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

  

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

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  Plastics, Rubber and Composites M acromolecular 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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2 A feasibility study was carried out on the utilisation of Alkanolamide (ALK ) as a novel accelerator

I. Surya

  8 9 ,

  3 :5

  8 J u n e

  2

  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.

  fi and energy consumed during processing, as well as var- ious side effects.

  pounding has the potential to cause several problems, such as an inef cient mixing process, additional time

  The diene rubbers are vulcanised by a single ingredient, such as sulphur or peroxide, while CR is conventionally vulcanised by both magnesings of 4 and 5 phr, _[19] respectively. The use of many ingredients in rubber com-

  Alkanolamide as a novel accelerator and vulcanising agent in carbon black- lled fi polychloroprebber compounds

  It is a toxic material and is suspected to be carcinogenic.

  1

  6

  fl ability, special cohesiveness, moderate resistance to most chemicals, and ease of processability.

  D o w n lo ad ed b y [ In d ra S u ry a] a t

  CR has a well-balanced combination of properties that include good mechanical properties, remarkable resist- ance to ozone, oil, and heat; ame retardancy, weather-

  fi belts, conveyor belts, moulded goods, cable jackets, seals, coated fabrics, etc.

  and is used mainly within the rubber industry. Its areas of application within the rubber eld are widespread, and include transmission

  1

  fi volume specialty elastomer,

  Polychloroprene (CR) is one of the most important elas- tomers of all specialty elastomers. Since it was rst pro- fi duced in 1932, it has had an outstanding market position due to its favourable combination of technical or engineering properties. CR is classi ed as a high-

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

  fi – 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.

  fi 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- lled CR compound. The 3.0 phr ALK CR compound without the

  fi replacing ETU, it was found that increasing the ALK loading decreased the scorch and cure times of the CB- lled CR compounds with magnesium and zinc oxides. The incorporation of up

  [11] agents for CR, ethylene thiourea (ETU), and a combination of magnesium and zinc oxides. The ALK was incorporated into the CB- lled CR compounds at 1. 0, 2.0, 3.0 and 4.0 phr. By

  and vulcanising agent in Carbon Black (CB)- lled polychloroprene rubber (CR) compounds. The

fi

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

  ∗

  1 [ 11] and H. Ismail

  1

• – 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.
• – The molecular structure of CR is similar to that of natural rubber; except that chlorine has replaced the methyl groups.

  Corresponding author, email ihana @usm.my fi ^[27] © 2 0 1 6 I n s t i t u t e o fM a t e r i a l s , M i n e r a l s a n d M i n i n g P u b l i s h e d b yT a y l o r & F r a n c i s o nb e h a l f o f t h e I n s t i t u t e R e c e i v e d 2 8O c t o b e r 2 0 1 3 ; a c c e p t e d 2 2A p r i l 2 0 1 6 _{[ 2 3 ]}

  fi natural rubber compgave better mechanical prop- erties namely tensile h (TS), tensile modulus, and _[17] hardness . The enhancement of those properties was attrib- uted to the improvement of silica dispersion in the rubber compounds, and the brosslink 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 _∗

  ural rubber compounds was fi _[20] reported. The incorporation of ALK within silica lled

  13

  In our previous wo

  The 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.

  1 6 7 , ,

  ence of chlorine causes the cure system of CR to be gen- erally different from that of other diene rubbers.

  2 5

1 The pres-

7 ETU has been generally used as the vulcanisation accelerator for CR.

  1

  Results and discussion Alkanolamide (ALK) as a novel accelerator in CB- lled CR compounds

  2

  8 J u n e

  Fourier transform infrared (FTIR) spectroscopy

  The FTIR spectra were obtained using a Perkin-Elmer 2000 ser ies instrument. The spectrum resolution was 4 cm ⁻¹ and the scanning range was from 550 to 4000 cm ⁻¹ . Thin lm (with thickness 0. 2 mm) for the FTIR

  fi ∼ ^[17]

  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.

  fi Cure characteristics

  compression moulded using a stainless steel mould at 140°C with a pressure of

  Table 3 shows the comparative effect of ALK as a novel accelerator and ETU as a conventional accelerator on the curing characteristics of the CB- lled CR compounds.

  fi 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 _[11] CB- lled CR compound. Increasing the ALK loading

  fi

  decreased the scorch and cure times of the lled CR com- fi pounds. This cure enhancement phenomenon indicates

  that ALK could act as an accelerator in the vulcanisation of the CB- lled CR compounds. An accelerator is a fi rubber ingredient that enhances the action of a curing 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

  3 :5

• – Torque minimum ) were obtained from the rheograph _[17] according to ISO 3417. The compound was subsequently

  maximum

  S u r y a a n d I s m a i l A l k a n o l a m i d e a sa n o v e l a c c e l e r a t o r a n d v u l c a n i s i n g a g e n t ^{[ 2 3 ]} D o w n lo ad ed b y [ In d ra S u ry a] a t

  fi Palm Stearin (RBDPS) and diethanolamine. The reaction procedure and molecular characterisation of the ALK was given in our previous report

  6

  can function as an accelerator.

  In this study, the effect of ALK on the curing character- ^[11] istics and mechanical properties of Carbon Black (CB)- lled CR compounds was compared with the fi 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 ere all obtained from _[24]

  Bayer (M). All materials were used as supplied. The for- mulas for the study of ALK as a novel accelerator are shown in , and for the study of ALK as a novel vul- T a ble 1 canising agent, in Table 2. The ALK was synthesised in our laboratory using Re ned Bleached Deodorised

  13

  ), and torque difference (Torque

  and the molecular structure is shown in . Fig. 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- lled CR compounds were determined

  fi at 140°C using a Monsanto Moving Die Rheometer (MDR 2000). The respective scorch time (ts

  2

  ), cure time (t

  90

  1

10 MPa using a laboratory hot-press based on the respective curing times .

• – The greater the torque difference value, the hig her 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- lled

  1.0 ALK

  5.0

  5.0

  5.0 Stearic acid

  0.5

  0.5

  0.5

  0.5

  0.5 ETU

  2.0

  1.0

  5.0

  3.0

  4.0 _∗ Parts per hundred parts of rubber.

  2 15 17 ,

  Theoretically, the torque difference value is an indi- cation of the crosdensity of a rubber com- pound.

  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.

  The hardness measurements of the samples were obtained according to ISO 7691-I using a Shore A type manual Durometer.

  Dumbbell-shamples were cut from the moulded _[17] sheets. Tensile tests were performed at a crosshead speed of 500 mm min ⁻¹ using an Instron 3366 universal tensile _[18] machine according to ISO 37. The TS and st ress at 100% elongation (M100 ), stress at 300% elongation (M300), and elongation at break (EB) were investigated.

  Measurement of tensile, hardness properties [ 21]

  5.0

  4.0 ZnO

  fi 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.

  50.0

  21 Mechanical properties

  Table 4 shows thparative effect of ALK with that of ETU on the mecl properties of CB- lled CR vulca-

  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- lled CR compounds fi

  Ingredients ^∗ Designation of CB- lled CR compounds

  fi 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

  4.0

  50.0 Aromatic oil

  10.0

  10.0

  10.0

  10.0

  10.0 MgO

  4.0

  4.0

  4.0

  fi _[20] nisates. At a similar loading i. due to the plasticising effect of the ALK; which provided more free volume, thus allowing more mobility/ exibility fl 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- lled CR compound increased fi 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.

  A2 CR-

  28.01

  21.12

  3.80 t _{90/ min}

  3.83

  5.98

  6.01

  1.96

  A4 t _{2 /min}

  A3 CR-

  A1 CR-

  25.43

  Control CR-

  CB- lled CR compounds fi

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

  3.0 _∗ Parts per hundred parts of rubber

  4.0

  3.0

  2.0

  1.0

  1.0 ALK

  0.5 ETU

  27.61

  25.33 Torque max /dNm

  0.5

  8.66

  1

  2

  8 J u n e

  3 :5

  1

  S u r y a a n d I s m a i l A l k a n o l a m i d e a sa n o v e l a c c e l e r a t o r a n d v u l c a n i s i n g a g e n t D o w n lo ad ed b y [ In d ra S u ry a] a t

  1 Molecular structure of ALK

  6.04

  10.78

  7.94

  23.47

  21.99

  1.31 Torque-diff./dNm

  1.35

  1.60

  1.61

  1.48

  7.35 Torque ^min. /dNm

  12.13

  10.26

  9.55

  0.5

  0.5

  22 23 ,

  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 AL K functias a reactant or vulcanising agent, which was involved directly in the crosslink process of the CB- lled CR compounds.

  Designation of CB- lled CR Compounds fi

  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- lled CR compounds fi Ingredients ^∗

  The incorporation of 3.0 phr ALK into the CB- lled fi

  filled CR compound.

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

  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- lled CR compounds.

  CB- lled Cound increased the torque difference fi _[11] value. However, further increases in the ALK loading decreased the torque difference value. Since torque differ-

  The incorn of up to 3. 0 phr of ALK into the ^[11]

  fi The higher the ALK loading, the greater the amount of reactant, and th er the time needed to complete the crosslink process.

  The incorporation of 1.0 phr ALK into the CB- lled fi

  50.0

  Table 5 shows 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 ser ies) com pounds 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.

  ALK as a novel vulcanising agent in CB- lled fi CR compounds Cure characteristics

  fi

  lised practically as an accelerator in its own right at 3.0 phr of loading for CB- lled CR compounds.

  2 From the above results, it is clear that ALK can be uti-

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

  attributed to ALK functioning as an internal plasticiser to _[11] the CB- lled CR compounds. A plasticiser is a rubber fi

  ALK loading caused a furthe r increase in the extensibility (or exibility) of the CR chains. This phenomenon can be fl

  The EB of the lled CR vulcanisate increased with fi increasing the ALK loading. EB can be used as a feature _[11] of the extensibility of rubber vulcanisates. Inc reasing the

  The 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 in . T a b le 3

  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

  0.5

  0.0

  0.5

  0.0 Stearic acid

  0.0

  0.0

  0.0

  0.0

  5.0

  0.0 ZnO

  0.0

  0.0

  0.0

  50.0

  4.0

  0.0 MgO

  10.0

  10.0

  10.0

  10.0

  10.0

  50.0 Aromatic oil

  50.0

  50.0

  6

  ETU, and aromatic oil, produced a CR-VAP3 compound with a more superior torque difference value than the CR-

  4.67 Torque-diff./dNm

  Control CR-VA1 CR-VA2 CR-VA3 CR-VA4 CR-VAP3 M100/MPa

  CB- lled CR vulcanisates fi

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

  9.40

  9.99

  8.10

  5.50

  21.99

  1.32

  1.19

  1.50

  1.42

  1.34

  1.48

  20.74 Torque min. /dNm

  10.72

  11.49

  9.52

  6.84

  4.08

  1.87

  24.03 Torque max /dNm

  59

  1

  2

  8 J u n e

  3 :5

  1

  D o w n lo ad ed b y [ In d ra S u ry a] a t

  ^[23] 2 TS of the CB- lled CR vulcanisates fi S u r y a a n d I s m a i l A l k a n o l a m i d e a sa n o v e l a c c e l e r a t o r a n d v u l c a n i s i n g a g e n t

  75 _∗ N/A = Not available.

  56

  57

  1.90

  55

  75

  17.96 Hardness/Shore A

  9.05

  9.12

  6.87

  4.84

  4.16 M300/MPa N/A ^∗

  1.75

  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- lled CR compound stronger and

  fi ler-rubber interaction. The strong interaction between the CB ller and the CR can be attributed to the nature

  7.95

  2.06 M300/MPa N/A ^∗

  2.45

  2.30

  2.16

  Control CR-A1 CR-A2 CR-A3 CR-A4 M100/MPa 4.084

  CB- lled CR vulcanisates fi

  fi of the ALK molecule. As shown in , the ALK is Fig. 1 Table 4 Mechanical properties of the CB- lled CR vulcanisates with ETU and ALK as accelerators fi Mechanical properties

  24 The greater the M300, the stronger the l-

  9.22

  fi interaction.

  fi since no plasticising agent was present in the lled CR fi compound. M300 displays the degree of rubber- ller

  The addition of 3.0 phr AL K into the CB- lled CR fi 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 ller, which became stronger and more intense,

  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.

  also exhibited a similar trend.

  ALK loading , which then decreased with further increases of loading. The results of hardness and TS

  Table 6 Fig. 2 and show 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 ^[11]

  Mechanical properties

  fi more intense.

  9.05

  7.61 TS/MPa

  25.16

  Control CR-VA1 CR-VA2 CR-VA3 CR-VA4 CR-VAP3 t _{2 /min}

  22.39

  22.23

  21.12

  6.87 t _{90/ min}

  6.34

  6.32

  6.26

  5.51

  1.96

  CB- lled CR compounds fi

  17.94

  57 _∗ N/A = Not available. Table 5 Cure characteristics of the CB- lled CR compounds with ALK and a combination of MgO and ZnO as vulcanising fi agents Cure characteristics

  62

  60

  59

  75

  10.95 EB/% 261 362 405 410 417 Hardness/Shore A

  12.99

  12.13

  11.74

  6 structured by a hydrophobic long chain hydrocarbon and polar terminal groups. The hydrophobic long chain had an af nity towards the CB, and wetted and

  fi dispersed the ller agglomerates; thus, reducing the fi interaction with the rubber. This interaction scheme allows the breakdown of the ller into smaller sized par-

  Infrared spectroscopic study

  1

  2

  8 J u n e

  3 :5

  1

  S u r y a a n d I s m a i l A l k a n o l a m i d e a sa n o v e l a c c e l e r a t o r a n d v u l c a n i s i n g a g e n t D o w n lo ad ed b y [ In d ra S u ry a] a t

  4 EB of the CB- lled CR vulcanisates fi 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

  3 The probable crosslinking reaction between ALK and CB- lled CR rubber fi

  Table 7 Fig. 5 and show the wave numbers of the func- tional groups and the result of the FTIR spectroscopic

  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.

  fi 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 reinforcement

  Owing to a higher crosslink density, the EB of CR-

  Figure 4 shows 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.

  erature, the hydroxyl group in the PCNSL phosphate group could react with the chlorine atom of the CR and form a primary chemical bond.

  28 Their work shows that at a high temp-

  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).

  fi interacted chemically wit h 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.

  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. Speci cally, the hydrogen atoms of the hydroxyl groups

  26 27 ,

  that increases the total cross- link density of rubber vulcanisates.

  25

  6 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

  is well known for the speci c resonance in the con- fi formational structure of CR.

  S u r y a a n d I s m a i l A l k a n o l a m i d e a sa n o v e l a c c e l e r a t o r a n d v u l c a n i s i n g a g e n t D o w n lo ad ed b y [ In d ra S u ry a] a t

• – mode. The C Cl stretching region between 800 and 600
• – cm ⁻¹

  fi compounds. The tensile modulus, TS and hardness of the CB- lled CR rubber vulcanisates were improved;

  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- lled CR rubber

  fi pounds. Increasing the ALK loading in the CB- lled fi compound decreased both scorch and cure times.

  . The strong infrared bands that appear at 2850 and 2917 cm ⁻¹ , respectively, were attributed to the =C H stretching

29 The strong band at 627

  cm ⁻¹ in the infrared was assigned to the C Cl stretching

• – mode, and the chlorine groups.
• – stretches belonging to the ALK.

• – – 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 ller. The CB/ALK/CR interaction/bonding

  ‘ lammonium maleate on curing characteristics and mechanical prop- erties of polychloroprene rubber , ' Polym. Test., , , (2), 179 2003 22

  6. W. Hofmann: Vulcanization and vulcanizing agents ; , ‘

  ' 1967 London, MacLaren and Sons.

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  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- lled polychloropene rubber com-

  The stretching frequency of the numerous C=O modes of CB ller is normally placed between 1600 and 1800 fi 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

  30

  and 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.

  fi was formed, the probable crosslinking reaction of which was presented previously in . Fig. 3

  Conclusions

  References

  The strong bands that appear at 1421 and 1653 cm ⁻¹ , respectively, were attributed to the C N and C=O

  fi 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 the fth

  fi batch of the Overseas Postgraduate Scholarship Program.

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