硫化天然橡胶的本征自修复与固相回收加工

通过小分子模拟试验和应力松弛,发现甲基丙烯酸铜(MA-Cu)比氯化铜(CuCl_2)更适合用作硫化天然橡胶中二硫键交换反应催化剂,并且硫化天然橡胶中的二硫键交换反应需要在高于120°C的温度下才能高效进行,这保障了相关制品在较低温工作时的结构与性能稳定.进一步的实验结果表明,硫化天然橡胶在MA-Cu辅助作用下获得了多次自修复与固相回收加工性能,损伤自修复后的硫化天然橡胶与固相回收加工的再生硫化天然橡胶,其拉伸强度均可恢复到原始材料强度的80%左右.

Intrinsic Self-healing and Solid-state Recycling of Vulcanized Natural Rubber

Sulfur-vulcanized natural rubber is constructed by three-dimensional crosslinked networks containing plenty of monosulfidic,disulfide and polysulfide linkages,which is insoluble and infusible and hence difficult to be reprocessed.Considering that disulfide bonds possess dynamic reversibility under certain circumstances,however,we might impart rehabilitation power and processibility to vulcanized natural rubber if disulfide exchange among different disulfide and polysulfide bonds were activated.Model disulfide metathesis between equimolar small-molecule disulfides and stress relaxation of vulcanized natural rubber reveal that copper(Ⅱ) methacrylate (MA-Cu) is an effective catalyst of disulfide metathesis.Compared with CuC12,MA-Cu is more suitable for working with vulcanized natural rubber from the view point of environmental polarity and activation energy involved in stress relaxation.By incorporating MA-Cu during compounding of natural rubber and other ingredients as defined by industrial formulation,built-in sulfur-crosslinked networks are created after vulcanization and become dynamically reversible at or above 120 ℃ under the action of MA-Cu.Accordingly,rearrangement of the crosslinked networks is enabled as a result of reversible exchange of the sulfur bonds,which not only provides thermal deformability like linear polymers,but also helps to re-establish covalent bonding across cracked surfaces.Based on this finding,the vulcanized natural rubber is successfully coupled with multiple arbitrarily reshaping,intrinsic self-healing and solid-state recycling capabilities.Either the cracked or the reprocessed vulcanized natural rubber can restore mechanical properties of the original version to a great extent (～ 80％).Because disulfide metathesis is triggered at temperature ≥120 ℃,above the working temperatures for most natural rubber products,the materials are allowed to keep their structure and properties stability in the course of the operation.The approach proposed here has nothing to do with conventional measures of rubber reclaiming via de-crosslinking,and is eco-friendly and energy-saving.Moreover,the sulfur-crosslinked networks are not intentionally introduced into the vulcanized natural rubber but present following traditional technique.All these factors benefit popularization of the concept in practical applications.