Alkanolamide as a novel accelerator and vulcanising agent in carbon black-filled polychloroprene rubber compounds
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.
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Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=yprc20 Alkanolamide as a novel accelerator and vulcanising agent in carbon black-filled polychloroprene rubber compounds
1 and H. Ismail
I. Surya
8 ,
Plastics, Rubber and Composites Downloaded by [Indra Surya] at 13:50 08 June 2016
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 ihanafi@usm.my © 2016 Institute of Materials, Minerals and Mining Published by Taylor & Francis on behalf of the Institute Received 28 October 2013; accepted 22 April 2016 DOI 10.1080/14658011.2016.1187477
the preparation and application of ALK in silica-filled natural rubber compounds was reported. The incorporation of ALK within silica filled 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
13
In our previous work,
Although 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.
10–12
Recently, newer curing agents, including thiopho- sphoryl disulphides, dimethyl l-cystine, and cetyltrimethy- lammonium maleate, have been reported.
10 A reduction of ingredients involved has also been demanded.
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.
9 The diene rubbers are vulcanised by a single ingredient,
It is a toxic material and is suspected to be carcinogenic.
∗2 A feasibility study was carried out on the utilisation of Alkanolamide (ALK) as a novel accelerator and vulcanising agent in Carbon Black (CB)-filled 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-filled 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-filled 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-filled 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.
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 The
1 , 6 ,
ence of chlorine causes the cure system of CR to be gen- erally different from that of other diene rubbers.
1 The pres-
The molecular structure of CR is similar to that of natural rubber; except that chlorine has replaced the methyl groups.
2–5
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.
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.
1
Polychloroprene (CR) is one of the most important elas- tomers of all specialty elastomers. Since it was first 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,
Keywords: Alkanolamide, Polychloroprene rubber, Accelerator, Vulcanising agent, Alkanolamide cross-linked polychloroprene Introduction
7 ETU has been generally used as the vulcanisation accelerator for CR.
incorporation of ALK. The results also indicated that ALK can function as an accelerator.
10.0
4.0
4.0
4.0
4.0
10.0 MgO
10.0
10.0
5.0
10.0
50.0 Aromatic oil
50.0
50.0
50.0
50.0
4.0 ZnO
5.0
Ingredients ∗ Designation of CB-filled CR compounds
1.0 ALK
2 Plastics, Rubber and Composites
Surya and Ismail Alkanolamide as a novel accelerator and vulcanising agent
4.0 ∗ Parts per hundred parts of rubber.
3.0
2.0
1.0
0.5 ETU
5.0
0.5
0.5
0.5
0.5
5.0 Stearic acid
5.0
Control CR-A1 CR-A2 CR-A3 CR-A4 CR 100.0 100.0 100.0 100.0 100.0 CB
Table 1 The compound designation and formulation used to compare the effect of ALK and ETU as accelerators in CB-filled CR compounds
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.
), cure time (t
) 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.
minimum
Torque
maximum –
), and torque difference (Torque
90
2
Dumbbell-shaped samples were cut from the moulded sheets. Tensile tests were performed at a crosshead speed of 500 mm min −1 using 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
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 (ts
Compounding and cure characteristics
and the molecular structure is shown in Fig. 1 .
13
(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 in Table 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 report
Experimental Materials CR [Skyprene B-30] was purchased from TOSOH Co.
Measurement of tensile, hardness properties
Durometer.
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
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.
21 Mechanical properties Table 4 shows the comparative effect of ALK with that of
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.
18–20
The greater the torque difference value, the higher the crosslink density.
2 , 15–17
Theoretically, the torque difference value is an indi- cation of the crosslink density of a rubber com- pound.
14 The torque difference value of the CR-A1 compound
Fourier transform infrared (FTIR) spectroscopy
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 the filled 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.
Table 3 shows the comparative effect of ALK as a novel
Cure characteristics
Results and discussion Alkanolamide (ALK) as a novel accelerator in CB-filled CR compounds
. Thin film (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.
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
Downloaded by [Indra Surya] at 13:50 08 June 2016 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.
A1 CR-
3.80 t 90/ min
3.83
5.98
6.01
1.96
A4 t 2 /min
A3 CR-
A2 CR-
Control CR-
28.01
Cure characteristics CB-filled CR compounds
Table 3 Cure characteristics of the CB-filled CR compounds with ETU and ALK as accelerators
3.0 ∗ Parts per hundred parts of rubber
4.0
3.0
2.0
1.0
1.0 ALK
21.12
27.61
0.5
1.31 Torque-diff./dNm
3 Downloaded by [Indra Surya] at 13:50 08 June 2016
Surya and Ismail Alkanolamide as a novel accelerator and vulcanising agent Plastics, Rubber and Composites
1 Molecular structure of ALK
6.04
10.78
8.66
7.94
21.99
1.35
25.43
1.60
1.61
1.48
7.35 Torque min. /dNm
12.13
10.26
9.55
23.47
25.33 Torque max /dNm
0.5 ETU
0.5
22 ,
The incorporation of up to 3.0 phr of ALK into the 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.
50.0
50.0
50.0
CR 100.0 100.0 100.0 100.0 100.0 100.0 CB
Designation of CB-filled CR Compounds Control CR-VA1 CR-VA2 CR-VA3 CR-VA4 CR-VAP3
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 ∗
The incorporation of 3.0 phr ALK into the CB-filled CR compound, without the addition of MgO, ZnO,
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 higher the ALK loading, the greater the amount of reactant, and the longer the time needed to complete the crosslink process.
50.0
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.
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.
Table 5 shows the comparative effect of ALK as a novel
Cure characteristics
ALK as a novel vulcanising agent in CB-filled CR compounds
lised practically as an accelerator in its own right at 3.0 phr of loading for CB-filled CR compounds.
2 From the above results, it is clear that ALK can be uti-
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 (or flexibility) 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.
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 in Table 3 .
50.0
50.0 Aromatic oil
0.5
0.0 ZnO
0.5
0.5
0.0 Stearic acid
0.0
0.0
0.0
0.0
5.0
0.0
10.0
0.0
0.0
0.0
4.0
0.0 MgO
10.0
10.0
10.0
10.0
23 The improvement of tensile modulus, TS,
ETU, and aromatic oil, produced a CR-VAP3 compound with a more superior torque difference value than the CR-
1.32
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
9.40
9.99
8.10
5.50
21.99
4.67 Torque-diff./dNm
1.50
Control CR-VA1 CR-VA2 CR-VA3 CR-VA4 CR-VAP3 M100/MPa
1.42
1.34
1.48
20.74 Torque min. /dNm
10.72
11.49
9.52
6.84
Properties CB-filled CR vulcanisates
4.08
24.03 Torque max /dNm
75
4 Plastics, Rubber and Composites
Surya and Ismail Alkanolamide as a novel accelerator and vulcanising agent
TS of the CB-filled CR vulcanisates
75 ∗ N/A = Not available.
56
59
57
55
17.96 Hardness/Shore A
1.19
9.05
9.12
6.87
4.84
4.16 M300/MPa N/A ∗
1.75
1.90
1.87
23.47
25.43
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.
Control CR-A1 CR-A2 CR-A3 CR-A4 M100/MPa 4.084
7.61 TS/MPa
9.22
9.05
7.95
2.06 M300/MPa N/A ∗
2.45
2.30
2.16
Mechanical properties CB-filled CR vulcanisates
11.74
Table 4 Mechanical properties of the CB-filled CR vulcanisates with ETU and ALK as accelerators
ler-rubber interaction. The strong interaction between the CB filler and the CR can be attributed to the nature of the ALK molecule. As shown in Fig. 1 , the ALK is
24 The greater the M300, the stronger the fil-
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 CB filler, 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.
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.
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.
Table 6 and Fig. 2 show the effect of ALK as a vulcanising
Mechanical properties
17.94
12.13
25.16
1.96
22.39
22.23
21.12
6.87 t 90/ min
6.34
6.32
6.26
5.51
Control CR-VA1 CR-VA2 CR-VA3 CR-VA4 CR-VAP3 t 2 /min
12.99
Cure characteristics CB-filled CR compounds
Table 5 Cure characteristics of the CB-filled CR compounds with ALK and a combination of MgO and ZnO as vulcanising agents
57 ∗ N/A = Not available.
62
60
59
75
10.95 EB/% 261 362 405 410 417 Hardness/Shore A
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Surya and Ismail Alkanolamide as a novel accelerator and vulcanising agent
3 The probable crosslinking reaction between ALK and CB-filled CR rubber 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
4 EB of the CB-filled CR vulcanisates 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 Table 7 The wavenumbers of functional groups of CR-VAP3 could take place in the presence of functionally active vulcanisate chemicals, such as Phosphorylated Cashew Nut Shell −1 Liquid (PCNSL). Their work shows that at a high temp-
28 Vibration Wavenumber (cm )
erature, the hydroxyl group in the PCNSL phosphate 627 group could react with the chlorine atom of the CR and
C–Cl
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791 C–Cl stretch form a primary chemical bond.
1010 C–O Alcohol stretch
Figure 4 shows the effect of ALK on the EB of the CB-
1154 C–O–C
filled CR vulcanisates. As can be seen, the EB of CR-VA 1421
C–N stretch series vulcanisates tend to decrease with an increasing
C=O stretch 1653 ALK loading of up to 3.0 phr. EB corresponds to the
C=O stretch 1739 crosslink density/torque difference value. This is simply
C=O carbonyl 1876 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 structured by a hydrophobic long chain hydrocarbon the excessive ALK, which lowers the crosslink density and polar terminal groups. The hydrophobic long and causes the CR segments to move more freely. chain had an affinity towards the CB, and wetted and
Owing to a higher crosslink density, the EB of CR- dispersed the filler agglomerates; thus, reducing the
VAP3 was lower than that of the CR-VA series. A higher interaction with the rubber. This interaction scheme EB of CR-VAP3 than the control can be attributed to the allows the breakdown of the filler into smaller sized par- more pronounced plasticising effect of the ALK than that ticles through mechanical shearing during the early stage of the aromatic oil. 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
Infrared spectroscopic study
ALK and the CB. Interfacial bonding is a feature of
25
modulus reinforcement that increases the total cross-
Table 7 and Fig. 5 show the wave numbers of the func- 26 ,
27 link density of rubber vulcanisates.
tional groups and the result of the FTIR spectroscopic
Plastics, Rubber and Composites
5 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 specific resonance in the con- formational structure of CR.
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.
Surya and Ismail Alkanolamide as a novel accelerator and vulcanising agent
5 The infrared spectrum of CR-VAP3 vulcanisate
29 The strong band at 627
and the spectra clearly show the characteristic wave numbers of a mixture of CR, ALK and CB in the CR-VAP3 vulcanisate.
2003
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.,
, 22, (2), 179– 183.
1967 , London, MacLaren and Sons.
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.
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- erature
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.
6 Plastics, Rubber and Composites
Downloaded by [Indra Surya] at 13:50 08 June 2016
7. M. Akiba and A. Hashim: ‘Vulcanization and crosslinking in elas- tomers’, Prog. Polym. Sci.,
6. W. Hofmann: ‘Vulcanization and vulcanizing agents’;
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 during 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 CB filler. The CB/ALK/CR interaction/bonding was formed, the probable crosslinking reaction of which was presented previously in Fig. 3 .
1. J. S. Dick and R. A. Annicelli: ‘Rubber technology: compounding and testing for performance’;
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.
30
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 the fifth batch of the Overseas Postgraduate Scholarship Program.
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