Alkanolamide as a novel accelerator and vulcanising agent in carbon black-filled polychloroprene rubber compounds

(1)

Full Terms & Conditions of access and use can be found at

http://www.tandfonline.com/action/journalInformation?journalCode=yprc20

Download by: [Indra Surya] Date: 08 June 2016, At: 13:50

Plastics, Rubber and Composites

Macromolecular Engineering

ISSN: 1465-8011 (Print) 1743-2898 (Online) Journal homepage: http://www.tandfonline.com/loi/yprc20

Alkanolamide as a novel accelerator and

vulcanising agent in carbon black-filled

polychloroprene rubber compounds

I. Surya & H. Ismail

To cite this article: I. Surya & H. Ismail (2016): Alkanolamide as a novel accelerator and vulcanising agent in carbon black-filled polychloroprene rubber compounds, Plastics, Rubber and Composites, DOI: 10.1080/14658011.2016.1187477

To link to this article: http://dx.doi.org/10.1080/14658011.2016.1187477

Published online: 07 Jun 2016.

Submit your article to this journal

View related articles

(2)

vulcanising agent in carbon black-

_ﬁ

lled

polychloroprene rubber compounds

I. Surya

1

and H. Ismail

∗2

A feasibility study was carried out on the utilisation of Alkanolamide (ALK) as a novel accelerator

and vulcanising agent in Carbon Black (CB)-

ﬁ

lled polychloroprene rubber (CR) compounds. The

functions of the ALK were compared with those of conventional accelerator and vulcanising

agents for CR, ethylene thiourea (ETU), and a combination of magnesium and zinc oxides. The

ALK was incorporated into the CB-

ﬁ

lled CR compounds at 1.0, 2.0, 3.0 and 4.0 phr. By

replacing ETU, it was found that increasing the ALK loading decreased the scorch and cure

times of the CB-

ﬁ

lled CR compounds with magnesium and zinc oxides. The incorporation of up

to 3.0 phr of ALK increased the torque differences, and tensile and hardness properties; and

decreased those properties with further increases of ALK loadings. It was also found that ALK

was able to vulcanise the CB-

ﬁ

lled CR compound. The 3.0 phr ALK

–

CR compound without the

ETU, magnesium and zinc oxides showed a higher tensile strength than that of the control

compound, which was cured by ETU, magnesium and zinc oxides.

Keywords:Alkanolamide, Polychloroprene rubber, Accelerator, Vulcanising agent, Alkanolamide cross-linked polychloroprene

Introduction

Polychloroprene (CR) is one of the most important elas-tomers of all specialty elaselas-tomers. Since it wasfirst pro-duced in 1932, it has had an outstanding market position due to its favourable combination of technical or engineering properties. CR is classified as a high-volume specialty elastomer,1 and is used mainly within the rubber industry. Its areas of application within the rubber field are widespread, and include transmission belts, conveyor belts, moulded goods, cable jackets, seals, coated fabrics, etc.

CR has a well-balanced combination of properties that include good mechanical properties, remarkable resist-ance to ozone, oil, and heat;ﬂame retardancy, weather-ability, special cohesiveness, moderate resistance to most chemicals, and ease of processability.2–5 The molecular structure of CR is similar to that of natural rubber; except that chlorine has replaced the methyl groups.1The pres-ence of chlorine causes the cure system of CR to be gen-erally different from that of other diene rubbers.1,6,7The chlorine atoms decrease the reactivity of double bonds on the CR backbone; and thus, the reactivity with sulphur becomes less. Metal oxides, thiuram, and thiourea based curing agents; particularly ethylene thiourea (ETU), are widely used as the cure system for CR.7 ETU has been

generally used as the vulcanisation accelerator for CR. It is a toxic material and is suspected to be carcinogenic.8,9 The diene rubbers are vulcanised by a single ingredient, such as sulphur or peroxide, while CR is conventionally vulcanised by both magnesium oxide (MgO) and zinc oxide (ZnO), at satisfactory loadings of 4 and 5 phr, respectively. The use of many ingredients in rubber com-pounding has the potential to cause several problems, such as an inefﬁcient mixing process, additional time and energy consumed during processing, as well as var-ious side effects.10 A reduction of ingredients involved has also been demanded.

Recently, newer curing agents, including thiopho-sphoryl disulphides, dimethyl l-cystine, and cetyltrimethy-lammonium maleate, have been reported.10–12Although there are many published works on various curing agents for CR, the most practical curing agents are still metal oxides (MgO and ZnO), due to the superior mechanical properties of the cured products. Thus, the appearance of an alternative vulcanisation accelerator and single vul-canising agent for CR that is capable of providing CR products/vulcanisates equivalent or superior to those pro-vided by the ETU and metal oxides has been in demand. In our previous work,13the preparation and application of ALK in silica-ﬁlled natural rubber compounds was reported. The incorporation of ALK within silicaﬁlled natural rubber compounds gave better mechanical prop-erties namely tensile strength (TS), tensile modulus, and hardness. The enhancement of those properties was attrib-uted to the improvement of silica dispersion in the rubber compounds, and the better crosslink density due to the 1_{Department of Chemical Engineering, Engineering Faculty, University of}

Sumatera Utara, Medan 20155, Sumatera Utara, Indonesia

2_{School of Materials and Mineral Resources Engineering, Universiti Sains}

Malaysia, Engineering Campus, Nibong Tebal, Penang 14300, Malaysia

∗_{Corresponding author, email ihana}_ﬁ_@usm.my

(3)

incorporation of ALK. The results also indicated that ALK can function as an accelerator.

In this study, the effect of ALK on the curing character-istics and mechanical properties of Carbon Black (CB)-ﬁlled CR compounds was compared with the conventional accelerator, ETU. The effect of ALK, as a novel vulcanising agent, was also compared with the con-ventional vulcanising agents for CR, of MgO and ZnO.

Experimental

Materials

CR [Skyprene B-30] was purchased from TOSOH Co. (Japan), CB N330 was obtained from Malayan Carbon (M) Sdn. Bhd., ethyelene thiourea (ETU), MgO, ZnO, stearic acid, and aromatic oil were all obtained from Bayer (M). All materials were used as supplied. The for-mulas for the study of ALK as a novel accelerator are shown inTable 1, and for the study of ALK as a novel vul-canising agent, in Table 2. The ALK was synthesised in our laboratory using Reﬁned Bleached Deodorised Palm Stearin (RBDPS) and diethanolamine. The reaction procedure and molecular characterisation of the ALK was given in our previous report13 and the molecular structure is shown inFig. 1.

Compounding and cure characteristics

The compounding ingredients were mixed using a labora-tory two-roll mill, Model XK-160. The cure character-istics of the CB-ﬁlled CR compounds were determined at 140°C using a Monsanto Moving Die Rheometer (MDR 2000). The respective scorch time (ts2), cure time

(t90), and torque difference (Torquemaximum–

Torqueminimum) were obtained from the rheograph

according to ISO 3417. The compound was subsequently compression moulded using a stainless steel mould at 140°C with a pressure of 10 MPa using a laboratory hot-press based on the respective curing times.

Measurement of tensile, hardness properties

Dumbbell-shaped samples were cut from the moulded sheets. Tensile tests were performed at a crosshead speed of 500 mm min−1using an Instron 3366 universal tensile machine according to ISO 37. The TS and stress at 100% elongation (M100), stress at 300% elongation (M300), and elongation at break (EB) were investigated. The hardness measurements of the samples were obtained

according to ISO 7691-I using a Shore A type manual Durometer.

Fourier transform infrared (FTIR) spectroscopy

The FTIR spectra were obtained using a Perkin-Elmer 2000 series instrument. The spectrum resolution was 4 cm−1 and the scanning range was from 550 to 4000 cm−1_{. Thin}_ﬁ_{lm (with thickness}

∼0.2 mm) for the FTIR spectra, was prepared for the CR-VAP3 compound by moulding the rubber compound sample at 140°C at a pressure of 10 MPa using a laboratory hot-press, based on the respective cure time.

Results and discussion

Alkanolamide (ALK) as a novel accelerator in

CB-

ﬁ

lled CR compounds

Cure characteristics

Table 3shows the comparative effect of ALK as a novel accelerator and ETU as a conventional accelerator on the curing characteristics of the CB-filled CR compounds. In the case of a comparable amount of those ingredients, it can be seen that scorch and cure times of the CR-A1 compound were longer than those of the Control com-pound. It can therefore be considered that ALK gave a longer crosslink process and caused scorch delay to the CB-filled CR compound. Increasing the ALK loading decreased the scorch and cure times of thefilled CR com-pounds. This cure enhancement phenomenon indicates that ALK could act as an accelerator in the vulcanisation of the CB-filled CR compounds. An accelerator is a rubber ingredient that enhances the action of a curing or vulcanising agent to speed up the resultant cure, even though it constitutes a very small part of a rubber compound.14

The torque difference value of the CR-A1 compound was lower than that of the Control compound. Increasing the ALK loading, by up to 3.0 phr, increased the torque difference value, while further increases of the ALK load-ing decreased the value.

Theoretically, the torque difference value is an indi-cation of the crosslink density of a rubber com-pound.2,15–17 The greater the torque difference value, the higher the crosslink density.18–20 Increased torque differences, of up to 3.0 phr of ALK loading can be attrib-uted to the function of ALK as an accelerator, which enhanced the cure rate and cure state of the CB-ﬁlled CR compounds. The deterioration of the value after 3.0 phr ALK loading i.e. the CR-A4 compound was probably due to the softening (or plasticising) effect of the excessive ALK causing a lower torque difference value or crosslink density. The plasticising effect of ALK is derived from the RBDPS, which is a product of the palm oil fractionation process. Palm oil has the effect of plasticising or lubricat-ing rubbers.21

Mechanical properties

Table 4shows the comparative effect of ALK with that of ETU on the mechanical properties of CB-ﬁlled CR vulca-nisates. At a similar loading i.e. 1.0 phr of accelerator, it can be seen that CR-A1 had lower tensile and hardness properties than the Control, except for M300 and EB. Higher M300 and EB CR-A1 properties may have been Table 1 The compound designation and formulation used to

compare the effect of ALK and ETU as accelerators in CB-ﬁlled CR compounds

Ingredients∗

Designation of CB-ﬁlled CR compounds

Control CR-A1 CR-A2 CR-A3 CR-A4

CR 100.0 100.0 100.0 100.0 100.0

CB 50.0 50.0 50.0 50.0 50.0

Aromatic oil 10.0 10.0 10.0 10.0 10.0

MgO 4.0 4.0 4.0 4.0 4.0

ZnO 5.0 5.0 5.0 5.0 5.0

Stearic acid 0.5 0.5 0.5 0.5 0.5

ETU 1.0 0 0 0 0

ALK 0 1.0 2.0 3.0 4.0

∗_{Parts per hundred parts of rubber.}

Surya and Ismail Alkanolamide as a novel accelerator and vulcanising agent

2 Plastics, Rubber and Composites 2016

(4)

due to the plasticising effect of the ALK; which provided more free volume, thus allowing more mobility/ﬂexibility for the CR chains and a break at a higher extension.

It can also be seen that the incorporation of up to 3.0 phr of ALK into the CB-ﬁlled CR compound increased the tensile modulus, TS, and hardness. However, further increases of the ALK loading decreased these properties. The modulus (or stiffness/hardness) and tensile properties of rubber vulcanisates are only dependent on the degree of crosslink.22,23The improvement of tensile modulus, TS, and hardness up to 3.0 phr was attributed to a higher crosslink density; while the deterioration of those proper-ties beyond 3.0 phr was attributed to a lower crosslink density. This explanation is in line with the torque differ-ence value trend shown inTable 3.

The EB of the filled CR vulcanisate increased with increasing the ALK loading. EB can be used as a feature of the extensibility of rubber vulcanisates. Increasing the ALK loading caused a further increase in the extensibility (orflexibility) of the CR chains. This phenomenon can be attributed to ALK functioning as an internal plasticiser to the CB-filled CR compounds. A plasticiser is a rubber

additive that can be used, not only to improve rubber compound processing, but also to modify physical proper-ties, such as the hardness and ﬂexibility of the rubber vulcanisates.2

From the above results, it is clear that ALK can be uti-lised practically as an accelerator in its own right at 3.0 phr of loading for CB-ﬁlled CR compounds.

ALK as a novel vulcanising agent in CB-

ﬁ

lled

CR compounds

Table 5shows the comparative effect of ALK as a novel vulcanising agent and the combination of MgO and ZnO as conventional vulcanising agents, with ETU as the accelerator on the curing characteristics of the

CB-ﬁlled CR compounds. CR-VA1, CR-VA2, CR-VA3, and CR-VA4 (CR-VA series) compounds were used to exam-ine the function of ALK as a vulcanising agent with the addition of an external plasticiser (i.e. the aromatic oil). Meanwhile, compound CR-VAP3 was used to examine the function of ALK as a vulcanising agent without the addition of any external plasticisers.

The incorporation of 1.0 phr ALK into the CB-ﬁlled CR compound, without MgO, ZnO and ETU, produced CR-VA1 with longer scorch and cure times and a lower torque difference value than that of the control. The increasing ALK loading increased both scorch and cure times. This can be attributed to ALK functioning as a reactant or vulcanising agent, which was involved directly in the crosslink process of the CB-ﬁlled CR compounds. The higher the ALK loading, the greater the amount of reactant, and the longer the time needed to complete the crosslink process.

The incorporation of up to 3.0 phr of ALK into the CB-ﬁlled CR compound increased the torque difference value. However, further increases in the ALK loading decreased the torque difference value. Since torque differ-ence value relates to the crosslink density of a rubber com-pound, and none of the conventional vulcanising agents existed in the CR-VA series compounds, it can be con-sidered that ALK can function as a crosslinking or vulca-nising agent in the vulcanisation or crosslink process of the CR-ﬁlled CR compounds.

Based on the torque difference value, 3.0 phr of ALK is the optimum loading for the crosslink process of the

CB-ﬁlled CR compound.

The incorporation of 3.0 phr ALK into the CB-ﬁlled CR compound, without the addition of MgO, ZnO, Table 2 The compound designation and formulation used to compare the effect of ALK and a combination of MgO and ZnO as

vulcanising agents in CB-ﬁlled CR compounds

Ingredients∗

Designation of CB-ﬁlled CR Compounds

Control CR-VA1 CR-VA2 CR-VA3 CR-VA4 CR-VAP3

CR 100.0 100.0 100.0 100.0 100.0 100.0

CB 50.0 50.0 50.0 50.0 50.0 50.0

Aromatic oil 10.0 10.0 10.0 10.0 10.0 0.0

MgO 4.0 0.0 0.0 0.0 0.0 0.0

ZnO 5.0 0.0 0.0 0.0 0.0 0.0

Stearic acid 0.5 0.5 0.5 0.5 0.5 0.5

ETU 1.0 0 0 0 0 0

ALK 0 1.0 2.0 3.0 4.0 3.0

∗_{Parts per hundred parts of rubber}

Table 3 Cure characteristics of the CB-ﬁlled CR compounds with ETU and ALK as accelerators

Cure

characteristics

CB-ﬁlled CR compounds

Control

t_90/min 21.12 28.01 27.61 25.43 25.33

Torquemax/dNm 23.47 9.55 10.26 12.13 7.35

Torquemin./dNm 1.48 1.61 1.60 1.35 1.31

Torque-diff./dNm 21.99 7.94 8.66 10.78 6.04

1 Molecular structure of ALK

(5)

ETU, and aromatic oil, produced a CR-VAP3 compound with a more superior torque difference value than the CR-VA series compounds. This can be attributed to a higher degree and state of curing caused by ALK; since the absence of aromatic oil made the interaction between the ALK and the CB-ﬁlled CR compound stronger and more intense.

Table 6andFig. 2show the effect of ALK as a vulcanising agent on the tensile modulus, hardness and TS of the

CB-ﬁlled CR vulcanisates. It can be seen that the tensile mod-ulus increased up to the maximum level, at 3.0 phr of ALK loading, which then decreased with further increases of loading. The results of hardness and TS also exhibited a similar trend.

The enhancement of tensile modulus, TS and hardness up to 3.0 phr ALK loading were attributed to a higher reinforcement level of CB to the CR rubber, due to the crosslink density improvements of the CR-VA series com-pounds. The deterioration of those properties beyond 3.0 phr can be attributed to a lower degree of crosslink den-sity and a more pronounced softening effect of the exces-sive ALK.

The addition of 3.0 phr ALK into the CB-filled CR compound, without any external plasticiser, produced the CR-VAP3 vulcanisate with superior tensile modulus (especially the M300) and TS, and a comparable hard-ness to Control vulcanisate. Both modulus and tensile reinforcements were observed. The modulus/stiffness reinforcement was attributed to ALK’s ability to interact with CBfiller, which became stronger and more intense, since no plasticising agent was present in the filled CR compound. M300 displays the degree of rubber-filler interaction.24The greater the M300, the stronger thefi l-ler-rubber interaction. The strong interaction between the CBfiller and the CR can be attributed to the nature of the ALK molecule. As shown in Fig. 1, the ALK is Table 4 Mechanical properties of the CB-filled CR vulcanisates with ETU and ALK as accelerators

CB-ﬁlled CR vulcanisates

Control CR-A1 CR-A2 CR-A3 CR-A4

M100/MPa 4.084 2.16 2.30 2.45 2.06

M300/MPa N/A∗ _7.95 _9.05 _9.22 _7.61

TS/MPa 17.94 11.74 12.13 12.99 10.95

EB/% 261 362 405 410 417

Hardness/Shore A 75 59 60 62 57

∗_{N/A = Not available.}

Table 5 Cure characteristics of the CB-ﬁlled CR compounds with ALK and a combination of MgO and ZnO as vulcanising agents

CB-ﬁlled CR compounds

t₂/min 1.96 5.51 6.26 6.32 6.34 6.87

t_90/min 21.12 22.23 22.39 25.16 25.43 24.03

Torquemax/dNm 23.47 6.84 9.52 11.49 10.72 20.74

Torquemin./dNm 1.48 1.34 1.42 1.50 1.32 4.67

Torque-diff./dNm 21.99 5.50 8.10 9.99 9.40 16.07

Table 6 Tensile modulus, and hardness of the CB-ﬁlled CR vulcanisates with ALK and a combination of MgO and ZnO as vulcanising agents

Properties

CB-ﬁlled CR vulcanisates

M100/MPa 4.08 1.19 1.87 1.90 1.75 4.16

M300/MPa N/A∗ _4.84 _6.87 _9.12 _9.05 _17.96

Hardness/Shore A 75 55 57 59 56 75

∗_{N/A = Not available.}

2 TS of the CB-ﬁlled CR vulcanisates

(6)

structured by a hydrophobic long chain hydrocarbon and polar terminal groups. The hydrophobic long chain had an affinity towards the CB, and wetted and dispersed the filler agglomerates; thus, reducing the interaction with the rubber. This interaction scheme allows the breakdown of thefiller into smaller sized par-ticles through mechanical shearing during the early stage of mixing. The smaller the particles sizes, the greater the available surface area for the interaction, and the stron-ger is the interfacial interaction/bonding between the ALK and the CB. Interfacial bonding is a feature of modulus reinforcement25 that increases the total cross-link density of rubber vulcanisates.26,27

Tensile reinforcement is attributed to ALK functioning as a vulcanising agent. As discussed earlier, the ALK mol-ecule also has polar terminal groups. Based on the FT-IR study (which will be discussed later), the hydroxyl groups of the ALK interacted with the chlorine atom of the CR. Speciﬁcally, the hydrogen atoms of the hydroxyl groups interacted chemically with the allylic chlorine of the CR, formed hydrogen chloride (HCl); which was released as a vapour during the crosslinking process. Simul-taneously, the oxygen atoms of the hydroxyl groups reacted with the carbon atoms of the CR, and cross-linked the CR molecule chains. Through this mechanism, an ALK cross-linked the CR. The probable crosslinking reaction between the ALK and the CR is presented in

Fig. 3.

Menon and Visconte found that the crosslinking of CR could take place in the presence of functionally active chemicals, such as Phosphorylated Cashew Nut Shell Liquid (PCNSL).28Their work shows that at a high temp-erature, the hydroxyl group in the PCNSL phosphate group could react with the chlorine atom of the CR and form a primary chemical bond.

Figure 4shows the effect of ALK on the EB of the

CB-ﬁlled CR vulcanisates. As can be seen, the EB of CR-VA series vulcanisates tend to decrease with an increasing ALK loading of up to 3.0 phr. EB corresponds to the crosslink density/torque difference value. This is simply due to the increasing crosslink density, which immobilises the CR segments from the CB surface. However, EB is found to increase beyond the 3.0 phr ALK loading. The explanation is again given by the plasticising effect of the excessive ALK, which lowers the crosslink density and causes the CR segments to move more freely.

Owing to a higher crosslink density, the EB of CR-VAP3 was lower than that of the CR-VA series. A higher EB of CR-VAP3 than the control can be attributed to the more pronounced plasticising effect of the ALK than that of the aromatic oil.

Infrared spectroscopic study

Table 7andFig. 5show the wave numbers of the func-tional groups and the result of the FTIR spectroscopic 3 The probable crosslinking reaction between ALK and CB-ﬁlled CR rubber

4 EB of the CB-ﬁlled CR vulcanisates

Table 7 The wavenumbers of functional groups of CR-VAP3 vulcanisate

Vibration Wavenumber (cm−1₎

C–Cl 627

C_–Cl stretch 791

C_–O Alcohol stretch 1010

C–O–C 1154

C–N stretch 1421

C=O stretch 1653

C=O stretch 1739

C=O carbonyl 1876

(7)

study on the CR-VAP3 vulcanisate. The stretching fre-quency of the numerous C–H modes of the CR molecule is normally placed between 3100 and 2800 cm−1_{. The}

strong infrared bands that appear at 2850 and 2917 cm−1_{, respectively, were attributed to the =C}_–_{H stretching}

mode. The C–Cl stretching region between 800 and 600 cm−1_{is well known for the speci}_ﬁ_{c resonance in the}

con-formational structure of CR.29The strong band at 627 cm−1_{in the infrared was assigned to the C}_–_{Cl stretching}

mode, and the chlorine groups.

The strong bands that appear at 1421 and 1653 cm−1_,

respectively, were attributed to the C–N and C=O stretches belonging to the ALK.

The stretching frequency of the numerous C=O modes of CB ﬁller is normally placed between 1600 and 1800 cm−1. The strong bands that appear at 1739 and 1876 cm−1_{, respectively, were attributed to the C=O stretching}

mode and C=O carbonyl groups of the CB.

These assignments are in good agreement with the lit-erature30and the spectra clearly show the characteristic wave numbers of a mixture of CR, ALK and CB in the CR-VAP3 vulcanisate.

In addition, a new strong band was observed at 1154 cm−1 and was assigned to the C–O–C stretching mode. This spectral feature indicates that a new chemical bond-ing occurred durbond-ing the vulcanisation of the CR-VAP3 compound. It was proposed that the ALK interacted strongly with the CR. The interaction was an ionic reac-tion i.e. the hydrogen atoms of the OH groups of the ALK, which had locally positive charges, interacted chemically with the chlorine atoms of the CR, which had locally negative charges, and formed hydrogen chlor-ide (HCl), which was released as a vapour during the vul-canisation. Simultaneously, several C–O–C chemical bonds were formed that cross-linked the CR molecules, instead of the non-polar hydrocarbon of the ALK inter-acted physically through moment dipole interaction with the CBﬁller. The CB/ALK/CR interaction/bonding was formed, the probable crosslinking reaction of which was presented previously inFig. 3.

Conclusions

ALK can be utilised, not only as a novel accelerator, but also as novel vulcanising agent in the vulcanisation of

CB-ﬁlled CR rubber compound. In the replacement of the conventional accelerator (ETU), ALK, together with the conventional vulcanising agents (MgO and ZnO),

vulcanised the CB-ﬁlled polychloropene rubber com-pounds. Increasing the ALK loading in the CB-ﬁlled compound decreased both scorch and cure times.

In the replacement of the conventional vulcanising agents, and without the presence of ETU, ALK can func-tion practically as a novel vulcanising agent in its own right at 3.0 phr, and vulcanise the CB-ﬁlled CR rubber compounds. The tensile modulus, TS and hardness of the CB-_ﬁlled CR rubber vulcanisates were improved; especially up to a 3.0 phr loading.

Acknowledgements

The authors would like to thank Universiti Sains Malay-sia for providing the research facilities for carrying out the experiment and for making this research work possible. One of the authors (Indra Surya) is grateful to the Direc-torate General of Higher Education (DIKTI), Ministry of Education and Culture (Kemdikbud) of the Republic of Indonesia, for the award of a scholarship under theﬁfth batch of the Overseas Postgraduate Scholarship Program.

References

1. J. S. Dick and R. A. Annicelli:‘Rubber technology: compounding and testing for performance’; 2001, Munich, Hanser Gardner Publications.

2. B. Rodgers:‘Rubber compounding: chemistry and Applications’;

2004, New York CRC Press.

3. R. Schatzel and G. Cassell:‘Synthetic elastic polymers in the cable industry_’,Ind. Eng. Chem.,1939,31, (8), 945_–949.

4. S. K. De and J. R. White:‘Rubber technologists handbook’;2001, Shawbury, Rapra Technology.

5. A. Ciesielsky: ‘An introduction to rubber technology’; 1999, Shawbury, iSmithers Rapra Publishing.

6. W. Hofmann: ‘Vulcanization and vulcanizing agents’; 1967, London, MacLaren and Sons.

7. M. Akiba and A. Hashim:‘Vulcanization and crosslinking in elas-tomers_’,Prog. Polym. Sci.,1997,22, (3), 475_–521.

8. D. M. Smith:‘Ethylene thiourea: thyroid function in two groups of exposed workers’,Brit. J. Ind. Med.,1984,41, (3), 362–366. 9. R. Chhabra, S. Eustis, J. Haseman, P. Kurtz and B. Carlton:

‘Comparative carcinogenicity of ethylene thiourea with or without perinatal exposure in rats and mice’,Fund. Appl. Toxicol.,1992,

18, (3), 405–417.

10. H. Ismail, Z. Ahmad and Z. Mohd Ishak:‘Effects of cetyltrimethy-lammonium maleate on curing characteristics and mechanical prop-erties of polychloroprene rubber’,Polym. Test.,2003,22, (2), 179–

183.

11. A. Das, N. Naskar and D. K. Basu:‘Thiophosphoryl disulﬁdes as crosslinking agents for chloroprene rubber_’,J. Appl. Polym. Sci.,

2004,91, (3), 1913–1919.

5 The infrared spectrum of CR-VAP3 vulcanisate

(8)

12. A. Das, N. Naskar, R. Datta, P. Bose and S. Debnath:‘Naturally occurring amino acid: Novel curatives for chloroprene rubber’,

J. Appl. Polym. Sci.,2006,100, (5), 3981–3986.

13. I. Surya, H. Ismail and A. Azura:‘Alkanolamide as an accelerator,

ﬁller-dispersant and a plasticizer in silica-ﬁlled natural rubber com-pounds’,Polym. Test.,2013,32, (8), 1313–1321.

14. H. Long:Basic Compounding and Processing of Rubber, Rubber Division. 1985, American Chemical Society Inc. The University of Akron, Ohio, USA.

15. B. Boonstra, H. Cochrane and E. Dannenberg:‘Reinforcement of silicone rubber by particulate silica’,Rubber Chem. Technol.,1975,

48, (4), 558–576.

16. H. Cochrane and C. Lin:‘The inﬂuence of fumed silica properties on the processing, curing, and reinforcement properties of silicone rubber’,Rubber Chem. Technol.,1993,66, (1), 48–60.

17. H. Ismail and C. Ng: ‘Palm oil fatty acid additives (POFA’s): Preparation and application’,J. Elastom. Plast.,1998,30, (4), 308–327. 18. J. S. Dick:‘Basic rubber testing: selecting methods for a rubber test

program’;2003, Pennsylvania, ASTM International.

19. P. Sae-Oui, C. Sirisinha, K. Hatthapanit and N. Phewthongin:

‘Inﬂuence of magnesium carbonate loading on the compound prop-erties of polychloroprene, natural rubber, and their blend’,J. Appl. Polym. Sci.,2008,110, (5), 2763–2769.

20. P. Kundu, D. Tripathy and B. Gupta:‘Blends of poly [ethylene (vinyl acetate)] and polychloroprene: Studies on capillary and dynamic

ﬂows’,J. Appl. Polym. Sci.,1997,63, (2), 187–193.

21. F. W. Barlow:‘Rubber compounding: principles, materials, and techniques’;1993, New York, CRC Press.

22. D. L. Hertz Jr and S. E. INC:Elastomerics,1984,116, (November), 17–21.

23. H. Ismail and H. Chia:‘The effects of multifunctional additive and vulcanization systems on silicaﬁlled epoxidized natural rubber com-pounds’,Eur. Polym. J.,1998,34, (12), 1857–1863.

24. S. Wolff:‘Optimization of silane-silica OTR compounds. Part 1: Variations of mixing temperature and time during the modiﬁcation of silica with Bis-(3-Triethoxisilylpropyl)-Tetrasulﬁde’, Rubber Chem. Technol.,1982,55, (4), 967–989.

25. E. Dannenberg:‘Filler choices in the rubber industry’, Rubber Chem. Technol.,1982,55, (3), 860–880.

26. G. Kraus:‘Interactions of elastomers and reinforcingﬁllers’,Rubber Chem. Technol.,1965, 38, (5), 1070–1114.

27. K. Polmanteer and C. Lentz:‘Reinforcement studies-effect of silica structure on properties and crosslink density’, Rubber Chem. Technol.,1975,48, (5), 795–809.

28. A. Menon and L. Visconte:‘Self crosslinkable blends of polychlor-oprene and phosphorylated cashew nut shell liquid prepolymer’,

J. Appl. Polym. Sci.,2004,91, (3), 1619–1625.

29. V. Arjunan, S. Subramanian and S. Mohan:‘Vibrational spectro-scopic studies on trans-1, 4-polychloroprene’, Turk. J. Chem.,

2003,27, (4), 423–432.

30. B. C. Smith: ‘Infrared spectral interpretation: a systematic approach’;1998, CRC Press.