螺杆挤压膨胀干燥对天然橡胶结构与性能的影响

天然橡胶的生产主要采用传统的热风干燥，但天然橡胶是热的不良导体且自粘性强，导致热风干燥普遍具有干燥效率低、胶料发粘和夹生等问题，这对产品的性能带来不利影响。而螺杆挤压膨胀干燥工艺作为一种新干燥工艺，已被广泛应用于合成橡胶工业，具有干燥效率高、自动化水平高和工艺稳定等特点，在天然橡胶（NR）生产加工中具有良好的发展和应用前景。本研究对比了传统热风干燥（NT）和螺杆挤压膨胀干燥（NCT）2种工艺制备NR的结构，分析NCT的性能特点，以探讨螺杆挤压膨胀干燥工艺运用在天然橡胶生产加工中的可行性。结果表明：在生胶层面，螺杆挤压膨胀干燥工艺由于干燥温度低、干燥用时短，能够有效降低NR分子链在干燥过程中受到的热氧降解，因此NCT相比NT而言具有更高的塑性初值、门尼粘度和凝胶含量，且对于蛋白质、挥发分等非胶组分的影响较小；对于纯胶配方硫化胶，NCT相较NT而言表现出更快的硫化速率。通过使用Mooney-Rivlin方程对硫化胶内部网络结构进行了拟合，发现NCT硫化后的有效交联密度和化学交联网络的数量相对较低，这使得NCT的拉伸强度、撕裂强度和模量等常规力学性能低于NT，疲劳性能方面也表现出了相对较高的压缩生热和蠕变。对于炭黑配方硫化胶，NCT与NT的常规力学性能无明显差异，这可能是由于硫化促进剂N-叔丁基-2-苯并噻唑次磺酰胺的硫化速率较快所导致。但在动态力学性能方面，NCT的疲劳寿命更长，表现出更优异的动态疲劳性能，这与螺杆挤压膨胀干燥工艺能改善炭黑分散性有关。

Influence of Screw Extrusion Expansion Drying on Structure and Properties of Natural Rubber

Natural rubber is mainly dried by hot air. However, natural rubber is a poor conductor of heat and has strong self-adhesion, which leads to low drying efficiency, sticky rubber and entrapment in hot air drying, and adversely affects the performance of the product. Screw extrusion expansion drying process, a new drying method, has been widely used in the synthetic rubber industry due to the high drying efficiency, high automation level and stable process. And the drying process also has a good application prospect in the production of natural rubber (NR). In this paper, the structure of NR prepared by traditional hot air drying and screw extrusion expansion drying (respectively denoted as NT and NCT) was compared, and the performance characteristics of NCT were analyzed to explore the feasibility of screw extrusion expansion drying process in the production and processing of natural rubber. For raw rubber, the screw extrusion expansion drying process could reduce the thermo-oxidative degradation of the NR molecular chain during the drying process because of its low drying temperature and short drying time, so NCT had higher initial plastic value, Mooney viscosity and gel content than NT. The screw extrusion drying process had little effect on the non-rubber components, so the change range of the non-rubber components such as protein and volatiles was low. For the pure compound vulcanizate, NT exhibited a faster cure rate than NT. The contribution of the internal network structure of the vulcanizate was fitted using the Mooney-Rivlin equation. The effective crosslink density and the number of chemical crosslink networks after NCT vulcanization were relatively low. The conventional mechanical properties such as tensile strength, tear strength and modulus of NCT were lower than those of NT, and NCT exhibited higher fatigue temperature rise and higher degree of creep during dynamic loading. For carbon black vulcanizate, the conventional mechanical properties of NCT and NT were not significantly different., this may be due to the faster vulcanization rate of vulcanization accelerator N-tert-butylbenzothiazole-2-sulphenamide. However, NCT had longer fatigue life and better dynamic fatigue properties, which means the screw extrusion drying process could improve the dispersion of carbon black.