CURE CHARACTERISTICS OF HYDROXYL TERMINATED POLYBUTADIENE PREPOLYMER WITH BLOCKED TOLUENE DIISOCYANATE-Ⅰ

Controlled release of TDI and hence the cure characteristics of several blocked TDI with HTPB are reported. The reactions were followed through viscosity measurements as a function of time and temperature under the catalytic influence of triethylamine. The effect of nature of substituents present on the end capping substrate, temperature, solvent, basicity of catalyst and kinetics thereon have been studied.

CURE CHARACTERISTICS OF HYDROXYL TERMINATED POLYBUTADIENE PREPOLYMER WITH BLOCKED TOLUENE DIISOCYANATE-Ⅱ

Cure characteristics of hydroxyl terminated polybutadiene (HTPB) prepolymer with avariety of blocked toluene diisocyanate (TDI) in the presence of triethylamine (TEA) andchloroacetic acid catalyst are reported. Phenol, thiophenol, p-chloropheno1, p-nitrophenol,p-cresol, resorcinol, naphthols, caprolactam and butylated-hydroxytoluene were used as blockingagents. Viscosity measurements have been carried out using a mixture of HTPB and blocked TDIin cyclohexanone in the presence of the catalysts at 50℃ and 60℃ using Haake rotational vis-cometer. Viscosity measurements have also been carried out with 50% solids such as ammonium sulphate along with HTPB and TDI adduct.

Nitrogen Metabolism and Curing Characteristics of Flue-cured Tobacco Variety NC71

[Objectives]To explore the growth characteristics,nitrogen metabolism and curing characteristics of the new variety NC71 in strongly aromatic tobacco leaves production area.[Methods]With Yunyan 87 as the control and NC71 as the experimental material,the experiment was carried out in Nanyang tobacco area for two consecutive years to study the growth characteristics of tobacco plants,the activity of key enzymes in nitrogen metabolism,the content of secondary metabolites,and the differences of tobacco-related water content,PPO enzyme activity and total phenol content.[Results]NC71 plants had lower height,better appearance quality and lower nicotine,total sugar and chlorine content.NC71 high nitrogen treatment and Yunyan 87 medium nitrogen treatment had similar key enzyme activity of nitrogen metabolism,content of secondary metabolites;Yunyan 87 and NC71 were easy to cure and resistant to curing.[Conclusions]This study provides a reference for measuring the appropriate nitrogen application rate and optimizing the curing process from the activities of the key enzymes NR and GS in nitrogen metabolism at the mature stage of the variety.

Sawdust Short Fiber Reinforced Epoxidized Natural Rubber: Insight on Its Mechanical, Physical, and Thermal Aspects

In this work,Epoxidized natural rubber/sawdust short fiber(ENR-50/SD)composites at different fiber content(5,10,15 and 20 phr)and size(fine size at 60–100μm and coarse size at 10–20 mm)were prepared using two-roll mill and electrical-hydraulic hot press machine respectively.Curing characteristics,water uptake,tensile,morphological,physical,and thermal properties of the composites were investigated.Results indicated that the scorch time and cure time became shorter whereas torque improved as SD content increase.Though the decline of tensile strength and elongation at break values,modulus,hardness and crosslinking density have shown enhancements with the increasing of SD content.The water uptake percentage of all samples has shown an increasing as SD content increase.However,the low SD content,particularly fine size have presented lower water uptake.The temperature of weight%loss(5 and 50 wt%loss)of 5 phr SD(low content)have recorded higher temperature compared to 20 phr SD(high content)in the rubber composites,which indicated higher thermal stability.The fine size of SD has recorded better overall properties than SD coarse size at same loading in the rubber composites.

EFFECT OF NANOCRYSTALLINE CELLULOSE ON THE CURING CHARACTERISTICS AND AGING RESISTANCE PROPERTIES OF CARBON BLACK REINFORCED NATURAL RUBBER

This work focused on the effect of nanocrystalline cellulose （NCC） on the curing characteristics, aging resistance and thermal stability of natural rubber （NR） reinforced with carbon black （CB）. Sharing the same fillers loading of 45 parts per hundred rubber （phr）, NR/NCC/CB composites with different NCC/CB ratios （i.e. 0/45, 5/40, 10/35, 15/30, 20/25 phr） were prepared and analyzed. Resorcinol and hexamethylene tetramine （RH）, acting as the modifier in NR/NCC interface, was also discussed for its influence. The result showed that an relatively higher ratio of NCC/CB led to a lower torque, a shorter cure time （Tg0）, a slightly longer scorch time （Ti0） and a bigger vulcanization rate constant （K）. This tendency suggested that the existence of NCC accelerated the vulcanization process. Additionally, modified by RH, NR/NCC/CB compounds exhibited a short T10 and a elevated torque. And a moderate RH content would lower the E of vulcanization. A 10 phr substitute of CB by NCC can help to improve aging resistance in terms of mechanical properties. In a high temperature aging condition, composites with 10 phr NCC also performed the highest storage modulus （G＇） among composites tested. A moderate NCC content contributed to the best retention of G＇ after high temperature aging, so did the incorporation of RH. With the partial replacement of CB by NCC, the temperature of 5% weight-lose had a slight drop and the apparent crosslink density showed a decrease. Thanks to the interaction of RH with both NR and NCC, composites showed an improvement in apparent crosslink density after modified by RH.

SBR COMPOSITES REINFORCED WITH N-ISOPROPYL-N'PHENYL-P-PHENYLENEDIAMINE-MODIFIED CLAY

SBR compounds including the N-isopropyl-N＇-phenyl-p-phenylenediamine-modified clay（organoclay） were prepared.Effects of modified clay and antioxidant（IPPD） contents on mechanical and rheological properties of SBR composites were studied.FTIR results confirmed that the clay was chemically modified by IPPD and changed into an organoclay.X-ray diffraction（XRD） results confirmed the increase in interlayer distance of the clay due to the insertion of IPPD.Rheological and cure characteristics of SBR compounds were determined using RPA（Rubber Process Analyzer） and rheometer.Scorch time and cure time of SBR compounds decreased with introduction of the organoclay.Mechanical properties and heat aging resistance of the SBR composites were improved significantly by incorporation of the organoclay.