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Bones are nanocomposites consisting of a collagenous fibre network, embedded with calcium phosphates mainly hydroxyapatite (HA) nanocrystallites. As bones are subjected to continuous loading and unloading process every day, they often tend to become prone to fatigue and breakdown. Therefore, this review addresses the use of nanocomposites particularly polymers reinforced with nanoceramics that can be used as load bearing bone implants. Further, nanocomposite preparation and dispersion modification techniques have been highlighted along with thorough discussion on the influence that various nanofillers have on the physico-mechanical properties of nanocomposites in relation to that of natural bone properties. This review updates the nanocomposites that meet the physico-mechanical properties (strength and elasticity) as well as biocompatibility requirement of a load bearing bone implant and also attempts to highlight the gaps in the reported studies to address the fatigue and creep properties of the nanocomposites. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HA) [Ca 10 (PO 4 ) 6 (OH) 2 ] is a bioactive ceramic with excellent osteoconductive properties. This characteristic helps HA to be integrated into the bone without provoking an immune reaction, thus making it a useful biocompatible material for load bearing bone implant. In this study, nanohydroxyapatite (NHA) was synthesised using a precipitation method assisted with ultrasonication. The process parameters such as ultrasonic time ( t ) (10–30 min), ultrasonic amplitude ( A ) (50–70%), solution temperature ( T ) (50–90 °C), and solution pH (7–9) were varied on the basis of single factor and their effects on NHA synthesis was investigated. Besides that, the effect of calcination on the NHA powder morphology was also studied by varying the calcination time (2, 4 and 6 h) and temperature (400, 800 and 1200 °C). The characterisations of the synthesised NHA powder were conducted using thermogravimetric analysis (TGA), field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), transmission electron microscope (TEM), zeta-sizer and Fourier transform infrared spectroscopy (FTIR). It was found that nano-sized HA particles can be produced at optimum set of process parameters of t =25 min, T =90 °C, A =65%, and pH=8. Results revealed that the thermal stability, morphology and crystallinity of the NHA powder was further improved by calcinating the powder at optimum temperature and time of 800 °C and 2 h, respectively. [ABSTRACT FROM AUTHOR]

Self-healing hydrogels have many advantages since they can resist various types of stresses including tension, compression, and shear, making them attractive for various applications. In this study, thermo-elastic and self-healing polymer composite hydrogels were prepared from polyacrylamide (PAM) and 2D fillers using an in-situ method. In addition, the PAM and fillers were prepared in the presence of organic crosslinkers, i.e. hydroquinone (HQ) and hexamethylenediamine (HMT). The swelling behavior of the prepared hydrogels was studied by hydrating the dried hydrogels. The thermal and rheological properties of the prepared hydrogels were evaluated before and after swelling study using thermogravimetric analysis (TGA), differential scanning calorimetric (DSC) techniques and dynamic mechanical analysis (DMA). From the results obtained, incorporating fillers into the PAM matrix enhanced the swelling degree of the hydrogels with satisfactory mechanical properties, attaining up to 77% self-healing efficiency compared to the neat-PAM (i.e. 29%). This, in turn, indicates the addition of 2D fillers improved self-healing properties of the polymer hydrogel, thus, making the prepared hydrogels applicable for water shutoff treatments under high temperature. Image 1 • Self-healing polyacrylamide composite hydrogels for water shutoff treatments. • The incorporation of 2D-nanofillers strengthened the hydrogel matrix. • The thermal stability of the composite hydrogels is as high as 186 °C. • The water absorption reached a maximum of ~30,000%. [ABSTRACT FROM AUTHOR]

Herein, we report mechanically reinforced dual-coated sand proppants for hydraulic fracturing operations. The dual-coated sand proppants were prepared by sequential surface modifications. The sand particles were firstly coated with polystyrene-polymethyl methacrylate copolymer (PS-PMMA) composite with commercial graphene (CG) (first composite layer) and subsequently coated with epoxy-CG composite (second composite layer). The copolymer-CG coating onto sand particles was carried out by mixing 1:1 styrene (S) and methyl methacrylate (MMA) monomers with the initiator AIBN along with CG followed by adding the mixture to sand particles with vigorous stirring and subsequent polymerization at 70 °C. The PS-PMMA-CG coated sand particles were then mixed with epoxy resin and a cure in a ratio of 4:1 along with CG and cured at 150 °C for 5 min. Chemical, mechanical, thermal, and morphological characterizations for the composite layers and dual-coated sand proppants were investigated in detail by Fourier transform-infrared spectroscopy (FT-IR), nano-indentation, thermogravimetric (TGA), optical, and scanning electron microscopic (SEM) techniques. The FT-IR results revealed that the successful formation of PS-PMMA-CG copolymer composite and cross-linked epoxy-CG composites. The XRD results indicated that the successful surface coverage of the dual composites coating onto the sand. The optical and SEM results revealed that the roundness and sphericity of the reinforced proppant particles were greater than 0.6. Interestingly, elasticity (E), and hardness (H) of the coating shells have reached a maximum of 3.97 GPa and 0.144 GPa, respectively. The thermal stability of the (PS-PMMA-CG)-(epoxy-CG) dual composite shell has reached as high as 363 °C. Furthermore, the stress resistance of the optimized dual-coated sand proppant (Sand-(PS-PMMA-CG)-(epoxy-CG)) reached as high as 10000 psi with a fine production of <10 wt%. The mechanically reinforced dual-coated sand including the most desirable characteristics of roundness and sphericity to be greater than 0.6, high-stress resistance with excellent thermal and mechanical stabilities confirmed its great potential to be applied as successful proppants in oil and gas upstream applications. Image 1 • Mechanically reinforced ((PS-PMMA)-Graphene)-(Epoxy-Graphene) dual-coated sand. • Elasticity and hardness of the coating shells are 3.97 GPa and 0.144 GPa. • The thermal stability is as high as 363 °C. • The stress resistance of the proppant is as high as 10000 psi. [ABSTRACT FROM AUTHOR]