Application Of Carbon Nanodots As Versatile Additives For Rubber

Nanocarbons,such as graphene,diamond,carbon black,and carbon nanotubes,are widely used in many fields due to their unique and excellent properties.Carbon nanodots(CNDs),a newly emerging nanocarbons,have exhibited great potential in polymer composites by virtue of the wide and renewable material sources,excellent biocompatibility,low or even non-toxicity,simple and efficient preparation,tunable surface functionalities,and excellent free radical scavenging activity.However,until now,most of the reported researches related to polymers contained CNDs are mainly focused on the preparation and characterization of solid-state luminescent polymer composites.In this thesis,CNDs are adopted as versatile rubber additives towards high-performance rubbers.The main contents of the thesis are as follows.(1)A one-step microwave pyrolysis method was adopted to synthesize CNDs by using critic acid and ethylenediamine as carbon source and surface passivation reagent,respectively.By virtue of the Lewis alkalinity of amino-functionalities,EDA-CNDs was incorporated into TESPT modified SBR/silica composites to promote the silanization reaction between silica and the silane,which significantly improve the dispersion of silica and enhance the interfacial interactions between silica and rubber matrix.The effects of EDA-CNDs on the microstructure and performance of TESPT modified SBR/silica composites were disclosed.With the addition of 3 phr EDA-CNDs,the mechanical and dynamic performance of the corresponding composite are effectively promoted.For instance,the modulus at 300 % strain of the composite is improved by nearly 30 % while its tan δ valus at 60 ℃ is declined by nearly 21 %.This should be attributed to the hybridization of EDA-CNDs and silica that improves the dispersion of silica,leading to more exposed surfaces of silica.Besides,the Lewis alkalinity of amino-functionalities can catalyze the silanization of silica.The above factors both contribute to promote the dispersion of silica particles and enhance the interfacial interactions between silica and rubber matrix,which finally enables the improvement on the performance of TESPT modified SBR/silica composites.(2)The as-prepared EDA-CNDs with abundant surface functionalities was employed as a brand new activator for sulfur vulcanization,to partially substitute zinc oxide(Zn O)in rubber composites.The influences of EDA-CNDs substitution of Zn O on the vulcanization process and overall performance of rubber composites were investigated.By taking the SBR composites incorporated with 5 phr Zn O as comparison,the optimal vulcanization time(Tc90)of the sample incorporated equivalent EDA-CNDs to substitute 60 wt.% of Zn O reduces from43 min to 19 min.Meanwhile,the cross-link density and mechanical performance of this sample are maintained.This is because the surface carboxyl functionalities on EDA-CNDs can interact with Zn O during vulcanization at elevated temperatures,leading to the improved dispersibility of Zn O in rubber matrix.Meanwhile,the amino functionalities on EDA-CNDs can also accelerat the conversion of cross-link precursors into cross-links by reducing the activation energy of cross-linking reactions.Accordingly,the vulcanization rate of SBR compound is dramatically promoted by the substitution of Zn O for EDA-CNDs which significantly lowers the content of Zn O in the sample.(3)By virtue of excellent radical scavenging capacity and antioxidant activity,EDA-CNDs was incorporated into natural rubber(NR)/carbon black(CB)composites as green antioxidant through open-milling/banburying.The effects of EDA-CNDs on the aging-resistance of NR/CB composites were studied.The retention of elongation at break(EAB)of NR/CB composite incorporated 1 phr EDA-CNDs is improved by 14.5 %,and16.7 % compared to those of NR/CB composite incorporated 1 phr antioxidant 4020 and the control sample without antioxidant,respectively.Besides,EDA-CNDs was also introduced into SBR/silica composites through similar process.It turns out that the retention of EAB of SBR/silica composite incorporated 1 phr EDA-CNDs is improved by 5.4 %,and 13.7 %compared to those of SBR/silica composite incorporated 1 phr antioxidant 4020 and the control sample without antioxidant,respectively.This should be due to the fact that the as-prepared EDA-CNDs can effectively scavenge the reactive radicals in the rubber matrix during thermo-aging and hence delay the oxidation of rubber composites.