The influences of chitosan-poly(vinyl alcohol) (CS-PVA) gel and different fillers [bamboo charcoal (BC) and silica (SI)] on the viscoelastic properties of styrene-butadiene rubber (SBR) were studied in this work. The chitosan-PVAbamboo charcoal/silica (BC/SI-CS-PVA) hybrid fillers compatibilized SBR composites were fabricated by interpenetrating polymer network (IPN) method. The viscoelastic behaviors of the rubber composites and their vulcanizates were explored using a rubber processing analyzer (RPA) in the modes of strain and frequency sweeps. Storage modulus (G') and elastic torque (S') of the SBR increased significantly with the incorporation of different hybrid filler. BC-CS-PVASBR composite showed the highest storage modulus and elastic torque and abrasion resistance, which means BC-CSPVA hybrid filler could make the best reinforcement of viscoelastic and mechanical properties for SBR material in this research.

키토산-폴리(비닐 알코올)(CS-PVA) 젤 및 충전제[뱀부차콜(BC) 및 실리카(SI)] 첨가에 대한 스티렌-부타디엔 고무의 점탄성 물성을 조사하였다. 스디렌-부타디엔 고무 라텍스에 상호 침투 가교 방법으로 제조된 키토산-PVA-뱀부차콜/실리카(BC/SI-CS-PVA) 혼성체를 혼합하여 고무복합체를 제조하였다. 고무 가공분석기의 변형 스윕(strain sweep) 및 주파수 스윕(frequency sweep) 기능을 사용하여 제조된 복합체(composites) 및 가황체(vulcanizates)의 점탄성을 조사하였다. 주사전자현미경 및 내마모성 측정을 통해서 가교 구성 및 기계적 물성을 확인하였다. 충전제의 종류에 따라서 스티렌-부타디엔 고무의 저장 탄성률(G') 및 탄성 토크(S')는 현저하게 증가하였다. 실험 결과를 통해서 BC-CS-PVA 혼성체가 가장 높은 저장 탄성률(G'), 탄성 토크(S') 및 내마모성의 결과를 보였다. 따라서 BC-CSPVA혼성체가 SBR 복합체에 가장 좋은 점탄성 물성 및 기계적 물성의 보강 효과를 보였다.

Keywords: chitosan, bamboo charcoal, silica, gel, styrene butadiene rubber, viscoelastic properties

In recent years, bio-charcoal has been widely utilized as an alternative of carbon black in the research field of rubbery materials.1 As a species of bio charcoal abundant in nature, bamboo charcoal (BC) has been proved a promising reinforcement in the fabrication of bio charcoal/polymer composites. Its reinforcing effects on the macroscopic properties of rubber materials are mainly originated from the porous structure and larger specific surface.²
Recent research works about BC/rubber composites mainly focused on the modification of BC interface and uniform dispersion of BC in the matrixes. In the past few years, a great deal of synthesis strategies has been developed and applied in the preparation of BC polymer composite for the purpose mentioned above. But the effect of reinforcement always was not ideal.³ Chitosan (CS) also is a common biomaterial with many
researches in recent years, but in rubbery filed, pure CS cannot provide any other reinforcement on mechanical properties due to its poor hydrophilicity which provide poor dispersion into rubber matrix. Li found that BC graft CS by synthesis sulfonated BC-CS hybrid could improve the mechanical properties with the carbon structure and the bio properties with the CS structure.⁴
And in the field of rubbery researches, the interpenetrating polymer network (IPN)⁵ and physical crosslinking had become hot issue in recent years. Almost physical crosslinking methods depend on noncovalent bond, such as hydrogen bond, van der Waals force and other intermolecular force.⁶ IPN is a polymer comprising two or more networks which are at least partially interlaced on a polymer scale but not covalently bonded to each other, which could provide more compact matrix structure. ⁷ In IPN, when the physical crosslinking and chemical crosslinking occur simultaneously in a polymer material, it is speculated that the material may have better viscoelastic properties.
However, researches on the properties during the processing of IPN are far from sufficient, especially studies on the viscoelasticity of BC/CS rubber composites. The viscoelasticity of BC/CS rubber composites and their raw materials is of prime importance for the process ability and the performances of rubber products. Investigations on the relationships between modulus and dynamic strain amplitude or frequency are helpful for the understanding of macromolecule motions,⁸ crosslinking and filler-rubber interactions. This work is also meaningful in rubber industry which could be used as references for the fixing of processing parameters. And CS-PVA (poly(vinyl alcohol)) hydrogel system has good IPN structure, also exists physical crosslinking shown in Figure 1 and Figure 3, which could short the distance of rubber chain in latex state,⁹ and improve some properties of rubber matrix, so some researchers also pay their attention to this filed. Also, some researchers found formaldehyde or glutaraldehyde have been used as crosslink agent to crosslink CS and PVA which could make better IPN and provide better mechanical properties for the CS-PVA hydrogel (shown in Scheme 1, Scheme 2, Figure 2 and Figure 3),¹⁰ due to the adsorption force (hydrogen bonds) with filler particles, which also could increase the application of this material, such as the fillers.
In this research, styrene-butadiene rubber latex composites compatibilized with bamboo charcoal (BC)/silica (SI) CS PVA hybrids by IPN method reported previously, and neat SBR, BC-SBR and SI-SBR composites were also synthesized as control group. Various interactions between fillers and rubber matrix were introduced by different hybrids, which led to various viscoelastic behaviors of the raw materials during strain amplitude sweep and frequency sweep. The viscoelastic behaviors were investigated in detail. Their relations with the interpenetrating structure with rubber chain and the other interactions between hybrid and matrix were explored, which are beneficial for better understanding of the filler-rubber system.