区别是：
reactant 指的是：反应物。
processing aid指的是加工助剂。
例句：
reactant
1、Oxygen is often used as reactant in chemical processes.
在化学过程中，氧气经常充当为反应物。
2、The effects of temperature, the quantity of catalyst used, and reactant feed rate on hydrosilylation was discussed.
考察了温度、催化剂用量、加料速率等因素对苯乙烯与甲基二氯硅烷硅氢加成反应的影响。
3、The effect of process conditions, such as microwave, reactant ratio, catalyst andsolvent etc, on the nucleophilic substitution and yield of product were investigated.
考察了微波技术、反应物料比、催化剂以及溶剂等主要条件对亲核取代反应和产物收率的影响。
processing aid
1、Effect of binary processing aid on rheology and mechanical properties of HDPE.
复合加工助剂对HDPE流变性能和力学性能的影响
2、Is the production of organic tin heat stabilizers, ACR processing aid of theintegrated enterprise.
是生产有机锡热稳定剂、ACR加工助剂的综合企业。
2、Other polymer additives are colorants, antistatic agents, foaming agents,preservatives, and processing aid or lubricants. fugitive tinting colours.
其它聚合物添加剂包括染色剂、抗静电剂、发泡剂、防腐剂和加工助剂或润滑剂。标志色，着色剂，指色剂