Analysis Of The Changes Of Natural Rubber Network Structure And Its Effect On The Properties During Storage

Natural rubber（NR）is widely used due to its excellent properties such as high elasticity,wear resistance and acid-alkali resistance.However,the change of NR network structure and performance during storage not only increases the processing energy consumption,but also severely affects the quality stability of NR products.In order to address the problem,it is necessary to fundamentally elucidate the influence of network structure on storage performance.Therefore,the effects of molecular weight and distribution,side group structure（aldehyde groups）,free non-rubber components,end group structure and particle size on network structure were systematically analyzed in the study,to provide a theoretical basis for regulating network structure and improving performance.Furthermore,the network structure and performance under high temperature-humidity in Hainan were analyzed to ascertain the intrinsic relationship between network structure and humidity-temperature,providing theoretical reference for the optimization of storage conditions.Finally,the influence of network structure on processing energy consumption and performance was clarified by studying the variation of NR performance under actual storage conditions,providing a theoretical basis for regulating the storage conditions in actual production.（1）The changes of network structure,machining properties,thermal stability,rheological properties and mechanical properties of NR during accelerated storage were analyzed.The results show that the gel content and crosslinking density of NR increase by12.45%and 0.43×10^-4 mol/cm³,respectively,resulting in molecular cross-linking reaction and the formation of cross-linking network structure after accelerated storage for 48 h.Moreover,the molecular chain is difficult to slip and orient.With the extension of the accelerated storage time,initial plasticity,Mooney viscosity,elastic modulus,thermal stability and mechanical properties,the ability to resist external heat and force are increased.This indicates that molecular crosslinking of NR occurs and network structure is formed with the prolonging of storage time.（2）Through mechanical plasticizing,hydroxylamine treatment,high-speed centrifugation,alkaline protease,esterification and differential centrifugation,the effect of molecular weight,aldehyde,non-rubber components,terminal groups and particle size on NR network and properties were analyzed during storage.The results show that the lower the molecular weight of NR,the more content of short molecular chains,the smaller the increasement of gel content,crosslinking density and glass transition temperature,the lower the degree of molecular crosslinking,and the smaller the changes of properties during storage.When the aldehyde group and hydroxylamine hydrochloride reactions,the changes of gel content,crosslinking density and properties are very small during storage,which is suggested that the aldehyde group induced the formation of network.The more content of the non-rubber components,the changes of molecular weight,gel content,crosslinking density,glass transition temperature and properties larger,and the degree of molecular crosslinking is higher.The tube model analysis show that the molecular crosslinking is mainly entanglement.Therefore,the deproteinized and esterification NR are prepared.The results suggest that the network density of deproteinized NR still increases during storage,while esterification NR has not change significantly.Thus,the key factor of NR network formation during storage is phospholipid.Furthermore,it is found that the large rubber particles with rich phospholipid on the surface are more conducive to the formation of the network during storage,which further proved that phospholipid plays an important role during storage.In summary,the changes of NR network during storage are affected by the combination of molecular weight,aldehyde,non-rubber components,terminal groups and particle size,among which the phospholipid plays a key role.（3）The effect of molecular weight,aldehyde,non-rubber components,terminal groups and particle size on the structure and properties of NR network was explored under high temperature-humidity storage conditions in Hainan.The results show that the network of all samples showed different degree of damage.Moreover,the change in esterification NR is the most obvious,which further illustrates that the phospholipid plays an important role in the formation of network during storage.It is worth noting that the changes of cross-linking network are mainly oxidation of chain scission under high temperature-humidity.Furthermore,the internal relationship between the changes of network structure and performance and temperature-humidity during NR storage are analyzed.The results show that low humidity is more conducive to the formation of crosslinking network,but high temperature could improve the degree of NR oxidation of chain scission.Through the storage life prediction,it is found that the storage life of NR is gradually shortened as the temperature increased.Therefore,the storage stability of NR under extreme conditions can be improved by the dual regulation of phospholipid,temperature and humidity.（4）The network structure and processing energy consumption of natural storage NR,and mechanical properties of vulcanized rubber were studied under constant low temperature-humidity and natural environment.The results show that the gel content and crosslinking density of NR-CE and NR-NE increased.In terms of processing energy consumption,NR-NE and NR-CE required additional 0.60 k W/h and 0.49 k W/h,and the cost is about 38.2 million and 29.8 million,respectively.It is found that the crosslinking structure,mechanical properties and aging properties of NR vulcanized rubber had no significant changed after storage.This fully demonstrates that it is of great significance to pay attention to the regulation of NR storage conditions to meet the needs of high-end fields,reduce energy consumption,save costs,and also conform to the development concept of the current energy-saving and environment-friendly society.