FIELD OF INVENTION

The present invention relates to a liquid epoxidized natural rubber and a method of preparing the same.

BACKGROUND ART

Liquid epoxidized natural rubber (LENR) is a modified natural rubber with shorter polymeric chain of epoxidized natural rubber (ENR) prepared from natural rubber latex of Hevea brasiliensis. The structures of ENR and LENR, respectively, are shown below. X2 and Y2 (ENR) represents the repeating units for epoxy (C-O-C) units and isoprene (C=C) units before degradation, respectively, and X1 and Y1 (LENR) represent the repeating units obtained after degradation, which has shorter chains.

(a) ENR (b) LENR

LENR consists some amount of epoxy group (C-O-C) as well as several other functional groups attached to the polyisoprene backbone. LENR can be prepared by chemical degradation/depolymerization of ENR or natural rubber (NR) in the latex stage in the presence of redox degrading agents, or via thermal or photochemical methods such as photo-oxidation with ultraviolet (UV) or radiation. The degradation also can be carried out not only in latex stage but also in solvent and solid stage. In addition, different degrading agents, for example, periodic acid, redox reagents, propanal, neodymium stearate leads to the formation of different functional end groups - hydroxyl or carbonyl or both as well as epoxy derivatives after degradation. Epoxy derivatives are functional groups formed from epoxy side reactions after or during the degradation. The formation of these functional groups is highly dependent on the reaction pathway as well as the degrading agent or chemical used. In this work, LENR is prepared by chemical degradation of ENR in latex stage in the presence of redox degrading agent. The molecular weight, gel content, and the viscosity of LENR decreases upon the degradation of ENR. The characteristics of the resulting LENR, as compared to ENR, is softer, stickier, and possesses a better flow at elevated temperature. The shorter the length of the polymer chain, the lower the molecular weight, hence, the softer and stickier the LENR produced. It is worth to note that the liquid ENR is totally distinguished from latex ENR, where the which shows the different between liquid ENR and latex ENR. The latter is milky and white in colour and consist approximately 70% water content. The attributes of LENR allows for its applications in impact modifiers, sealants, processing aids, toughening agents, and precursors for polyurethane-based products.

The starting material of LENR, ENR is also a chemically modified natural rubber. ENR was synthesized using in-situ hydrogen peroxide and formic acid at a controlled temperature. The reaction converted the double bonds of natural rubber to epoxy groups randomly along the backbone of natural rubber. The presence of epoxy group significantly improved NR’s properties such as oil resistance, good compatibility with polar polymers and low air permeability.

Rooshenass et al., (2018) in the Journal of Polymers and the Environment (2018) discloses the preparation of LENR by oxidative degradations using periodic acid, potassium permanganate, and UV radiation. Rooshenass et al., (2016) in the Rubber Chemistry and Technology discloses different methods of preparing LENR; mechanical milling, chemical degradation initiated by potassium peroxodisulfate, and photooxidation initiated by ultraviolet (UV) radiation. These studies involve the usage of solvents in the degradation process and epoxidized natural rubber, ENR, with 25 mole% epoxidation as the starting material. The usage of solvents during the processing step is not only harmful due to the release of toxic fumes, thus creating a health hazard, but also produces an end product that is not environmentally friendly. The stability of the liquid epoxidized natural rubber, LENR, is crucial for the subsequent stages of processing and eventually use in other rubber-based products. Therefore, there is a need for liquid epoxidized natural rubber, LENR, produced without the usage of harmful solvents, and also stable for further processing to produce other rubberbased products.

Patent international application number PCT/GB2008/050272 relates to a method of treatment of epoxidized natural rubber latex only. The method comprises steps of (a) adding a salt of divalent metal to the epoxidized natural rubber latex; (b) heating the latex to coagulate the rubber; and (3) recovering the coagulated rubber.

SUMMARY OF INVENTION

Accordingly, the present invention relates to a method of producing liquid epoxidized natural rubber. The method comprises the following steps of: (a) diluting an epoxidized natural rubber latex with an anionic surfactant at a concentration in a range of 0 wt% to 3 wt% to form a latex mixture with a total solid content in a range of 25 wt% to 40 wt%; (b) incubating the latex mixture from step (a) in a capacity reactor in a range of 400 L to 500 L at room temperature for a duration in a range of 24 hours to 48 hours; (c) stirring the latex mixture from step (b) and heating the latex mixture to a temperature in a range of 50°C to 55°C; (d) degrading the latex mixture from step (c) with hydrogen peroxide and sodium nitrite, wherein the hydrogen peroxide and the sodium nitrite are at a concentration in a range of 2 phr to 28 phr and in a 1 : 1 ratio; (e) pursing the reaction from step (d) for a time period of 6 to 24 hours at temperature in a range of 60°C to 70°C; (f) cooling the latex mixture from step (e) to room temperature for at least 12 hours; (g) coagulating the latex mixture from step (f) with a coagulant for at least 12 hours to form a coagulated wet liquid epoxidized natural rubber, the coagulant comprising a salt solution in a concentration in a range of 1 wt% to 20 wt% spiked with an alcohol in a concentration in a range of 5 wt% to 20 wt%; (h) rinsing the coagulated wet liquid epoxidized natural rubber from step (g) with water; (i) drying the coagulated wet liquid epoxidized natural rubber from step (h) at a temperature in a range of 60°C to 150°C using a dryer for a duration of 3 hours to 2 weeks to produce liquid epoxidized natural rubber wherein the epoxidized natural rubber latex in step (a) has an epoxidation level in a range of 47 mol% to 53 mol% at a pH in a range of pH 5 to pH 12; further wherein the epoxidized natural rubber latex is stored for a period of 0 day to 150 days at room temperature prior to use in step (a).

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows (a) 400 litre reactor to produce LENR and (b) the reaction in latex stage.

Figure 2 shows parts of the kneader which consist of (a) drying reservoir with twin-Z blade; (b) oil bath for thermal system; (c) control panels of the twin-Z blade; (d) the outlet pipe; (e) the LENR in the drying reservoir; (f) dried LENR; and (g) pipping our of LENR after drying.

Figure 3 shows the effect of soaking period on M _n and M _w crf LENR.

Figure 4 shows the effect of soaking period on the EL and ED

Figure 5 shows the effect of drying temperature on M _n and M _w of LENR

Figure 6 shows the M _n of ENR 50 and LENR 50 for study on relationship between properties and physical character (stickiness) of LENR

Figure 7 shows the EL, mol% of ENR 50 and LENR 50 for study on relationship between properties and physical character (stickiness) of LENR

Figure 8 shows the T _g for ENR 50 and LENR 50 for study on relationship between properties and physical character (stickiness) of LENR

Figure 9 shows the effect of incubation time of ENR 50 latex on the molecular weight of LENR 50.

Figure 10 shows the schematic reaction between sodium nitrite (SN) and hydrogen peroxide (HP) to produce LENR 50 at pH 8.

Figure 11 shows the effect of chemical concentrations on the molecular weight of LENR 50. Figure 12 shows the effect of chemical concentrations on gel content of LENR 50.

Figure 13 shows the FTIR spectrum for ENR 50 and LENR 50.

Figure 14 shows the ¹ H spectrum of ENR50 rubber from factory Figure 15 shows the ¹ H spectrum of ENR50 latex Figure 16 shows the ¹ H spectrum of LENR50

Figure 17 shows the expanded ¹ H-NMR spectra of ENR 50 and LENR 50 from 9 to 10 ppm

Figure 18 shows side reaction in the region 3.00 to 5.00 ppm.

Figure 19 shows the FESEM images for (a) ENR 50 and (b) LENR 50 at 10000x magnification.

Figure 20 shows the particle size distribution of ENR 50 and LENR 50 latexes

Figure 21 shows the DSC thermograms for the ENR 50 and LENR 50.

Figure 22 (a) and (b) shows the TG and DTG curves of ENR 50 and LENR 50.

Figure 23 shows the contact angle analysis of ENR 50 and LENR 50.

Figure 24 shows the relationship of number average molecular weight, M _n , and viscosity for five batches of LENR 50

Figure 25 shows the number average of molecular weight M _n of LENR 50 prepared by 400L reactor upon storage.

Figure 26 shows the weight average of molecular weight M _w of LENR 50 prepared by 400L reactor upon storage.

Figure 27 shows the gel content for LEN 50 prepared by 400L reactor upon storage,

Figure 28 shows the ratio of selected peak to absorbance of internal standard during long storage of 400 days.

Figure 29 shows the epoxidation level and epoxidation derivatives of LENR 50 prepared by 400L reactor upon storage

Figure 30 shows the epoxidation level and the ring opening level for 10 batches of LENR 50.

Figure 31 shows the percentage of gel content for 10 batches of LENR 50.

Figure 32 shows the molecular weight for 10 batches of LENR 50.

Figure 33 shows the maximum degradation temperature for 10 batches of LENR 50

Figure 34 shows the molecular weight for 10 batches of LENR 50 (20phr)

Figure 35 shows the molecular weight and polydispersity of liquid rubbers at the different reagent level (5 - 25 phr)

Figure 36 shows the gel content of liquid rubbers at different reagent level (5 to 25 phr).

Figure 37 shows the viscosity of liquid rubbers at different reagent level (5 to 25 phr).

Figure 38 shows the effect of epoxidation level and polar groups on the decomposition temperature of liquid rubbers at different reagent level (5 to 25 phr)

Figure 39 shows the percentage of epoxy, ROi (furan), and RO2 (diol) for liquid natural rubber (LNR).

Figure 40 shows the spectrum of ¹ H NMR of LNR.

Figure 41 shows the percentage of epoxy, O1 (furan), and RO2 (diol) for LENR 25.

Figure 42 shows the spectrum of ¹ H NMR of LENR 25

Figure 43 shows the relationship between epoxidation level and chemical concentration. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to a liquid epoxidized natural rubber and a method of producing the liquid epoxidized natural rubber. The method comprises the following steps of: (a) diluting an epoxidized natural rubber latex with an anionic surfactant at a concentration in a range of 0 wt% to 3 wt% to form a latex mixture with a total solid content in a range of 25 wt% to 40 wt%; (b) incubating the latex mixture from step (a) in a capacity reactor in a range of 400 L to 500 L at room temperature for a duration in a range of 24 hours to 48 hours; (c) stirring the latex mixture from step (b) and heating the latex mixture to a temperature in a range of 50°C to 55°C; (d) degrading the latex mixture from step (c) with hydrogen peroxide and sodium nitrite, wherein the hydrogen peroxide and the sodium nitrite are at a concentration in a range of 2 phr to 28 phr and in a 1 : 1 ratio; (e) pursing the reaction from step (d) for a time period of 6 to 24 hours at temperature in a range of 60°C to 70°C; (f) cooling the latex mixture from step (e) to room temperature for at least 12 hours; (g) coagulating the latex mixture from step (f) with a coagulant for at least 12 hours to form a coagulated wet liquid epoxidized natural rubber, the coagulant comprising a salt solution in a concentration in a range of 1 wt% to 20 wt% spiked with an alcohol in a concentration in a range of 5 wt% to 20 wt%,; (h) rinsing the coagulated wet liquid epoxidized natural rubber from step (g) with water; (i) drying the coagulated wet liquid epoxidized natural rubber from step (h) at a temperature in a range of 60°C to 150°C for a duration of 3 hours to 2 weeks to produce liquid epoxidized natural rubber wherein the epoxidized natural rubber latex in step (a) has an epoxidation level in a range of 47 mol% to 53 mol% at a pH in a range of pH 5 to pH 12; further wherein the epoxidized natural rubber latex is stored for a period of 0 day to 150 days at room temperature prior to use in step (a).

1 . Production of Liquid Epoxidized Natural Rubber, LENR a. About 400 litre reactor - to produce LENR

The reactor is a jacketed mixing tank with capacity of 400 litre. The reactor was equipped with stirrer, hot and water circulation system, temperature control system and outlet pipe at the bottom of the reactor. In this case, the water is used to control the temperature of reaction. Figure 1 (a) shows 400 litre reactor to produce LENR - 250 kg per batch and Figure 1(b) the process in latex stage. b. Twin-Z blade kneader for drying LENR

A Twin-Z blade kneader is used for uniform mixing of semi solid materials. The tangential action of mixing and kneading is thoroughly obtained by two 'Z' shaped kneading blades, which rotates very accurately at different speed towards each other causing the product to be transferred from one blade to the other. The mixing action is a combination of bulk movement, stretching, folding, dividing, and recombining of the material. The shearing and tearing action of the material against blades and the side walls causes size reduction of the solids. With this concept of operational method, it was chosen to be a suitable machine to dry LENR. The physical character of LENR is goldish colour, sticky and soft. c. Specifications of Twin-Z blade kneader The kneader has 3 main parts which consist of drying reservoir with twin-Z blade (Figure 2a); an oil bath for thermal system (Figure 2b); control panels of the twin-Z blade (Figure 2c); the outlet pipe (Figure 2d); the LENR in the drying reservoir (Figure 2e); dried LENR (Figure 2f) ; and pipping our of LENR (Figure 2g) after drying. The images of the twin-Z blade kneader are shown in Figure 2. The duration of drying was optimally 4 to 5 hours at the operating temperature of 90 - 95°C. With the usage of the machine, about 60-70 kg per batch of LENR can be dried at a time. The specifications of kneader for drying LENR are shown in Table 1.

Table 1: Specifications of Twin-Z blade kneader for drying LENR d. Effect of soaking period on the molecular weight of LENR

Figure 3 shows the effect of soaking period on M _n and M _w of LENR. Soaking is a stage where the period of wet coagulated LENR was soaked with water after rinsing process, waiting for drying process to take place. The purpose of study is to investigate whether the soaking period influence the properties of LENR after drying.

Study on the effect of soaking period was carried out for four batches of LENR production, with soaking period from Day 1 to Day 30 (about 1 month). The M _n and M _w showed no significant changes as the soaking period increased. This implies that storage of LENR in wet condition (soaking in water) for about 1 month is not giving any changes to the molecular weight.

Table 2 shows effect of soaking period on gel content of LENR. The gel content was less than 1 wt%, in which the gel content was not affected by soaking period of LENR. e. Effect of drying temperature on the molecular weight of LENR

Figure 5 shows the effect of drying temperature on M _n and M _w of LENR. Study on the effect of drying temperature was carried out for four batches of LENR production, with drying temperature ranged from 60°C to 150°C. The M _n decreased slightly as the drying temperature increased, whilst, the M _w increased as the drying temperature increased. This implies that high drying temperature may lead to the occurrence of side reactions or crosslinks.

Table 3: Effect of drying temperature on M„//Vf _n , gel content, epoxidaton level (EL) and epoxidation derivatives (ED)

Temperatur Gel content Epoxidation Epoxy e(°C) M _v /M _n (w/w%) level (mol%) Derivatives

60 3.293 0.039 45.0 9.35 70 2.963 0.046 46.3 7.96

80 2.693 0.036 44.7 10.44

90 2.728 0.038 42.4 12.04

100 2.701 0.016 42.2 13.24

120 2.774 0.015 43.2 12.32

150 2.787 0.017 47.0 7.14

Table 3 shows the effect of drying temperature on polydispersity, gel content, epoxidation level (EL) and ring opening. The polydispersity decreased slightly as the drying temperature increased. Overall, the gel content was less than 1 w/w%, which implies no further crosslinks occurred. The EL was about the similar, i.e., about 45 mol%, as well. On the other hand, the epoxy derivatives (ED) increased as the drying temperature increased, which may be explained to be due to the formation of either end groups such as hydroxyl groups or side reactions such as furans or hydroxyl groups (intermediate). Based on the findings, the range temperature that suitable to dry LENR was from 60°C -150°C as the properties such as M„, gel content and EL were not affected much. f. Drying LENR using Near Infra-Red (NIR) method

Table 4 shows the comparison of LENR properties using different drying method. Three methods were used to dry LENR, i.e. vacuum (A), convection (B) and NIR (C) ovens. The M _n and M _w of A was highest compared to B and C. In contrast the polydispersity, Mw/M _n of C was the highest amongst all. This implies that random chain scissions may occur for C, which may be possibly due to high temperature of drying, i.e. 130°C. In the case of gel content (w/w%) and ring opening (mol%), C obtained the highest values, which confirmed there are some ring openings and crosslinks occurred. This can be said (1) drying LENR more than 100°C affected the LENR, for instance side reactions occurred during drying process, (2) using NIR oven may not be suitable due to the sticky behaviour of LENR, which is difficult to handle and recover the material when using the oven.

Table 4: The comparison of properties of LENR dried using vacuum oven, conventional oven and NIR method

(A)

(B) (C) NIR 2

Vacuum oven

Oven (120 °C) (130 °C)

(45 °C)

M _n 10326 3976 4050

M _w 29829 15801 19268 Mw/Mn 2.891 3.976 4.766

Gel content (w/w%) 0.48 0.28 0.75

Epoxidation level (mol%) 55.7 - 51.3

Ring opening (mol%) 1.44 - 7.13 g. Evaluation properties of LENR 50 prepared using 400 L capacity reactor

Table 5 shows the properties of eight batches of LENR 50 prepared using 400 litre reactor. The average molecular weights, i.e., M _n and M _w of P1 to P8 were about 10 000 g/mol and 30 000 g/mol, respectively. The difference of each batch was +5000 g/mol. The molecular weights were similarto LENR produced using 50 litre reactor. In the case of M _v /M _n , the values were quite erratic but not so high, which was below than 4. This suggests that the reaction was controlled. Furthermore, such values of M _v M _n were similar to neat natural rubber. It can be deduced that the molecular weight obtained for eight batches LENR production were consistent.

The gel content obtained for P1 to P8 was less than 1 wt%. These results supported the low molecularweight, where the chain scission occurred effectively. The shorter chain easy to swell in the solvent resulted to very low gel content after degradation. As an overall, the gel content for eight batches LENR was consistently less than 1 wt%. The EL of P1 to P8 were measured by NMR spectrometer.

The average EL obtained were relatively high which was above 55 mol%, i.e. P1 , P3, P5, P7 and P8. The high EL may probably due to the initial EL of ENR 50 was high or formation of epoxy actively occurred during the reaction. In the case of ED of LENR, the values were significantly increased compared to ENR 50. During the degradation, formation of derivative groups such as furan and diol/hydroxyl may be occurred, resulting to the increase of ED. Glass transition temperature, T _g of P1 to P8 was found to be fluctuated. The T _g of ENR 50 wasabout -23 to -27°C. High TgS was obtained for P1 , P3, P5, P7 and P8. The increased of T _g was expected as the EL increased. However, the values deviated very far from each batch. The physical character of LENR for each batch was also observed. It was found that the physical characters of LENR were different for each batch. Some were sticky and soft (P2, P4and P6), some were not sticky but soft (P5, P7 and P8), and some were not sticky and not soft(P1 and P3).

Due to fluctuation of properties and physical characters among eight batches of LENR, thus, investigation on relationship between properties and physical characters was carried out.

Table 5: Properties of LENR 50 (P1 to P8)

Physical character Not Sticky Not Sticky Not Sticky Not Not sticky, and sticky, and sticky and sticky sticky not soft not soft but soft but but soft soft soft soft soft h. Investigations on the relationship between properties and physical character (stickiness) of LENR 50

Figure 6 shows the M _n of ENR 50 and LENR 50. The M _n of ENR was about 11 % higher than LENR. After degradation of ENR, the M _n of was decreased to less than about 10 000 g/mol for all batches. This indicates that the molecular weight was significantly reduced and consistent aslong as the degradation pursued. Based on the Table 9, the physical character of LENR were different for each batch even though the molecular weight was consistent. In order to investigate the disparity of the physical character, the EL of these LENRs were determined.

Figure 7 shows the EL, mol% of ENR 50 and LENR 50. The EL of ENRs was fluctuated for every batch, indicating the production of ENR itself may not be consistent. The EL of LENR were depended on the EL of ENR, where higher EL of ENR resulted to the higher EL of LENR. Comparing the physical character and EL, it seemed that some LENRs with EL higher than 55 mol%, i.e. P1 , P3, P5, P7 and P8 may cause lesser stickiness to the LENR. Whilst, LENR with EL less than 55 mol% gave sticky and soft character. However, bold deduction could not be made, hence the relationship with T _g s was carried out. Figure 8 shows the T _g for ENR 50 and LENR 50. From the graph, the T _g s of ENR were varied from-8 to -27°C, which was reflected to the T _g s of LENR. The LENRs with T _g higher than - 15°C resulted to non-sticky and hard character, i.e. P1 , P3, P5, P7 and P8. In contrast, the LENR with T _g lower than -15°C exhibited soft and sticky character, i.e. P2, P4 and P6.

As an overall, the physical character of LENR 50 was significantly dependent upon EL as well as T _g , not the molecular weight and ED. The higher the EL and T _g , the physical character of LENR will gradually change to non-sticky and not soft material. Thus, the properties such as EL and T _g are very important, in which they could influence the physical character of LENR. It is worth to note that the EL of ENR 50 as a starting material must be carefully controlled in between 47 to 53 mol% in order to obtain the good physical character of LENR. The relationship between properties and physical character of LENR is summarized in Table 5. i. Evaluation properties of LENR 50 using controlled EL of ENR 50 latex (47 to 53 mol%) Table 6 shows the LENR 50 properties using controlled EL of ENR 50 latex. The ELwas controlled from 47 to 53 mol%. The properties of LENRs were measured (1 ) to assure the consistency of LENRs and (2) to observe the physical character of LENR when using controlled EL of ENR 50 latex. Three batches of LENR were prepared namely P9, P10 and P11 . It was found that the M _n and M _w obtained for all batches were about 7000- 9000 g/mol and 20000 - 23000 g/mol, respectively. There was not much difference observed between batches, where the difference was only about ± 3000 g/mol. The gel content also was very low, i e. less than 0.05 wt%. The EL for the LENRs was within 47 to 53 wt% and the T _g for two batches was lower than -15°C. The physical character of LENRs showed sticky and soft. Hence, it is confirmed that the EL and T _g play an important role to bring about the good physical characteristics of the LENR. The production of LENR and drying using the twin-Z blade kneader provide consistent and reliable results. Table 7 depicts the summary of the properties of the LENR.

Table 6: The LENR 50 properties using controlled EL of ENR 50 latex

Gel content 0.04 0.04 0.02

(w/w%)

Epoxidation level 49.9 52.0 48.41

Glass transition -13.89 - -15.19 temperature, °C

Sticky and Sticky and Sticky and

Physical character soft soft soft

Table 7 Summary of the properties of LENR 50

Gel content 0.48 0.02 0.82 0.04 0.04 0.02

(w/w%)

Epoxidation

51.4 44.5 52.7 49.9 52.0 48.4 level (mol%)

Epoxy derivatives 6.8 11.9 7.3 5.85 10.47 13.89

(mol%)

Glass transition -16.18 -17.86 -12.89 -13.89 - -15.19 temperature, °C

Sticky Sticky Sticky Sticky Sticky Sticky

Physical and and and and and and character soft soft soft soft soft soft Condition for ENR latex for LENR production a. Effect of ENR 50 latex storage as starting material on LENR 50 properties

Table 8: Properties of LENR 50 prepared from ENR 50 latex

0 ENR 50 14.3 34.5 49.0 40.0

1 LENR 1 1.40 5.04 52.1 0.59

30 LENR 2 1.52 4.69 53.9 0.93

60 LENR 3 1.39 4.24 54.7 0.73

90 LENR 4 1.44 4.58 53.3 0.77

120 LENR 5 1.48 4.51 52.7 0.38

150 LENR 6 1.57 4.65 54.5 0.75

Table 8 shows the properties of LENR 50 prepared using ENR 50 latex stored at the different periods before degradation was performed. The number average molecular weight, M _n and weight average molecular weight, /W _w for ENR at Day 0 were 14.3 x 10 ⁴ g/mol and 34.5 x 10 ⁴ g/mol, respectively with high gel content, i.e. 40 wt%. The epoxidation level was calculated to be 49 mol%, which reflected the efficiency of the epoxidation of ENR with the targeted at 50 mol%. The molecular weight and gel content were then significantly decreased after degradation of ENR took place, i.e. LENR 1 to 6. However, the epoxidation level showed a slight increase which may due to the formation of C-O-C due to incomplete chain scission onto C=C during degradation. When using ENR latex stored from Day 1 to Day 150, the molecular weight, epoxidation level, and gel content of LENRs showed not many changes upon storage. This implies that ENR latex is good to store up to 150 days before degradation is carried out since the properties of LENR 50 showed quite consistent along the storage period of latex. Optimally, the epoxidized natural rubber latex is stored for 5 days to 7 days prior to use. b) Effect of surfactant concentrations on the ENR 50 latex stability

Table 9 shows the effect of surfactant, sodium dodecyl sulfate (SDS) on the stability of the latex throughout the reaction. The purpose of this study is to determine the suitable concentration of SDS in latex throughout the reaction. Longer stability of the latex was observed as the concentration of SDS increased. The O, P and Q lattices remained stable after 8 hours of reaction. This implies that the suitableconcentration of SDS for 8 hours reaction at 65°C was found to be 2 wt% of an overall solution. Hence, this is the reason such concentration was used to prepare liquid epoxidized natural rubber. In order to investigate whether the properties of LENR affected with different concentration of SDS, thus, the properties of LENR, i.e. N, O, P, Q and R were measured. The surfactant used can be an anionic surfactant is a long hydrophobic alkyl chain surfactant with a sulfate, or a sulfonate charged hydrophilic end group together with sodium, potassium, or ammonium counterions. For example, anionic surfactants such as ammonium lauryl sulfate, sodium laureth sulfate, sodium lauryl sarcosinate, sodium myreth sulfate, sodium pareth sulfate, sodium stearte, sodium lauryl sulfate, a olefin sulfonate, or ammonium laureth sulfate.

Table 10 shows the properties of LENR 50 at different surfactant concentrations. The properties particularly gel content and molecular weight of LENR, i.e. N, O, P, Q and R was significantly lower than ENR, which substantially reflects the efficiency of degradation of ENR in latex stage. As the surfactant concentration increased, the properties such as gel content and EL showed no significant changes. However, the molecular weight and epoxy derivatives showed a slight decrease as the surfactant concentration increased. The decrease of the molecular weight upon surfactant concentrations may be possibly due to the role of surfactant that contributes to the effectiveness of the reaction. In this case, the optimal surfactant concentration was chosen to be 2 wt%, since high amount of surfactant may lead to coagulation difficulty after the reaction completed.

Table 9: Effect of surfactant on the stability of the reaction (latex) based on observations.

Sample Percentagein

Observations name mixture (%)

B 0.3 Coagulated immediately

C 0.45 Coagulated during addition of chemicals

D 0.6 Coagulated during addition of chemicals

E 0.75 Coagulated during addition of chemicals

F 0.9 Coagulated during addition of chemicals

G 1 .05 Coagulated after addition of chemicals

H 1.2 Coagulated after addition of chemicals

Coagulated 30 minutes after reaction

I 1.35 started

Coagulated 30 minutes after reaction

J 1.5 started

Coagulated 30 minutes after reaction

K 1.65 started

L 1 .8 Coagulated 2 hours after reaction started

M 1 .95 Coagulated 4 hours after reaction started

N 2.1 Reaction completed after 8 hours

O 2.25 Reaction completed after 8 hours

P 2.4 Reaction completed after 8 hours

Q 2.55 Reaction completed after 8 hours

R 3 Reaction completed after 8 hours Table 10: Effect of LENR 50 properties at different surfactant concentrations Gel Molecular weight Epoxy

Sample Epoxidation, . . content (x 10 ³ ) g/mol ^K derivatives, name mol%

7 64.98 71.85 310.70 4.32 58.32 5.60

(control)

N 2.97 12.25 38.22 3.12 60.54 4.14

O 3.39 13.93 46.64 4.26 60.66 4.31

P 3.45 12.62 42.05 4.69 60.83 3.77

Q 3.16 11.22 36.69 4.51 61.79 2.28

R 3.43 10.69 36.45 4.43 60.75 2.65 c) Effect of incubation period of ENR 50 latex with surfactant

Figure 9 shows the effect of incubation time of ENR 50 latex on the molecular weight of LENR 50. The ENR latex was firstly incubated with surfactant for a range of time such as 0 (control), 24 and 48 h. The M _n and M _w of ENR latex without incubation were about 33 000 g/mol and 110 000 g/mol, respectively. Then, the M _n and M _w were substantially decreased as the incubation time increased. From the figure, the M _n and Mw were decreased to about 15 000 g/mol and 50 000 g/mol after 24 and 48 h incubation, respectively. Based on the previous literatures, natural rubber latex particles were surrounded by a layer consisted of proteins and phospholipids. While, an anionic surfactant such as SDS was used to assist in the removal of proteins from the surface of latex particles. Besides enhancing the stability of ENR latex, the surfactant may change the structure of the naturally occurring proteins and weaken the proteins-phospholipids attachments on the latex particles, which causes the proteins to lose their functions. Consequently, the proteins-phospholipids may no longer can protect the outer layer of latex particles. Once the outer proteins-phospholipids layer is loosened, the chemicals such as hydrogen peroxide (HP) and sodium nitrate (SN) may easily penetrate into the latex particles resulted in the higher efficiency of lowering molecular weight of LENR. In addition, the size of SDS molecule is very far smaller compared with the phospholipid macromolecule, which may offer easier penetration of the chemicals. This postulation is supported by the nitrogen content of ENR latex incubated with surfactant as shown in Table 11 . It showed that the nitrogen content decreased as the incubation time of ENR latex with surfactant increased. Since incubation time of 24 and 48 h were not giving much difference with regards to M _n , M _w and polydispersity, it is thus, the incubation time of 24 h of ENR latex with surfactant before the reaction was chosen for this work. Table 11 : Nitrogen content of ENR 50 latex incubated with surfactant (2.1 wt%)

Samples Nitrogen content, w/w%

ENR latex with surfactant - O h incubation 0.97

ENR latex with surfactant - 24 h incubation 0.85

ENR latex with surfactant - 48 h incubation 0.84 d) Effect of pH of ENR 50 latex

Table 12: Effect of pH of ENR 50 latex on the molecular weight and epoxidation level of LENR 50.

Table 12 shows the effect of pH of ENR 50 latex on the properties of LENR 50. In this study, sample labelled ENR 1 to 3 were named as a control for every pH condition. Three pHs of ENR latexes were studied, i.e. 6, 8, and 11 to prepare LENR in the latex stage. The LENR 1 showed the highest increment of the epoxidation level, followed by LENR 3 and subsequently, LENR 2. On the other hand, LENR 2 gave the major percentage of M _n and M _w reduction, i.e. 88.85% and 90.59%, respectively compared with LENR 1 and LENR 3.

The reaction between sodium nitrite (SN) and hydrogen peroxide (HP) to produce LENR occurs in two steps, which are shown in the proposed schematic reaction in Figure 10 . In the first step, alkene was epoxidized by peroxynitrite to form epoxidation of NR. It is then followed by the oxidation of hydrogen peroxide by the second mole of peroxynitrite ion to produce nitrite ion, water, and oxygen. Nitrite ion which is highly nucleophilic then will attack the epoxy ring and form chain scission. In the presence of highly basic condition at pH 11, i.e. LENR 3, HP tend to decompose to water and oxygen. In the state of reduced HP, the second step of the reaction could not occur, leading to a higher epoxidation value (16.67% increased) and lower reduction of molecular weight (67%).

In a mild basic condition at pH 8, i.e. LENR 2, the chain scission occurred more effectively with a lower epoxidation percentage and higher reduction. Which contributed by the more stable HP to continue the second step of the reaction.

On the other hand, in the mild acidic condition at pH 6, i.e. LENR 1 , HP was a very strong oxidizing agent which tends to oxidize alkene to epoxy Thus, the efficient decrease of molecular weight occurred and the epoxidation level was increased markedly. The increase of epoxy groups in the acid medium was reported in the previous work.

Since the highest reduction of the and the smallest increase in epoxidation level amongst all was found to be in mild base medium, i.e. pH 8 - 9, therefore, it was chosen to be the suitable pH for the preparation of LENR in the latex stage, in this case. Optimally, the pH of the epoxidized natural rubber latex is pH 8

3. Properties of LENR 50 produced a. Effect of chemical concentrations on molecular weight and gel content

Figure 11 shows the effect of chemical concentrations on the molecular weight of LENR 50. The ENR 50 latex as a control showed a typical range of M _w and M _n , which was about 1.5 x 10 ⁶ g/mol and 4.4 x 10 ⁵ g/mol, respectively. As the chemical concentrations increase, the molecularweight decreased significantly. The lowest M _n achieved was about 13000 g/mol at 20 phr of chemical concentrations. The M _n then became constant at 24 and 28 phr, respectively, whilst the M _w continuously decreased. This finding suggests that the higher amount of chemicals, the faster rate of chain cleaving occurred, resulted to low molecular weight. The physical character of LENR was stickier and softer as the molecular weight reduced.

Figure 12 shows the effect of chemical concentrations on gel content of LENR 50. The gel content of ENR as starting material was the highest. The gel content was then decreased gradually as the chemical concentrations increased. The lowest gel content was found to be less than 1 wt%. Thus, the gel content was dependent upon chemical concentrations. b. FTIR spectroscopy

Figure 13 shows the FTIR spectrum for ENR 50 and LENR 50. The peaks at 3464, 1737, 1663, 879 and 834 cm ^-1 were belonged to ENR characteristics. Whilst, LENR, which is after degradationof ENR, the broad peaks appeared at 3459, 1774, 1716, 1083, 1062, 1025 and 840 cm' ¹ and therest were remained the same.

Based on Table 13, the peaks of ENR 50 and LENR 50 were assigned. Peaks at 3459 and 3464 cm' ¹ were belonged to OH group of ENR and LENR. The peak at 1737 cm ^-1 of ENR was belongedto aldehyde groups. After degradation of ENR, the peaks at 1774 and 1716 cm ^-1 were appeared, hich are belonged to aldehyde and ketone groups. These abnormal groups were postulated toform after degradation of ENR, i.e. LENR. In the case of ether groups at the range of 1113 - 1022 cm ^-1 for both ENR and LENR, they were belonged to either C-OH or C-OC groups. C- OH may form as terminal groups or intermediate groups, i.e. diols. Whilst, 879 and 875 cm ^-1 were belonged to epoxy groups of both rubbers. The peak of C-H from natural rubber was at 834 and 840 cm ^-1 .

Table 13: Peak assignment of ENR 50 and LENR 50

A schematic mechanism was proposed that the redox reagents may be attracted only to C=C and C-O-C bonds for chain scission. On the other hand, CH ₂ was not significantly affected by the degradation of ENR to produce LENR. Thus, in order to confirm the peak intensity quantitatively, the absorption peak area ratio of certain functional groups to reference peak was carried out. The absorption peak area ratio was calculated by using CH ₂ at 2962 cm ¹ as a reference and the peak area of these functional groups, for instance OH, C=O, C=C, CO, and C-O-C before (ENR) and after (LENR) degradation.

Table 14: Absorption peak area ratio for ENR 50 and LENR 50 (**FG - Functional group)

The absorption peak area ratios for ENR 50 and LENR 50 is tabulated in Table 14. From the table, the peak area ratios of OH, C-O, and C-O-C of LENR was higher than that of LENR.

The peak area ratio of OH and C=O groups of LENR was increased by twice compared to ENR. However, the peak area ratio of C=C of LENR was decreased compared to ENR. This can be explained to be due to the redox reagents may prone to attack C=C more than C-O- C. Furthermore, the peak area ratio of C-O-C of LENR was higher than ENR, which probably resulted from re-combination of C-O-C after being attacked by redox reagents during the reaction. Hence, the FTIR spectroscopy and absorption peak area ratios confirmed the degradation has occurred, in which more polar functional groups, i.e. OH (hydroxyl), C=O (carbonyl), C-O, C-O-C groups were formed. According to the previous work, carbonyl and small amount of hydroxyl groups were belonged to terminal ends of ENR. These findings were corresponding with the degradation of LNR, where the carbonyl and hydroxyl groups formed after degradation in base medium. c. NMR spectroscopy

LENR 50 was characterized using proton NMR to understand if there are an increase in the side reactions. Detailed study was performed in order to identify each chemical shifts in the spectrum. The starting material of LENR which is ENR latex was firstly analysed to determine the existing side reaction from epoxidation reaction. The ¹ H spectrum of ENR50 is presented in Figure 14 and 15, in which the chemical shift at 5.17-5.12 ppm (-C(CH3)=CH-), 2.18-2.06 ppm (broad, CH2 of repeating polyisoprene unit) and 1.70-1.59 ppm (broad, CH3 of repeating polyisoprene unit) were clearly observed and attributed to the isoprenic unit. While chemical shift at 2.72 ppm (t, epoxide-CH-CH2) and 1.30 ppm (s,-CH2C(CH3)-epoxide) were clearly observed and attributed to epoxide unit. The spectrum also shows the presence of side reaction at chemical shift 8.19 ppm, attributed to cyclic proton which suggest a small amount of rearrangement of NR chain has occurred during the epoxidation reaction. Ring opening of epoxide group to alcohols were also observed at 4.01 3.74 ppm (-CH-OH) and 3.53-3.24 ppm (diol of C-OH and -CH-OH).

It is also observed that the chemical shift of isoprenic unit were splitted into another identical peak at slightly lower chemical shift. This is because of the two different repeating unit in the polymeric chain. The isoprenic unit neighbouring another isoprenic unit gives slightly higher chemical shift compared to an isoprenic unit neighbouring an epoxide unit in the polymer chain.

ENR 50 block rubber and ENR 50 latex was compared in order to determine any irregularities in the starting material of LENR 50 production. Both spectrums show no significant difference in the main chain peaks and impurities. The main chain was described as above. The chemical shift of first impurity is at 3.65ppm (s, sharp, attributed to ethoxylate group of teric) for both block and latex samples. The second chemical shift is at 3.45ppm (s, methanol) resulted only in ENR latex which is due to residues from coagulation of the latex using methanol. The alcohol of the coagulant in step is an isopropyl alcohol, methyl alcohol, or ethyl alcohol, optimally, methanol at a concentration of 5 wt%. The salt solution of the coagulant comprises potassium, sodium, calcium, ammonium salts, chloride, or nitrate salts, optimally, calcium chloride solution at a concentration of optimally 10 wt%. The ¹ H spectrum of LENR 50 is presented in Figure 16, in which the chemical shift at 5.17- 5.12ppm (-C(CH3)=CH-), 2.18-2.06 ppm (broad, CH2 of repeating polyisoprene unit) and 1.70- 1.59ppm (broad, CH ₃ of repeating polyisoprene unit) were clearly observed and attributed to the isoprenic unit. While chemical shift at 2.72 ppm (t, epoxide-CH-CH ₂ ) and 1.30 ppm (s, - CH ₂ C(CH ₃ )-epoxide) were clearly observed and attributed to epoxide unit.

Figure 17 shows the expanded ¹ H-NMR spectra of ENR 50 and LENR 50 from 9 to 10 ppm. There were two new proton signals appeared at the chemical shift from 9 to 10 ppm in the ¹ H- NMR spectrum of LENR, which was in contrast to the ¹ H-NMR spectrum of ENR. These proton signals at 5 = 9.3 - 9.4 ppm and 9.8 ppm apparently belonged to the proton of aldehyde (O=C- H) functional end group in LENR structure.

Figure 18 shows side reaction in the region 3.00 to 5.00 ppm of LENR 50. Whereby the multiple chemical shifts at 3.9 ppm to 4.22 ppm is attributed to the phosphate lipid group of natural rubberThe chemical shifts at 6 = 3.2 -3.4 ppm were from the diol group. The formation of diol group may be possibly contributed by the occurrence of secondary epoxide ring opening reaction during epoxidation and degradation to form ENR and LENR, respectively. Besides, a broad signal that appeared at 3 = 3.6 - 3.8 ppm was assigned to furan ring which may form due to the interaction of two adjacent epoxy groups during the opening reaction. Apart from this, there was a significant proton signal at 5 = 3.58 ppm between the furan and diol signals. The proton signal was attributed to non-ionic surfactant, Teric, which was used as a stabilizer during the preparation of ENR from NR latex. Thus, it can be deduced that the formation of (1 ) aldehyde (carbonyl) as a functional end group, (2) diol and furan as other functional groups were occurred during the degradation of ENR to form LENR. d. FESEM images

Figure 19 shows the FESEM images for (a) ENR 50 and (b) LENR 50 at 10 OOOx magnification. The particles size of ENR latex showed typical size of natural rubber latex, which ranging from 0.2 to 1 micron with bimodal distribution. In contrast, the latex particles of LENR were distinguished with regards to characters, where the particles were enlarged and the shape was more uniform compared to ENR latex. This may possibly due to ENR latex particles consists of long polymer chains with controlled epoxy groups, in which the chains are preferred to be in the most stable state, i.e. random coil. In the case of LENR, it consists of shorter polymer chains with more polar functional groups than ENR. The repelling forces between the polar groups within the latex particles will lead to swelling, which seen as enlarged particles. In addition, the polar groups also will enhance the intermolecular attractive forces with water medium outside of the latex particle. High polarity of LENR latex particles in water medium resulting in low surface tension. Therefore, the size of LENR latex particles were larger and more uniform compared to ENR. e. Particle size distribution

The particle size distribution of ENR 50 and LENR 50 latexes is shown in Figure 20. The ENR latex showed a similar particle distribution to natural rubber latex, that is a bimodal particle distribution [15], There were two peak modes of ENR latex particle size were observed around 0.3 microns and 1 micron, respectively. Whilst, the LENR latex particles showed a narrow and unimodal distribution, where the single peak mode was shifted to a slightly larger region [16]. This implies that the particle size of LENR latex is larger and more uniform f. Differential Scanning Calorimetry (DSC) measurement

Figure 21 shows the DSC thermograms for the ENR 50 and LENR 50. The glass transition temperature, T _g was determined as an inflection point. From the thermogram, only one T _g was observed for both ENR and LENR, indicating the homogeneity of the rubbers. The T _g of LENR, i.e. 253 K was higher compared to T _g of ENR, i.e. 246 K. Furthermore, the abrupt slope of LENR was observed compared to ENR.

According to the Flory-Fox equation, the T _g is proportional to the molecular weight of polymer. The lower the Tg, the lower the molecular weight. However, in the case of LENR, the T _g was inversely proportional to molecular weight, where T _g increase with shorter polymeric chain. This may be explained to be due to the increase interactions of polar functional groups, which directly attached to the polymer backbone of LENR than ENR. The strong intermolecular interactions by highly polar groups may slow down the segmental dynamics of the polymer with an increase of temperature, resulting in higher T _g . Another possibility could be the hindrance of chain flexibility due to a decrease of C=C groups in LENR. Thus, the polar functional group present in LENR significantly influenced the glass transition temperature. g. Thermogravimetric (TG) Analysis

Figure 22 (a) and (b) shows the TG and DTG curves of ENR 50 and LENR 50. The TG curves revealed a single-step degradation for both rubbers, showing the degradation of the major polymer, i.e. ENR. The slope of the weight percentage of LENR 50 was shifted forward as the temperature increased. This reflected the increase of maximum decomposition temperature of LENR 50, i.e. 427 °C compared to ENR 50, i.e. 402 °C, as shown in DTG curves. A single sharp peak was observed for both rubbers, which consistent with the TG curves. This suggests that the increase in the polar groups improve the thermal stability of LENR. h. Contact Angle Analysis

Figure 23 shows the contact angle analysis of ENR 50 and LENR 50. The contact angle was measured to observe the response of the water droplet on the surface of the sample. The lower the contact angle, the more hydrophilicity of the surface. A lower contact angle also results in higher surface energy. From the graph, the contact angle of LENR was lower than ENR. Furthermore, the values were decreased every 60 seconds, reflecting the hydrophilicity increased and higher surface energy. The increase in hydrophilicity in LENR may due to the presence of polar groups on the structure resulted from degradation. i. Viscosity

The viscosity measurement is performed at 120 °C to measure the flow characteristics of the polymer. Since the LENR is intended to be used in an adhesive application, thus, the viscosity is one of the important parameters to be determined. The relationship of number average molecular weight, Mn, and viscosity for five batches of LENR 50 is shown in Figure 24. The viscosity measured was in the range of 11000 cP to 16000 cP for the Mn ranged from 6.5 x 10 ³ to 7.5 x 10 ³ g/mol. This indicates that the viscosity of five batches of LENR 50 showed consistent values against the Mn.

4. Storage properties of LENR 50 produced (400 L) a. Molecular weight

Seven batch (P1-P7) of ENR 50 latex as starting material for LENR 50 was successfully prepared using reactor 400 L. The changes in molecular weight and gel content were evaluated upon storage time. Figure 25 and Figure 26 show the number average of molecular weight Mn and weight average of molecular weight M _w of LENR prepared by 400L reactor upon storage. The M _n and M _w showed no significant changes as the storage time increased within ±3000 g/mol. This indicates that storage of LENR more than 21 months is not giving any changes in molecular weight. Furthermore, the M _n and M _w were about similar for every batch from first to seven batches, which denotes the molecular weight of LENR produced by 400L reactor were consistent. b. Gel Content The gel content for LENR 50 prepared by 400L reactor upon storage was carried out (Figure 27). At one day storage, the gel content of LENR was found less than 1.0%. Similar observation was obtained after 657 days of storage. The possibility of radical cross linkage or other reaction would not happen during storage due to the low molecular weight and short chain of LENR. The processing condition of LENR such as coagulated by alcohol, dried and stored may increase the gel content of the rubber. This might be due to the free radicals cross linkage or reaction of aldehyde groups on the rubber molecules with free amino acids or protein molecules which are present in the non-rubber fraction. However, gel content of LENR was still low indicating that there is no reaction has occurred during the storage time. c. Study on the functional groups in LENR 50 upon storage based on absorbance ratio measure from FTIR spectra

FTIR spectrums of LENR 50 with different storage time were integrated by taking the ratio cf absorbance selected peak to absorbance internal reference in order to monitor the changes of functional groups present in LENR samples with storage time. The peak of methylene CH2 was used as the internal reference for current study since CH2 it was not noticeably unchangedduring the storage. The ratio of the other absorbance peak such as 3460, 1770, 1714, 1060, 1025 and 873 were chosen for the purpose of determine the changes occurring during the storage. The ratio of selected peak to absorbance of internal standard during long storage of 400 days are plotted in Figure 28, respectively. It was clear that the A3460/A2962 of LENR samples showed a significant increase until it became constant after 300 days of storage time. It might be due to the prolonged storage; the oxidative degradation will be occurred. For ratio such as A1714/A2962, A1061/A2962, A1025/A2962, A873/A2962 it showed decreasing after 150 days of storage and keep constantly after 300 daysof storage. This suggest that LENR sample store at ambient temperature was stable and there is no further reaction such as chain scission or storage hardening occurred.

Figure 29 shows the epoxidation level (EL) and epoxidation derivatives (ED) of LENR 50 prepared by 400L reactor upon storage. The epoxidation levels showed not much changes, in which the values fluctuate within ±5 mol%. However, the epoxy derivatives show slightly increased after 200 days of storage. This might be due to the modification peak of phosphate lipid, ethoxylate group, methanol and ring opening of epoxide to diols and formation of terminal hydroxy) group.

5. Consistency of properties of LENR 50 for 10 batches The total solid content (TSC) in the context of natural rubber polymer consist of rubber and non- rubber component (e.g. carbohydrates and proteins). TSC was calculated before and after the reaction to observe and dilution during the reaction. TSC before the reaction was maintained at 38% as shown in Table 5 to maintain the condition of rubber component that undergo the reaction.

The total solid content of all ten batches after the reaction was calculated to be 30±3% as shown in Table 15. No significant difference in the percentage of TSC was obtained in ten batches of LENR 50 (20phr) samples. Hence, the reaction has maintained the dilution of the latex despite the addition of reagents.

The total solid content of step (a) is optimally 30 wt%.

Table 15: Total Solid Content (TSC) before and after reaction for 10 batches of LENR 50 (20phr)

The LENR 50 samples were characterised using NMR to check the variation in epoxidation level and ring opening percentage. Seven of the ten batches have epoxidation level of 45 - 50% and the ring opening level within the range 6-12% as depicted in Figure 30. However, batch 4 illustrated 41% of epoxidation with increasing level of ring opening up to 16%, batch 5 illustrated 44% of epoxidation with increasing level of ring opening up to 14% and while batch 7 showed 34% of epoxidation level and decrease of ring opening at 6%. Batch 4 and 5 has low epoxidation and higher ring opening, which may be due to secondary ring opening reaction. On the other hand, batch 7 has low epoxidation and also low ring opening which may be due to inefficient of reaction performed in the laboratory. Figure 31 shows the percentage of gel content in the batches shows a range of 0.1-2%. Only sample batch 6 and 9 showed high gel content percentage at 2%. However, the other sample batches show percentage of gel content being below 1 %, which is in the acceptable range. The result does not correlate with the epoxidation or ring opening percentage of the sample as anticipated.

Figure 32 shows the molecular weight of all the batches shows a molecular weight and polydispersity ranging from 6 x 10 ³ - 7.8 x 10 ³ g/mol and 2.3-2.8 respectively. This observation shows that LENR 50 (20phr) within the appropriate range can be synthesized. It also worth to note that epoxidation level and ring opening does not correlate directly to molecular weight of the samples.

The maximum degradation temperature of the samples showed a consistent value at 428+1 °C which is illustrated in Figure 33. However, the sample batch 6, 7 and 8 showed decrease in the degradation temperature to 419±2°C while sample batch 10 showed a decrease in the degradation temperature by 12°C (416.16°C).

Figure 34 shows the molecular weight of ten batches of LENR 50 (20phr) versus the viscosity of the samples. Eight batches of LENR 50 (20phr) showed an average viscosity of 12,962+1888cP while the other two batches (Batch 7 and 9) illustrated higher viscosity with a difference of of 10,000cP . There is no consistent correlation with the molecular weight and viscosity obtained from the ten samples of LENR 50 (20phr). However, the viscosity of the polymer could be deduced between 11,000 to 15,000cP.

6. Properties of LNR and LENR at different reagent level

A series of LENRs with different molecular weight was synthesised to carry out chemical analysis in relation to its viscosity measurements. a. Other properties of LNR and LENR at different reagent level

Table 16: Summary of the synthesized LENR in laboratory (200g), the starting material and the concentration of hydrogen peroxide used.

The samples were prepared with variation on the reagent concentration H ₂ O ₂ and NaNO ₂ based on 5, 10, 15, 20 and 25 phr. The molecular weight and polydispersity were measured by GPC and the results as shown in Figure 35. Polydispersity (D) is the measure of distribution of molecular weight in given polymer sample. £) with value equal or higher than 1 is termed as having variety chain length over a wide range of molecular weight (polydisperse) while as the polymer f) approaches 1 , the polymer is termed as having uniform chain length (monodisperse). Based on Figure 35, all the samples illustrates E) value of higher than 1 , which indicates the sample to be polydisperse. The polydispersity of the depolymerized rubber is also lower compared to the starting material. However, LENR 25 (20phr) has higher polydispersity compared to ENR 25. A difference in the trend can be observed only in this sample. This may be caused by uneven breaking of the chain and chain cross-linking between the chain ends. The concentration of hydrogen peroxide and sodium nitrite are optimally 20 phr.

The reduction of molecular weight of each starting material after the oxidative degradation reaction was also observed. All the starting material decreased significantly according to the amount of redox reagent added. The results show there is an optimum level of reagent concentration that gives lowest molecular weight, at 20phr for LATZ and ENR starting materials. The reduction of molecular weight for LATZ are more profound compared to ENR. Minimum molecular weight for LATZ, ENR 25 and ENR 50 achieved at 20 phr were 5261 , 6511, 7804 gmol-1 respectively. The polydispersity of LATZ, in the range of 2.0-2.7 D were lower compared to ENR (2.7-4.4 D). High PDI of the starting material itself are mainly the reason for the differences.

Figure 36 shows the gel content of each sample at different reagent level. Due to lower molecular weight, the gel content naturally will decrease as observed in LATZ and ENR 50. However, ENR 25 shows contradictory results which could not be explained. Gel content of natural rubber consist of sol and gel component. The sol component dissolves easily in a good solvent such as toluene, cyclohexane, and tetrahydrofuran while the gel component swell without dissolving. This is caused by cross-linking of protein and phospholipids at the chain ends of two or more chain of natural rubber and polar forces (e.g. induced dipole and hydrogen bridges) which can be decomposed by adding polar solvent. Lower gel content results in decrease in the cross-liking chains between the polymers. Thus, this lower cross-linking causes the decrease in the strength of the polymer.

Choosing the right viscosity is important to facilitate application or processing. For an example, adhesive that has low viscosity tend to flow readily. If a required adhesive is needed to be placed exactly at a place that is required, rather than spreading out, a high viscosity adhesive will be suitable. Viscosity of the samples were measured using Brookfield DV2T Viscometer, at temperature 135°C and speed 20 rpm. The results in Figure 37 shows that the three materials have different viscosity even at the same molecular length. LNR obtained from LATZ have viscosity in the range of 53.8-66.1 Pa.S, LENR 25 (27.1-32.1 Pa. S) and LENR50 (1.2- 3.2Pa.S). At the temperature of the measurement was carried out, 135°C, the sample with different molecular weight does not show significant differences. However, each material shows distinctive behaviour at high temperature. The shear stress and viscosity of the material decreased significantly as the epoxidation level increased, LENR 50 < LENR 25 < LNR. It can be concluded that, LENR 50 behaves more liquidly and flows easily at high temperature compared to LENR 25 and LNR. These viscosity differences even at the same molecular weight are due to the fact that the three materials have different hydrodynamic volume and broad molecular weight distributions. The polymer chains have different chemical composition such as alkene and epoxy which plays an important role in their hydrodynamic volume.

Figure 38 shows the effect of epoxidation level and polar groups on the decomposition temperature of LENRs. The maximum degradation temperatures were increased for ENR 25 and ENR 50 when compared to NR. This indicates that the improvement of the thermal stability of ENR as the epoxidation level increases. Interestingly, the temperatures also increased slightly for LENR 25 and 50 compared to LNR. This may be possibly due to the formation of polar groups as a result of degradation that contributes to better thermal stability. In this case, the polar groups are referred to as diol, carbonyl, and furan. b. NMR analysis of LNR, LENR 25 and LENR 50

LNR

Naturally, NR has existing epoxy and ring opening groups. Hence NMR analysis of LNRs were carried out to determine the concentration of these groups. These can be a base line to determine the effect of chemical concentration in LENR synthesis on the percentage level of epoxy and ring opening group.

LNR was prepared via oxidative degradation using H ₂ O ₂ and NaNO ₃ . These H ₂ O ₂ and NaNO ₃ acts as oxidizing agent in oxidative degradation of NR chain. It oxidizes vinylic carbon to form epoxy ring and H2O as by product. Epoxy ring in sp ³ hybridization is highly strained and unstable. NO ₂ ’ as nucleophilic will attack substituted carbon, which resulting scission chain. During this process, absents of either H ₂ O ₂ or NaNO ₃ at the reaction site will contribute to the formation of diols or furan.

Figure 39 shows the percentage of epoxy, Oi (furan), and RO ₂ (diol) for liquid natural rubber (LNR) as the chemical concentrations increased. The percentage of epoxy and furan significantly increased as the concentration of H ₂ O ₂ and NaNO ₃ increased to 15 and 20phr and dropped at 25phr. Generally, the epoxy and furan stay less than 3% while diol less than 0.5% with different level of chemical concentration.

Figure 40 shows that the spectrum of ¹ H NMR of LNR. ¹ H NMR of LNR spectrum show three major signals appear at 5.05 (2), 1.90 (3) and 1.52 (1) ppm assigned to (=CH), (-CH2) and (- CH3) respectively.

LENR 25

Figure 41 shows that the epoxidation level maintained at 26% and the percentage of epoxy, ROi (furan), and RO ₂ (diol) relatively increased as the concentration of H ₂ O ₂ and NaNO ₃ increases. The furan increased from 3.6% to 7.7% while diol increased from 1.0% to 2.9% for 10phr and 20phr respectively.

Figure 42 shows that the spectrum of ¹ H NMR of LENR 25 which is similar to LENR 50. The signals at 6 = 5.10 (1) indicate (=CH) proton. Signals at 5 = 2.15 (5) and 1 .32 (3) ppm were assigned to methylene (-CH2-) and methyl (-CH3) groups of cis-1,4-isoprene units, respectively. The epoxidation group shows a signals at 6 = 2.73 (2), 1 .63 (6) and 1 .04 (4) ppm appeared. Those signals were assigned to methine, methylene and methyl groups of epoxidized-cis-1 ,4-isoprene units, respectively. LENR 50

Figure 43 shows the epoxidation level decreased from 54.3 to 48.5 % as the chemical concentration increased. Meanwhile, the furan increased from 2.6 to 4.3 % from 5 to 20 phr and dropped to 1% for 25 phr. Similarly, diol increased from 0.34 to 1.1 % from 5 to 20 phr and dropped to 0.5% for 25 phr. At high epoxidation levels, in which most epoxy groups are close together, furan formation in favoured. A drop in the epoxidation level and furan indicates that most probably a chain scission reaction occurred at this stage. In comparison LENR 50 has higher furan level while LENR 25 has higher diol level. This could be due to the factor; at low epoxidation levels, in which most epoxy groups are isolated, simple diols are formed compared to higher level of epoxy in LENR50 which favour formation of cyclic furan.

7. Purification of polymer for FTIR and NMR analysis

Precipitation was used as a technique to isolate and purify polymers. The polymer sample is dissolved in a 'good' organic solvent, and this solution is then poured into a 'poor' solvent. Introduction of the polymer to the poor solvent causes the polymer chains to collapse, aggregate and come out of solution. In order to determine a poor solvent which will aggregate the polymer, different ratio of solvent was used to purify LENR 50 (20 phr) sample. ENR has polar functional group of oxirane which has different polarity than NR’s double bond. At high epoxidation level, ENR’s polarity totally changed, hence mixture of solvent was used which consist of hexane (non-polar) and methanol/propanol (polar).

Tetrahydrofuran (THF) and dichloromethane (DCM) were used as a good solvent to solubilize the polymer. This method is used to determine the structure of LENR by FTIR and NMR spectrometer. They are medium polar solvent where the sample will be dissolved totally. The sample were then re-precipitate with the mixture of solvent hexane and methanol/propanol. All the impurities are expected to be dissolved in the solvent while the polymer product precipitated due to its large molecular structure. Several combinations of solvent used in order to change its polarity and the most effective system was concluded to be used LENR purification. The purified sample then was dissolve in solvent CDCI3 for NMR analysis with TMS as an internal standard.

The liquid epoxidized natural rubber is purified for analyses, a purification method comprising steps of; (a) dissolving the liquid epoxidized natural rubber of step (i) in hexane and methanol wherein ratio of hexane and methanol is 98:2; (b) precipitating the liquid epoxidized natural rubber in dichloromethane to obtain purified liquid epoxidized natural rubber wherein the purified liquid epoxidized natural rubber is analysed for functional groups, epoxidation level, and epoxidation derivatives. The liquid epoxidized natural rubber is purified for analyses, a purification method comprising steps of; (a) dissolving the liquid epoxidized natural rubber of step (i) in hexane and propanol wherein ratio of hexane and propanol is 98:2; (b) precipitating the liquid epoxidized natural rubber in tetrahydrofuran to obtain purified liquid epoxidized natural rubber wherein the purified liquid epoxidized natural rubber is analysed for functional groups, epoxidation level and epoxidation derivatives.

In order to investigate further the effectiveness of the purification solvents, integration of signals from 1 H NMR was used to estimate the epoxy content, X _ep oxy, furan content, Y _fU ran and diol content, Z _d ioi. Xepoxy (i), Yfuran (ii) and Zdioi (iii) were calculated by comparing the integration area of the signals at chemical shifts 2.66, 3.8 -3.6 and 3.4 -3.2 ppm that correspond to epoxy methine, furan and diol protons respectively, as shown:

Table 17: Percentage of epoxy, ROi (Furan) and RO2 (Diol) for purified samples at different mixture of solvent. The epoxidation, ROi (furan) and RO? (diol) percentages have been tabulated in Table 17. LENR 50 (20 phr) unpurified shows epoxy percentage of 44 1% while the ROi (furan) and RO ₂ (diol) shows 10.7% and 4.4% respectively. After purification, the sample maintained the epoxy ring percentage by a difference of ±2.5% compared to unpurified sample for all the solvent mixtures. The ROi (furan) percentage of the samples are in between 8.8-11.5% and RO ₂ (diol) in between 0.7-5.2%. Solvent with ratio hexane: methanol, 98:2 dissolve in DCM and hexane.propanol, 98:2 dissolve in THF give a higher percentage of epoxy compared to other solvent mixtures. Moreover, these solvent mixtures show a lower percentage of ROi and RO ₂ . Furthermore, for solvent ratio hexane.methanol, 97:3 dissolved in THF, hexane:methanol, 98:2 dissolved in THF, hexane.propanol, 98:2 dissolved in THF, hexane:propanol, 97:3 dissolved in THF, hexane: propanol, 99:1 dissolved in DCM and hexane: propanol, 98:2 dissolved in DCM, have a similarity whereby there are new peak near the chemical shift of ROi (furan) as shown in Figure 40. This peak interferes in the calculation of furan percentage, hence mislead the data analysis. Hence, solvent with ratio of hexane: methanol, 98:2 dissolved in DCM and hexane: propanol, 98:2 dissolved in THF was chosen as the best two options to purify the LENR polymer.

The LENR comprising an average molecular weight in a range of 20000 g/mol to 30000 g/mol; an average number molecular weight in a range of 5000 g/mol to 15000 g/mol; an epoxidation level in a range of 47 mol% to 53 mol%; a low gel content of less than or equal to 2 wt%; a glass transition temperature in a range of -12°C to -18°C; a viscosity in a range of 12500 cP to 13500 cP; a decomposition temperature in a range of 420°C to 430°C; and a contact angle in a range of 100 0 to 60 0 for 0 to 240 second wherein the LENR with a glass transition temperature higher than -15°C is a soft and non-sticky and the LENR with a glass transition temperature lower than -15°C is a soft and sticky liquid epoxidized natural rubber. The LENR has a shelf life of at least 2 years.