Synthesis Of Reactive Plasticizers For Sustainable Development And Their Potential Applications In Rubber Composites

The current industrial revolution emphasized the necessity to use environmentally friendlier sources and strategies to meet the sustainable economy challenges of the modern world.Owing to the finiteness,migration problems,impact on human health,and environmental impacts of fossil resources,current research efforts are switched to search and develop renewable,sustainable and eco-friendly alternatives of commercial plasticizers to meet the green agenda to establish a green society.The substitution of petroleum-based plasticizers with bioplasticizers offers noteworthy advantages,such as recyclability,biodegradability,high lubricant power,low diffusion coefficients in the polymeric matrix and exceptionally low volatility.In this context,biodegradable polymeric materials and the polymer recycling are two major routes towards sustainable development.Rubber recycling contributes to the reduction of pollution by the waste tires and brings an improvement to the environment;however,three-dimensional crosslinked network prevents it further recycling into value added products.In this regard,an eco-friendlier approach towards the recycling of the waste rubber as multifunctional additive is quite necessary.In this work,reactive plasticizers based on soybean oil(SBO)and recycled rubber are designed and synthesized.Moreover,reactive plasticizers are further applied in SBR/silica composites.Firstly,silanized plasticizer(SP)was chemically derived and synthesized from SBO co-vulcanized with bis-(3-(triethoxysilyl)-propyl)tetrasulfide(TESPT)by using the sulfur-accelerated curing system.Characterization of SP,obtained by the inter-mixing of SBO,sulfur and bis-(3-(triethoxysilyl)-propyl)tetrasulfide(TESPT)along with curing additives,was investigated.SP was analyzed for varied TESPT contents and compared with the controlled plasticizer(CP)(having no TESPT content).Free sulfur and acetone extract values of SP were controlled by optimum increase in TESPT content on the cost of gel time.Structural differences were elucidated by attenuated total reflectance Fourier transform infrared spectroscopy(ATR-FTIR),where disappearance of peaks at 3010 cm^-1 and 1650 cm^-1 belong to stretching vibrations of the olefinic bonds and the appearance of new peaks at 1075 cm^-1 and 792 cm^-1 corresponding to stretching vibrations of the Si-O and Si-C bonds,respectively,occurred with the formation of SP.The results were further confirmed with proton nuclear magnetic spectroscopy(¹H-NMR)where the signals corresponding to the vinylic and allylic protons were chemically shifted to 5.3 ppm and 2.8 ppm,respectively.Thermal changes were demonstrated with varying contents of TESPT.The morphology was elucidated by optical microscope and scanning electron microscope(SEM),specified the fineness of the structure following the addition of TESPT.Secondly,SP extended styrene-butadiene rubber(SBR)/silica composites have been studied for their improved filler dispersion through coupling interaction at the SBR/silica interface.The effect of SP on cross-link density,thermal,static and dynamic mechanical properties of SBR composites related to the tire performance,were investigated.The results revealed that SP enhanced tensile strength,modulus and hardness of the composites due to enhanced matrix-filler interactions while concurrently maintained higher elongation at break due to the presence of SBO.Further reinforcement was observed for SP extended SBR/silica vulcanizates with higher TESPT content,what was related to the development of additional polysulfidic crosslinks the maximum tensile strength was recorded for the SBR/SP20 vulcanizate with a value of 28.9 MPa.SP reduced Payne effect in silica filled SBR composites by providing coupling interface which appreciable limits the filler secondary structures,resulted in an improved morphology.The dynamic curves indicated the highest efficacy for wet and dry traction performances of SP extended SBR composites comparing to unmodified reference standard.Thirdly,an eco-friendly synthesis of reactive plasticizer(RP)was derived from waste rubber,wherein high reclaiming degree of GTR was achieved by low-temperature oxidation under swollen action of SBO.In-situ reclaimed GTR with SBO was cured into RP through a free-radical chain reaction between activated molecular rubber chains and SBO.GPC analysis supported that number average molecular weight(M_n)of natural rubber(NR)increased whereas M_n of synthetic rubber(SR)gradually decreased by increasing the sulfur content in RP.During the curing process,degraded rubber chains were involved in synergistic reactions of recombination to strengthen bound rubber involved with core-shell structure carbon black in the gel part and grafting with SBO which mainly attributed to the sol part.RP was obtained by modification of highly reclaimed rubber to control oil migration and to modulate the reaction.Reactive plasticizers were further explored as a multifunctional additive to SBR/silica composites.Reactive plasticizers performed the following three functions towards SBR/silica composites:i)value-added rubber substitute;ii)reinforcing filler with the increase in tensile strength maximum up to 112%approximately on account of bound rubber involved with core-shell structure carbon black;and most importantly,as a iii)reactive plasticizer together with good control over oil extractability.Finally,reactive plasticizers were further derived from the fast reclamation of GTR by self-designed thermo-oxidative reactor under the controlled action of natural oxidation.Wherein high shearing stress was applied along tangential directions at moderate temperature(200oC)for 20min.By explicitly envisage the effects of heat and oxygen,the fast reclamation underwent through the autocatalytic free-radical chain reaction,propagated through the oxidative cleavage of sulfur crosslinks.FTIR and SEM results confirmed the partial oxidation and micron-sized bound rubber domains dispersion in devulcanized state.Reclaimed rubber(RR)was further incorporated into SBR/silica composites to study the reinforcing and dispersing effects under the reclaimed environment.Results assured that reactive plasticizers have an excellent reinforcement to the rubber composites,together with a marginal potential for future applications.Overall,this work has deep strategic importance for the preparation and characterization of variety of bio-oil derived reactive plasticizers and recycled rubber which can be further applied as multifunctional additive to rubber composites.This research can lead to a real contribution to the feedstock recycling together with a noticeable improvement to the environment.