In-situ preparation of TBIR/CB nanocomposites and its regulation in structure and properties of NR based composites

Highlights

• Synthesis of new synthetic rubber composites by in-situ polymerization.

• NR/TBIRCB46 vulcanizate improve the dispersion of filler in natural rubber.

• The rolling resistance, heat build-up and wear of NR/TBIRCB composites are significantly reduced.

Abstract

In order to construct the rubber nanocomposites with desired dual network structures, the trans-1,4-poly (butadiene-co-isoprene) copolymers (TBIR)/carbon black (CB) nanocomposites were prepared by in-situ polymerization in the presence of large amounts of CB using TiCl₄-type Ziegler-Natta catalysts. It was found that the addition of CB had no obvious negative effects on the catalytic behaviors. Further, the TBIRCB were used to modify NR and the NR/TBIRCB vulcanizates were investigated. Compared with the NR compound, the NR/TBIRCB compounds presented weakened Payne effects and increased bound rubber contents with the increase in CB filling in TBIRCB. Compared with NR and NR/TBIR vulcanizates, the NR/TBIRCB46 vulcanizate with features like excellent filler dispersion and high CB in-situ filling, enhanced interaction between CB and rubber matrix and special polymer network structure constructed from NR/TBIR matrix, showed outstanding comprehensive properties, including greatly reduced rolling resistance, much lower heat built-up and increased abrasion resistance.

Introduction

With the dramatic increase in car population in the world, rubber products like tires have become an inseparable part of human life. However, using of the tires also brings a series of problems like oil-consuming, environmental pollution from grinding microsize particles, oil incomplete combustion and discarded tires, etc. Developing “green” rubber materials presenting characteristics like oil-saving, lower abrasion loss, longer serving-life, and advanced rubber fabrication technologies are interesting and deserving works [[1], [2], [3], [4]].

For highly filling rubber composites, factors including the filler dispersity, filler-rubber interaction, and polymer matrix, have great influences on the performances of the rubber composites [[5], [6], [7]]. Efforts had been tried to enhance the dispersity of fillers in polymer matrix with various methods [[8], [9], [10], [11], [12], [13], [14], [15], [16]]. In-situ polymerization method was deemed as the best effective method to fabricate highly dispersed polymer composites with improved thermal stability [12,13] and mechanical properties [14]. In addition, rubber/rubber pairs like natural rubber(NR)/cis-1,4-polybutandien(BR), solution polymerized butadiene-styrene rubber (SSBR)/BR, or rubber/plastics pairs like trans-1,4-poly(isoprene-co-butadiene) rubber (TBIR)/polypropylene (PP), were used to construct the rubber matrix for improved abrasion resistance or fatigue resistance or desired rolling resistance [[17], [18], [19], [20]]. However, the thermodynamic incompatability between the two polymers induced micro phase separation and then brought a series of problems like filler segration in one polymer phase and poorer cut-growth resistance. And in rubber/plastics pairs, plastics do not participate in the vulcanization process, which may affect the vulcanization speed.

Our previous work showed that TBIR was special kind of copolymer with crystalline trans-1,4-polyisoprene (TPI) segments showed crystalline melting temperature at 25–45 °C [[21], [22], [23], [24], [25], [26], [27]]. It was proved that TPI was miscible with NR whenever in melt state or crystallized state for TPI [28,29].Blending 10–30 phr TBIR with other general rubber materials, like NR, NR/BR, SSBR, chloroprene(CR), the corresponding rubber vulcanizates presented excellent mechanical properties, such as lower rolling resistance and heat build-up, outstanding fatigue and abrasion resistance, etc [17,30,31,33]. It was believed that the contributions of TBIR included constructing special polymer network structures containing TPI lamellar structures and co-vulcanization reactions, realizing better filler dispersion and enhanced filler-rubber interactions. The anisotropic TPI lamellae not only reinforced rubber matrix and then suppressed the filler re-aggregation, but also inhibited or branched the crack growth [30,32].

In order to fabricate high performance rubber composites by combining the advantages from TBIR and highly dispersed fillers, TBIR/CB nanocomposites (TBIRCB) with desired filler dispersity were in-situ synthesized by polymerizing the mononmers with Ziegler-Natta catalyst in the presence of CB. The obtained TBIRCB were characterized by ¹H Nuclear Magnetic Resonance Spectra (¹H NMR), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA) and Gel Permeation Chromatography (GPC) tests. Then the TBIRCB as master batches were mechanically blended with NR. The physical and mechanical properties of the NR, NR/TBIR, NR/TBIRCB vulcanizates were studied. It was found that the NR/TBIRCB46 vulcanizate with 46% CB filling by in-situ polymerization in TBIRCB46 showed outstanding dynamic properties, like much lower rolling resistance and heat built-up, reduced abrasion loss and improved rebound when compared with that of NR vulcanizate. This work is attempting to work out rubber materials for tire tread stocks with anticipated performances.