Article
  • Hydrogenation of Liquid Natural Rubber Using 2,4,6-Trimethylbenzenesulfonylhydrazide: Optimisation of Reaction Parameters via Response Surface Methodology

  • Mohamad Shahrul Fizree Idris*, Hamizah Md Rasid*, Fazira Firdaus*, and Siti Fairus M. Yusoff*,**,†

  • *School of Chemical Sciences and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia
    **Polymer Research Center (PORCE), Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia

  • 2,4,6-Trimethylbenzenesulfonylhydrazide를 이용한 액상 천연고무의 수소화: 반응표면분석법을 이용한 반응 매개변수 최적화
Abstract

Hydrogenation of liquid natural rubber (LNR) using 2,4,6-trimethylbenzenesulfonylhydrazide (MSH) in toluene was studied. HLNR structure was characterized by nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). Response surface methodology (RSM) based on 5-level-2-factor central composite rotatable design (CCRD) was used to analyze the correlative effects of reaction, MSH:LNR weight ratio (0.5-1.0) and reaction time (20-60 min) with a fixed reaction temperature of 100 ℃. Multivariate statistical analysis was developed in a form of quadratic model in order to correlate the reaction parameter to the response received. The optimum conditions derived via RSM were the MSH:LNR weight ratio of 0.7 and a reaction time of 25.86 min. The R2 value of 0.9557 showed that the model was well-fitted with the experimental data, whereby the model was almost ideal while the lack-of-fit considered rather unseemly (i.e. insignificant).


Keywords: response surface methodology (RSM), central composite rotatable design (CCRD), optimization, liquid natural rubber, hydrogenation

Introduction

Natural rubber (NR) is a valuable material originated from the rubber trees Hevea brasiliensis, and its major component is polyisoprene.1 NR is a cheap and versatile elastomer, thus being widely used in adhesive and automobile industries because of its elasticity and high mechanical strength properties. Nowadays, NR is being recognized as a renewable resource and this has attracted more attention to itself because of the requirement of environmental protection and resource saving.2 However, the NR possessed low resistance to heat, ozone and chemical reagents of NR because of its unsaturated chain structure. Through the production of highly saturated NR, these drawbacks can be improved. Therefore, researchers have focused on chemical modification of NR to reduce the unsaturation in the main chain. The desired product must restrain high temperature conditions so that it could be used in a variety of practical applications, such as rubber blending and vulcanization.3 A simple modification of NR is liquid natural rubber (LNR). LNR can be produced via depolymerization that converts solid-phase NR to liquid-phase NR.4-6 After depolymerization, LNR will have an active group in the isoprene chain such as –OH, –OOH and –C=O.7,8 Seng et al. stated LNR offers as a good dispersing and toughening agent into epoxy matrix in order to improve the toughness of cured epoxy due to the presence of active groups.9 Hisham et al. also reported the mechanical properties of the unsaturated polyester resin can be improved by introducing the LNR.10 The short polymeric chain of LNR expands its applicability in many fields compared to dried rubber due to the possible chemical modifications made.11
Hydrogenation is an effective method in lowering the level of C=C unsaturation in the polymeric chain. Generally, hydrogenation involves the addition of hydrogen atom in the unsaturated bond of alkenes/alkynes. Saturated moiety in the polymer chain has led to the improvement in its physical properties, such as its stability against thermal, oxidative and radiation-induced.12-14 Basically, saturation of NR through hydrogenation process can be divided into two methods, which are catalytic and non-catalytic hydrogenation. Catalytic hydrogenation is the reaction of catalyst that will activate the hydrogen molecules and the carbon-carbon double bond species.15 However, catalytic hydrogenation is costly because the reaction uses expensive catalyst such as ruthenium,16 iridium17 or rhodium18 complexes and it has to be carried out at high pressure and temperature in the presence of hydrogen gas.
Meanwhile, non-catalytic hydrogenation is a method using diimide molecule that supplies hydrogen to the C=C bond. Non-catalytic hydrogenation uses a cheaper reagent and requires milder conditions compared to catalytic hydrogenation. This hydrogenation method has two major advantages, which are avoiding handling of hydrogen gas and removal of reaction catalyst. Mahittikul et al. reported the hydrogenation of natural rubber latex uses p-toluenesulfonyl hydrazide (TSH) as diimide source.19 Recently, hydrogenation of LNR using TSH as diimide sources has also been reported.20,21 Rasid et al. successfully reported the hydrogenation of LNR using 2,4,6-trimethylbenzenesulfonylhydrazide (MSH) with slightly milder conditions compared to using TSH.22 Basically, they have studied the main reaction parameters such as weight ratio of diimide source to LNR, reaction temperature and reaction time.
Response surface methodology (RSM) has been widely used for designation and optimization of experiments by combining statistical techniques and mathematical modeling.23,24 The main advantage of RSM is the reduced number of experimental runs needed to provide sufficient information for the statistically acceptable result.25 RSM based on CCRD was used in this study to correlate the relationship between the reaction parameters and response with a smaller number of experimental runs. RSM comprising a five-level-two-factor central composite rotatable design (CCRD) was used in our work to evaluate the interactive effect and obtain the optimum conditions for the hydrogenation process. In this work, optimization of hydrogenation of LNR using MSH by RSM has been reported. The parameters in this study were selected based on the previous work.22

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  • Polymer(Korea) 폴리머
  • Frequency : Bimonthly(odd)
    ISSN 0379-153X(Print)
    ISSN 2234-8077(Online)
    Abbr. Polym. Korea
  • 2022 Impact Factor : 0.4
  • Indexed in SCIE

This Article

  • 2018; 42(4): 544-550

    Published online Jul 25, 2018

  • 10.7317/pk.2018.42.4.544
  • Received on Sep 26, 2017
  • Revised on Feb 5, 2018
  • Accepted on Mar 20, 2018

Correspondence to

  • Siti Fairus M. Yusoff

  • *School of Chemical Sciences and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia
    **Polymer Research Center (PORCE), Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia

  • E-mail: sitifairus@ukm.edu.my
  • ORCID:
    0000-0002-1892-2850