A New Processing Additive for Natural Rubber from Agricultural Waste
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ROHSTOFFE UND ANWENDUNGEN RAW MATERIALS AND APPLICATIONS Anti-oxidant · Adhesion · Waste · Rubber · Renewable resources. A New Processing Additive for The leaves of the oil palm species Elaeis Guineensis were found to be a rich Natural Rubber from Agricultural source of phenolic compounds. In an effort to dispose waste oil palm leaves usefully, our research team explored the antioxidant characteristics and Waste tackifying ability of oil palm leaf extract (OPE) in a natural rubber-based formulation. After simulated ageing of the natural rubber (NR) compounds containing the OPE, the reduction in mechanical properties of the NR Malaysia, being the world’s largest produc- The total antioxidant action would ordinar- compounds was within acceptable er of palm oil, generates a huge amount of ily involve three functions. First would be limits. It was also observed that the oil palm waste. This is true in the cases of the absorption of UV light which catalyzes OPE improves the tack strength of NR appreciably. The OPE could be a promis- some other Asian countries as well. On an oxidation. Second would be the decomposi- ing multifunctional additive in green average, every year Malaysia generates tion of initiating peroxides which are con- polymer processing technology. 7.7 million tonnes of empty fruit bunches, verted into non-radical products. It is be- 6.0 million tonnes of fiber, 2.4 million tonnes lieved that the phenolic antioxidants func- of palm shell. The fiber waste is used to gen- tion in this way. The final one would be the Neue Verarbeitungshilfsmittel erate energy to run the palm oil mill and for stopping of the radical chain reaction. für NR aus landwirtschaftlichem fertilizer purposes. There are more than 270 Synthetic antioxidants such as 2,2,4-trime- Abfall palm oil mills operating in Malaysia that thyl quinoline (TMQ) have been used widely utilize mainly fiber and partly shell in their in polymer formulations to prevent the Alterungsschutzmittel · Adhäsion · boilers as fuel to generate power and steam thermo-oxidative degradation of polymers, Abfall · Kautschuk · erneuerbare required by the industry. About 30 % of the but they are not environment-friendly. Also, Ressourcen shell is utilized for this purpose [1]. On the their manufacture contributes significantly Die Blätter der Ölpalme Elaeis Guineen- other hand, almost whole of the oil palm to carbon foot print. sis enthalten höhere Mengen phenoli- leaves have been discarded as a waste. From environmental point of view, instead scher Verbindungen. Um diese Blätter Oil palm fruit shell has been reported to be of the synthetic antioxidants, natural ones sinnvoll zu entsorgen hat unsere a good source of phenolic compounds [2]. could be used. Phenolic antioxidants are well Arbeitsgruppe die Eigenschaften als Previously some authors reported the pres- known for trapping. Free radicals, such as Alterungsschutzmittel und Klebrigma- ence of phenolic compounds in some natural peroxy radicals, to prevent oxidative degrada- cher des Extraktes (OPE) in NR Com- food materials [3-5]. We have found out the tion in organic materials such as plastics [9]. pounds untersucht. In Alterungsversu- chen mit OPE wurde eine Abnahme der leaves of oil palm to be a good source of phe- Even though there have been numerous re- mechanischen Eigenschaften innerhalb nolic compounds that can trap free radicals. ports on use of natural materials in rubber akzeptabler Grenzen beobachtet. Es Unsaturated polymers such as polyisoprene formulations, there have been only a few wurde ebenfalls gezeigt, dass durch or polybutadiene undergo thermo-oxida- reports on the use of oil palm-based mate- OPE die Schälkraft von NR deutlich tive degradation readily at elevated tem- rials in rubbers. Ismail et al. studied the ef- gesteigert wird. OPE kann ein multi- peratures [6,7]. Oxidative degradation usu- fects of palm oil fatty acid on curing char- funktionelles Additiv in der „grünen“ ally leads to hardening, discolouration, as acteristics, reversion and fatigue life of Verarbeitungstechnologie werden. well as surface changes. Oxidative degrada- tion involves formation of free radicals on polymer chain backbone followed by the Authors formation of peroxy radical. The peroxy S. Anandhan, Karnataka (India), radical can attack the neighbouring seg- C. J. Viknesh, Kedah (Malaysia), ments, abstract hydrogen and form a hy- N. Othman, S. Sasidharan, Penang droperoxide and a new free radical site. The (Malaysia) hydroperoxide formed can lead to the for- Corresponding author: mation of several new free radical sites. S. Anandhan With so many free radicals being formed, National Institute of their recombination can occur and result in Technology-Karnataka the termination of the chain reactions [7]. Division of Mechanical and Currently used rubber antioxidants can be Chemical Systems classified into amines, phenols and Department of Metallurgical and thioesters. The main phenolic antioxidants Materials Engineering Surathkal, Mangalore – belong to five types, namely, hindered phe- 575025 Karnataka, India. nols, hindered bisphenols, hindered thiobi- Phone: +91-824-2474000 Figures and Tables: sphenols, polyphenols and polyhydroxy- Fax: +91-824-2474033 By a kind approval of the authors phenols [8]. E-mail: [email protected] 44 KGK · März 2011 1 2 1 Phenolic and reducing agent content in various antioxidants 2 Total radical scavenging activity of various antioxidants various natural rubber compounds [10]. Preparation of oil palm leaf extract Finally, the solution was brought up to They also reported palm oil fatty acid as an 10 mL by adding distilled water. After activator in natural rubber gum com- Collection of oil palm leaves 1.5 hour, the absorbance at 750 nm was pounds [11, 12]. Guhathakurta et al. [13] Around 1 kg of the palm oil leaflets was col- taken using a visible spectrophotometer reported that Bahera gum, a natural mate- lected. The leaflets were washed using tap (Thermoscientific GeneSYS20, USA). The rial, can be used as a multifunctional addi- water and then cut approximately into results were expressed as Gallic acid tive for rubbers. Bahera gum was also used 1 cm2 sized pieces. The thus obtained pieces equivalents (Table 1). The Folin-Ciocalteu as an adhesion promoter in an adhesive were dried in an oven for about 5 to 7 days reagent is a mixture of phosphomolyb- formulation [14]. at 30-40 °C. The leaves were avoided from date and phosphotungstate used for the In an effort to dispose waste oil palm leaves being exposed to excessive heat. Heat and colorimetric assay of phenolic antioxi- usefully, our research team explored the air could destroy the beneficial natural dants and polyphenol antioxidants. It antioxidant characteristics and tackifying products at above of 70 °C. After drying, the works by measuring the amount of a sub- ability of oil palm leaf extract in a natural leaflets were ground using a heavy duty stance needed to inhibit the oxidation of rubber-based formulation. This was due to blender. this reagent. However, this reagent does the abundance of phenolic compounds in not only measure total phenols and will oil palm leaves. To the best of the authors’ Extraction of oil palm leaves with react with any reducing substance. The knowledge, there has been no report(s) on methanol reagent therefore measures the total re- the use of oil palm leaf extract in rubbers. In The extraction was done using the tradi- ducing capacity of a sample, not just the this paper, we report the results of our stud- tional soaking method. The leaves were level of phenolic compounds. ies on the characterization of OPE, evalua- finely powdered and put into a big contain- tion of the radical quenching ability of the er, covered with methanol. For about 100 g DPPH Radical scavenging activity OPE, and antioxidant characteristics and of the powder 250 mL of methanol was Free radical scavenging activity was meas- tackifying properties of the oil palm leaf ex- added. The plant material was left to soak ured by 1,1-diphenyl-2-picrylhydrazyl tract in natural rubber. in methanol for 5 days in a Quiet warm (DPPH) by the method of Shimada etal. [16]. place and shaking was occasionally done. The antioxidant solution was kept in a uni- Experimental Then filtrate was separated out from the versal bottle at 1 mg/mL. Then 5 mL of a residue. Using a rotary evaporator (EYELA, 0.04 % solution of DPPH was added to anti- Materials USA) methanol was evaporated from the oxidant solution and was shaken vigorously. Oil palm leaves were collected at Semeling filtrate at 64.8 °C. Then the bottles were incubated in the dark Oil Palm Estate, Malaysia. NR used in this at room temperature for 30 minutes. A con- study was SMR-5 with a Mooney viscosity Characterization of the oil palm leaf trol sample was also prepared. The changes of 86 (ML1+4 at 100 ˚C = 86) and was pro- extract in the absorbance of the samples were cured from Revertex (Malaysia) Sdn. Bhd. measured at 517 nm (Table 2). Radical scav- The antioxidants IPPD(N‘-phenyl-N-propan- Determination of total phenolic (TP) enging activity was expressed as the inhibi- 2-yl-benzene-1,4-diamine), BKF (2-[(2-hy- and the reducing agent contents tion percentage and was calculated using droxy-5-methyl-3-tert-butyl-phenyl) The total phenolic content of the extracts the following formula [17]: methyl]-4-methyl-6-tert-butyl-phenol) was determined with the Folin–Ciocalteau and TMQ (5-methyl-6-[[(3,4,5-trimethoxy- method [15]. Briefly, 0.5 mL of diluted ex- OD− OD RSA(%) = CS×100 phenyl)amino]methyl]quinazoline-2,4-di- tract solution at 100 mg/mL was shaken ODC amine) were procured from Bayer Malaysia. for 1 minute with 100 l of Folin–Ciocal- Other curatives were purchased from in- teau reagent and 6 mL of distilled water. Where, RSA radical scavenging activity digenous resources.