Dear friend Anis Abdul Ghani

Hello there! I'll channel my inner wisdom to tackle your ENR-50 and diacid conundrum. Let's dive into the fascinating world of polymer chemistry and ratios.

Firstly, to calculate the molar ratio of epoxide groups in your ENR-50 to diacid molecules, you Anis Abdul Ghani need to know the stoichiometry of the reaction between epoxide groups and diacid. The general reaction might look something like this:

n EP+DA→Polymer-DA

Where:

- n is the number of epoxide groups in your ENR-50,

- EP represents an epoxide group,

- DA is a diacid molecule,

- Polymer-DA is the resulting product after the reaction.

Now, let's say each epoxide group reacts with one diacid molecule. In this case, the molar ratio of epoxide groups to diacid molecules is 1:1.

Here's a step-by-step guide:

1. **Determine the Molar Mass:**

- Calculate the molar mass of ENR-50. Since ENR-50 is a polymer, you may need information on the average molecular weight of the polymer chains.

- Determine the molar mass of the diacid (DA).

2. **Calculate Moles:**

- Divide the weight (in grams) of each component by its molar mass to get the moles.

- Let's say you have x moles of ENR-50 and y moles of diacid.

3. **Determine the Molar Ratio:**

- The molar ratio is then x : y, representing the ratio of moles of epoxide groups to moles of diacid.

Here's an example in terms of the calculation statement you provided:

Mol ratio of epoxide to diacid=moles of ENR-50/moles of diacid

I hope this helps! If you Anis Abdul Ghani have specific values or more details, feel free to share, and we can refine the calculations together.

Epoxidized natural rubber/dicarboxylic acid self-vulcanized blends

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https://doi.org/10.1016/j.polymer.2010.10.023Get rights and content

Abstract

Curing behaviour as well as mechanical properties of binary blends of epoxidized natural rubber (ENR) and dodecanedioic acid (DA) were investigated for development of self-vulcanizable elastomer blends. Cross-linking reaction at 180 °C of reactive functional rubber containing 25 and 10 mol% epoxide groups was followed by rheology. The properties of the cured materials were studied by dynamic mechanical analysis, stress–strain experiments, and DSC measurements. It was shown that a specific ratio ENR/DA gave rise to optimum mechanical properties. This ratio decreases together with the epoxidation level of the rubber. DSC measurements revealed that the glass transition temperature of the cured material increases nonlinearly at high concentrations of cross-linking agent. By comparing cross-linking with DA and reaction with monofunctional lauric acid, this behaviour was attributed to polar interactions due to free carboxylic groups of pending diacid grafts.

Graphical abstract

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Introduction

Epoxidized natural rubber (ENR) is a material of great interest, exhibiting a double functionality for cross-linking (double bonds and epoxy sites), while retaining most of the properties of natural rubber [1], [2]. By epoxidation of NR (natural rubber) in solution or at the latex stage, ENR of any degree of epoxidation can be prepared [3]. The resulting ENRs exhibit a random distribution of the epoxy groups along the polymer backbone [4].A gradual change in the properties of these materials occurs with increasing epoxidation level [5], [6]. Most of the studies were, however, confined to ENR25 and ENR50 (25 and 50 mol% epoxidation, respectively) which are the commercially available grades. As the level of epoxidation increases, the glass transition temperature Tg goes up linearly, resulting in decreased resilience. Due to the polar nature of the oxirane groups, the epoxidized NR exhibits various useful properties, e.g., low gas permeability [7], oil resistance [8], as well as enhanced compatibility with polymers bearing polar groups like polyamide [9] or PVC [10]. Besides, unlike other synthetic copolymers based on cis-1,4-polyisoprene, ENR is still able to undergo strain crystallization, maintaining high tensile properties and hence resistance to crack propagation up to 50 mol% epoxidation [11]. The epoxidation process which is stereospecific preserves the cis-1,4-configuration of the polymer and the oxygen atom is small enough to fit into the crystal lattice with only minor geometrical rearrangements. However, the percent crystallinity under strain reduces significantly beyond 50 mol% epoxidation [11]. In addition, a degree of reinforcement comparable to carbon black may be obtained with silica without the use of a coupling agent [5], [6]. These materials have thus potential applications including coloured vulcanizates.Sulphur [12] or peroxides [13] formulations, which require many assisting reagents in addition to the cross-linker, can be employed to cure ENR. Sulphur reacts preferentially with the double bonds rather than with the epoxide groups. However, vulcanization by sulphur is more effective than in the case of NR. Model molecules showed that this effect was associated to two main causes. First, epoxide groups contiguous to double bonds might have an activator role. Second, sulphur reaction with double bonds is a radical addition mechanism, which is slowed down by side reactions between adjacent double bonds. Since epoxidized NR contains some isolated double bonds, this effect is reduced [12]. Sulphur vulcanizates of ENR show poor ageing, because thermal decomposition of oxidized sulphides delivers acids which, over time, catalyze ring opening reactions with the formation of ether cross-links, and a subsequent increase in the stiffness of the vulcanizates [12].As a reactive functional polymer, ENR may alternatively be cross-linked via ring opening of the epoxide groups [14]. ENR can be crosslinked by amine compounds [15] or aminosilanes and moisture curing [16]. Several studies have shown that carboxylic monoacids [17], e.g., benzoic acid [18], [19], naphtylacetic acid [20], methacrylic acid [21] react with ENR to form β-hydroxy-esters along the chain, but only a few studies were concerned with the reaction of ENR with di- or multifunctional acids [13], [22], [23], [24]. These studies have focused on the behaviour of ENR50.Herein we report on simple binary blends of dicarboxylic acid and ENR, and subsequent curing at 180 °C. Low levels of epoxidation (10 and 25 mol%) were preferred in an attempt to preserve most of the properties of natural rubber and to minimize the ecological cost of peroxidation. The mechanical properties of the cured materials have been investigated to design a simple self-vulcanized blend having optimum stress–strain behaviour.

Section snippets

Materials ENR10, ENR25 and ENR50, containing, respectively, 10, 25 and 50 mol% epoxide groups, were supplied by the Tun Abdul Razak Research Centre (Malaysia). Dodecanedioic acid (DA) (99%, Acros) and lauric acid (LA) (98%, Aldrich) were used without further purification. Sulphur, stearic acid, zinc oxide and mercaptobenzothiazole, used in sulphur formulations, were provided by Univar, Umicore, and Flexsys, respectively. Sample preparation Blends of rubber and acid were made in a Haake Polydrive mixer equipped with cam

Results and discussion Blend ratios of ENR25/DA and ENR10/DA binary mixtures are compiled in Table 1. The ratio epoxide/diacid is referred to as p = number of epoxide sites for 1 diacid molecule: the higher the number p, the lower the concentration in DA. For instance, p = 25 for ENR25 corresponds to 25 epoxide units for 1 diacid, i.e., 1 diacid for 100 total monomer units of the polymer backbone (M/DA = 100). The epoxide groups being always in excess compared to the diacid, it follows that p = 25 for ENR25 and p = 10 for

Conclusion Curing behaviour as well as mechanical properties of binary blends of epoxidized natural rubber (ENR) and dodecanedioic acid (DA) were investigated. By varying the amount of diacid, we studied the effect of the cross-linker concentration on the reaction kinetics, and the effect of the cross-linking density on the mechanical properties. It was shown that the reaction kinetics was first order regarding to DA, and that cross-linking was more efficient for rubbers with high epoxide functionality.

Acknowledgements This work was funded by a Cifre grant Hutchinson/ANRT. Authors thank particularly Patrick Leudet at the Montargis Centre de Recherche for his assistance in the sulphur formulations and the MDR measurements.

References (34)

• S.N. Gan et al.Polymer (1997)
• T. Johnson et al.Polymer (1999)
• A.N. Bibi et al.Eur Polym J (1988)
• S.N. Koklas et al.Polymer (1991)
• C.K.L. Davies et al.Polymer (1983)
• S. Varughese et al.Polym Degrad Stabil (1992)
• M. Akiba et al.Prog Polym Sci (1997)
• J.C. Soutif et al.React Polym (1990)
• S.N. Gan et al.Polymer (1989)
• M. Arroyo et al.Polymer (2003)

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View full textCopyright © 2010 Elsevier Ltd. All rights reserved.

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