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Abstract Melt crystallization of isotactic Polypropylene (PP) on open platform during 3D processing is critical and often challenging. Numerous factors that influence the melt extrusion of PP directly influence its [...]

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. [ABSTRACT FROM AUTHOR]

Hyperbranched polyesters with polyionic character and high hydrodynamic sizes were synthesized at four different monomer mole ratios (An/B3 = 1:0.5, 1:1, 1: 3 and 1:5) by melt condensation of ecofriendly Poly (ethylene glycol) or PEG and Aconitic acid or AA via An+ B3 approach. The products were characterized by FTIR, 1H NMR, FESEM, TEM and DSC techniques to establish the microstructure as well as the hyperbranched architecture. The degree of branching was estimated to be within 89%-33% by 1H NMR measurements. Polyesters synthesized from 1:3 and 1:5 contained low (12%) to moderately high (40%) crosslinked structure as well. Gelation was effectively avoided at 1:0.5 and 1:3 mol compositions by keeping the AA content at lower values than PEG. The most soluble hyperbranched polyester was spherical having a dense core and a higher shell morphology. Whereas, the more crosslinked molecule was spherical but uniformly dense. Due to of the polyelectrolytic nature, the polyesters were used as flocculant to unsettle highly stable kaolin suspension at low suspension concentration maintained at 0.25% concentration by weight. The highest hydrodynamic size of the sample synthesized from 1:1 mole composition, was able to flocculate at the fastest rate (39 s) at pH 2.0 than at the iso-electric point (pH 4.2) of kaolin as well as reproduced the pure water with highest clarity (turbidity: 4 NTU). [ABSTRACT FROM AUTHOR]

The utilization of copiously available bio-waste significantly contributes to sustainable development and solid waste management. In the present study, the pyrolytic extract of coconut shell bio-waste is evaluated as a plasticizer in carbon black filled styrene butadiene rubber (SBR) compared with conventionally used aromatic oil (AO) at varied levels of 5, 10, 20, 30, and 40 phr. The pyrolysis of the coconut shell was accomplished in an inert environment using a tube furnace. The coconut shell oil (CSO) was evidenced to take part in the curing reaction increasing mechanical properties. Tensile strength increased to ~36% and tear strength by ~30%, which is attributed to the reactivity of CSO with sulfur. 1H NMR studies and the lower percentage of solvent extract for CSO filled vulcanizates confirmed the chemical interaction of CSO with sulfur and subsequent bonding to the rubber chain. The De Mattia flexing resistance showed a multi-fold improvement of 657% for CSO filled vulcanizates pertaining to enhanced internal lubrication and coherent movement of chemically bonded plasticizer with rubber chains under dynamic conditions. Thermogravimetric analysis indicated a shift in the onset of volatilization temperature from 250 °C to 370 °C upon replacement of AO with CSO showing enhanced thermal stability. Glass transition temperature was decreased by 5 °C at 40 phr plasticizer loading for CSO filled vulcanizates indicated better plasticization. CSO is a potential cost-effective, non–toxic, and sustainable alternative to the conventionally used petroleum-based aromatic oil as the plasticizer. [ABSTRACT FROM AUTHOR]

Role of silane-treated stöber silica as reinforcing filler for nitrile rubber (NBR) has been studied. Stöber silica is synthesized by sol–gel method, and the surface of silica is modified with the treatment of silane-coupling agent viz. γ-mercaptopropyltrimethoxysilane (γ-MPS) in varying proportions. Average particle size of stöber silica of spherical shape in the range of 200 to 400 nm is evident from scanning electron microscopy (SEM). Surface modification of silica particle with silane-coupling agents decreases surface energy and reduces agglomeration of silica particles in rubber matrix. Stress–strain study and dynamic mechanical analysis of silica-filled composites are compared with the unfilled ones. Analysis of cross-linking density, mechanical properties, and storage moduli indicates a strong rubber–filler interaction in the silane-treated, silica-filled NBR composites. Silane treatment is found to be effective in uniform dispersion of silica in rubber matrix and in improving the mechanical properties of rubber composite. Different functionalities of organosilane at its both end improve the compatibility of silica with rubber matrix and offer better rubber–filler interaction. [ABSTRACT FROM PUBLISHER]

ABSTRACT The proposed study attempted to explore the role of stearic acid modification on the properties of zinc-aluminum based layered double hydroxides (LDH) and their composites with acrylonitrile butadiene rubber (NBR). Three distinctive LDH systems were adapted for such comparison; an unmodified LDH and two stearic acid modified LDH. The use of zinc oxide and stearic acid in the rubber formulation was avoided as the modified LDH would be able to deliver the necessary activators for the vulcanization process. Emphasis was predominantly given to reconnoiter the merits of stearic acid modification on the increase in interlayer distance of the LDH. X-ray diffraction studies and transmission electron microscope morphological investigations of LDH powders indicated that modification with stearic acid increased the interlayer spacing which would favor the intercalation of NBR polymer chains into the layered space. However, stress-strain studies indicated better mechanical properties for composites with unmodified LDH. Composites with LDH showed higher crosslinking densities than conventionally sulfur cured control compounds using zinc oxide/stearic acid as activators. This was evident from equilibrium swelling method as well as statistical theory of rubber elasticity. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41539. [ABSTRACT FROM AUTHOR]

ABSTRACT Nitrile rubber/silica composites are prepared by a sol-gel process using tetraethoxysilane as precursor in the presence of γ-mercaptopropyltrimethoxysilane as a silane coupling agent. Here, we follow a novel processing route where the silica particles are generated inside the rubber matrix before compounding with vulcanizing ingredients. The effect of in situ generated silanized silica on the properties of the rubber composite has been evaluated by studying curing characteristics, morphology, mechanical and dynamic mechanical properties. Enhanced rubber-filler interaction of these composites is revealed from stress-strain studies and dynamic mechanical analysis. Excessive use of silane shows an adverse effect on mechanical properties of the composites. Due to finer dispersed state of the in situ silica and enhanced rubber-filler interaction, the mechanical properties and thermal stability of the composites are improved compared to corresponding ex situ processed composite. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40054. [ABSTRACT FROM AUTHOR]

A suitable polar additive‐like zinc stearate (ZnSt) was incorporated in varied amounts to the mixture of carboxylated acrylonitrile–butadiene rubber and zinc oxide in the pursuit to introduce smart traits in the composites. Zinc stearate is not reported to effectively crosslink carboxylated nitrile rubber as compared to ZnO but, by the virtue of its strong crystalline nature (solid particles), it enhances the mechanical properties like stress–strain, tear strength, hardness, and so forth of the rubber composites. Moreover, due to the melting nature of the ZnSt at a relatively higher temperature, an alteration of the mechanical behavior of the composite is observed. In addition to the mechanical adaptability, the sample is also found to offer shape memory properties. Initially, the specimens were deformed above the melting temperature (Tm) of ZnSt (∼121 °C) to create a temporary shape, and then they were fixed into that shape by quenching the material to a temperature much below Tm, keeping the stress constant. The permanent form was recovered when the specimens were reheated above Tm without applying any stress. The efficiency of shape fixing was used as the determinant of the shape memory behavior, and up to 90% efficiencies were achieved. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48271. [ABSTRACT FROM AUTHOR]