Batch Mixing for the In Situ Grafting of Epoxidized Rubber onto Cellulose Nanocrystals

Abstract

Cellulose nanocrystals (CNCs) are sustainable nanomaterials commonly employed as biofillers in polymer composites. However, they disperse poorly in hydrophobic polymers in their pristine state, leading to premature failure under stress. Thus, there is an ongoing research effort to enhance the dispersion of CNCs in various polymer matrices to obtain their touted reinforcing potential. In this work, the CNC formation of covalent grafts with epoxidized natural rubber (ENR) and the formation of secondary hydrogen bonds in a base-catalyzed reaction was studied at varying temperatures. The grafting reaction was confirmed using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and toluene swelling experiments. ENR-CNCs processed at 180 °C showed an 83% increase in tensile strength compared to neat ENR. While the 180 °C treated ENR reinforced with CNCs showed superior properties, all temperaturetreated composites exhibited improved tensile strength and elongation at break. Toluene swelling tests confirming the ENR-CNC composites' insolubility treated at 180 and 220 °C. This was corroborated by a 342% increase in Mooney viscosity and improved rheological properties. Overall, the catalyzed thermal treatment of the ENR-CNC composite system generates covalent cross-links between the CNCs and ENR that result in enhanced physicomechanical properties. Such composites could be employed as a masterbatch filler for other hydrophobic rubbers, which can consequently enhance the compatibility of CNCs with the rubbers.

Sustainable natural rubber composites: masterbatch development of epoxidized natural rubber grafted to designed enzymatic polysaccharides

“…This indicated that although these groups took part in hydrogen bond formation, more C-O-C bonds were generated from the epoxy ring opening and subsequent ether bond formation. 27 Therefore, these results provide further evidence that grafting has occurred between the ENR and glucan, which was previously observed by FTIR measurements.…”

“…48 Overall, the incorporation of the glucan in the ENR system led to a higher viscosity of the composite, which can be associated with the occupation of the free volume of the ENR matrix succeeded by restriction of the ENR chains movement. 27,49 It was evident that using a catalyst for producing the masterbatch composite positively correlates with the viscosity increase as composites with a catalyst displayed greater viscosity than the samples without a catalyst. This could be attributed to the formation of more irreversible ether bond grafting of the ENR onto the glucan with the assistance of the catalyst.…”

“…[36][37][38][39] The control ENR showed peaks at 3000-2800 cm À1 (C-H stretching), 1650 cm À1 (CQC stretching), and 1452 and 1378 cm À1 (C-H deformation). 27,40,41 The peaks at 872 and 1250 cm À1 are attributed to the asymmetrical and symmetrical stretching vibration of the C-O-C of the epoxidized groups in ENR chains. 26,28 For ENR-grafted glucan, an increase in the intensity of the broad peak in the range of 3000-3600 cm À1 associated with the OH peaks of glucan is observed.…”

“…[22][23][24] Additionally, the oxygenous groups of ENR make it more polar than NR, allowing it to be more compatible with polar fillers, such as glucan. For instance, the improved compatibility of ENR with polar fillers including cellulose nanocrystals, [25][26][27][28] lignin, 29 silica, 21,30 clay, 31 starch, 32 and chitosan 33 to fabricate ENR composites is reported. In this study, a high temperature and shear-mediated reaction of the oxirane group of ENR with the electronegative hydroxyl groups of glucans via a ringopening reaction to form covalent grafts is investigated.…”

Hydrothermally Treated Lignin as a Sustainable Biobased Filler for Rubber Compounds

“…Currently, the rubber industry is highly dependent on nonrenewable petroleum-based materials for manufacturing of their products, which has a tremendous impact on global concerns like CO 2 emission and overexploitation of natural resources. This poses threats for their business and society as well as the environment and drives toward the development of energy-efficient and environmentally friendly products which are less dependent on fossil resources. − During the past few decades, this problem has been addressed by replacement of one of the inevitable and voluminous petrochemical rubber additives, carbon black filler with mineral based silica. , These fillers, when incorporated, can remarkably enhance the mechanical and dynamic properties of the green (nonreinforced) rubber. Though silica technology meets the desired performance criteria of certain rubber products, in particular passenger car tire treads, it is still not feasible to meet the sustainability goals as the manufacturing process involves nonrenewable chemicals.…”