This study investigates the effect of a nickel complex of 2,6-pyridinedicarboxylic acid (Ni-PDC) in modulating the properties of hydrogenated nitrile butadiene rubber (HNBR) composites. The composites were prepared via dicumyl peroxide (DCP) crosslinking, with varying Ni-PDC loadings. Structural analyses via Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) confirm successful integration of the Ni-PDC complex into the HNBR matrix. However, X-ray photoelectron spectroscopy (XPS) supports the presence of Ni2+ and validates Ni-PDC coordination within the HNBR matrix. Curing studies reveal a reduction in viscosity and an alternative in crosslink density. Mechanical testing reveals appreciable reinforcement, with a significant enhancement in tensile strength and elongation at break in comparison with unreinforced HNBR. Furthermore, the conduction of cyclic stress-strain study demonstrates a reduction in hysteresis losses, thereby signifying an enhancement in elastic recovery. Thermogravimetric analysis (TGA) reveals increased thermal stability, while differential scanning calorimetry (DSC) indicates a downward shift in glass transition temperature, consistent with enhanced segmental mobility imparted by dynamic coordination of Ni-PDC complex. The present study reports the combined effect of DCP curing and Ni-PDC incorporation in HNBR composites, with a view to enhancing their mechanical performance, flexibility (viscoelasticity) and thermal resistance.

This work presents synergistic reinforcement of zirconia (ZrO2) particles impregnated cellulose nanocrystals (CNC) in acrylonitrile butadiene rubber (NBR). The CNC-ZrO2 dual phase filler is prepared by in situ grafting of ZrO2 particles from its precursor (zirconium (IV) propoxide) on CNC via sol-gel route in the NBR solution. Such functionalization of filler enables its better dispersion in rubber matrix. The interaction between ZrO2 and CNC is established by FTIR and XPS studies, while SEM images reveal homogeneous morphology. The modification of CNC surface by ZrO2 particles and the anisotropic character of CNC trigger high reinforcing effect of the dual phase filler. This is reflected in the excellent mechanical performance of the NBR composites due to efficient interactions between the filler and rubber chains. For example, tensile strength becomes nine times higher for a particular formulation (In-CNC10-Zr15) compared to that of pure NBR. In addition, the tested composites show very good resistance to aging and attack of oil and ozone. This study demonstrates the potential of integrating bio-derived flexible CNC with inorganic rigid ZrO2 to offer a multifunctional filler platform for the advancement of elastomer applications.

The reinforcement of elastomeric composites by inorganic non-black fillers such as metal oxides is primarily governed by their shape, size, and state of dispersion. However, the filler incorporation technique can also play a critical role in this regard. This study investigates the efficacy of a masterbatch approach for in situ zirconia reinforced nitrile butadiene rubber (NBR) composites. A comprehensive characterization of all the composites is carried out, including evaluation of their rheological, thermal, mechanical, morphological and dynamic mechanical properties. This approach is found to be very efficient in strengthening composite properties, such as enhancements in their mechanical and thermal properties, along with other properties like aging resistance, viscoelastic behaviour and compression set. The masterbatch-derived 20 phr zirconia containing NBR composite shows better performance than externally filled zirconia-NBR composite at the same filler content. The masterbatch approach ensures superior filler dispersion and enhanced interfacial interaction. Beyond performance metrics, this method represents a greener approach by reducing solvent usage and energy input with respect to the purely sol-gel derived in situ filler incorporation method, aligning with sustainable development goals and promoting eco-friendly material processing.

Cellulose nanofiber aerogel-based PCM composites exhibit high thermal stability, flame-retardant properties, and excellent acoustic damping, owing to their porous structure and stable encapsulation.

Acrylic-based wood adhesives are widely recognized for their durability, UV resistance, and rapid drying properties, traditionally achieved using isocyanate-based curing systems despite their inherent toxicity. In this study, the potential of polysilazane (PSZ) as an alternative cross-linker for functional acrylic polymers was evaluated, focusing on adhesive properties. The crosslinking interactions between the acrylic polymer and PSZ formed a highly stable Si-O reinforced three-dimensional network, as characterized by analytical techniques and further supported by enhanced thermal stability and adhesive performance. The PSZ-cured acrylic system exhibited a glass transition temperature (Tg) increase to 56 degrees C from 31 degrees C of the uncrosslinked copolymer. In the tested range of 10-25 wt% of PSZ, the formulation containing 20 wt% PSZ achieved a 97.9% degree of crosslinking. Compared to traditional diisocyanate-crosslinked systems, better adhesive performance was obtained with maximum tensile shear strength values of 4.4 MPa for wood substrates (substrate failure) and up to 4.0 MPa for aluminum substrates. These findings confirm that PSZ enhances the mechanical properties of acrylic adhesives, offering optimal performance and ease of application and underscoring their practical utility.

This study presents a cross-linked bisphenol A propoxylate diglycidyl ether network (BP17) synthesised via a dynamic transesterification reaction.

Metal ion-assisted hydrogels are of growing interest because of their excellent mechanical properties, fast recovery, and self-healing ability. However, affording all these properties in a single polymeric framework is very challenging. This paper presents a facile one-pot synthesis of Zn2+ coordinated hydrogels by using acrylic acid and acrylamide monomer as precursors. Special emphasis has been placed on the types of zinc salt that have not been studied before. Zinc coordination provides the hydrogel with prominent mechanical strength, toughness, stretchability, and self-healing properties without any stimulation, due to the numerous entanglements of polymeric chains. Rheology studies demonstrate that various zinc salts used for coordination with polymeric functional groups could influence the mechanical properties of the gels to different extents. The highest self-healing potential is exhibited by MGel-ZnCl2 (up to 90% recovery) while those for MGel, MGel-Zn(NO3)(2), and MGel-ZnSO4 are 60%, 62%, and 64%, respectively. Dynamic mechanical analysis reveals higher compressive strength (0.86 MPa) of MGel-ZnSO4 when compared to other samples viz. MGel (0.48 MPa), MGel-Zn(NO3)(2) (0.49 MPa), and MGel-ZnCl2 (0.45). On the other hand, MGel-Zn(NO3)(2) offers remarkable compressive strain stability at epsilon % = 66.63 surpassing those of MGel (epsilon % = 11.05), MGel-ZnCl2 (epsilon % = 55), and MGel-ZnSO4 (epsilon % = 17).

This study investigates the potential of Tris(hydroxymethyl)aminomethane (Tris) as a surface modifier for zirconia to enrich the ultimate properties of nitrile rubber (NBR) composites. By substituting commonly used organosilanes with Tris to modify the surface of zirconia, significant improvement in zirconia particle dispersion within the NBR matrix is achieved, leading to a stronger rubber-filler interaction. Scanning electron microscopy (SEM) images reveal a finer dispersion of zirconia particles, facilitated by the efficient surface modification of zirconia by Tris. Rubber-filler interactions, examined through the Lorenz-Park principles and viscoelastic properties, demonstrate that Tris modification reduces the surface energy of zirconia, enhancing its dispersibility and improving interfacial bonding between the rubber and the zirconia due to increased reactivity. This causes significant improvement in mechanical and other composite properties such as thermal stability, oil resistance, flame retardancy for the Tris modified in situ zirconia filled composites. Among the compositions examined, the composite containing 2 phr of Tris and 30 phr of zirconia (In-2T-Zr-30) exhibits a substantial improvement in tensile strength, over 20 times higher than that of the unfilled sample. These findings highlight the potential of Tris as an effective surface modifier for zirconia, enhancing filler performance and offering a promising alternative to organosilanes in the development of high-performance nitrile rubber composites.

Metal-ligand coordination bonds have been recognized as promising cross-linkers for elastomeric materials. In this work, the interaction between the carboxylate group of carboxylated nitrile butadiene rubber (XNBR) and the ferric ion (Fe3+) generates a dynamic cross-linked network in XNBR matrix. Furthermore, by introducing, 4aminopyridine in the system, we are able to control the degree of cross-linking. The dynamic nature of the coordination bonds imparts recyclability feature to the composite when exposed to thermal stimuli. Prepared composites are thoroughly characterized using Fourier transform infrared spectroscopy (FT-IR), Swelling study, Differential scanning calorimetry (DSC), Rheometric Study, and Cyclic stress-strain study to investigate the crosslinking process and evaluation of the composite's properties. It has been found that variation in the 4-aminopyridine content has a strong influence on the properties including the recycling efficiency and the mechanical strength of the composite. The highest recycling efficiency, after the third recycling, is found as high as 80 % for a particular composition (XNBR-AP-1-Fe) while highest tensile strength of 3.81 MPa is shown by another composition (XNBR-AP-2-Fe).

The use of environment-friendly fillers, derived from natural sources, towards the reinforcement of elastomers, including natural rubber (NR), has become an emerging area of contemporary research. Cellulose appears to be such a promising reinforcing filler owing to its abundance, nontoxicity, biodegradability, and inexhaustibility. With time, research work on cellulose-filled NR composites has grown significantly. This chapter primarily focuses on the fascinating studies on nanocellulose (NC) filled NR composites. It begins with the potential of NC in replacing the traditionally used industrial fillers for NR. This is followed by a general description of NC and their composites with NR in the context of reported works. A concise description of different processing techniques of NR/NC composites is elaborated next. Various physicochemical techniques, generally employed to assess the quality and performance of the composites, are also covered. Finally, some novel and possible areas of application are mentioned evidencing their practical importance and usefulness.

Hydrogels have emerged as promising candidates for biomedical applications, such as replacing natural articular cartilage, owing to their unique viscoelastic properties. However, sufficient mechanical properties, self-healing ability, and adhesive nature are some issues limiting its application window. Here, a facile one-pot synthesis of dual cross-linked zinc-coordinated copolymer hydrogels is presented. The network structure of the copolymer hydrogels is strategically developed via dynamic and reversible physical cross-linking by Zn2+ ions and simultaneous covalent cross-linking through a covalent cross-linker viz methylene bisacrylamide. Fourier-transform infrared (FTIR), X-ray diffraction (XRD) scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) analysis have thoroughly characterized the structure of the synthesized hydrogels. The introduction of Zn2+ offers dynamic and reversible complexation, leading to excellent mechanical properties and self-healing features. Moreover, the percentage of the equilibrium water content of zinc-coordinated copolymer hydrogel samples is comparable with that of natural articular cartilage. The Shear sliding study shows the dominant adhesive behavior of HGel-Zn(NO3)2 sample compared to the parent HGel sample. This facile dual cross-linked hydrogel, HGel-Zn(NO3)2, with a combination of good mechanical properties, efficient self-recovery, adequate water content, and favorable adhesive nature, seems very promising to mimic the articular cartilage.

Metal-ligand coordinated cross-linked polymer composites, have been recognized as promising candidates to address the shortcomings of conventional cross-linked composites. In this report, we present how the carboxylic functional group of carboxylated nitrile rubber (XNBR) is exploited to coordinate with ferric ions (Fe 3+ ), resulting in a cross-linked rubber composite via a simple but efficient approach. FeCl 3 content could be reached as high as 30 mmol, for a practically usable composite, by judiciously employing a tertiary aliphatic amine viz. triethylamine, TEA that is otherwise not possible. The development of metal-ligand assisted cross-links in the XNBR matrix is established by rheological and swelling studies. The cross-linking mechanism and ferric-carboxylate interaction are investigated by Fourier transform infrared spectroscopy (FTIR). Strong and favorable ferric-carboxylate interaction leads to adequate improvement of mechanical and viscoelastic properties of the composite.

Metal-ligand coordinated cross-linked polymeric composites that can alter the network topology via a dynamic bond-exchange mechanism have been recognized as very promising candidates to address the shortcomings of conventional cross-linked composites, such as poor recyclability and self-healing ability. This has led to much interest in the cross-linking of elastomers via non-covalent interactions with suitable metal ions. In this report, we present a simple but efficient approach to ferric ions (Fe3+) assisted crosslinking of carboxylated nitrile rubber (XNBR) in the presence of an aliphatic amine (Et3N). The dynamic coordination reaction via carboxylate functional group of nitrile rubber (XNBR) is employed to fulfill the coordination requirements of the central Fe3+ metal ion. This is confirmed by x-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. The crucial role of Et3N in partially hindering and regulating the extent of crosslinking is investigated and mechanistically interpreted by swelling, differential scanning calorimetry, and rheological study. The tensile strength of ferric crosslinked XNBR could be enhanced up to four times than that of pure XNBR. Furthermore, the dynamic coordination-driven network of XNBR offers excellent self-healing (90% efficiency) and recyclability features (80% efficiency) for a composite of appropriate formulations. image

Metal-ligand coordinated cross-linked polymer composites, which can alter the network topology via a dynamic bond exchange mechanism, have been recognized as promising candidates to overcome the shortcomings of conventional cross-linked composites such as poor recyclability and self-healing ability. In this letter, we present how the carboxylic functional group of carboxylated nitrile rubber (XNBR) is utilized to coordinate with ferric ions to produce a cross-linked rubber composite via a simple but efficient approach. This has been achieved by cross-linking of commercially available XNBR by direct physical mixing of it with ferric salt and thus eliminating the use of any solvent. The development of metal-ligand-interactive cross-links in the XNBR matrix is established by rheological and swelling studies. The use of a small amount of a heterocyclic base, dimethylaminopyridine (DMAP) is found to play a crucial role by influencing the extent of cross-linking between ferric and carboxylate groups. The proposed cross-linking mechanism is validated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and differential scanning calorimetry studies. Strong and favorable ferric-carboxylate coordination interaction and cluster formation are believed to provide reinforcement to the rubber composite to maintain adequate mechanical properties. In addition, the optimum composition of the composite is found to impart features like recyclability and weldability.

Carboxylated nitrile rubber (XNBR) is crosslinked via metal-ligand coordination bond by simple mixing and compounding as an alternate to chemically rich traditional vulcanization route. Basis of the generation of reversible non-covalent crosslinks, in the rubber matrix, is copper (I)-carboxylate metal-ligand interaction that is evidenced by XPS, FTIR, and rheological studies. At low copper content (5 phr), self-healing property is exhibited by the composite while adequate mechanical strength is obtained at higher copper content (20 phr). For 20 phr filled composite (XNBR-Cu20), the tensile strength reaches up to 5.41 +/- 0.28 MPa, which is almost 19 times higher than that of pure XNBR (0.29 +/- 0.02 MPa). On the other hand, tensile strength is not so high (1.95 +/- 0.20 MPa) for composite XNBR-Cu5, however, this one shows the self-healing efficiency of around 75% for the first cycle, 71% for second cycle, and 56% for the third cycle. The positive shift of glass transition temperature (T-g) takes place with the increasing content of copper (I)-carboxylate crosslinking that is caused by the lowering in segmental mobility of the rubber chains. Reversible nature of the metal-ligand coordination, recoverability, and hysteresis in the XNBR-Cu (I) composite are studied by cyclic stress-strain loading. The CuCl content greatly influences the inherent crosslinking nature of the elastomeric network and the ultimate properties of the composites.

Uniform dispersion of metal oxide-like zirconia in elastomeric matrix is an essential requisite to deliver proper reinforcement. However, inadequate compatibility between the hydrophobic elastomer and the hydrophilic zirconia surface makes this a difficult task. In this work, three different surface modifiers, namely, sodium dodecyl sulfate (SDS: a surfactant), 3-(trimethoxy silyl) propyl methacrylates (MPS: an organosilane), and tris (hydroxymethyl) aminomethane (Tris: an amine buffer) are employed to modify the surface of sol-gel derived in-situ generated zirconia. Effect of surface modification of zirconia by these different kinds of surface modifiers on zirconia-filled nitrile rubber (NBR) composite has been critically investigated in terms of thermal, morphological, mechanical, swelling, rheological, and dielectric properties. Temperature of maximum degradation (T-max) of the NBR gum (439 & DEG;C) is improved upon incorporation of all type of modified zirconia while that is maximum for Tris-modified zirconia-filled composite (458 & DEG;C). Similar trend is observed in stress-strain study where Tensile strength is enhanced up to six times for the filled composites relative to NBR gum (1.03 MPa) and the highest value is shown by Tris-modified zirconia-filled composite (6.35). This study reveals that Tris could be a potential surface modifier for metal oxides like zirconia, as an alternate to organosilane, to reinforce the elastomer matrices.

This review article focuses on recent advances in zirconia-based polymer matrix composites. Zirconia (ZrO 2 ), as a non-black inorganic filler, has attracted a lot of attention owing to its attractive and rich materialistic properties. Considerable number of reports are documented in literature in which the effects of zirconia incorporation into polymeric matrix have been studied from different perspectives. These include studies on mechanical, thermal, dynamic mechanical, morphological, rheological, optical, electrical, and antimicrobial properties of the zirconia-filled polymer composites. In those studies, zirconia is highly recognised for its capability to improve the ultimate composite properties. In some of the studies, zirconia has been used in combination with other metal oxides to take advantage of the hybrid filler. In current report, we present an overview on zirconia-based polymer composites in context of the precise role of zirconia on the composite properties, their significance, and the outcome of the studies. Overall, zirconia appears as a potential candidate for the development of industrially important polymer composites, and ongoing work in this area is expected to bring more novel and fascinating results to further enrich this area.