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Journal of Oleo ScienceCopyright ©2017 by Japan Oil Chemists’ Societydoi : 10.5650/jos.ess16190J. Oleo Sci. 66, (7) 677-687 (2017)

Performance of Palm-Based C16/18 Methyl Ester Sulphonate (MES) in Liquid Detergent FormulationZulina Abd Maurad＊ , Zainab Idris and Razmah GhazaliAdvanced Oleochemical Technology Division, Malaysian Palm Oil Board, 6, Persiaran Institusi, Bandar Baru Bangi, 43000 Kajang, Selangor, MALAYSIA

1 INTRODUCTIONMethyl ester sulphonate（MES）was first used commer-

cially in the late 1970s and early 1980s in a French deter-gent Le Chat Auto. However, it was discontinued from the market when Henkel took over the brand in the mid-1980s1）. Since early 1990s, Lion Corporation of Japan used C16/18 MES in some of its laundry detergents, especially in the compact formula. In the United States, Stepan Company developed the coco-range MES and promoted their usage during the same period2, 3）. To date, there are two suppliers of MES in Malaysia, i.e. Lion Eco Chemicals Sdn Bhd（50,000 MT production capacity）in Tanjung Langsat, Johor and KL Kepong Oleomas（150,000 MT pro-duction capacity）in Pulau Indah, Selangor. Major global producer of MES is also tabulated in Table 14, 5）. The tech-nology providers of MES are described in patent literature by Lion Corporation6, 7）, Henkel KGaA8, 9）and The Chemithon Corporation10－12）.

＊Correspondence to: Zulina Abd Maurad, Advanced Oleochemical Technology Division, Malaysian Palm Oil Board, 6, Persiaran Institusi, Bandar Baru Bangi, 43000 Kajang, Selangor, MALAYSIAE-mail: zulina@mpob.gov.myAccepted February 13, 2017 (received for review September 28, 2016)Journal of Oleo Science ISSN 1345-8957 print / ISSN 1347-3352 onlinehttp://www.jstage.jst.go.jp/browse/jos/　　http://mc.manusriptcentral.com/jjocs

MES is an anionic surfactant derived from an oleochemi-cal feedstock. Its advantages however, have been overshad-owed by the petroleum-based linear alkyl benzene sulpho-nates（LAS）. Typically, the alkyl chain distribution of LAS was 14.2％ C10, 35.6％ C11, 29.6％ C12 and 20.6％ C13

13）. Due to the increased awareness among consumers for “green-products” and favorable prospects in using renewable re-sources, many soap and detergent manufacturers ex-pressed interests in developing the capacity of MES worldwide. Its biodegradability profiles are comparable to that of LAS14）. Furthermore, palm-based MES exhibit good calcium tolerance, thus greater detergency and less sensi-tivity to water hardness than other anionic surfactants15）. Palm-based MES can be produced at lower cost than LAS and would be significantly competitive even if the cost of methyl esters is as high as that of raw materials for LAS production16－18）. Until recently, MES seemingly has not been used worldwide in modern laundry detergent formu-

Abstract: Liquid detergents are more convenient than powdered detergents as they dissolve readily in water, generate less dust and dosing is easy. However, the stability of liquid detergents is an issue of concern. Therefore, the objective of this research is to study the formulation requirement to produce heavy-duty liquid detergents based on palm-based methyl esters sulphonate (MES) with desirable properties and performance. MES is produced from renewable and sustainable feedstock suitable to replace the conventional fossil-based surfactant, linear alkyl benzene sulphonates (LAS). Five palm-based liquid detergents (PBLDs) were formulated using C16/18 MES as the primary surfactant. The physical properties, washing performance, stability and biodegradability of PBLDs were evaluated. Performance of the PBLDs was evaluated against two commercial liquid detergents which use LAS and alcohol glucoside as surfactant (benchmark product) and it was found that the PBLDs exhibited excellent performance. PBLDs can be formulated with or without phosphates and still demonstrate good detergency. The stability study of PBLDs indicated that no appreciable hydrolysis occurred. PBLDs exhibited better biodegradability profiles compared to commercial detergent containing LAS. PBLDs passed the 60% biodegradability level within 3 to 8 d, while commercial detergent took 24 d. It was shown that palm-based C16/18 MES could be potentially formulated into liquid detergents and gave better performance than LAS based liquid detergent. Attributes of C16/18 MES should not be overlooked, which include an abundant and naturally derived palm stearin as raw material and environmental safety profiles that are superior to most synthetic surfactants.

Key words: anionic surfactant, methyl ester sulphonates, palm-based liquid detergents, stable, detergency, biodegradability

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lations19）. Lion Corporation in Japan has used MES in their powder formulations since 1991. Lion Eco Chemicals, founded in Malaysia in 2007, has established MES supply to the detergent industries worldwide. They have also pro-duced MES-based powder detergent, with brand name TOP, sold in Malaysia. In 2010, Lion Corporation introduced Beat Drum powder detergent, a brand sold in South Korea, which is said to be Lion’s first MES-based detergent sold outside Japan15）. A distinctive mixture of surfactants con-taining MES and other surfactants was identified in some US formulations in 200720）.

In Asia, laundry detergent markets as a whole, are very active and show trends of expansion in many countries. The Malaysian market share of auto liquid detergents has been steadily increasing since 2009 and is forecasted to grow even more in the next couple of years21）. Liquid de-tergents have several advantages over powder detergents. Liquid detergents readily and completely dissolve in water, even in cool or cold water, thus less messy than powder detergents. In the form of liquids, problem such caking upon storage is eliminated as often seen with powders when exposed to moisture. However, challenges arise in formulating a stable liquid detergent from saturated based MES. Previously, development of liquid detergent was focused on the use of medium chain length methyl esters（C12/14）obtained from lauric oils22）. This paper assesses the stability and performances of liquid detergents formulated with C16/18 MES including their physical properties, active content, detergency, foaming, wetting characteristic and biodegradability property.

2 EXPERIMENTAL PROCEDURES2.1 Materials

Palm stearin-based MES with mixture of fatty acid

carbon chain length of 60.4％ C16 and 38.3％ C18 was pre-pared using a 20 kg/h capacity sulphonation pilot plant at the Malaysian Palm Oil Board（MPOB）. The properties of C16/18 MES are as in Table 2. Ingredients used to formulate PBLDs such as acrylic polymer was procured from Rohm and Haas, optical brightener from Miles Inc. and protease enzyme from Novozyme. Other ingredients as listed in Table 3 and reagents for the analyses were obtained from local suppliers. COM L1 and COM L2 were procured from local supermarkets. Basically, COM L1 and COM L2 com-posed of ethanol, LAS, alcohol glucoside, soda ash and for-malin23）.

2.2 MethodsThe process to produce a stable liquid detergent can

either be through continuous process, batch making pro-cesses or combination of the two. Similarly, it is known that some ingredients may be sensitive to the order of addition, while others can be included into the formulation at any time during the process. The PBLDs were produced using batch process in the liquid detergent pilot plant. This plant was equipped with two mixing tanks（A and B）with capaci-ty 50 and 120 L, respectively（Fig. 1）. During the produc-tion of liquid detergents, hot process was required in tank A when handling with solid palm-stearin MES. Stirring and

Table 1　Global major producer of MES4, 5）.

Companies Location Annual capacity(MT)

Guangzhou Keylink Chemical Co. China 40,000Stepan USA 50,000USA Huish Detergent Inc USA 80,000Dersa, Bogota Colombia 15,000Lion Corporation Japan 40,000Zhejiang Zanyu Technology Co., Ltd. China 60,000Guangzhou Langqi China 36,000Shandong Zoupingfuhai China 30,000Shandong Jinlun China 60,000Jiangsu Haiqing China 100,000PT Wilmar Nabati, Gresik Indonesia 50,000

Table 2　 Characteristics and composition of palm-based C16/18 MES.

Parameter C16/18 MESActive (%) 89.53Disalt/Active (%) 5.115% Klett Colour 25.57Peroxide content (%) 0.16Appearance flakes

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heating would increase the rate of dissolution of the MES. The stirrer is attached in a manner that will not cause foaming during production. The ingredients for PBLDs（LI-L5）and their dosages are listed in Table 3. Other ingre-dients that were sensitive to heat, such as enzyme, optical brightener, preservative and fragrance were added during the cooling stage in tank B. The pH of the solution must be controlled not to exceed pH 10. MES was found to be

stable up to pH 9.5 - 10 at moderate temperatures. Above pH 10, the rate of hydrolysis increases8）.

2.3 Analyses2.3.1 MES Specifications

The method for specifications of MES were described by Battaglini et al.24）. The disalt content was determined from two titrations（methylene blue and phenol red titration）and a result from the free oil determination. Measurement for colour determined by Klett-Summerson colorimeter. Per-oxide content was determined by using titration of sodium thiosulfate and potassium iodide and starch solution as in-dicator. All analyses were performed in duplicate with data reported representing average values.2.3.2 Active Content

The active component or purity of the surfactant in de-tergent was determined by potentiometric titration proce-dure（anionic and nonionic）according to ASTM D4251-8925）. The analysis was performed in triplicate with data reported representing average values.2.3.3 Viscosity

The viscosity of PBLDs were measured using Anton Paar Rheoplus rheometer. The data reported representing average values.2.3.4 Detergency Test

Evaluation of washing performance of PBLDs and com-mercial detergents（COM L1 and COM L2）was performed using top loading washing machine（6 kg capacity, National

Table 3　�The list of ingredients and dosages in palm-based liquid detergents（PBLDs）formulations.

ComponentsFormulations (% by weight of composition)L1 L2 L3 L4 L5

Palm-based C16/18 MES (89.53 % active) 10 10 15 10 10LAS (50.24% active) 10 － － － －Fatty Alcohol Ether Sulphates (FAES) (37% active) － 15 10 15 15Nonionic － 1 1 1 1Sodium polyphosphate 5 － 5 5 －Sodium citrate － 5 － － 5Optical brightener 0.1 0.25 0.1 0.25 0.1Polymer ―――――― 0.5 ――――――Protease enzyme ―――――― 0.25 ――――――Perfume ―――――― 0.5 ――――――Preservative ―――――― 0.05 ――――――and water ―――――― Add up to 100 ――――――

L1: liquid detergent contained 50:50 C16/18 MES and LAS with phosphate and 0.1% brightenerL2: liquid detergent contained 40:60 C16/18 MES and FAES with citrate and 0.25% brightenerL3: liquid detergent contained 60:40 C16/18 MES and FAES with phosphate and 0.1% brightenerL4: liquid detergent contained 40:60 C16/18 MES and FAES with phosphate and 0.25% brightenerL5: liquid detergent contained 40:60 C16/18 MES and FAES with citrate and 0.1% brightener

Fig. 1　 Liquid detergent pilot plant comprising of two mixing tanks.

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NA-F600KM）on at least 10 artificially soiled swatches under ordinary washing conditions in Malaysia of water hardness 50 ppm, temperature 29℃ with ratio of wash liquor of 1:18.5（dry laundry: volume of wash liquor）and detergent dosage of 1.62 g/L. Four types of oil-based stained（mineral oil, pigment/ oil/ milk, pigment/ oil and sebum）and six types of protein-based stained（mango, cocoa, grass, spinach, curry and tea）were chosen based on the lifestyle of Asian culture as shown in Table 4. These swatches were obtained from Testfabrics, USA. The test was followed a series steps according to the methods for measuring the performance of electrical clothes-washing machine for household use IEC 6045626）. The measurement of swatches from was carried out using Minolta spectro-photometer DM 3600d and at least 8 readings were mea-sured, 2 on each side of the selected swatches with data reported representing 4 average values of percentage of soil removal. The percentage of soil removal was calculated using the following formula［1］:

Percentage of soil removal＝［ AW－BWOC－BW ］×100 ［1］

where AW is the reflectance（whiteness）of the swatches after washing, BW is the reflectance of the swatches before washing and OC is the reflectance of the origin cloth before soiling provided by the manufacturer, Testfabrics, USA.2.3.5 Foaming Power

A 200-mL of 0.1％ solution of PBLDs was filled into a 500-mL measuring cylinder. Using a glass rod with perfo-rated base, the PBLDs solution was stroked for 30 times at a constant rate to induce foam formation. The immediate volume of the foam was recorded and the foam generated is a measure of the foamability. The foam was left to rest for 5 min, after which, the final volume of the foam was re-corded. After 5 min, the foam will decay and the rate of decay is a measure of the foam stability. The analysis was performed in triplicate with data reported representing average values. This method was a modified method from

Ross and Miles27）and Japanese JIS K 3362:2008 Test Method Of Household Synthetic Detergent28）.2.3.6 Wetting power

A 250-mL of 0.1％ solution of PBLDs was prepared and poured into a 100 mL round container. Dried unsoiled cotton swatch was cut into 2 cm×2 cm and conditioned at 20％ relative humidity for 24 h. The conditioned unsoiled cotton swatch was then dropped into the solution using a pair of tweezers. The time taken for the swatch to be wetted and dropped into solution was recorded29）. The measurement was performed until 3 repeated similar reading obtained.2.3.7 Biodegradability profile

The biodegradability profile curve of all the five PBLDs were established using standard method OECD 301D, Closed Bottle Test according to the Organization for Eco-nomic Cooperation and Development30）. The solution of the test substance in mineral medium, at 2 mg/L, was inoculat-ed with a 75×106 colonies forming unit（cfu）number at 0 d and kept in completely full closed bottles in the dark at constant temperature. In a typical test run, 16 bottles were used containing test substances, reference substances and inoculum. Biodegradation profile of the test substances were constructed by determination of the dissolved oxygen content over a 28 d period at 20℃. The amount of oxygen taken up by the microbial population during the biodegra-dation of the test substance, corrected for uptake by the blank inoculum（source from effluent of a waste water treatment）run in parallel, was expressed as a percentage of Theoretical Oxygen Demand（ThOD）. The ThOD of the PBLDs was calculated using the formula describe by Gerike31）. Duplicate bottles of all series were withdrawn every 4 d to measure the dissolved oxygen of the samples and to allow construction of the biodegradation curve.

3 RESULTS AND DISCUSSION3.1 Physical Properties

Concentrated PBLDs（L1-L5）have been formulated with C16/18 MES as the active ingredient. The PBLDs were formed when all ingredients were solubilized in an aqueous medium forming a clear appearance, single phase and thin solution. This phenomenon is classified as unstructured liquid32）. Table 5 shows the properties of five formulated PBLDs in comparison with two commercial detergents. COM L1 and COM L2 were opaque and thick, and classified as structured liquid. Structured liquids are formed when surfactant molecules arrange themselves as liquid crystals. Structured liquids are capable of suspending undissolved particles while remaining pourable behavior by aggregates the active detergent molecules to lamellar liquid crystalline phases33, 34）. Structured liquids utilize more builders and electrolytes that contributed to the high solid content35）.

Table 4　 Description of artificially soiled swatches obtained from Testfabric, Inc.22）.

Swatches SoilingAS 12 Pigment, groundnut oil and milkAS 9 Pigment and groundnut oilCS 2 CocoaBC 3 TeaCS 8 Grass stainCS 23 MangoCS 25 SpinachCS 32 SebumBC 4 CurryAS 1 Soot and mineral oil

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Total solid contents of PBLDs were in range 24.53％ to 33.14％, which was lower than COM L1 and COM L2 with 64.79％ and 62.56％. More builders and salts might be added to increase the total solid content in PBLDs without interfering the clear and single phase appearance of formu-lated products. The unstructured liquid contains soluble builder such as citrate36）. PBLDs formulations using citrate, L2 and L5, gave similar pH value of 7.83 and 7.68, respec-tively. Meanwhile PBLDs formulations containing phos-phates, L1, L3 and L4, were more alkaline with pH above 9 and that were similar to commercial detergents（COM L1 and COM L2）because the phosphates acted as a buffer. Heavy duty liquid detergents are performing optimally at lower pHs compare to powder detergent which perform optimally at higher pHs37）. Crystal morphology of PBLDs and commercial samples were done under polarized light microscopy. The appearance of formulation L4 crystals with dendritic shape was similar to commercial samples which might be due to presence of same builder. Formula-tion L3 have bigger crystals shape compared to formulation L4 and commercials as L3 had high level MES content. However, formulations L1, L2 and L5 show neat crystal ap-pearance. This indicates that citrates formulation exhibited liquid crystalline neat except for formulation L1 which is phosphates based with combined surfactants, MES-LAS.

The viscosities of PBLDs were in the range of 0.90 to 2.37 Pa.s as shown in Fig. 2. The PBLDs were pourable. PBLDs and COM L1 described as newtonian fluids and stable even at different shear rate. While COM L2 unveiled a dilatant fluid which some precipitation has been ob-served.

3.2 Active levelsSurfactants or active contents in detergent formulations

are primarily responsible for wetting the surface of fabrics as well as the soil, helping to lift the stain off the fabric surface and to retain dirt particulates at the surface of wash water or to emulsify grease droplets38－40）. The active contents in the formulated PBLDs and commercial deter-gents are illustrated in Table 6. The formulated PBLDs possessed a higher anionic active content than the com-

mercial detergents（COML1 and COM L2）. As unstructured liquids, PBLDs were formulated with higher amount of sur-factants, in contrast to structured liquids which require more builders but lower active contents35）. COM L1 and COM L2, generally contain LAS and alcohol glucoside derived from petroleum as their active ingredient23）. COM L1 and COM L2 has higher nonionic surfactants compared to PBLDs.

3.3 Detergency TestThe excellent performances of MES have been well doc-

umented41, 42）. However, little data on the application of MES in cleaning products. This study revealed that the PBLDs exhibited excellent stain removal through deter-gency test for oil based stained; mineral oil, pigment/ oil/ milk, pigment/ oil and sebum（Fig. 3）and protein-based stained; mango, cocoa, grass, spinach, curry and tea（Fig. 4）.

One of the important cleaning agent is builder. Builder is essential in formulating PBLDs mainly to sequester the hardness of water as well as to disperse the dirt and soil

Table 5　 Properties of formulated palm-based liquid detergents（PBLDs）and commercial detergents（COM L1 and COM L2）.

Characteristics L1 L2 L3 L4 L5 COM L1 COM L2pH (1% solution) 9.16 7.83 9.35 9.32 7.68 9.54 9.55Total solid content, % 30.45 33.14 30.12 28.65 24.53 64.79 62.56

Crystal morphology

Appearance ――――――― clear and translucent ――――――― ―― opaque ――

Fig. 2　 Viscosity profiles of palm-based liquid detergents（PBLDs）and commercial detergents（COM L1 and COM L2）.

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particulates in the wash water. Common builders used are sodium and potassium polyphosphates, silicates, carbon-ates, alumino silicates and citrates35）. Sodium polyphos-phates are widely used as builders in most detergent for-mulation, however, they have adverse effects on the aquatic environment43, 44）. The situation in presence of cya-nobacterial blooms and turbidity is still an important envi-ronmental issue in many European countries, the USA and Japan45）. The PBLDs were formulated with phosphate and non-phosphates based. Sodium citrates was used as build-ers for non-phosphates based formulation because it is an excellent salting-out electrolyte46）, high solubility in water and it has a positive effect on the calcium binding proper-ties of a liquid laundry detergent mixture46）. The perfor-mance of different builders was investigated using formula-tion L2 which contained citrates and L4 which contained sodium polyphosphates as builders. Formulation L2 with citrates was good in removing pigment/oil/milk, mango, cocoa, spinach, curry and tea compared to formulation L4 with sodium polyphosphates. Detergents with MES can be formulated with or without phosphates and still able to demonstrate good detergency. The reason for the good washing properties in the absence of phosphates was prob-ably due to MES is low sensitivity towards water hard-ness47）. This is an important feature because in many coun-tries, due to the strong environmental concerns, the use of phosphates in detergents has been banned.

Optical brighteners are colourless dyes that absorb ultra-violet rays and radiate bluish light which results in better whiteness and impression of super cleanliness. Most deter-gents contain brighteners according to the marketing claims and the high level of optical brightener represents a significant portion of the total raw material cost48）. The brightener used in PBLDs was fully dissolved and clear. An addition of 0.25％ of brightener in L2 gave higher percent-age of soil removal compared to L5, which consisted 0.1％ brightener.

A pre-mix formulas were also carried out to compare the detergency power of MES C16-18 with LAS without interfer-ence from cleaning agent such as builder, enzyme, optical brightener and bleaching agent. Each formula has the same

Table 6　 Active levels in palm-based liquid detergents（PBLDs）and commercial detergents（COM L1 and COM L2）.

Products Anionic active content (%) Nonionic active content (%)L1 15.57 Not detectedL2 20.60 1.25L3 22.13 1.45L4 20.03 1.54L5 20.82 1.89

COM L1 11.55 8.81COM L2 15.24 3.26

Fig. 3　�Detergency of palm-based liquid detergents（PBLDs）and commercial detergents（COM L1 and COM L2）on oil based stained.

Fig. 4　 Detergency of palm-based liquid detergents（PBLDs）and commercial detergents（COM L1 and COM L2）on protein based stained.

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ingredients containing surfactant either MES C16-18 or LAS C11 and fillers which is sodium carbonate and sodium sul-phate. MES F1 has MES C16-18 as the active whereas LAS F1 has LAS C11 with equal weight percentage（Fig. 5）. Results showed that pre-mix based on MES gave better percentage of soil removal on 10 soiled swatches. The highest difference of percentage of soil removal is on pigment/oil soiled swatch with 21.3％ as compared to de-tergents based on LAS C11.

3.4 Foaming and StabilityFilms formed as bubbles or foams, help to elevate soil

particle to the surface and remove soil away from the cloth surface during rinsing. That is why consumer perceives foams as good cleaning. Foams can also act as anti-rede-positing agent. Two parameters typically used to report foaming power are foamability and foam stability49）. Sup-pression or control of foam plays an important role during fabric washing processes50）. The C16/18 MES possess moder-ate foam compared to LAS, whereas C14 MES has high foam characteristic51）. Based on Fig. 6, the foaming power of PBLDs exhibited similar foaming power to commercial samples COM L1 and COM L2, even formulated with C16/18 MES. The PBLDs were formulated with inclusion of co-sur-factants of fatty alcohol ether sulphates, a C12-14 medium chain-based surfactant act as a foam booster. Initial foams of products were in the range of 345－385±0.1 ml and L3 generated the largest foam volumes of 385±0.1 ml. L3 has high level of C16/18 MES in the formulation compare to others. The foam volumes of all other detergents decreased with time（after 5 min）.

3.5 Wetting CharacteristicsIn cleaning process, surface tension must be reduced so

that water can easily spread and wet the surfaces. Chemi-cals that are capable to do this effectively are called surfac-tants. In lowering these boundary tensions, the surfactant improves fabric wetting, so that soil may be more readily removed by mechanical action52）. Fig. 7 shows the wetting characteristics of PBLDs are superior to the commercial COM L1 and COM L2, especially the formulation without LAS（L2-L5）. The wetting time was within 60 seconds. This might be due to the presence of higher number of surfac-tants in formulation and on the liquid and air interface which contributed to better surface activity. This short

　Condition: 50 ppm, 30℃, ratio wash liquor 1:18.5, dosage 0.8 gL－1.　Fig. 5　Detergency of pre-mix based on MES C16-18 in comparison with LAS C11.

Fig. 6　 Foaming stability test on detergent concentration（0.1％） at 25℃ in deionized water.

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time of water-oil interfacial kinetics maximize the perfor-mance of surfactant in the fast-paced wash cycles, which meets the demands of today’s fast-paced society53）. There-fore, MES surfactant acts as a good wetting agent.

3.6 StabilityStability of aesthetic properties of a detergent formula-

tion is paramount, because any change implies poor quality and negatively impact consumers’ acceptance54）. The for-mulation success of a liquid detergent is very much depen-dent on the physical stability of the product where no visible phase separation after storage occurred. A random inventory of PBLDs for stability was carried out, where

sets of three L2 samples were stored for 18 months at cold（5℃）, room（25℃）and elevated（45℃）temperatures. The formulation L2 showed no significant phase separation and change in active and disalt content（Fig. 8）. This indicated that no appreciable hydrolysis had occurred and hydrolysis can be prevented. The formulated MES based products were stable for a long period, even at elevated temperature（45℃）. The hydrolytic stability of MES（the ester group）was reported to be remarkably stabilized by the α-sulfo group on the methyl ester backbone47）.

Addition of protease enzyme in the MES based formula-tion were found to be stable. Proteases with high activity and stability in high alkaline range are suitable for deter-gent industry55）. This protease enzyme is recommended to be used in washing solutions with a pH ranging from 6.5-11 and temperatures ranging from 10- 65℃56）. The used of ci-trates as chelator in PBDLs does not compete with the enzyme for the available Ca2＋ as according to Lund, H. et al.57）.

3.7 BiodegradabilityThe PBLDs, after being used in washing process, would

eventually be released into rivers. It is therefore important that the biodegradability of MES be evaluated since in ad-dition to excellent performance, it must also fulfill ecologi-cal requirements to be accepted in global market. A sub-stance is considered readily biodegradable if it is ≥ 60％ biodegraded during the test period58）. The biodegradability of the reference compound（sodium acetate）should be at least 60％ within 14 d to confirm the validity of the test. It was observed that the biodegradability of reference reached 63％ within 12 d（Fig. 9）. Biodegradability study

Fig. 8　 Stability of active and disalt content in formulation L2 at three different conditions（5℃, 25℃ and 45℃） for 18 months.

Fig. 7　 Wetting characteristics of of palm-based liquid detergents（PBLDs）and commercial detergents（COM L1 and COM L2）.

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reports59, 60）of PBLDs showed that samples L2-L5 biode-graded faster than the commercial detergent, COM L1 where they reached the pass level（60％）in only 3 to 8 d. PBLDs L1 which consist of blended MES and LAS, biode-graded by more than 55％ in 12 d. Even though its biode-gradability did not reach the pass level（60％）, it does not mean that it will not biodegrade, but may take longer time due to slower biodegradation rate and more time was re-quired by the microbes to degrade the substance into simple molecules. Besides, palm-based MES are readily biodegradable surfactants61）. There is a need to study the synergistic effect between MES and LAS at certain ratios to improve the performance and its biodegradability. Si-wayanan et al. reported that the formulated detergent with ideal ratio of MES and LAS possess excellent biodegrad-ability62）. The biodegradability of commercial detergent（COM L1）took longer time to reach the pass level where it only readily biodegraded after 24 d. Comparative analysis of environmental evaluation of MES and LAS in detergent determined elsewhere concluded that MES was more envi-ronmental friendly than LAS63）.

4 CONCLUSIONMES has shown excellent surfactant properties in deter-

gent formulations that meet many requirements in term of detergency, wetting, foaming, stability and environmental. MES has huge potentials to be used as a primary surfactant in cleaning products.

ACKNOWLEDGEMENTThe authors thank Mr. Roslan Ramli, Mr. Azman Rafiei,

Mrs. Rozaini Shaukad Ali and Mrs. Norizan Ali for their analysis assistance.

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