THE METHOD OF PRODUCING THE ALKYD AND USE OF THE ALKYD

FIELD OF INVENTION

This invention generally relates to alkyds. More particularly, the invention relates to a nontoxic palm kernel oil-based alkyd, the method of producing the alkyd and uses of the alkyd aqueous dispersion.

BACKGROUND ART

Natural rubber latex concentrate serves as raw material in the production of various rubber products such as gloves, condoms, adhesives, balloons etc. Natural rubber latex concentrate is derived from field natural rubber freshly tapped from the Hevea brasiliensis tree. Freshly tapped natural rubber latex is subject to degradation immediately after tapping which results in coagulation and putrefaction.

To minimize the coagulation of freshly tapped latex, it must be preserved as soon as possible thereafter. The most used commercial compound in the latex industry is ammonia which acts as a stabiliser and a bactericide. It also acts as a base to catalyse the hydrolyzation of naturally occurring phospholipids and glycolipids in the natural rubber latex to produce negatively charged fatty acids. These charged fatty acids absorb on the rubber membrane to impart extra electrostatic repulsion between rubber particles and consequently increasing the natural rubber latex's colloidal stability.

However, it is very well documented that ammonia is highly toxic and corrosive. Exposure to high concentrations of ammonia can cause immediate burning of the eyes, nose, throat and respiratory tract and can result in blindness, lung damage and even death. When ammonia enters the human body as a result of breathing, swallowing or skin contact, it reacts with water to produce ammonium hydroxide. This chemical is very corrosive and damages cells in the body upon contact.

Aside from ammonia, other antioxidants and chemicals are also used to increase the shelf life of natural rubber latex compounds such as zinc oxides and thiuram disulfide. Long term exposure to metal fumes such as those of zinc oxide may risk the development of serious lung diseases. Zinc oxide is also harmful to aquatic organisms. Whereas the use of thiuram disulfide in latex may result in the formation of nitrosamines and nitrosatable substance which are carcinogenic.

Alkyd resins are generally used in paints and coatings. The non-reliance on petroleum-based raw materials to produce alkyds has made them highly competitive and low cost. However, the use of alkyds in natural rubber latex applications is rarely explored, particularly, palm oilbased alkyds. Malaysia is a country rich in palm oil and it is a readily available, cheap raw material that would be advantageous to be used in the production of alkyds in Malaysia.

According to the state of the art, non-toxic palm oil-based alkyds are a relatively new area of research. Many vegetable oil-based alkyds use linseed, soybean, sunflower, coconut oil etc. Few documents disclose the use of palm oil as a cheap, suitable, and widely available vegetable oil in Malaysia as a raw material. Lee ¹ discloses an early attempt of a palm kernel oil-based alkyd formulation comprising mainly palm kernel oil, glycerol, phthalic anhydride, lithium hydroxide, xylene and maleic anhydride. Glycerol and phthalic anhydride are common raw materials used in the manufacture of alkyds.

Studies have reported that phthalic anhydride is a toxic chemical that cause irritation in humans when exposed to the eyes, respiratory tract, and skin. Lithium hydroxide is also a toxic chemical that causes severe irritation to skin, eyes, and mucous membranes of humans. Xylene used in the formulation is also a toxic chemical that causes irritation to the eyes, nose, skin and throat and can also cause headaches, dizziness, confusion, loss of muscle coordination and in high doses, death. Similar symptoms are also observed during exposure to maleic anhydride.

WO 2013/056162 Al discloses an aqueous alkyd resin dispersion comprising a drying/semi drying oil which includes palm kernel oil and a polyhydroxyl alcohol such as glycerol. These two compounds are subsequently reacted with a suitable glycol which includes dimethylolpropionic acid and a polycarboxylic acid such as phthalic anhydride, maleic acid, benzoic acid and the like. It is noted that the use of this alkyd resin dispersion is specially formulated for use in the coatings industry. The use of the polycarboxylic acid in the process is toxic and harmful. Teo ² discloses an alkyd derived from palm kernel oil. The palm kernel oil is reacted with glycerol with sodium hydroxide as a catalyst. It is subsequently reacted with sebacic acid which produces the alkyd. This is an early example of an attempt to produce an alkyd using purely non-toxic substances. However, the alkyd disclosed is not formulated for specific use in the latex industry such as for the stabilization of natural rubber latex but rather it was disclosed to be used as a nanoscale drug carrier.

Hence, it is an aim of the present invention to manufacture non-toxic alkyds derived from cheap, abundant raw material in Malaysia i.e., palm oil and using bio-sourced compounds that are environmentally friendly and non-toxic. This invention thus aims to alleviate some or all the problems of the prior art. More specifically for use in Hevea brasiliensis rubber latex applications.

¹ Lee, S. Y., Gan, S. N. & Leong Y. C. (2004). Modification of Natural Rubber Pressure Sensitive Adhesive by Palm Kernel Oil Alkyd. Proceedings of the Regional Conference for

Young Chemists 2004. vol 1: Polymer Chemistry. Universiti Sains Malaysia

² Teo, S. Y., Lee, S. Y., Coombes, A., Rathbone, M. J., & Gan, S. N. (2015). Synthesis and characterization of novel biocompatible palm oil-based alkyds. European Journal of Lipid Science and technology. 118. 10.1002/ejlt.201500456

SUMMARY OF THE INVENTION

In accordance with an aspect of the invention, there is provided a palm kernel oil-based alkyd. The anionic alkyd comprises palm kernel oil, glycerol, a hydrophilic trifunctional neopentyl monomer and an octyl-decyl alcohol mixture.

In an embodiment, the hydrophilic trifunctional neopentyl monomer may be 2,2- bis(hydroxymethyl)propionic acid.

In another embodiment, the alkyd may comprise about 60 wt% to about 65 wt%, preferably about 63 wt% of palm kernel oil, about 3 wt% to about 7 wt%, preferably about 5 wt% of glycerol, about 15 wt% to about 20 wt%, preferably about 16 wt% of a hydrophilic trifunctional neopentyl monomer; and about 15 wt% to about 20 wt%, preferably about 16 wt% of an octyl-decyl alcohol mixture.

In an embodiment, the octyl-decyl alcohol mixture comprises 45% to 65%, preferably 55% of octyl alcohol and 35% to 55%, preferably 45% of decyl alcohol.

In another aspect of the present invention, there is provided a method for manufacturing the alkyd. The method comprises the steps of: i) providing palm kernel oil and glycerol; ii) mixing the palm kernel oil and glycerol together to form a first mixture; iii) subjecting the first mixture to an alcoholysis reaction in the presence of a catalyst to form a monoglyceride blend; iv) adding a hydrophilic trifunctional neopentyl monomer and an octyl-decyl alcohol mixture into the monoglyceride blend to form a second mixture; and v) subjecting the second mixture to an esterification reaction under a stream of nitrogen.

In an embodiment, the hydrophilic trifunctional neopentyl monomer may be 2,2- bis(hydroxymethyl)propionic acid. The catalyst used may be sodium hydroxide and the amount of the catalyst provided may be about 0.1 wt% to about 0.5 wt%.

The temperature of the alcoholysis reaction of step (iii) is about 180° to about 220°C, whereas the reaction time is about 1 hours to about 2 hours.

The temperature of the esterification reaction of step (v) is about 180° to about 220°C whereas the reaction time is about 16 hours to about 20 hours.

In a further aspect of the present invention, there is provided a method of producing an alkyd aqueous dispersion. The method comprises the steps of: i) providing the alkyd and a base to form a mixture; ii) adding water gradually to the mixture to form an aqueous mixture; and iii) mixing the aqueous mixture until homogeneous.

In an embodiment, the base provided in step (i) may be potassium hydroxide.

In another embodiment, the amount of alkyd provided in step (i) may be about 15 wt% to about 20 wt%, preferably 17 wt% whereas the amount of base provided may be about 3 wt% to about 5 wt%, preferably 4 wt%. The amount of water added in step (ii) is about 70 wt% to about 80 wt%, preferably 75 wt%.

In a further embodiment, the mixing of step (iii) is conducted at a temperature of about 60°C to about 90°C, preferably about 80°C, for about 1 hour to about 2 hours.

In a further aspect of the invention, there is provided use of the alkyd aqueous dispersions as a stabiliser in freshly tapped field natural rubber latex, low ammonia natural rubber latex concentrate or ammonia-free natural rubber latex concentrate.

The alkyd of the present invention provides for various beneficial properties such as being non-toxic, as well as having excellent surface active and wetting properties that are suitable for use as a stabiliser in latex applications especially for natural rubber latex concentrates with or without ammonia. The invention provides for various advantages as outlined above and will be further elaborated in the following pages.

DETAILED DESCRIPTION

The present invention is directed at a non-toxic alkyd derived from palm kernel oil, the method of producing the alkyd and its use.

Non-toxic palm kernel oil-based alkyd

In an embodiment of the present invention, there is provided a palm kernel oil-based alkyd. The alkyd comprises palm kernel oil, glycerol, a hydrophilic neopentyl monomer and an octyldecyl alcohol mixture.

Palm kernel oil is extracted from the seeds of oil palm fruits. It contains mainly saturated fatty acids at about more than 80%. The most abundant fatty acid present in palm kernel oil is lauric acid. Of all the triglycerides present in palm kernel oil, 99% will contain at least one molecule of lauric acid. The presence of lauric acid makes palm kernel oil highly resistant to oxidation. The palm kernel oil used in the present invention has an iodine value of at least 21%, preferably 25%.

Glycerol is a simple polyol compound that is colourless, odourless, viscous, and non-toxic. Glycerol is also known to have antimicrobial and antiviral properties. The purity of glycerol used in the present invention is at least 95%, preferably at least 97%.

The hydrophilic neopentyl monomer comprises at least one hydroxy and at least one carboxy functional group. The hydrophilic neopentyl monomer preferably comprises a combination of two hydroxy and one carboxy functional groups. The hydrophilic neopentyl monomer may be 2,2-bis(hydroxymethyl)propionic acid, or also named as 3-hydroxy-2-(hydroxymethyl)-2- methylpropanoic acid. This hydrophilic neopentyl monomer hereinafter is referred to as dimethylol propionic acid (DMPA). The purity of DMPA is at least 98%. DMPA is a non-toxic compound. DMPA is used to enhance water solubility and hydrolytic stability of the alkyd, in particular, to stabilize ester linkages against hydrolysis.

Octyl-decyl alcohol mixture is a fatty alcohol mixture comprising mainly octyl (C ₈ ) and decyl (Cio) alcohols that have to the following formula (I) and formula (II) respectively:

C ₈ HI ₇ OH (I) C10H23OH (II)

The octyl-decyl alcohol mixture used in the present invention comprises octyl alcohol (Cs) of about 45% to about 65%, preferably about 55% and decyl alcohol (Cio) of about 35% to about 55%, preferably 45%. The octyl-decyl alcohol mixture used in the present invention preferably has a hydroxyl value ranging about 385 mg KOH/g to about 410 mg KOH/g.

Octyl-decyl alcohols are widely used as emulsifying, dispersing, wetting agents, or surfactants. These alcohols are known to be extremely safe and non-toxic and may even be used in certain food processing and transdermal drug delivery applications.

The composition of the alkyd comprises:

1. palm kernel oil of at least about 60 wt% to at most about 65 wt%, preferably about 63 wt%;

2. glycerol of at least about 3 wt% to at most about 7 wt%, preferably about 5 wt%;

3. DMPA of at least about 15 wt% to at most about 20 wt%, preferably about 16 wt%; and

4. an octyl-decyl alcohol mixture of at least about 15 wt% to at most about 20 wt%, preferably about 16 wt%.

The alkyd of the present invention was subjected to several characterization tests to determine the acid values through acid value titration adapted from ASTM D1980-87 (1998), glass transition temperatures through differential scanning calorimetry from ASTM D3418-15 (2015) and molecular weights through gel permeation chromatography. The test results are shown in Table 1 below.

Table 1: Physiochemical properties of the alkyd

Acid number Glass transition Gel permeation chromatography analysis

(mg KOH/g) temperature ( T _g , °C) M _n M _w PDI

3.0-5.0 -85 to -70 650-680 850-920 1.2-1.5

The test results confirm that the alkyd have a polydispersity index (PDI) of more than 1 i.e., the alkyd have a wide range of molecular masses which enables them to act as effective additives for Hevea brasiliensis rubber latex. Also, the alkyd was determined to have a low acid number indicating that it has achieved a high conversion rate of 97-98%. The alkyd also exhibited low glass transition temperatures, T _g indicating that the alkyd has a rubbery behaviour at room temperature making it flexibly and difficult to break and a molecular weight that falls within those of the most practically useful polymers.

Method of producing the alkyds

The alkyd was manufactured by reacting the reagents via stepwise polymerization i.e., in two steps namely alcoholysis and esterification. The entire process does not require the use of any solvent.

The method for producing the anionic alkyd of the present invention mainly comprises the following steps: i) providing palm kernel oil and glycerol; ii) mixing the palm kernel oil and glycerol together to form a first mixture; iii) subjecting the first mixture to an alcoholysis reaction in the presence of a catalyst to form a monoglyceride blend; iv) adding a hydrophilic trifunctional neopentyl monomer and an octyl-decyl alcohol mixture into the monoglyceride blend to form a second mixture; and v) subjecting the second mixture to an esterification reaction under a stream of nitrogen.

The catalyst used is sodium hydroxide. Sodium hydroxide is a non-toxic compound and is used in the present invention to substitute commonly used metal oxide catalysts such as lithium hydroxide or tin oxides. There metal oxide catalysts are highly toxic. The use of sodium hydroxide in the present invention provides for the non-toxic properties of the present invention. The preferred amount of catalyst is about 0.1 wt%.

In the alcoholysis reaction of step (iii), the palm kernel oil, an excess amount of glycerol and a catalyst are mixed in any suitable vessel. A reaction flask is used in the present invention as it provided effective control of the reaction. The reaction flask is equipped with a mechanical agitator, thermometer, nitrogen gas inlet and a Dean-Stark decanter.

The alcoholysis reaction is carried out at a temperature of at least about 180°C and at most about 200°C. The reaction time is at least about 1 hour and at most about 2 hours. Any other suitable reaction temperature and time may be applied. The alcoholysis reaction of palm kernel oil and glycerol results in the production of monoglycerides with minor mixtures of diglycerides, unconverted triglycerides and unreacted glycerol. The resulting monoglycerides have only one fatty acid chain and thus less steric hindrance. This would help in speeding up the subsequent esterification reaction with further addition of monomers.

During the esterification reaction of step (v), heat is applied to the reaction vessel and gradually increased and subsequently maintained for a specific length of time. This allows for a slow polyesterification rate to occur, allowing uniform distribution of monomers to form hydrophobes and hydrophilies along the alkyd's backbone structure.

The esterification reaction is carried out at a temperature of about 180°C to about 200°C, for at least about 16 hours to at most about 20 hours under a stream of nitrogen until reaching at least about 3 to about 5 mg KOH/g of resin acid value measurements.

During the esterification reaction, the carboxyl (-COOH) groups of the fatty acids in the monoglyceride blend, through condensation, reacts with the hydroxy (-OH) groups of the octyldecyl alcohol mixtures first, followed by the hydroxy groups in DMPA which are more hindered and finally with the hydroxy groups in the unreacted glycerol, forming ester linkages. The esterified monoglyceride moieties forms the hydrophobes while the unreacted carboxyl groups of DMPA moieties forms the hydrophiles on the alkyd's backbone structure. The purpose of adopting the alcoholysis reaction was to introduce monoglycerides into the alkyd's backbone structure which may lead to branching or a three-dimensional structure. This three- dimensional structure of the alkyd's backbone has several advantages when used in certain applications which will be elaborated the following sections.

A by-product comprising water is generated and collected at the decanter whereas the finished alkyd is a yellowish liquid.

Method of producing an alkyd aqueous dispersion

An alkyd aqueous dispersion is an intermediate product that is used in many applications. Several specific applications are described in the following sections.

The method for producing an alkyd aqueous dispersion using the alkyds of the present invention mainly comprises the following steps: i) providing the alkyd and a base to form a first mixture; ii) adding water to the first mixture to form an aqueous mixture; iii) mixing the aqueous mixture until homogeneous.

The amount of alkyd provided is about 15 wt% to about 20 wt%, preferably 17 wt%.

The base used in the above method is potassium hydroxide. It neutralizes the acid groups in the alkyds' backbone to form soluble salts i.e., the alkyd aqueous dispersion. The amount of base provided is about 3 wt% to about 5 wt%, preferably 4 wt%.

The amount of water added to the mixture in step (ii) is about 70 wt% to about 80 wt%, preferably 75 wt%. The water is added gradually into the mixture allowing the formation of a homogeneous alkyd aqueous dispersion.

The mixing step (iii) is conducted constantly at a temperature of about 60°C to about 90°C, preferably 80°C, for at least about 1 hour or at most 2 hours. Any other suitable mixing temperature or time may be applied.

Tests were conducts to determine the surface-active properties of the alkyd aqueous dispersion. The results of the tests are shown in Table 2 below.

Table 2: Surface-active properties of the alkyd aqueous dispersion

Total solid Brookfield Critical micelle _{Surface tensi<} , _{n Contact} a. *. ,n/ Viscosity, pH concentration _ i- content ( /o) 25 °C (mPa.s) (CMC, mM/L) (mN/m) angle ( )

19.0-26.0 250-350 (Spindle 4) 12.0-13.0 0.006937 - 0.0212 70.2-71.1 < 90

Critical micelle concentration (CMC) and surface tension of the alkyd were recorded as 0.006937 - 0.0212 mM/L and 70.2-71.1 mN/m respectively. The alkyd aqueous dispersion indicated a contact angle of < 90° suggesting that the alkyd has potential wetting properties. The alkyd is anionic charged polymeric surfactant. These results confirm that the alkyd is suitable for use as a stabiliser for natural rubber latex as will be further elaborated the in following sections. Use of the alkyd aqueous dispersion as a stabiliser for Hevea brasiliensis \

The inventors have discovered that the alkyd aqueous dispersion is suitable for use as stabiliser for latex compounds and more specifically for freshly tapped field Hevea brasiliensis rubber (natural rubber) latex as well as low ammonia and ammonia-free natural rubber latex.

Natural rubber latex is exposed to oxygen and coagulation the moment the trees are tapped up to the vulcanisation and manufacture of the finished product. Changes in latex stability still occurs even when the latex already contains preservatives and will degrade the quality of the latex when it is finally being used. Natural rubber latex is commercially preserved typically with ammonia. Ammonia is a known toxic compound which is known to cause irritation and serious burns in the mouth, lungs, and eyes upon inhalation. Chronic exposure can increase the risk to respiratory irritation, cough, wheezing, tightness in the chest and impaired lung function in human.

Ammonia inhibits bacteria activity in natural rubber latex with its high pH and at the same time it hydrolyses naturally occurring fatty acids in latex to form soaps that act as stabilizing bodies. However, ammonia is volatile in nature and requires that the natural rubber latex is constantly preserved with additional ammonia to maintain latex stability.

On the other hand, inadequately preserved natural rubber latex is subject to aerobic bacteria degradation where oxygen is absorbed rapidly by the bacteria, leading to formation of low molecular weight fatty acids in the latex. These fatty acids destabilize and degrade the latex which can be detected by an increase in volatile fatty acid content in the latex. Bacteria activity can be inhibited by the addition of more ammonia. However, after a period of several weeks or months, the stability of the latex begins to deteriorate due to the gradual volatilization of ammonia which reduces its effectiveness as a bactericide.

Natural rubber latex can also be destabilized by anaerobic bacteria which happens during the handling of bulk natural rubber latex when the latex is transported in a closed container. It is possible that ammonia-resistant strains of bacteria can develop over time. To overcome this problem, antiseptic, antiviral and antifungal agents such as boric acid, orthoboric acid, sodium pentachlorophenol, formaldehyde, methylol compounds were experimentally added to increase stability of the latex but these agents are usually toxic. Hence, there is a need to find non-toxic alternatives to substitute the use of ammonia as a stabiliser of natural rubber latex. When the alkyd aqueous dispersion of the present invention is present in the natural rubber latex compound, the alkyd polymer is likely to adsorb on the latex particles, with its long hydrophobic chains of glycerides moieties (hydrophobes) looping around the outer layer of latex particles, leaving more ionic head groups or pendant acid groups in DMPA moieties (hydrophiles) on the outside of the alkyd's backbone structure. The use of the octyl-decyl alcohol mixtures in the present invention results in a longer alkyd backbone structure i.e., longer hydrophobic chains allowing the alkyd to loop around the outer layer of the latex particles. The hydrophobes provide electrostatic stabilisation while the hydrophiles provide steric stabilisation to rubber latex particles.

The alkyd polymer provides a hairy layer i.e., a three-dimensional structure that extends from the surface of latex particles into the aqueous media. This provides a strong repulsion force to maintain a safe distance between the latex particles and thus, effectively preventing latex coagulation. Hence, the alkyd of the present invention can provide a combination of both strong steric and electrostatic stabilization mechanisms to the natural rubber latex particles.

A test was conducted by adding the alkyd aqueous dispersion of the present invention to a sample of freshly prepared freshly tapped field natural rubber latex, low ammonia latex concentrate and another sample of an ammonia-free latex concentrate.

The freshly tapped field natural rubber latex was subjected to stabilization testing for up to 3 days, whereas, both the low ammonia and ammonia-free latex concentrates were subjected to stabilization testing for up to 6 months. The results indicated an improvement when compared to the control group that does not contain the alkyd aqueous dispersion. The test is evident that the alkyd aqueous dispersion of the present invention is successful in stabilising freshly tapped field natural rubber latex, low ammonia and ammonia free natural rubber latex concentrates compared to the use of conventional preservatives such as ammonia. The results of the tests are further elaborated in Examples 1 and 2.

Advantages of the palm kernel oil-based alkyd

As the alkyd is synthetically designed, there is a high opportunity to alter the functional groups and structures of the alkyd to enhance its antimicrobial potential compared to the use of conventional bactericides that requires frequent change of formulations as the bacteria becomes resistant. In some cases, latex manufacturers are required to change the bactericides annually due to the rapid mutational changes of bacteria. With the efficacy of the alkyd's antimicrobial effects, the containers used for collecting field rubber are only required to be washed with tap water unlike current standard operating procedures which requires special cleaning and sterilization.

With the alkyd aqueous dispersion of the present invention able to preserve natural rubber latex concentrates for 6 months or more, there is a high potential for natural rubber latex concentrates preserved with the alkyd to overcome insufficient supply of natural rubber particularly during wintering seasons. This would also overcome large price fluctuations during the wintering seasons.

Finally, the alkyd of the present invention contains zero environmentally damaging and non- carcinogenic chemicals that are commonly used in the manufacture of latex compounds such as ammonia, thiuram disulfide and zinc oxide. The use of thiuram disulfide in latex may result the formation of nitrosamines and nitrosatable substance which are carcinogenic. Resides of thiuram disulfide on the latex product may potentially cause Type IV allergic contact dermatitis whereas zinc oxide is a known hazard to aquatic organisms. Long term exposure to metal fumes such as those of zinc oxide may risk the development of serious lung diseases as well.

EXAMPLES

The following Examples illustrate methods of testing the various physicochemical properties of the alkyds of the present invention. These Examples do not limit the invention, the scope of which is set out in the appended claims.

Example 1

Preparation and characterization of low ammonia natural rubber latex concentrate

Field Hevea brasiliensis (natural rubber) latex was first preserved with 0.5 wt% ammonia. The latex was diluted to about 30 wt% dry rubber content before subjecting to Alfa Laval centrifugation. The ammonia content of latex was tested using the alkalinity test to calculate its ammonia content. Subsequently, the ammonia content was adjusted to 0.2-0.3 wt% by alternately adding a small amount of ammonia solution and aeration by magnetic stirring until the required wt% is achieved.

About 0.1 - 0.4 wt% of palm kernel oil-based alkyd aqueous dispersions were added separately into this latex concentrate.

Stabilization testing was repeated for up to 6 months and the results are summarized in Table 3 below.

The control group in Table 3 refers to low ammonia natural rubber latex concentrate derived from freshly tapped field natural rubber latex that does not contain any alkyd aqueous dispersions but instead contains ammonia, thiuram disulfide (TMTD), zinc oxide (ZnO) and potassium laurate. The control group was prepared from field natural rubber latex preserved with 0.5 wt% ammonia. The latex was diluted to about 30 wt% dry rubber content before subjecting to Alfa Laval centrifugation. The ammonia content of latex was tested using the alkalinity test to calculate its ammonia content. Subsequently, the ammonia content was adjusted to 0.2-0.3 wt% by alternately adding a small amount of ammonia solution and aeration by magnetic stirring until the required wt% is achieved. About 0.013% TMTD, 0.013% ZnO and 0.05% potassium laurate were added into the latex concentrate. The control group was formulated to be similar to commercially available low ammonia natural rubber latex concentrate (LATZ). Table 3: Six-month stabilization testing of low ammonia field natural rubber latex concentrates stabilized with palm kernel oil-based alkyd aqueous dispersions added in different percentages

Stability measurement for up 6 months Low ammonia field natural rubber latex concentrates with added palm kernel oil-based alkyd aqueous dispersions . _

0.1% 0.2% 0.3% 0.4% ^{9l 0up}

DRC (%) 62.2 - 64.0 62.1 - 63.8 62.7 - 64.2 62.4 - 64.3 60.8. - 61.7

TSC (%) 64.3 - 65.4 64.7 - 65.8 64.4 - 65.6 64.2 - 65.7 60.3 - 62.3

MST (s) 430 - > 1800 962 - > 1800 > 1800 > 1800 180 - 1140

VFA 0.025 - 0.070 0.024 - 0.060 0.025 - 0.060 0.026 - 0.060 0.015 - 0.075

Alkalinity test 0.24 - 0.28 0.24 - 0.28 0.24 - 0.28 0.26 - 0.31 0.25 - 0.30

Brookfield viscosity (cps) 162 - 84 146 - 82 131 - 91 127 - 92 91 - 43 pH 10.22 - 11.31 10.64 - 11.37 10.62 - 11.39 10.95 - 11.44 10.50 - 10.98

* Control group refers to freshly prepared low ammonia natural rubber latex concentrates that does not contain palm kernel oil-based alkyd aqueous dispersions but instead contains 0.2-0.3% ammonia, 0.013% TMTD, 0.013% ZnO, 0.05% potassium laurate.

The palm kernel oil-based alkyd aqueous dispersions ranging from 0.1-0.4 wt% were able to maintain the latex testing values of TSC up to 66%, DRC up to 64%, pH up to 11, VFA no. up to 0.07, alkalinity less than 0.3 and MST more than 1800s during storage of up to 6 months. The Brookfield viscosity of the latex concentrates ranged between 82 cps to 162 cps, in the presence of the palm kernel oil-based alkyd aqueous dispersions of 0.1-0.4 wt%, for up to six months of storage. These values were either comparable or superior to those of the control group in Table 3, as well as within the acceptable range of ISO standard requirements for latex stabilization applications.

However, in consideration for cost effectiveness, the formulation with 0.2 wt% of palm kernel oil-based alkyd aqueous dispersions is adequate for the stabilization of low ammonia field natural rubber latex concentrates as the values were found to be comparable with those of the latex concentrates stabilized with 0.4 wt% of palm kernel oil-based alkyd aqueous dispersion.

Example 2

Preparation and characterization of freshly tapped field natural rubber latex ammonia-free natural rubber latex concentrate

Freshly tapped field natural rubber latex was first preserved with two formulations with 1.3 wt% and 1.4 wt% of palm kernel oil-based alkyd aqueous dispersions and 0.2 wt% and 0.1 wt% potassium hydroxide solution respectively. Stabilization testing was repeated for up to 3 days and the results are summarized in Table 4. Ammonia-free natural rubber latex concentrate was prepared by diluting the freshly prepared field natural latex within three days after field latex collection. The field latex was diluted to about 30 wt% dry rubber content before subjecting to Alfa Laval centrifugation to produce ammonia-free natural rubber latex concentrates.

Stabilization testing was repeated for up to 6 months and the results are summarized in Table 5. The control group in Table 4 refers to freshly tapped field natural rubber latex while the control group in Table 5 refers to ammonia-free natural rubber latex concentrates derived from freshly tapped field natural rubber latex that does not contain alkyd aqueous dispersions but instead contains ammonia. The control groups were prepared from freshly tapped field natural rubber latex preserved with 0.5 wt% ammonia. The latex was diluted to about 30 wt% dry rubber content before subjecting to Alfa Laval centrifugation. The ammonia content of the latex was tested using the alkalinity test to calculate its ammonia content. Subsequently, the ammonia content was adjusted to 0.7 wt% by alternately adding a small amount of ammonia solution and performing alkalinity test until the required wt% is achieved. The control groups were formulated to be similar to commercially available low ammonia natural rubber latex concentrate (LATZ).

Table 4: Three-day stabilization testing of freshly tapped field natural rubber latex stabilized with palm-based alkyd aqueous dispersion added in different percentages

Stability measurement for up 3 days

_ .. Field natural rubber latex with added palm kernel oil- _ ,

Properties . . „ . .. Contro based alkyd aqueous dispersions

1.3% alkyd/0.2% KOH 1.4% alkyd/0.1%KOH ^{9l 0up}

DRC (%) 46.3 - 46.4 45.7 - 45.8 45.4 - 45.5

TSC (%) 51.0 - 51.1 50.8 - 50.9 49.8 - 49.9

VFA 0.024 - 0.031 0.021 - 0.029 0.016 - 0.017

Alkalinity test 0.07 - 0.08 0.05 - 0.06 0.4 - 0.5 pH 12.70 - 12.90 11.30 - 11.50 12.30 - 12.50

* Control group refers to freshly prepared field natural rubber latex that does not contain palm kernel oil-based alkyd aqueous dispersions but instead contains 0.5% ammonia.

Table 5: Six-month stabilization testing of ammonia free field natural rubber latex concentrates stabilized with palm kernel oil-based alkyd aqueous dispersions added in different percentages

Stability measurement for up 6 months

P nnprfpc Ammonia-free field natural rubber latex concentrates with r ^{p 1} added palm kernel oil-based alkyd aqueous dispersions ^{0,1 r} °

1.3% alkyd/0.2% KOH 1.4% alkyd/0.1%KOH ^{9l 0up}

DRC (%) 62.7 - 64.3 62.4 - 64.9 59.4 - 61.5

TSC (%) 64.2 - 65.1 64.3 - 65.4 60.8 - 62.7

MST (s) 480 - 1500 > 1800 384 - 1175

VFA 0.021 - 0.060 0.018 - 0.053 0.024 - 0.075

Alkalinity test 0.06 - 0.07 0.04 - 0.05 0.6 - 0.7

Brookfield viscosity (cps) 316 - 102 299 - 216 44 - 109 pH 11.67 - 12.90 10.56 - 12.30 11.01 - 11.42

* Control group refers to freshly prepared low ammonia natural rubber latex concentrates that does not contain palm kernel oil-based alkyd aqueous dispersions but instead contains 0.7% ammonia.

From Table 4, the formulations of palm kernel oil-based alkyd aqueous dispersions ranging from 1.3-1.4 wt%, together with 0.1-0.2 wt% potassium hydroxide were able to maintain the latex testing values of TSC up to 51%, DRC up to 46%, pH up to 13, VFA no. up to 0.03 and alkalinity up to 0.08, in the presence of the palm kernel oil-based alkyd aqueous dispersions and potassium hydroxide, for up to three days of storage. These values were either comparable or superior to those of the control group in Table 4.

From Table 5, the formulations of palm kernel oil-based alkyd aqueous dispersions ranging from 1.3-1.4 wt%, together with 0.1-0.2 wt% potassium hydroxide were able to maintain the latex testing values of TSC up to 65%, DRC up to 65%, pH up to 13, VFA no. up to 0.06, alkalinity up to 0.07 and MST more than 1800s. The Brookfield viscosity of the latex concentrates ranged between 100 cps to 300 cps, in the presence of the palm kernel oil-based alkyd aqueous dispersions and potassium hydroxide, for up to six months of storage. These values were either comparable or superior to those of the control group in Table 5.

Both alkyd aqueous dispersion formulations are suitable for stabilization of freshly tapped field natural rubber latex concentrates without using ammonia as the testing values are within the acceptable range of ISO standard requirements for latex stabilization applications.

Conclusion

Based on the examples above, the palm kernel oil-based alkyd aqueous dispersions are suitable for use as stabilisers for freshly tapped field natural rubber latex as well as both low ammonia natural rubber latex concentrates and ammonia-free natural rubber latex concentrates where both latex concentrates are derived from freshly tapped field natural rubber latex. This can be achieved without needing to rely on commercial high ammonia (HA) latex concentrate which require additional processing to lower the ammonia content or to totally remove the ammonia. On the other hand, commercial low ammonia latex concentrate (LATZ) contains toxic and environmentally damaging preservatives present which would also require additional processing to remove these compounds to produce an environmentally friendly, non-toxic LATZ. Sourcing the latex raw material directly from freshly tapped field natural rubber would be more cost effective. It also would eliminate the use and presence of all toxic and environmentally damaging preservatives commonly found in commercial HA latex and LATZ from the entire process chain.

As will be readily apparent to those skilled in the art, the present invention may easily be produced in other specific forms without departing from its scope.