การใชยางธรรมชาตน าหนกโมเลกลตาและยางธรรมชาตเหลวทมหมฟงกชนปรบปรงสมบต การแปรรปและการเสรมแรงของสารตวเตมในยางธรรมชาต

Utilization of Low Molecular Weight Natural Rubber and Functionalized Liquid Natural Rubber to Improve Processing Property and Reinforcement in Filled NR Compounds

Prachid Saramolee 5320330106

Thesis Proposal for Doctor of Philosophy in Polymer Technology Faculty of Science and Technology

Prince of Songkla University Academic Year 2010

2

1. Thesis Title (Thai) การใชยางธรรมชาตน าหนกโมเลกลตาและยางธรรมชาตเหลวทมหมฟงกชนปรบปรง

สมบตการแปรรปและการเสรมแรงของสารตวเตมในยางธรรมชาต (English) Utilization of Low Molecular Weight Natural Rubber and Functionalized

Liquid Natural Rubber to Improve Processing Property and Reinforcement in Filled NR Compounds

2. Program of Study Polymer Technology

3. Researchers 3.1 Student’s Name Mr.Prachid Saramolee ID 5320330106 3.2 Thesis Advisors’ Names Asst. Prof. Dr. Kannika Sahakaro Advisor Asst. Prof. Dr. Natinee Lopattananon Co-advisor Prof. Dr. Jacques W.M. Noordermeer Co-advisor

4. Background and Rationale Nowadays, tire industry has been developed in several aspects including

processing technology, raw materials and compound formulations. Especially, the product regulations have included product specifications and other requirements such as a ban on aromatic oil which contains toxic polycyclic aromatics (PCA) in tire compounds in Europe (Commission Regulation (EC) No 552/2009). Moreover, the European Union has enacted legislation on tire labeling, based on rolling resistance, wet grip and noise levels (Regulation (EC) No 1222/2009). Tire properties are improved by reinforcing fillers such as carbon black and silica. Silica-filled rubber compounds have been increasingly used after an achievement of fuel saving “Green Tire” by Michelin (Rauline, 1992). The use of silica-filled tire treads results in an excellent wet traction and a lower rolling resistance in comparison to carbon black leading to fuel or energy saving. However, mixing of silica-filled compounds is more difficult and complicated compared to that of carbon black due to silica is inorganic filler which has a number of highly polar hydroxyl groups on the surface. Therefore, a basic difficulty lies on the incompatibility between inorganic silica and organic rubbers. In addition, silica-filled rubber compound without coupling agents or organic compounds (e.g. amines and alcohols) has high viscosity and increasing in mixing temperature which

3

might be risk of compound scorch. Moreover, a serious problem for the utilization of silica is its poor dispersion in the rubber matrix leading to the reduction of vulcanizate mechanical properties. For general products, amines or alcohols are used to reduce the polarity and increase the hydrophobicity of silica surface resulting in good dispersion within the rubber matrix (Jesionowski and Krysztafkiewicz, 2001). For high performance products such as tires, coupling agents are used to bridge the polymer to silica, in which the process has to be controlled the conditions and step of mixing in order to allow functional groups on silane to fully react with silanol groups on silica surface during mixing stage (Luginsland et al., 2002; Ansarifar et al., 2003; Reuvekamp et al., 2009). Furthermore, high filler loading in the compound requires a use of processing oil to control compound viscosity and flow properties during processing stage.

This research focuses on the effect of low molecular weight natural rubber (LMWNR) or liquid natural rubber (LNR) and functionalized liquid natural rubber (FLNR) on processing properties and the reinforcement in filled NR compounds. The use of LNR or FLNR is expected to enhance flow properties and compatibility between rubber and filler. The LNR will be modified to have epoxide groups as the main functional group which will also be later extended to other types of functionalized low molecular weight natural rubber. Effects of different molecular weight and amount of LMWNR as well as modification levels of modified LNR on cure characteristic, processing properties, mechanical and dynamic mechanical properties of filled NR compound will be investigated. Moreover, the effect of LMWNR and/or FLNR will be compared to that of conventional silane coupling agent in silica-filled compounds.

5. Objectives of Research 5.1 To prepare low molecular weight natural rubber or liquid natural rubber

with various levels of molecular weight and analyze for their characteristics and properties

5.2 To modify liquid natural rubber by creating functional groups attached onto the main chains such as epoxidized liquid natural rubber (ELNR) and graft copolymer of LNR with vinyl monomers

5.3 To investigate the effect of molecular weights and amounts of LNR on processing and vulcanizate properties of unfilled NR compounds

4

5.4 To investigate the influence of unmodified LNR and modified LNRs, when they are used as compatibilizer in carbon black and silica-filled NR compounds, on the compound and vulcanizate properties

5.5 To compare the effect of modified LNRs with conventional silane coupling agent on compound and vulcanizate properties of silica-filled compounds

6. Expected Advantages The reinforcing fillers have been widely developed for tire compounds, especially the use of silica with silane coupling agent. This is in order to meet many requirements in tire industry, especially for environmental saving, energy reduction and chemical toxicity minimization. The use of natural-based products such as LMWNR and/or modified LNR to improve processing properties and increase filler-rubber interaction in carbon black- and silica-filled compounds will encourage more use of NR and develop more environmental friendly products. This research will provide the knowledge of relationships between molecular weight, types and functionality of modified LNRs and filler-rubber interaction which influence on compound and vulcanizate properties of filled NR compounds.

7. Literature Review 7.1 Low molecular weight natural rubber

Natural rubber is an unsaturated hydrocarbon consisting solely of carbon and hydrogen atom with an empirical formula of C5H8. Isoprene is a repeating unit of natural rubber in which one double bond unit exists for each C5H8 group. NR latex is the form in which rubber is exuded from the Hevea brasiliensis tree as an aqueous emulsion. The size of rubber particles is in a range from about 50oA to about 30,000oA

(3 m). The molecular weight (Mw) is normally in the range of 104-107g/mol (Subramanium, 1980), depending on the age of the rubber tree, weather, method of rubber isolation and other factors. The polydispersity of molecular weight is usually in the region of 2.5-10 (Eng and Ong, 2001). Furthermore, NR is a long chain molecule with terminal groups that are able to form branch points by hydrogen bonding with proteins and/or phospholipids (Morton, 1987; Tanaka, 2001; Amnuaypornsri et al., 2010). During storage, the hardness of NR will increase and this will be in accordance with increasing value of Mooney viscosity. The higher value of Mooney viscosity will

5

give the better resistance of that rubber to deformation. The advantages of NR are outstanding flexibility, excellent heat built up properties and high mechanical strength. Moreover, the presence of reactive double bonds in cis-1,4-polyisoprene in natural rubber renders the macromolecule to be chemically modifiable via the addition or creation of small functional groups. Therefore, degradation of NR into low molecular weight rubber and then functionalization with specific functional groups would widen the applications of NR (Brosse et al., 2000).

Low molecular weight or liquid natural rubber is depolymerised NR, which has a shorter polymeric chain, as a consequence, good rheological property, chain flexibility and also easy to chemically modify. It is tacky but has excellent crosslinking reactivity when the molecular weight (Mw) is less than 105 g/mol (Ibrahim and Dahlan, 1998). The properties depend on the techniques used to produce it. It has been widely used as a raw material for adhesive, pressure-sensitive adhesive, binder, sealing materials, reactive plasticizer for improving processing property of solid rubber such as compounded rubber for tires, and can be also used as a starting material for functionalized liquid natural rubber. It is now attracting attention in various industrial fields. As compared with solid rubber, liquid rubber is advantageous for the production of various products because it can be easily processed and requires less energy (Tanaka et al., 1996). The development of methods for the preparation of LNR began in the 1970’s. The depolymerization of NR to form liquid rubber has been carried out under various experimental conditions, i.e., mastication, pyrolysis, photolysis and chemical decomposition methods. The first and second methods are applied to solid NR, whereas the third and fourth are for both latex and solution NR.

Mastication is a method for accelerating reduction in the molecular weight by breaking the rubber molecular chains of the raw material through mechanical action and heat on two roll mills or in internal mixer (Ehabe et al., 2008) and then adding a peptizer (which is an organic compound giving low plasticity even when used in a small amount, thereby reducing mastication time and is also called a mastication accelerator) such as a mercaptan (Okwu and Akinlabi, 2007) to the resulting rubber to prevent the recombination of the broken molecular chains. This method permits the production of depolymerized rubber having a low molecular weight and aldehyde or

6

ketone terminal groups. However, this method is accompanied with the problem that the molecular weight distribution (MWD) is wide and cannot be controlled easily.

In pyrolysis process, NR is depolymerised at high temperature about 200 – 600oC in oxygen or nitrogen atmosphere, so called pyrolysis or thermal methods, respectively. The reaction temperature is high so that not only decomposition but also crosslinking or recombination inevitably occurs. This makes it difficult to control the molecular weight distribution. Cataldo (1998) prepared liquid polyisoprene by thermal depolymerization at 300–380°C. The pyrolysis of natural and synthetic cis-1,4-polyisoprene produces mainly dipentene with small amounts of isoprene (2-5%).

Photolysis is a method for breaking the molecular chains with light energy such as solar radiation, ultraviolet or visible light. Chain breaker compounds such as nitrobenzene, hydrogen peroxide or photosensitisers are used together in degradation process, so called photochemical methods. However, it is difficult to control the molecular weight or molecular weight distribution. Moreover, isomerization reaction tends to proceed from a cis-1,4-structure to a trans-1,4-structure.

With regard to chemical decomposition, the controlled degradation of NR involves photochemical degradation, ozone cleavage, metathesis degradation and oxidative degradation. Cunneen (1973) prepared LNR by irradiation with ultraviolet light in a presence of nitrobenzene as a photosensitizer to give LNR having Mn of about 3,000 g/mol. Ravindran et al. (1986, 1988) prepared LNR via photochemical degradation from NR using hydrogen peroxide and light energy from both medium pressure mercury vapor lamp and sunlight. LNR bearing hydroxyl end groups were obtained and the side products of around 10% were observed such as carbonyl and carboxylic compounds. Solanky et al. (2005) studied cis-1,4-polyisoprene degradation using first and second generation Grubbs catalysts to achieve end functionalized acetoxy oligomers in both an organic solvent and a latex state at room temperature. Moreover, the use of a sodium tungstate/acetic acid/hydrogen peroxide as a catalyst to prepare LNR was studied (Zhang et al., 2010).

The method of ozone degradation has been applied only for a research purpose and so far has no industrial value, because the reaction should be conducted at low temperature and treatment of a large amount of ozonide is dangerous. Montaudo et al. (1992) reported that ozonolysis reaction of cis-1,4-polyisoprene in

hexane at ice bath temperature without further treatment with either oxidizing or

7

reducing agents led to the formation of LNR bearing only ketone and carboxylic acid end groups. Nor and Ebdon (2000) studied ozonolysis of NR in diluted chloroform solution at 0oC. They found that the number average molecular weight of less than 900 g/mol was obtained after 20 min of ozonolysis. However, the methods mentioned above are limited either because of difficulty in control of reaction, highly toxic, or contaminant in LNR. Thus, oxidative degradation or redox system is preferred. This method can cleave polymer chains with the concomitant introduction of reactive terminal groups on the resulting oligomers. The oxidizing agents such as an organic peroxide, hydrogen peroxide, atmospheric oxygen or ferric chloride-oxygen, coupled with a reducing agent such as an aromatic hydrazine or sulfanilic acid were employed to depolymerize NR to yield LNR (Pautra and Marteau, 1974, 1976). In the early days, the liquid NR was prepared by redox system of phenylhydrazine/O2. The reactive functional end groups such as phenylhydrazone and carbonyl were obtained and molecular weights, Mn, were between 3,000 and 35,000 g/mol and the polydispersities were between 1.70 and 1.97 (Derouet et al., 1990; Brosse et al., 1981; Phinyocheep and Duangthong, 2000). However, phenylhydrazine is toxic and may cause cancers. Mauler et al. (1995) investigated the chain cleavage of styrene butadiene rubber (SBR) by using periodic acid (H5IO6) and/or ultrasonic radiation. They showed that the degradation of SBR by H5IO6 can induce degradation of SBR from Mw of 325,000 to 80,000 g/mol. Later, Mauler et al. (1997) studied the chain cleavage of natural rubber by using periodic acid (H5IO6) in various solvents (2/10 v/v) and reaction temperatures. They found that, at low temperature, the chain degradation using H5IO6 was better in chloroform than in toluene and n-hexane. Reyx and Campistron (1997) used H5IO6 to prepare LNR from epoxidised natural rubber (ENR). They found the decrease of epoxidised unit content from 25% in the starting rubber to 8% in the resulting degraded rubber. 1H-NMR spectrum revealed the presence of aldehyde and methylketone at the chain ends, residual oxiranes, secondary furanic and cyclic structures. Ritoit-Gillier et al. (2003) studied the chain degradation of polyisoprene (IR) and epoxidised polyisoprene (EIR) using H5IO6 in tetrahydrofuran (THF). Both final products contained aldehyde and ketone terminal ends. Tanaka et al. (1996) proposed the process for depolymerizing natural rubber by adding a carbonyl compound to NR latex or deproteinized natural rubber (DPNR) latex, and then subjecting the resulting NR or DPNR to air oxidation in the presence of a radical

8

forming agent. Tangpakdee et al. (1998) prepared LNR by oxidative degradation using 1 phr of potassium persulfate (K2S2O8, initiator) and 15 phr of propanal (encapsulator) at 60oC. Phetphaisit and Phinyocheep (2003) also used 1 phr of K2S2O8 together with 32 phr of propanal and the reaction mixture was stirred at 400 rpm at 60-80oC over 30 h. The mechanism was proposed as shown in Scheme 1. Moreover, the intensity of depolymerization and the extent of the chain scission reaction depend on temperature, reaction time and concentration of the degradation agent (Okieimen and Akinlabi, 2001; Isa et al., 2007). Okwu and Akinlabi (2007) studied the effect of Funtumia latex, which is low molecular weight NR from wild rubber in Africa, blended with NR latex and compared to the low molecular weight NR depolymerized by using nitrobenzene as a molecular weight depressant at various reaction time. They found that the use of 27.9 wt.% of Funtumia rubber in a Funtumia/NR blend reduced the molecular weight of NR from 7.02 x 105 to 3.12 x 105 g/mol. This was at the same level with the low molecular weight NR obtained from the reaction of NR with nitrobenzene (1–2 wt.% of the DRC of the latex) over a period of 10 h.

Scheme 1 The mechanism of oxidative degraded reaction of DPNR in the presence of K2S2O8 and propanal

Source: Tangpakdee et al. (1998) 7.2 Chemical modification of natural rubber

Natural rubber is an important and renewable material with unique and special characteristics used in a wide range of engineering applications, e.g. tires, rubber spring,

9

vibration mounts etc. NR is quite sensitive to heat and oxidation due to the presence of the reactive double bond on its chains. These inherent drawbacks of NR limit its use for several applications in industry. In efforts to extend its use, various methods have been developed to modify its properties through physical and chemical modifications. Chemically modified natural rubber would increase the areas of application and well expanding opportunities for novel polymers such as epoxidised natural rubber, chlorinated natural rubber, and hydrogenated natural rubber (Brosse et al., 2000). Thus, chemical modifications of NR have been carried out to overcome those inferior properties and create new polymers, in which the reaction can be carried out either in latex, solution or dry state. The chemical modifications of NR can be classified into 3 main categories, i.e. modifications by bond rearrangement, modifications by attachment of new chemical groups and modifications by grafting (Gelling and Porter, 1988).

Modifications by bond rearrangement involve carbon-carbon cross-linking, cyclization, cis-, trans-isomerization and depolymerization, the latter is as described in section 7.1. Cyclized NR can be formed by treating NR with conventional strong acids such as sulfuric acid, sulfonic acid and stannic chloride under heating condition. The reaction can be carried out by milling the acid into rubber on an ordinary mixing roller or by allowing acid to react with the rubber solution, or by adding sulfuric acid to NR latex. The reaction is carried out using a temperature range of 70-100oC. Cyclized NR is reported to be tough, hard and brittle but still has some elastic behaviour (Memmler, 1934; Kumar, 1998). Furthermore, hydrogenated natural rubber is more stable against thermal, oxidative, and radiation induced degradation because they are more saturated. Hydrogenation is a useful method for the reduction of unsaturation in diene polymers. It can be performed with elemental hydrogen in the presence of a transition metal catalyst (Hinchiranan et al., 2006; Tangthongkul et al., 2005) or by a noncatalytic method (Samran et al., 2005).

Modified rubbers having new chemical groups are such as chlorinated natural rubber (CNR) and epoxidised natural rubber (ENR). Zhong et al. (1999) prepared CNR using the method of adding chlorine gas to stabilized NR latex in a presence of suitable amount of catalyst. Epoxidized natural rubber (ENR) was first realized in the 1980s. Epoxidation reaction can be carried out in either solution or latex form, but only the latter is of commercial value. Peracid is usually used in the epoxidation of NR

10

in latex form because of its compatibility with the aqueous system (Burfield et al., 1984; Gelling, 1984, 1991). The mechanical properties of ENR such as tensile and fatigue behaviour, damping properties, bonding to metal and wet grip are expected to be better than those of NR (Gelling and Porter, 1988). The epoxidation performed by using performic acid generated in situ from the reaction of hydrogen peroxide and formic acid has been studied for both IR and NR lattices, with regard to nature and concentration of surfactant, reaction temperature and quantities of formic acid and hydrogen peroxide (Derouet et al., 2006). Klinklai et al. (2003) prepared liquid ENR by epoxidation using peracetic acid and subsequently depolymerization with (NH4)2S2O8 and propanal at 65oC over 12 h. The liquid ENR showed aldehyde, ketone and unsaturated carbonyl group at terminals of the rubber chain without a loss of epoxy group. Phinyocheep et al. (2005) and Akinlabi et al. (2005) prepared the epoxidised NR in latex phase using performic acid generated in situ by the reaction of hydrogen peroxide and formic acid before oxidative degradation of ENR by using periodic acid at 30oC for 24 h. Moreover, Phinyocheep and Duangthong (2000) studied the addition of acrylic acid onto liquid epoxidized natural rubber (LENR) molecules by reacting LENR with acrylic acid at 60 and 80oC in toluene for 5 h without adding any catalyst.

Modifications of NR by grafting reaction are commonly done by emulsion polymerization process. NR-g-PMMA can be prepared by using bipolar redox initiator system such as cumene hydroperoxide (CHP) and tetraethylene pentamine (TEPA) in NR latex. It was found that the increase of molar ratios of MMA to NR resulted in the increase of glass transition temperature (Tg) and decomposition temperature (Td). The quantities of grafted polymer on NR molecules are affected by various parameters such as monomer and initiator concentrations, reaction time and reaction temperature (Nakason et al., 2003; Nakason et al., 2006; Kalkornsurapranee et al., 2009). Oliveira et al. (2005) investigated the grafting efficiency of dimethylaminoethylmethacrylate (DMAEMA) grafted onto NR. The results from 1H-NMR spectroscopy showed no detectable grafting between NR and DMAEMA when 10 wt% of DMAEMA were used, but the amount of grafting increased to a significant amount when NR was grafted with 30 wt% of DMAEMA. Derouet et al. (1990) studied the modifications of NR with maleic anhydride. The obtained product was subsequently reacted with photo-reactive alcohols such as 2-hydroxyethyl acrylate (HEA) and 2-hydroxyethyl cinnamate (HEC) to give ultraviolet curable telechelic natural rubber (TLNR). Nakason et al. (2004) studied

11

the grafting of maleic anhydride (MA) onto NR in a toluene solution. It was found that quantities of the grafted MA on NR molecules increased with increasing monomer and initiator concentrations. An increase of reaction time and reaction temperature also caused the increasing level of grafted MA. 7.3 Rubber processability improvement

An application of processing aids or plasticizers in rubber compounds are driven by expectation to improve some original properties of rubbers and products such as to decrease the glass transition temperature of the polymer, to make the material more flexible, to increase elongation and decrease tensile strength, to improve its impact resistance and to control viscosity. Plasticizers are low viscosity liquids, which reduce viscosity of polymer and improve processability of complex industrial formulations. Addition of low molecular weight plasticizers improves processing properties but may induce some problems arising by their migration or volatilization. The reactive plasticizers which can chemically react with polymer will eliminate those afore mentioned problems.

LNR can be used as viscosity modifier, tackifier, and plasticizer to improve the processability of rubbers used in tire compounds (Hashim et al., 2002). The utilization of LMWNR blended with the high molecular weight natural rubber (HMWNR) in filled rubber compound will enhance processability and other properties due to LMWNR is able to penetrate between the chains of HMWNR. Okieimen and Akinlabi (2002) investigated the processing characteristics and physic-mechanical properties of NR modified with LNR of varying molecular weights. The decrease of Mw of LNR used in the blend of NR/LNR (70/30 wt/wt) resulted in better solubility in solvents, lower initial plasticity and Mooney viscosity, lower maximum torque and crosslink density, and lower modulus and tensile strength. Furthermore, the LNR was used as a plasticizer in nitrile rubber compared with dibutyl phthalate (DBP) (Nair et al., 1997; Mounir et al., 2004). Hydroxylated liquid natural rubber (HLNR) of different proportions was mixed with epoxy resin (Mathew et al., 2010). Furthermore, Dahlan (2000) and Dahlan et al. (2002) investigated the used of LNR as a compatibilizer in NR/LLDPE binary blends. The addition of low Mw (in a range of 9.25 x 104) LNR reduced the interfacial tension, therefore improved the interactions between the phases in the blends, while high Mw (in a range of 4.80 x 105) LNR showed some plasticizing effect to the blends. Epoxidised LNR (ELNR) had been used as plasticizer or processing aid during processing

12

of some polymers, such as NR/acrylonitrile butadiene rubber (NBR) blend (Wonkam et al., 2000) and PVC/ENR blend (Nair et al., 2007; Biju et al., 2007; Nair et al., 2009). In addition, ELNR could enhance the compatibility in the blend of liquid deproteinized natural rubber having epoxy group (LEDPNR) with poly(L-lactide) (PLLA) (Nghia et al., 2008). It was observed that an increase in mol percent epoxidation of the liquid rubber enhanced compatibility and the lower molecular weight epoxidized rubber yielded better property modifications than the higher molecular weight rubber. 7.4 Rubber-filler interaction improvement

A wide variety of particulate fillers are used in the rubber industry to improve the physical and mechanical properties of elastomeric materials. The addition of filler usually leads to an increase of modulus, whereas significant improvements in tensile and tear strength, and wear resistance will depend on type and amount of filler used. Filler morphology such as particle size and structure as well as specific surface activity has a large influence on the physical properties of the elastomeric material (Bokobza and Rapoport, 2001). The mechanism of rubber reinforcement involves an adsorption of the network chains onto the particle surfaces resulting from either physical interactions, e.g. Van der Waals forces between the filler surface and the polymer, or chemical interaction or both. These characteristics contribute to the reinforcement of the elastomers through interactions between elastomers and fillers (Wolff and Wang, 1994). Silica filler has become more important in tire applications since the introduction of the “Green Tire” by Michelin (Rouline, 1992). Silica has some greater reinforcing performance such as tear strength, heat resistance and adhesion properties compared to carbon black. However, due to the strong interparticle hydrogen bonds between hydroxyl groups, silica is generally in the form of agglomerates which will be broken down into aggregates during mixing or under certain level of dynamic deformation. Compared to reinforcing carbon black, silica retards the sulfur vulcanization reaction of the filled compounds, which is attributed to the adsorption of curatives on the silica surface and acidic nature of silica. Furthermore, the silanol content, adsorbed water content and surface area of the silica also affect the cure time (Wolff et al., 1993; Wagner, 1976). The addition of glycols, amines or guanidines such as diethylene glycol or triethanolamine in silica-filled compounds can reduce the Mooney viscosity and scorch time.

13

The strategies to improve silica- rubber interaction and reduce the rolling resistance are, for examples, a use of coupling agent, chemical modifications of rubbers by attaching functional groups which can interact with silica, and modification of silica surface. Silane coupling agent is used to chemically bind the polymer to silica, thus increasing the level of reinforcement. However, silane coupling agent voids some disadvantages such as high cost, toxicity, risk of precuring during the mixing stage and the generation of ethanol during mixing so that limit its widespread use (Wolff, 1996). The interaction between the silica surface and the polar groups of the elastomer should make it possible to omit a silane coupling agent out of compound formulations (Choi, 2001; Suzuki et al., 2005). The nitrile groups (-CN) of acrylonitrile butadiene rubber (NBR) are expected to form hydrogen bond with silica in the silica-filled NBR compound. In addition, it has been reported that the properties of silica-filled natural rubber (NR) compounds were improved by using chloroprene rubber (CR) (Choi, 2002). The increasing of bound rubber content of the compound and physical properties were attributed to the good dispersion of silica by adding CR. Dileep and Avirah (2003) prepared carboxy-terminated liquid natural rubber (CTNR) by a photochemical reaction and was then applied as a potential modifier in filled NR vulcanizates. It was found that CTNR could improve the tensile properties, ageing and oil resistance of NR vulcanizates due to the improvement of the rubber-filler interaction in NR vulcanizates. Furthermore, it could also act as a polymeric plasticizer in filled NR vulcanizates. Choi et al. (2003) improved filler dispersion of the silica-filled SBR compound by adding the liquid polybutadiene (PBD). The faster cure time and cure rate were observed when the 1,2-unit content of the liquid PBD was increased. In addition, crosslink density, modulus and tensile strength increased with increasing the 1,2-unit content.

Varkey et al. (1998) indicated that a small proportion of ENR could be used as an interface modifier for NR-silica systems and as a reinforcement modifier for silica-filled NBR. Incorporation of an optimum concentration of about 15% of ENR on total rubber in silica-filled NBR compound was found to improve bound rubber, mechanical and dynamic mechanical properties (George et al., 2002, 2006). As shown in Scheme 2, it was postulated that the ENR could react with the silanol group of the silica surface and the double bond of ENR underwent crosslinking by reacting with sulfur added in the compound during vulcanization (Manna et al., 1998, 1999, 2002; Cataldo, 2002; Xu

14

et al., 2007). ENR with up to 50 mole % epoxide had been used alone and in combination with other diene rubbers such as NR, SBR or BR at a level of ENR higher than 30 phr with precipitated silica and a mixture of silica with carbon black to improve wet skid resistance, however, poor tire tread abrasion and tear properties were observed (Nasir et al., 1989; Varughese and Tripathy, 1992). As shown in Figure 1, it was demonstrated that tire treads made from silica-filled ENR-25 had both lower rolling resistance and better wet grip when compared to the carbon black-filled NR or SBR tread compounds (Baker et al., 1985; Chapman, 2007).

Scheme 2 The mechanism of bonding between ENR and precipitated silica Source: Manna et al. (1999)

Figure 1 Relation between wet grip and rolling resistance of retreaded passenger car

tyres Source: Chapman (2007)

15

Furthermore, epoxidized rubber seed oils have been reported to enhance the adhesion properties of rubber with silica, as indicated by the better physical and mechanical properties (Joseph et al., 2004). The use of diamine salt of fatty acid in silica-filled NR and ENR could improve silica dispersion, mechanical properties and also crosslink density (Ismail and Chia, 1998). In addition, maleated natural rubbers (MNRs) can be used as a compatibilizer in silica-filled NR compounds. The MNR with 6 phr of maleic anhydride showed the lowest filler-filler interaction and optimum mechanical and dynamic mechanical properties due to succinic anhydride groups grafted onto natural rubber molecules of the MNRs could interact with hydroxyl groups on silica surface (Sahakaro and Beraheng, 2008).

8. Scope of the Research 8.1 Preparation and characterization of low molecular weight natural rubbers

with Mw in a range of 5,000 – 100,000 g/mol 8.2 Synthesis and characterization of functionalized liquid natural rubber, i.e.,

epoxidixed natural rubber (ELNR) and graft copolymer of liquid natural rubber with vinyl monomer possessing different degree of functional groups

8.3 Studies on influence of low molecular weight natural rubber and functionalized liquid natural rubber on processing and vulcanizate properties of unfilled compounds

8.4 Studies on influence of low molecular weight natural rubber and functionalized liquid natural rubber on processing properties and vulcanizate properties of carbon black and/or silica-filled compounds

8.5 Comparison of silica-filled compounds when compatibilized with commercial silane versus functionalized liquid natural rubber in term of various properties (i.e., mechanical, morphological, dynamic mechanical, rheological properties, filler-rubber and filler-filler interactions)

9. Research Methodology

9.1 Materials and Instruments 9.1.1 Materials

- Ribbed smoked sheet (RSS)#3 natural rubber

- High ammonia concentrated latex

16

- Potassium persulfate

- Propanal

- Sodium hydrogen phosphate

- Non-ionic surfactant Teric N-30

- Formic acid

- Hydrogen peroxide

- Methyl methacrylate

- Cumene hydroperoxide

- Tetraethylenepentamine

- Silica

- Bis-(3-triethoxysilylpropyl) tetrasulfide

- Zinc oxide

- Stearic acid

- Diphenyl guanidine

- N-cyclohexyl-2-benzothiazyl sulfenamide

- Sulfur

- Treated distillate aromatic extract (TDAE) oil

- Solvents, e.g., toluene methanol, acetone and chloroform 9.1.2 Instruments

- Internal mixer

- Two roll mills

- Compression molding machine

- Ubbelhode viscometer

- Gel permeation chromatograph (GPC)

- Fourier transform infrared spectrometer (FT-IR)

- Proton nuclear magnetic resonance spectrometer (1H NMR)

- Capillary rheometer

- Moving die processability tester (MDPT)

- Oscillating disk rheometer (ODR)

- Mooney viscometer

- Tensile testing machine

17

- Scanning electron microscope (SEM)

- Dynamic mechanical analyzer (DMA) 9.2 Experiment

Part I: Preparation and characterization of low molecular weight natural rubbers Low molecular weight natural rubber (LMWNR) or liquid natural rubber (LNR) will be prepared by oxidative degradation method in latex state (20%DRC of high ammonia-concentrated NR latex) using 1 phr of potassium persulfate (initiator) with 15 and 30 phr of propanal (encapsulator) (Tangpakdee et al., 1998). The rubber latex will be sampled at various reaction times and coagulated in acetone. After coagulation, the LNR will be reprecipitated from toluene using methanol, washed thoroughly with

water and dried in a vacuum at 40C. The obtained LNR are to be characterized by GPC and Ubbelhode viscometer for molecular weight and FT-IR for structure. Mooney viscosity and other physical properties (e.g. Po, PRI and color) will be also investigated. The conditions for oxidative degradation will be optimized to obtain LMWNRs with Mw in a range of 5,000-100,000 g/mol. Part II: Synthesis and characterization of functionalized liquid natural rubbers (FLNR) The LNR with assigned molecular weight will be modified by various conditions and reagents. Epoxidized LNR (ELNR) of 10–50 mol % epoxidation (ELNR-10, ELNR-20, ELNR-30, ELNR-40, and ELNR-50) will be prepared using performic acid generated in situ from hydrogen peroxide/formic acid (Gelling, 1984). During the epoxidation, latex samples will be taken at various times and isolated by coagulation in methanol. The coagulum formed will be washed several times with water, sheeted and finally dried under vacuum at 40 OC for approximately 3 days or to a completed dry. Molecular weight of ELNR will be again characterized after finishing the epoxidation reaction. The reaction time of epoxidation will be set according to the required level of epoxide groups in the ELNR products which will be characterized by FT-IR and 1H NMR techniques. Moreover, graft copolymer of LNR with vinyl monomers such as LNR-g-PMMA with different weight ratios of NR/MMA will be prepared by emulsion polymerization at 50 OC using cumene hydroperoxide (CHP) with tetraethylene pentamine (TEPA) (Kalkornsurapranee et al., 2009). The LNR-g-PMMA

18

with different mole percentages of PMMA in the copolymer will be synthesized and analyzed by FT-IR and 1H NMR techniques. Part III: Influence of LNR and FLNR on processing and vulcanizate properties of unfilled compounds Influence of low molecular weight natural rubber with varying Mw on the properties of unfilled NR compounds will be studied. LNR will be mixed with NR using internal mixer at various blend ratios using the formulations as shown in Table 1. The unfilled compounds will be tested for their Mooney viscosity, cure characteristics such as minimum and maximum torque, scorch time, cure time and cure rate index. Moreover, flow properties (by using capillary rheometer) and mechanical properties such as hardness, modulus, tensile strength and elongation at break will be investigated.

Table 1 Formulation of gum rubber compounds

Ingredients Amount (phr)

A B C D E

Natural rubber (RSS3) 100 95.0 90.0 85.0 80.0

LNR a - 5.0 10.0 15.0 20.0

ZnO 3.0 3.0 3.0 3.0 3.0

Stearic acid 1.0 1.0 1.0 1.0 1.0

TMQ 1.0 1.0 1.0 1.0 1.0

CBS 1.2 1.2 1.2 1.2 1.2

DPG 0.3 0.3 0.3 0.3 0.3

Sulfur 1.5 1.5 1.5 1.5 1.5

a LNR with varied molecular weight (Mw) will be used.

Part IV: Influence of LNR and FLNR on processing and vulcanizate properties of carbon black-filled compounds. The influence of low molecular weight natural rubber and functionalized liquid natural rubber such as ELNR and LNR-g-PMMA in carbon black filled compounds will be investigated in this part. The compound formulation is as shown in Table 2. Optimization of the mixing conditions such as compound dump temperatures and filler-rubber mixing step will be performed. Molecular weights, amounts and

19

functionalized degrees of LNR and modified LNR will be subjected to study for their influence on the carbon black filled compounds. Properties of the filled compounds under investigations are processing properties such as Mooney viscosity, shear viscosity and mixing energy; filler-rubber and filler-filler interactions such as bound rubber, Payne effect; and cure characteristics such as minimum and maximum torque, scorch time, cure time and cure rate index. Moreover, mechanical and dynamic properties such as hardness, modulus, tensile strength, elongation at break, tear strength,

abrasion resistance, storage modulus, loss modulus and tan will be investigated. Filler dispersion will be investigated by using Scanning Electron Microscope (SEM).

Table 2 Formulation of carbon black-filled compounds

Ingredients Amount (phr)

F G H I J

Natural rubber (RSS3) 100.0 95.0 90.0 85.0 80.0

LNR or FLNR a - 5.0 10.0 15.0 20.0

HAF black 55.0 55.0 55.0 55.0 55.0

TDAE oil 5.0 5.0 5.0 5.0 5.0

ZnO 3.0 3.0 3.0 3.0 3.0

Stearic acid 1.0 1.0 1.0 1.0 1.0

TMQ 1.0 1.0 1.0 1.0 1.0

6PPD 1.0 1.0 1.0 1.0 1.0

Wax 0.5 0.5 0.5 0.5 0.5

CBS 1.2 1.2 1.2 1.2 1.2

DPG 0.3 0.3 0.3 0.3 0.3

Sulfur 1.5 1.5 1.5 1.5 1.5

a LNR with varied molecular weights and FLNR with varied functionalized degrees will be used.

Part V: Influence of FLNR on processing and vulcanizate properties of silica-filled compounds in comparison with a use of commercial silane. The influence of functionalized liquid natural rubber in silica-filled compounds with and without silane coupling agents will be studied. Modified LNR with varying degrees of functional groups will be mixed with NR at various blend ratios using

20

the formulations as shown in Table 3. Optimization of mixing conditions will be studied. The rubber compounds and vulcanizates will be tested and characterized as the compounds obtained in Part IV.

Table 3 Formulation of silica-filled compounds.

Ingredients Amount (phr)

K L M N O

Natural rubber (RSS3) 100.0 95.0 90.0 85.0 80.0

FLNR a - 5.0 10.0 15.0 20.0

Silica (Ultrasil VN3/Zeosil 1165MP) 55.0 55.0 55.0 55.0 55.0

Silane (TESPT) b, c 4.7 or 0 4.7 or 0 4.7 or 0 4.7 or 0 4.7 or 0

TDAE oil 5.0 5.0 5.0 5.0 5.0

ZnO 3.0 3.0 3.0 3.0 3.0

Stearic acid 1.0 1.0 1.0 1.0 1.0

TMQ 1.0 1.0 1.0 1.0 1.0

6PPD 1.0 1.0 1.0 1.0 1.0

Wax 0.5 0.5 0.5 0.5 0.5

CBS 1.2 1.2 1.2 1.2 1.2

DPG c 1.1 1.1 1.1 1.1 1.1

Sulfur 1.5 1.5 1.5 1.5 1.5 a FLNR with varied molecular weights (Mw) and functionalized degrees will be used. b The properties of compounds with and without silane will be compared. c TESPT (phr) = 0.00053 x Q x CTAB DPG (phr) = 0.00012 x Q x CTAB Q is the silica content (phr) CTAB is specific surface area of silica (m2/g)

21

10. Research Schedule Project duration is 36 months starting from June 2010 to May 2013.

Activities Months

1-3 4-6 7-9 10-12 13-15 16-18 19-21 22-24 25-27 28-30 31-33 34-36

1. To prepare LMWNR with various levels of MW and analyze for their characteristic and properties

2. To modify LNRs (i.e. ELNR, LNR-g-PMMA) with various functional groups levels and analyze for their characteristic and properties

3. To study the effect of MW levels and amounts of LNR on properties of unfilled NR compounds

4. To optimize the mixing conditions for the compounds with various MW, amounts and functionalized degrees of LNR and modified LNR

5. To study the effect of unmodified LNR and modified LNRs on properties of carbon black- and silica-filled NR compounds

6. To compare the effect of modified LNRs versus conventional silane coupling agent on properties of silica-filled compound

7. Final report

22

11. Places - Department of Rubber Technology and Polymer Science, Faculty of Science and Technology, Prince of Songkla University, Pattani Campus, Thailand. - Wood Science and Engineering Research Unit, School of Engineering and Resources Management, Walailak University, Nakhon Si Thammarat, Thailand.

- Department of Elastomer Technology and Engineering, Faculty of Engineering Technology, University of Twente, the Netherlands.

12. References Akinlabi, A.K., Okieimen, F.E., Egharevba, F. and Malomo, D. 2006. Investigation of the

effect of mixing schemes on rheological and physico-mechanical properties of modified natural rubber blends. Materials and Design. 27, 783-788.

Amnuaypornsri, S., Tarachiwin, L. and Sakdapipanich, J.T. 2010. Character of long-chain branching in highly purified natural rubber. Journal of Applied Polymer Science. 115, 3645-3650.

Ansarifar, A., Nijihawan, R., Nanapoolsin, T. and Song, M. 2003. Reinforcing effect of silica and silane filler on the properties of some natural rubber vulcanizates. Rubber Chemistry and Technology. 76, 1290-1310.

Baker, C.S. L., Gelling, I.R. and Newell, R. 1985. Epoxidized natural rubber. Rubber Chemistry and Technology. 58, 67-85.

Biju, P.K., Nair, R.M.N., Thomas G.V. and Nair, G.M.R. 2007. Plasticizing effect of epoxidized natural rubber on PVC/ELNR blends prepared by solution blending. Materials Science. 25, 919-932.

Bokobza, L. and Rapoport, O. 2002. Reinforcement of natural rubber. Journal of Applied Polymer Science. 85, 2301-2316.

Brosse, J.C., Boccaccio, G. and Pautra, R. 1981. Proceedings of a Symposium ‘Powdered, Liquid and Thermoplastic Natural Rubber’, Phuket, Thailand, May 14-15, 1981, 195-205.

Brosse, J. C., Campistron, I., Derouet, D., El Hamdaoui, A., Houdayer, S., Reyx, D. and Ritoit-Gillier, S. 2000. Chemical modifications of polydiene elastomers: A survey and some recent results. Journal of Applied Polymer Science. 78, 1461-1477.

23

Burfield, D.R., Lim, K-L., Law, K-S. and Sanglaw, K. 1984. Epoxidation of natural rubber lattices: Methods of preparation and properties of modified rubber. Journal of Applied Polymer Science. 29, 1661-1673.

Burfield, D.R. 1987. The formation of trans-epoxides during the photochemical oxidation of cis-polyisoprene to liquid rubbers. Makromolekulare Chemie. 189, 523-527.

Cataldo, F. 1998. Thermal depolymerization and pyrolysis of cis-1,4-polyisoprene: preparation of liquid polyisoprene and terpene resin. Journal of Analytical and Applied Pyrolysis. 44, 121–130.

Cataldo, F. 2002. Preparation of silica-based rubber compounds without the use of a silane coupling agent through the use of epoxidized natural rubber. Macromolecular Materials and Engineering. 287, 348-352.

Chapman, A.V. 2007. Proceedings of 24th International H.F. Mark-Symposium ‘Advances in the Field of Elastomers & Thermoplastic Elastomers’, Vienna, Austria, November 15-16, 2007.

Choi, S.S. 2001. Improvement of properties of silica-filled styrene–butadiene rubber compounds using acrylonitrile–butadiene rubber. Journal of Applied Polymer Science. 79, 1127–1133.

Choi, S.S. 2002. Improvement of properties of silica-filled natural rubber using polychloroprene compound. Journal of Applied Polymer Science. 83, 2609-2616.

Choi, S.S., Chung, K.H. and Nah, C. 2003. Improvement of properties of silica-filled styrene-butadiene rubber (SBR) compounds using acrylonitrile-styrene-butadiene rubber (NSBR). Polymers for Advanced Technologies. 14, 557-564.

Choi, S.S., Park, B.H. and Nah, C. 2003. Effect of low molecular weight polybutadiene as processing aid on properties of silica-filled styrene-butadiene rubber compounds. Journal of Applied Polymer Science. 90, 3135-3140.

Cunneen, J.I. 1973. Research and the improvement of tire performance. NR Technology. 4, 65- 75.

Dahlan, H.M., Khairul Zaman, M.D. and Ibrahim, A. 2000. Liquid natural rubber (LNR) as a compatibilizer in NR/LLDPE blends. Journal of Applied Polymer Science. 78, 1776–1782.

24

Dahlan, H.M., Khairul Zaman, M.D. and Ibrahim, A. 2002. The morphology and thermal properties of liquid natural rubber (LNR)-compatibilized 60/40 NR/LLDPE blends. Polymer Testing. 21, 905–911.

Derouet, D., Brosse, J.C. and Tillekeratne, L.M.K. 1990. Fixation of methacrylic acid onto epoxidised liquid natural rubber. Journal of Natural Rubber Research. 5, 296-300.

Derouet, D., Houdayer, S. M. and Brosse, J.C. 2006. Comparative study of the epoxidation of natural and synthetic rubber latices. Journal of Rubber Research. 9, 1–20.

Dileep, U. and Avirah, S.A. 2003. Studies on carboxy-terminated natural rubber in filled NR and NR latex vulcanizates. Iranian Polymer Journal. 12, 441-448.

Ehabe, E.E., Nkeng, G.E., Collet A. and Bonfils, F. 2009. Relations between high-temperature mastication and Mooney viscosity relaxation in natural rubber. Journal of Applied Polymer Science. 113, 2785–2790.

Eng, A.H. and Ong, E.L. Hevea natural rubber. In Handbook of Elastomers, 2nd ed., A.K. Bhowmick and H.L. Stephens, editors. Marcel Dekker, New York, p.36.

Fröhlich, J., Niedermeier, W. and Luginsland, H.D. 2005. The effect of filler-filler and filler-elastomer interaction on rubber reinforcement. Composites Part A. 36, 449-460.

Gelling, I.R. 1984. Modification of natural rubber latex with peracetic acid. Rubber Chemistry and Technology. 18, 86-96.

Gelling I.R. 1991. Epoxidised natural rubber. Journal of Natural Rubber Research. 6, 184-205.

Gelling, I.R. and Porter, M. 1988. Chemical modification of natural rubber. In Natural Rubber Science and Technology, A.D. Roberts, editor. Oxford University Press, Oxford, pp. 359-362.

George, K.M., Varkey, J.K., Thomas, K.T. and Mathew, N.M. 2002. Epoxidized natural rubber as a reinforcement modifier for silica-filled nitrile rubber. Journal of Applied Polymer Science. 85, 292-306.

George, K.M., Varkey, J.K., George B., Joseph, S., Thomas, K.T. and Mathew, N.M. 2006. Physical and dynamic mechanical properties of silica filled nitrile rubber modified with epoxidised natural rubber. Kautschuk Gummi Kunststoffe. 10, 544-549.

25

Hashim, A.S., Ong, S.K. and Jessy, R.S. 2002. A general review of recent developments on chemical modification of NR. Rubber Stiching. 28, 3-9.

Heinrich, G., Klüppel, M. and Vilgis, T.A. 2002. Reinforcement of elastomers. Current Opinion in Solid State and Material Science. 6, 195-203.

Hinchiranan, N., Charmondusit, K., Prasassarakich, P. and Rempel, G.L. 2006. Hydrogenation of synthetic cis-1,4-polyisoprene and natural rubber catalyzed by [Ir(COD)py(PCy3)]PF6. Journal of Applied Polymer Science. 100, 4219-4233.

Hourston, D.J. and Romaine, J. 1990. Modification of natural rubber latex. II. Natural rubber poly(methyl methacrylate) composition latexes synthesized using an amine activated hydroperoxide. Journal of Applied Polymer Science. 39, 1587-1594.

Ibrahim, A. and Dahlan M. 1998. Thermoplastic natural rubber blends. Progress in Polymer Science. 23, 665-706.

Isa, S.Z., Yahya, R., Hassan, A. and Tahir, M. 2007. The influence of temperature and reaction time in the degradation of natural rubber latex. Malaysian J. Anal. Sci. 11: 42-47.

Ismail, H. and Chia, H.H. 1998. The effects of multifunctional additive and epoxidation in silica filled natural rubber compounds. Polymer Testing. 17, 199-210.

Jesionowski, T. and Krysztafkiewicz, A. 2001. Influence of silane coupling agents on surface properties of precipitated silicas. Applied Surface Science. 172, 18-32.

Joseph, R., Alex, R., Madhusoodanan, K.N., Premalatha, C.K. and Kuriakose, B. 2004. Use of epoxidized rubber seed oil as a coupling agent and a plasticizer in silica-filled natural rubber compounds. Journal of Applied Polymer Science. 92, 3531–3536.

Kalkornsurapranee, E., Sahakaro, K., Kaesaman, A. and Nakason., C. 2009. From a laboratory to a pilot scale production of natural rubber grafted with PMMA. Journal of Applied Polymer Science. 114, 587-594.

Klinklai, W., Kawahara, S., Mizumo, T., , Yoshizawa, M., Sakdapipanich, J.T., Isono, Y. and Ohno, H. 2003. Depolymerization and ionic conductivity of enzymatically deproteinized natural rubber having epoxy group. European Polymer Journal. 39, 1707-1712.

Kumar, A., Gupta, A. and Rakesh K. 1998. Fundamental of Polymers, McGraw-Hill Book Corporation, Singapore.

26

Luginsland, H.D., Frohlich, J. and Wehmeier, A. 2002. Influence of different silanes on the reinforcement of silica-filled rubber compounds. Rubber Chemistry and Technology. 75, 563-579.

Manna, A.K., Bhattacharyya, A.K., De, P.P., Tripathy, D.K., De, S.K. and Peiffer, D.G. 1998. Effect of silane coupling agent on the chemorheological behaviour of epoxidised natural rubber filled with precipitated silica. Polymer. 39, 7113–7117.

Manna, A.K., De, P.P., Tripathy, D.K., De, S.K. and Peiffer, D.G. 1999. Bonding between precipitated silica and epoxidized natural rubber in the presence of silane coupling agent. Journal of Applied Polymer Science. 74, 389-398.

Manna, A.K., De, P.P. and Tripathy, D.K. 2002. Dynamic mechanical properties and hysteresis loss of epoxidized natural rubber chemically bonded to the silica surface. Journal of Applied Polymer Science. 84, 2171-2177.

Mathew, V.S., Sinturel, C., George, S.C. and Thomas, S. 2010. Epoxy resin/liquid natural rubber system: secondary phase separation and its impact on mechanical properties. Journal of Materials Science. 45, 1769–1781.

Mauler, R.S., Martins, F.G. and Samios, D. 1995. Investigation on the styrene-butadiene rubber cleavage with periodic acid under the influence of ultrasonic radiation. Polymer Bulletin. 35, 151-156.

Mauler, R.S., Guaragna, F.M., Gobbi, D.L. and Samios, D. 1997. Sonochemical degradation of 1,4- cis-polyisoprene using periodic acid-solvent and temperature effect. European Polymer Journal. 33, 399-402.

Montaudo, G., Scamporrino, E., Vitalini, D. and Rapisardi, R. 1992. Fast atom bombardment mass spectrometric analysis of the partial ozonolysis products of poly(isoprene) and poly(chloroprene). Journal of Polymer Science Part A: Polymer Chemistry. 30, 525-532.

Morton, M. 1987. Rubber Technology, 3rd Ed., New York: Van Nostrand Reinhold Company.

Mounir, A., Darwish, N.A. and Shehata, A. 2004. Effect of maleic anhydride and liquid natural rubber as compatibilizers on the mechanical properties and impact resistance of the NR-NBR blend. Polymers for Advanced Technologies. 15, 209–213.

27

Nakason, C., Kaesaman, A. and Yimwan, N. 2003. Preparation of graft copolymers from deproteinized and high ammonia concentrated natural rubber latices with methyl methacrylate. Journal of Applied Polymer Science. 87, 68-75.

Nakason, C., Kaesaman, A. and Ajinsamajarn, A. 2004. The grafting of maleic anhydride onto natural rubber. Polymer Testing. 23, 35-41.

Nakason, C., Pechurai, W., Sahakaro, K. and Kaesaman, A. 2006. Rheological, thermal, and curing properties of natural rubber-g-poly(methyl methacrylate). Journal of Applied Polymer Science. 99, 1600–1614.

Nair, M.N.R., Thomas, S. and Mathew, N.M. 1997. Liquid natural rubber as a viscosity modifier in nitrile rubber processing. Polymer International. 42, 289-300.

Nair, M.N.R., Thomas, G.V. and Nair, M.R.G. 2007. Miscibility studies of PVC / ELNR blends. Polymer Bulletin. 59, 413–426.

Nair, M.N.R., Biju, P.K., Thomas G.V. and Nair, G.M.R. 2009. Blends of PVC and epoxidized liquid natural rubber: Studies on impact modification. Journal of Applied Polymer Science. 111, 48–56.

Nasir, M., Poh, B.T. and Ng, P.S. 1989. The effect of γ-mercaptopropyltrimethoxysilane coupling agent on t90, tensile strength and tear strength of silica-filled ENR vulcanisates. European Polymer Journal. 25, 267-273.

Nghia, P.T., Siripitakchai, N., Klinklai, W., Saito, T., Yamamoto, Y. and Kawahara, S. 2008. Compatibility of liquid deproteinized natural rubber having epoxy group (LEDPNR)/Poly (L-lactide) blend. Journal of Applied Polymer Science. 108, 393–399

Nor, H.M. and Ebdon, J.R. 1998. Telechelic liquid natural rubber: A review. Progress in Polymer Science. 23, 143-177.

Okieimen, F.E. and Akinlabi, A.K. 2002. Processing characteristics and physicomechanical properties of natural rubber and liquid natural rubber blends. Journal of Applied Polymer Science. 85, 1070–1076.

Okwu, U.N. and Akinlabi, A.K. 2007. Production of low-molecular-weight natural rubber: comparative assessment of a nonchemical route. Journal of Applied Polymer Science. 106, 1291-1293.

28

Oliveira, P.C., Oliveira, A.M., Garcia, A., Souza Barboza, J.C., Carvalho Zavaglia, C.A. and Santos, A.M. 2005. Modification of natural rubber: A study by 1H NMR to assess the degree of graftization of polyDMAEMA or polyMMA onto rubber particles under latex form in the presence of a redox couple initiator. European Polymer Journal. 41, 1883–1892.

Pautra, R. and Marteau, J. 1974. Procédé de Préparation de Caoutchouc de Faibie Masse Moléculaire par Degradation de Polyènes Macromoléculaires, et Produits Obtenus. F.R. Pat 7403052, January 1974.

Pautra, R. and Marteau, J. 1976. Method for the Preparation of Rubbers with Low Molecular Weights though Degradation of Macromolecular Polymers and the Products thus Obtained. U.S. Pat 3957737, May 1976.

Phetphaisit C.W. and Phinyocheep, P. 2003. Kinetics and parameters affecting degradation of purified natural rubber. Journal of Applied Polymer Science. 90, 3546–3555.

Phinyocheep, P. and Duangthong, S. 2000. Ultraviolet-curable liquid natural rubber. Journal of Applied Polymer Science. 78, 1478-1485.

Phinyocheep, P., Phetphaisit, C.W., Derouet, D., Campistron, I. and Brosse, J.C. 2005. Chemical degradation of epoxidized natural rubber using periodic acid: Preparation of epoxidized liquid natural rubber. Journal of Applied Polymer Science. 95, 6-15.

Ravindran, T., Nayar, M.R.G. and Francis, J.D., 1986. A novel method for the preparation of hydroxyl terminated liquid natural rubber. Makromolekulare Chemie Rapid Communications. 7, 159-163.

Ravindran, T., Nayar, M.R.G. and Francis, D.J. 1988. Production of hydroxyl-terminated liquid natural rubber - mechanism of photochemical depolymerization and hydroxylation. Journal of Applied Polymer Science. 35, 1227-1239.

Rauline R. 1992. Rubber Compound and Tires based on Such a Compound. E.P. Pat 0501227A1, February 1992.

Regulation (EC) No 1222/2009 of 25 November 2009 on the labelling of tyres with respect to fuel efficiency and other essential parameters. Official Journal of the European Union, L342/46-58.

Reuvekamp, L.A.E.M., Swaaij,P.J.V. and Noordermeer J.W.M. 2009. Silica reinforced tire tread compounds. Kautschuk Gummi Kunststoffe. 62, 35-43.

29

Reyx, D. and Campistron, I. 1997. Controlled degradation in tailor-made macromolecules elaboration. Controlled chain cleavages of polydienes by oxidation and by metathesis. Angewandte Makromolekulare Chemie. 247, 197- 211

Ritoit-Gillier, S., Reyx, D., Campistron, I., Laguerre, A. and Singh, R.P. 2003. Telechelic cis-1,4-oligoisoprenes through the selective oxidolysis of epoxidized monomer units and polyisoprenic monomer units in cis-1,4-polyisoprenes. Journal of Applied Polymer Science. 87, 42-46.

Sahakaro, K. and Beraheng, S. 2008. Reinforcement of maleated natural rubber by precipitated silica. Journal of Applied Polymer Science. 109, 3839-3848.

Samran, J., Phinyocheep, P., Daniel, P. and Kittipoom, S. 2005. Hydrogenation of unsaturated rubbers using diimide as a reducing agent. Journal of Applied Polymer Science. 95, 16-27.

Solanky, S.S., Campistron, I., Laguerre, A. and Pilard, J.F., 2005. Metathetic selective degradation of polyisoprene: Low-molecular-weight telechelic oligomer obtained from both synthetic and natural rubber. Macromolecular Chemistry and Physics. 206, 1057-1063.

Subramanium, A. 1980. Molecular weight and molecular weight distribuion of natural rubber. RRIM Technology Bulletin. 4, 16.

Suzuki, N., Ito, M., Ono, S. 2005. Effects of rubber/filler interactions on the structural development and mechanical properties of NBR/silica composites. Journal of Applied Polymer Science. 95, 74–81.

Tanaka, Y., Aik-Hwee, E., Ohya, N., Nishiyama, N., Tangpakdee, J., Kawahara, S. and Wititsuwannakul, R. 1996. Initiation of rubber biosynthesis in Hevea brasiliensis: characterization of initiating species by structural analysis. Phytochemistry. 41, 1501-1505.

Tanaka, Y. 2001. Structural characterization of natural polyisoprenes: Solve the mystery of natural rubber based on structural study. Rubber Chemistry and Technology. 74, 355-375.

Tangpakdee, J., Mizokoshi, M., Endo, A. and Tanaka, Y., 1998. Novel method for preparation of low molecular weight natural rubber latex. Rubber Chemistry and Technology. 71, 795-802.

30

Tangthongkul, R., Prasassarakich, P. and Rempel, G.L. 2005. Hydrogenation of natural rubber with Ru[CHCH(Ph)]Cl(CO)(PCy3)2 as a catalyst. Journal of Applied Polymer Science. 97, 2399-2406.

Varkey, J.K., Joseph, S. and George, K.M. 1998. Indian Patent Application No. 1109, MAS/99-98/RQ/CHE/04.

Varughese, S. and Tripathy, D.K. 1992. Chemical interaction between epoxidized natural rubber and silica: Studies on cure characteristics and low-temperature dynamic mechanical properties. Journal of Applied Polymer Science. 44, 1847–1852.

Wagner, M.P. 1976. Reinforcing silica and silicates. Rubber Chemistry and Technology. 49, 740-774.

Wolff, S. 1996. Chemical aspects of rubber reinforcement by fillers. Rubber Chemistry and Technology. 69, 325-376.

Wolff, S., Wang, M.J. and Tan, E.H. 1993. Filler-elastomer interactions. Part VII. Study on bound rubber. Rubber Chemistry and Technology. 66, 163-177.

Wonkam, D., Ehabe, E., Ngolemasango, F., Nkouonkam, B. and Livonnie`re, H., 2000. Effect of epoxidised liquid natural rubber on nitrile/butadiene rubber based mixes. Plastics Rubber and Composites. 29, 420-426.

Xu, H., Liu, J., Fang, L. and Wu, C. 2007. In situ grafting onto silica surface with epoxidized natural rubber via solid state method. Journal of Macromolecular Science – Physics. 46, 693–703.

Zhang, J., Zhou Q., Jiang, X.H., Du, A.K. Zhao, T., Kasteren, J. and Wang, Y.Z. 2010. Oxidation of natural rubber using a sodium tungstate/acetic acid/hydrogen peroxide catalytic system. Polymer Degradation and Stability. 95, 1077-1082.

Zhong, J.P., Li, S.D., Wei Y.C., Peng, Z. and Yu, H.P. 1999. Study on preparation of chlorinated natural rubber from latex and its thermal stability. Journal of Applied Polymer Science. 73, 2863-2867.

31

Prachid Saramolee (Mr.Prachid Saramolee) Student Date 15/08/2011

Kannika Sahakaro (Asst. Prof. Dr. Kannika Sahakaro) Advisor Date 15/08/2011

Natinee Lopattananon (Asst. Prof. Dr. Natinee Lopattananon) Co-Advisor Date 15/08/2011

Jacques W.M. Noordermeer (Prof. Dr.J.W.M. Noordermeer) Co-Advisor Date 15/08/2011