The reprocessed nanocomposites exhibited values for tensile and flexural strengths and Izod impact, in general, greater than or near to those of PP with the same number of reprocessing cycles. The increase or maintenance of mechanical properties seems to depend on a balance between the extent of intercalation/exfoliation and dispersion of OVMT in the PP matrix, and the degree of degradation of the PP matrix. POLYM. ENG. SCI., 59:2110–2120, 2019. © 2019 Society of Plastics Engineers

Plasticiser effect of oleic acid polyester on polyethylene and polypropylene

The potential application of a polymeric fatty acid derivative as a plasticiser for polyethylene and polypropylene was evaluated through the study of torque during melt processing, apparent crystallinity, crystalline plane orientation, plane strain compression and thermogravimetric analysis of polymer blends. The polymeric derivative is a polyester produced from epoxidised oleic acid, cis-1,2-cyclohexanedicarboxylic anhydride and triethylamine as initiator. The results suggested that the oleic acid polymer had a plasticising effect in blends with polyethylene (PE) and polypropylene (PP). Reduction of processing torque, no loss of crystallinity, maintenance of mechanical properties and an improvement in thermal stability were observed for PP. For PE, a slight reduction of processing torque, crystallinity and mechanical resistance were observed.

Study on development and in vitro biodegradation behaviour of poly(D, L-lactide-co-glycolide) 75/25 bioscaffolds

Three-dimensional porous scaffolds based on biodegradable polymers are widely researched for applications to replace and restore the functions of diseased or damaged organs. The requirements for the scaffolds include: highly interconnected pore structures to facilitate cell adhesion for tissue regeneration, maintenance of mechanical properties and structural integrity until cells adapt to its environment and biodegradability with a controlled degradation rate. This paper focuses on the development and in vitro biodegradation behaviour of poly (D,L-lactide-co-glycolide acid) (PLGA) 75/25 and changes on pore morphology affected by initial pore sizes and degradation media. The pore morphology, mechanical properties, and geometric transformation were examined over the course of 13 weeks. It is concluded that the PLGA 75/25 scaffolds degraded after seven weeks and completely degraded after 13 weeks. The degradation time of scaffolds with small pores and in distilled water was comparatively shorter due to poorer interconnectivity of the pores and a more aggressive environment.

Wear of sequentially enhanced 9‐Mrad polyethylene in 10 million cycle knee simulation study

Highly crosslinked polyethylene (HXPE) has been shown to be effective in reducing wear in total hip replacements. HXPE has not found widespread use in TKR, because the crosslinking inevitably leads to reductions in critical properties such as toughness and fatigue strength. Sequentially enhanced crosslinking (SXPE) have been suggested for improved wear resistance for tibial inserts with maintenance of mechanical properties and anticipated high oxidation resistance superior to conventional polyethylene (XLPE). We compared the wear of SXPE (9Mrad) to XLPE inserts (3Mrad) to 10 million cycles. Triathlon femoral condyles were identical in both. This is the first wear study of SXPE inserts. According to the power law relating irradiation dose to wear of XLPE inserts, wear of 9 Mrad inserts should be reduced by 70% compared to 3Mrad controls. The wear rates of the SXPE inserts were reduced by 86% at 10 million cycles duration, somewhat greater than predicted. The one prior investigation by the manufacturer reported a 79% wear reduction for SXPE compared to controls in a 5 million cycle simulator study in knee design and test parameters. There were important differences between the two studies. Nevertheless there clearly appeared to be a major benefit for sequentially enhanced polyethylene in tibial inserts. This combined wear reduction of 80-85% with improved oxidation resistance and retention of mechanical properties may prove beneficial for active patients who may otherwise risk high wear rates over many years of use.

Effect of multiple unconfined compression on cellular dense collagen scaffolds for bone tissue engineering

Plastic compression of hydrated collagen gels rapidly produces biomimetic scaffolds of improved mechanical properties. These scaffolds can potentially be utilised as cell seeded systems for bone tissue engineering. This work investigated the influence of multiple unconfined compression on the biocompatibility and mechanical properties of such systems. Single and double compressed dense collagen matrices were produced and characterised for protein dry weight, morphology and mechanical strength. Compression related maintenance of the seeded HOS TE85 cell line viability in relation to the extent of compression was evaluated up to 10 days in culture using the TUNEL assay. Fluorescence Live/Dead assay was conducted to examine overall cell survival and morphology. Cell induced structural changes in the dense collagenous scaffolds were assessed by routine histology. The mechanical properties of the cellular scaffolds were also evaluated as a function of time in culture. It is clear that a single plastic compression step produced dense collagenous scaffolds capable of maintaining considerable cell viability and function as signs of matrix remodeling, and maintenance of mechanical properties were evident. Such scaffolds should therefore be further developed as systems for bone tissue regeneration.

Protection of Natural Rubber against Atmospheric Agents. I. The Effects of Nickel Dibutyldithiocarbamate Alone and in Combination with Protective Agents

Abstract Latex-rubber mixtures vulcanized with zinc diethyldithiocarbamate as accelerator show excellent resistance to sunlight if they contain 1.5–5 per cent of NBC. Combinations of protective agents which were tested contributed nothing to the protective effect of NBC alone as far as resistance to cracking is concerned; in fact, under some conditions they had an unfavorable influence. Only with respect to the maintenance of mechanical properties do these combinations have any noticeable protective effect, as do combinations of NBC with DNPD and with methyl di (tert.-butyl)phenol. However, such combinations should not be disregarded a priori, for it is possible that some of them would impart an appreciable increase of resistance to heat. In the present investigation, natural aging in darkness at ordinary temperature for twenty-four months was excellent, and this is at variance with the accelerated aging tests, except for the oxidizability measurements. The behavior of dry-rubber vulcanizates accelerated by mercaptobenzothiazole differs greatly from that of corresponding latex-rubber vulcanizates. Only NBC showed any protective effect against cracking; on the contrary, it promoted a rapid loss of the mechanical properties of vulcanizates when they were exposed to light or were stored in darkness. The action of heat or oxygen under pressure is still more striking from this viewpoint. By the concurrent action of structurizing agents, among which DPPD has been found to be the most effective, it is possible to attain a final protective effect which is manifest by a notable retardation of the appearance of cracks on exposure to light and by outdoor weathering, and at the same time, by a satisfactory retention of good mechanical properties during aging. Aging at ordinary temperature in darkness is likewise good, since the loss of tensile strength in two years was only 2–3 per cent. By way of comparison, a control vulcanizate, protected by PBN and stored under the same conditions, lost approximately 1 per cent of its tensile strength. Recent experiments indicate that some carbon blacks have a very favorable effect. This should make it possible to utilize simultaneously effective protection against cracking, maintenance of good mechanical properties during exposure to light and during aging in darkness, and increased resistance to heat. This remarkable resistance to exposure cracking and to cracking by light of rubber-carbon black vulcanizates indicates the possibilities in the practical application of combinations of NBC and DPPD. In the case of reinforced mixtures, the combined effect of a complex nickel compound, a structurizing agent, and a deactivating agent seems to be the most effective system. The choice of the structurizing agent is very important, as are also the proportions of all the agents. A later study will be concerned with establishing the best proportions from the viewpoint of obtaining satisfactory protection with the minimum quantities of these agents. Finally, it must always be kept in mind that there may be other protective agents which would make superior combinations with NBC or with other organic nickel complexes.