Investigation Of The Preparation And Properties Of Rubber/Cellulose Nanocrystals Composites Based On β-hydroxy Ester Bonds

To alleviate the burden of conventional vulcanized rubber materials on the environment and to obtain recyclable rubber-based composites,this study introduces β-hydroxy ester exchange bonds into elastomeric composites.In this work,we proposed to introduce carboxylated CNC to prepare and characterize rubber-based composites containing β-hydroxy ester exchange bonds.ⅰ)Cellulose nanocrystals were used as raw material,and a large number of carboxyl groups were introduced to the CNC surface by the TEMPO oxidation reaction.In this work,we proposed to introduce epoxidized soybean oil(ESO)as a cross-linking agent into carboxyl nitrile butadiene rubber(XNBR)/TEMPO-oxidized cellulose nanocrystals(TO-CNC)composites,and successfully prepared ESO-cured XNBR/TO-CNC elastomeric vitrimer withβ-hydroxyl esters dynamic covalent bonds,which are formed between the epoxy group of ESO and the carboxyl group of XNBR or TO-CNC.The TEMPO oxidation of CNC is validated by a series of characterizations such as FTIR,conductometric titration,and element analysis.The formation of theβ-hydroxyl esters is as well evidenced by the FTIR analysis and the curing curves.Interestingly,the TO-CNC exhibits good dispersion in the composite,and a remarkable mechanical reinforcement is observed for ESO-cured XNBR/TO-CNC elastomer,for instance,when 15 phr of TO-CNC were added,the tensile strength was 237% greater than that of the unfilled sample.Moreover,this composite as well shows good reshaping capability and reprocessability.Generally,this work offers a novel approach to preparing green cross-linked elastomer/bio-based CNC composites that can potentially overcome the bottleneck of the non-recycling of traditional vulcanized rubber.ⅱ)The epoxidized EPDM is obtained by modifying the double bonds in the side chains of EPDM to epoxy groups.By introducing carboxyl groups on the CNC surface through DDSA modification with cellulose nanocrystals as raw material,these carboxylated CNCs can be used not only as fillers for epoxidized EPDM but also as cross-linking agents.Moreover,β-ester dynamic exchange bonds are generated at the rubber-filler interface.The composites thus prepared can rearrange the network topology by the ester exchange reaction,thus giving the composites a vitrimer-like behavior.Compared with the sulfur vulcanized samples,the EPDM/CNC composites exhibited higher elongation at break,which was about seven times higher than that of the sulfur vulcanized samples.