Volume 42, Issue 7

Natural fibres as reinforcement for composite materials have witnessed a resurgence of interest in the past few years, largely due to ecological concerns, legislative directives and technological advancements. Hemp is one of the most popular natural fibres used as reinforcement in polymers owing to its superior mechanical properties. At present, hemp fibres have attracted the global interest of design engineers for developing composites having extensive applications in automobiles, electrical, construction and packaging industries. Although several literatures explore different aspects of hemp fibre reinforced composites, there is no proper literature that summarizes the surface treatment, processing techniques, mechanical performance and hybridization of hemp fibre composites. This review is envisioned to put forth a comprehensive summary of the research work published in the field of hemp fibre reinforced composites with special reference to the structure of hemp fibres, different methods for surface modification and processing techniques to fabricate the composites based on thermoplastic, thermoset and biopolymers. The paper also focuses on the effects of surface treatment on the mechanical performance of the composites.

Thermally conductive polymer composites that retain mechanics and processing properties have attracted significant attention because of promising high thermal conductivity. Herein, plasticized polyvinyl chloride (P-PVC)/graphite composites were successfully prepared via melt blending. Following the addition of graphite rising from 0 to 300 phr, the thermal conductivity of P-PVC/graphite composites increases from 0.18 to 3.01 W m −1  K −1 . The thermal conductivity of P-PVC/graphite composites with 300 phr graphite is 17 times that of the P-PVC matrix. P-PVC/graphite composites with high thermal conductivity have excellent performance in thermal management for LEDs. Therefore, the high thermal conductivity allows for the LED’s temperature to drop 44%, compared with the P-PVC matrix, at 1.5 V. The notably cooling effect provides the ideas for the future application of the P-PVC/graphite composites in the thermal management for electronic components.

In order to improve the effective damping of nitrile-butadiene rubber (NBR) in a wider temperature range, Eucommia ulmoides gum (EUG) was incorporated into NBR to prepare nanocomposites. Atomic force microscopy (AFM) showed that EUG was dispersed in NBR matrix in the form of nanocrystals. Compared with pure NBR, the mechanical properties of NBR/EUG (80/20) composites are significantly improved. Dynamic thermo-mechanical analysis (DMA) showed that there are two dynamic mechanical loss peaks in two composites. With the increase of EUG component, the peak value of loss factor (tan δ ) decreases gradually at −10 °C, and the temperature corresponding to the peak value tends to move towards high temperature, while the peak area increases gradually at −50 °C. Parking and repeated mixing make both loss peaks move towards high temperature. The differential scanning calorimetry analyzer (DSC) results expressed that the melting temperature and peak area of EUG after vulcanization decreased significantly compared with that before vulcanization. Hence, the damping effect of NBR can be improved and its damping temperature range can be widened by adding EUG and changing processing conditions.

As a commonly used reinforcement, glass fiber (GF) can improve the mechanical properties of thermoplastics. However, previous studies have suggested that GF was not good for the flame retardancy of thermoplastics because of “wick effect.” Herein, a novel flame retardant emulsion was synthesized, containing film-former, lubricant, silane coupling agent, and ammonium polyphosphate modified by 3-aminopropyltriethoxysilane (mAPP). The GF impregnated with flame retardant emulsion and aluminum diethlyphosphinate (ADP) were blended with polyamide 6 (PA6) to prepare flame retardant GF reinforced PA6 (FRGFPA6/ADP). The LOI of FRGFPA6/ADP-15 can reach 34.7%, which is much higher than that of GF reinforced PA6 (GFPA6) and it also pass the UL-94 test and reach V-0 rating without dripping. The mHRR, pHRR, and THR of FRGFPA6/ADP-15 are reduced by 44.2, 121.0, and 26.3% compared to GFPA6. After burning, the surface of flame retardant GF can form a carbon layer, which improved the efficiency of interfacial flame retardancy between GF and PA6 and weakened the “wick effect.” At the same time, ADP is added to the matrix to release free radicals to capture oxygen in the air, and carbon layer is formed to isolate the air. The synergistic effect of ADP and mAPP increased the flame retardancy of GFPA6.

Today, the separation and purification processes are highly preferred over the affinity interactions in the scientific world. Among the materials used for this purpose, magnetic particles and cryogels are very popular. Both polymeric structures have their advantages and disadvantages. In this study, poly(2-Hydroxyethyl methacrylate-N-methacryloyl-L-aspartic acid), poly(HEMA-MAsp), magnetic microparticles, and cryogels were synthesized, and adsorption performances of both polymeric structures were investigated by using invertase from aqueous systems. Invertase ( β -fructofuranoside fructohydrolase, EC 3.2.1.26) is a commercially important enzyme used in the food industry to obtain the product called invert sugar, which consists of a mixture of equivalent amounts of glucose and fructose. Therefore, it was preferred as a model enzyme in adsorption studies of polymeric structures. According to the results, 104.1 mg g −1 and 135.5 mg g −1 of adsorption capacity values were obtained for cryogel and magnetic microparticle forms, respectively. Increasing temperature slightly reduced the adsorption capacity of both polymeric structures. In the adsorption/desorption cycle studies performed five times with poly(HEMA-MAsp) polymers, both forms were found to have high reusable properties. It was determined that the activity of invertase immobilized on polymeric structures was preserved at a rate of 83.6% for the particle form and 89.2% for the cryogel form.

Flexible, pressure-sensitive composites can be prepared through the inclusion of electrically conductive particles as functional fillers into an elastomeric polymer matrix, which have been used for the applications of wearable devices for health monitoring and electronic skins. A key challenge associated with these composites is developing anisotropic pressure sensitivity while retaining their flexibility (or low filler content). Herein, we demonstrate a simple and scalable method for aligning anisotropic nickel-coated carbon fibers (NiCF) along with the thickness direction of a polymer matrix by applying a magnetic field. The aligning mechanisms and kinetics of NiCF in the polydimethylsiloxane (PDMS) precursor are revealed by in situ optical microscopy images while a magnetic field is applied. The aligned nickel-coated carbon fibers in the polymer effectively endow the composite films excellent pressure-sensitive performance. The pressure sensitivity of NiCF/PDMS composite films has been systematically studied and can be used for biological monitoring. We believe that this magnetic field assisted processing strategy provides a promising material solution for manufacturing fiber embedded polymer composites with enhanced pressure sensitivity, which is essential for future wearable health monitoring electronics and electronic skin.

Fluctuations in the injection moulding process are affecting component quality. A pressure control can be used to increase process consistency. However, current control systems cannot influence the melt flow in the mould specifically for individual cavities. Therefore, a control concept is being developed in which commercially available, servo-electrically driven hot runner valve pins are used to control the cavity pressure in the holding pressure phase. By varying the stroke, the pressure resistance in the hot runner and thus the pressure transfer into the cavity are influenced. A one cavity mould with two pressure sensors and a servo-electrical driven hot runner was used to evaluate the control setup, implementing a PID controller. The evaluation criterion for the setup is to what extent the reference curve measured in advance can be reproduced after provoked disturbance. The control calculates the difference between the actual pressure and the reference curve. The control compensates the pressure difference by a pin movement. The control concept can compensate for disturbances that do not change the material behaviour, such as changes in holding pressure. Changes in the material behaviour, for example due to fluctuations in the mould temperature, cannot be compensated due to the reference control.

The avian eggshell membranes’ composition depicts close resemblance with the extracellular matrix of the cells, and therefore being widely employed as potential biomaterials for tissue engineering applications. However, the optimization of process conditions for collagen extraction, the main constituent of eggshell membranes is still challenging. In the present study, extraction of collagen was performed by an enzymatic method optimized through the one-factor-at-a-time (OFAT) technique for three parameters viz. pepsin concentration, treatment time and pH. The process optimization resulted in the maximum yield of 56% collagen with 350 U/mg pepsin concentration at pH 3 treated for 9 days, not reported yet. The collagen extraction was confirmed by OD at 232 nm; and its viscoelasticity behaviour at pH 5. The physico–chemical characterization of extracted collagen with FESEM, ATR-FTIR, surface roughness analysis and contact angle measurement revealed the morphological and topological alteration during the collagen extraction. The process optimization and characterization of eggshell membrane derived collagen can aid in the significant biomaterials development for tissue regeneration.

In this study, the rectilinear, sine, and spiral paths of polymer transmission welding were used to perform welding comparative experiments, and the influence of various parameters in the polymer transmission welding of different laser paths on the joint performance and the formation of molten pool was discussed. The spiral path exhibited the highest joint strength, that increased by more than 50% compared with conventional rectilinear welding. The molten pool formed by spiral welding had a high depth-to-width ratio. Microscope observations revealed that the glass fiber flow signs in the molten pool were obvious, the glass fiber in the molten pool was abundant, and the bubble generation rate in the molten pool was lower. In this paper, Fortran language was used to construct Gaussian body heat source movement model with different paths. Results show that the spiral welding had higher welding stability than traditional rectilinear welding, welding defects caused by the lack of heat in the previous period can be properly compensated by selecting the appropriate welding period, Therefore, good joint performance can be achieved. In addition, amplitude and period are two important process parameters of spiral welding, and their sizes have important effects on joint strength and molten pool formation