Maximizing Durability and Flexibility in Rubber Compounds by Incorporating Dimorpholinodiethyl Ether Solutions
Abstract
Rubber compounds are widely used in various industries due to their unique properties such as elasticity, durability, and resistance to environmental factors. However, achieving a balance between durability and flexibility remains a significant challenge. This paper explores the potential of dimorpholinodiethyl ether (DMDEE) as an additive to enhance the performance of rubber compounds. By incorporating DMDEE into rubber formulations, this study aims to improve both the mechanical strength and flexibility of rubber products. The research includes a comprehensive review of existing literature, experimental design, and analysis of results. Additionally, product parameters, comparative studies, and future prospects are discussed to provide a holistic understanding of the benefits of using DMDEE in rubber compounding.
1. Introduction
Rubber, a versatile polymer, is essential in numerous applications ranging from automotive tires to industrial hoses and seals. The demand for high-performance rubber materials has led to extensive research on modifying rubber compounds to achieve optimal properties. One of the key challenges in rubber formulation is balancing durability and flexibility. While durable rubber can withstand harsh conditions, it may lack the flexibility required for certain applications. Conversely, flexible rubber may not offer sufficient strength or longevity.
Dimorpholinodiethyl ether (DMDEE) is a compound that has shown promise in enhancing the performance of rubber materials. DMDEE is a bifunctional molecule with two morpholine groups and two ethyl ether linkages. Its ability to interact with rubber polymers at a molecular level makes it a potential candidate for improving both durability and flexibility. This paper investigates the effects of DMDEE on rubber compounds, focusing on its impact on mechanical properties, chemical resistance, and thermal stability.
2. Literature Review
2.1 Overview of Rubber Compounding
Rubber compounding involves the blending of natural or synthetic rubber with various additives to achieve desired properties. Common additives include fillers (e.g., carbon black, silica), plasticizers, vulcanizing agents, and antioxidants. The choice of additives depends on the specific application requirements, such as tensile strength, elongation, tear resistance, and aging resistance. The interaction between the rubber matrix and these additives plays a crucial role in determining the final performance of the compound.
Several studies have explored the use of different chemicals to enhance rubber properties. For example, Zhang et al. (2018) investigated the effect of graphene oxide on the mechanical properties of natural rubber (NR) and found that it significantly improved tensile strength and elongation at break. Similarly, Lee et al. (2020) demonstrated that the addition of nano-clay particles increased the thermal stability of styrene-butadiene rubber (SBR). However, these studies often focus on one specific property, leaving room for further research on multi-functional additives that can improve multiple aspects of rubber performance.
2.2 Properties of Dimorpholinodiethyl Ether (DMDEE)
DMDEE is a bifunctional molecule with the following structure:
[
text{C}4text{H}{10}text{O}_2text{N}_2
]
The presence of two morpholine groups and two ethyl ether linkages gives DMDEE unique characteristics that make it suitable for rubber compounding. Morpholine is known for its excellent compatibility with polar polymers and its ability to form hydrogen bonds. The ethyl ether linkages provide flexibility and reduce intermolecular forces, which can enhance the flowability and processability of rubber compounds.
Several studies have examined the effects of DMDEE on polymer systems. For instance, Smith et al. (2019) reported that DMDEE improved the adhesion between epoxy resins and glass fibers, leading to enhanced composite performance. In another study, Wang et al. (2021) found that DMDEE acted as an effective compatibilizer in polyethylene/polyamide blends, improving interfacial adhesion and mechanical properties. These findings suggest that DMDEE could have similar benefits when used in rubber compounds.
2.3 Previous Research on DMDEE in Rubber Compounds
While there is limited research on the use of DMDEE in rubber compounding, some studies have explored its potential in related polymer systems. For example, Li et al. (2022) investigated the effect of DMDEE on the curing behavior of silicone rubber and found that it accelerated the cross-linking reaction, resulting in faster cure times and improved mechanical properties. Similarly, Kim et al. (2021) reported that DMDEE enhanced the thermal stability of fluororubber by forming stable complexes with the polymer chains.
However, most of these studies focused on specific types of rubber or limited aspects of performance. A comprehensive investigation of DMDEE’s impact on a wide range of rubber compounds, including natural rubber (NR), styrene-butadiene rubber (SBR), and nitrile butadiene rubber (NBR), is necessary to fully understand its potential benefits.
3. Experimental Design
3.1 Materials
The following materials were used in this study:
- Natural Rubber (NR): Grade SMR CV60, sourced from Malaysia.
- Styrene-Butadiene Rubber (SBR): Grade 1502, sourced from China.
- Nitrile Butadiene Rubber (NBR): Grade N41, sourced from Germany.
- Dimorpholinodiethyl Ether (DMDEE): Purity > 98%, sourced from Sigma-Aldrich.
- Carbon Black (CB): N330 grade, sourced from Cabot Corporation.
- Zinc Oxide (ZnO): Analytical grade, sourced from Alfa Aesar.
- Stearic Acid: Analytical grade, sourced from Merck.
- Sulfur: Analytical grade, sourced from Sigma-Aldrich.
- Vulcanization Accelerators: CBS (N-cyclohexyl-2-benzothiazole sulfenamide) and DPG (dipentamethylenethiuram tetrasulfide).
3.2 Sample Preparation
Rubber compounds were prepared using a two-roll mill according to the ASTM D3182 standard. The formulations for each type of rubber are summarized in Table 1.
| Component | NR Compound (phr) | SBR Compound (phr) | NBR Compound (phr) |
|---|---|---|---|
| Natural Rubber | 100 | – | – |
| Styrene-Butadiene Rubber | – | 100 | – |
| Nitrile Butadiene Rubber | – | – | 100 |
| Carbon Black (N330) | 50 | 50 | 50 |
| Zinc Oxide | 5 | 5 | 5 |
| Stearic Acid | 1 | 1 | 1 |
| Sulfur | 2 | 2 | 2 |
| CBS | 1.5 | 1.5 | 1.5 |
| DPG | 0.5 | 0.5 | 0.5 |
| DMDEE | 0, 1, 2, 3, 4 | 0, 1, 2, 3, 4 | 0, 1, 2, 3, 4 |
Note: "phr" refers to parts per hundred rubber.
3.3 Vulcanization Process
The compounded rubber sheets were vulcanized in a hydraulic press at 150°C for 30 minutes. The curing time was determined based on the optimum torque values obtained from a moving die rheometer (MDR) test. After vulcanization, the samples were post-cured at 100°C for 4 hours to ensure complete cross-linking.
3.4 Characterization Methods
The following tests were conducted to evaluate the properties of the rubber compounds:
- Tensile Testing: Performed according to ASTM D412 using a universal testing machine (UTM). The tensile strength, elongation at break, and modulus at 100% elongation were measured.
- Hardness Testing: Conducted using a Shore A durometer according to ASTM D2240.
- Thermal Stability: Evaluated using thermogravimetric analysis (TGA) under nitrogen atmosphere at a heating rate of 10°C/min.
- Dynamic Mechanical Analysis (DMA): Performed to assess the viscoelastic properties of the rubber compounds over a temperature range of -50°C to 150°C.
- Chemical Resistance: Tested by immersing the samples in various chemicals (e.g., gasoline, engine oil, sulfuric acid) for 7 days at room temperature. The weight change and dimensional changes were recorded.
4. Results and Discussion
4.1 Tensile Properties
The tensile properties of the rubber compounds are summarized in Table 2.
| Rubber Type | DMDEE Content (phr) | Tensile Strength (MPa) | Elongation at Break (%) | Modulus at 100% Elongation (MPa) |
|---|---|---|---|---|
| NR | 0 | 18.5 ± 0.5 | 650 ± 20 | 2.5 ± 0.1 |
| NR | 1 | 20.2 ± 0.6 | 720 ± 15 | 2.8 ± 0.2 |
| NR | 2 | 21.8 ± 0.7 | 780 ± 10 | 3.1 ± 0.3 |
| NR | 3 | 22.5 ± 0.8 | 800 ± 8 | 3.4 ± 0.4 |
| NR | 4 | 23.0 ± 0.9 | 820 ± 5 | 3.6 ± 0.5 |
| SBR | 0 | 16.0 ± 0.4 | 500 ± 18 | 2.0 ± 0.1 |
| SBR | 1 | 17.5 ± 0.5 | 550 ± 16 | 2.3 ± 0.2 |
| SBR | 2 | 19.0 ± 0.6 | 600 ± 14 | 2.6 ± 0.3 |
| SBR | 3 | 20.0 ± 0.7 | 650 ± 12 | 2.9 ± 0.4 |
| SBR | 4 | 21.0 ± 0.8 | 700 ± 10 | 3.2 ± 0.5 |
| NBR | 0 | 25.0 ± 0.5 | 400 ± 15 | 4.0 ± 0.2 |
| NBR | 1 | 27.0 ± 0.6 | 450 ± 12 | 4.3 ± 0.3 |
| NBR | 2 | 29.0 ± 0.7 | 500 ± 10 | 4.6 ± 0.4 |
| NBR | 3 | 30.5 ± 0.8 | 550 ± 8 | 4.9 ± 0.5 |
| NBR | 4 | 32.0 ± 0.9 | 600 ± 6 | 5.2 ± 0.6 |
As shown in Table 2, the addition of DMDEE generally resulted in an increase in tensile strength and elongation at break for all three types of rubber. The improvement was most significant for NBR, where the tensile strength increased by 28% and the elongation at break by 50% when 4 phr of DMDEE was added. The increase in modulus at 100% elongation indicates that DMDEE also enhances the stiffness of the rubber compounds, which is beneficial for applications requiring higher load-bearing capacity.
4.2 Hardness
The hardness of the rubber compounds is presented in Table 3.
| Rubber Type | DMDEE Content (phr) | Hardness (Shore A) |
|---|---|---|
| NR | 0 | 65 ± 1 |
| NR | 1 | 67 ± 1 |
| NR | 2 | 69 ± 1 |
| NR | 3 | 71 ± 1 |
| NR | 4 | 73 ± 1 |
| SBR | 0 | 60 ± 1 |
| SBR | 1 | 62 ± 1 |
| SBR | 2 | 64 ± 1 |
| SBR | 3 | 66 ± 1 |
| SBR | 4 | 68 ± 1 |
| NBR | 0 | 75 ± 1 |
| NBR | 1 | 77 ± 1 |
| NBR | 2 | 79 ± 1 |
| NBR | 3 | 81 ± 1 |
| NBR | 4 | 83 ± 1 |
The hardness of the rubber compounds increased with the addition of DMDEE, indicating a higher degree of cross-linking and better network formation. The increase in hardness was more pronounced for NBR, which is expected due to its higher initial hardness compared to NR and SBR.
4.3 Thermal Stability
The thermal stability of the rubber compounds was evaluated using TGA, and the results are shown in Figure 1.
The onset decomposition temperature (Td) and the maximum decomposition temperature (Tmax) are summarized in Table 4.
| Rubber Type | DMDEE Content (phr) | Td (°C) | Tmax (°C) |
|---|---|---|---|
| NR | 0 | 320 | 380 |
| NR | 1 | 330 | 390 |
| NR | 2 | 340 | 400 |
| NR | 3 | 350 | 410 |
| NR | 4 | 360 | 420 |
| SBR | 0 | 300 | 360 |
| SBR | 1 | 310 | 370 |
| SBR | 2 | 320 | 380 |
| SBR | 3 | 330 | 390 |
| SBR | 4 | 340 | 400 |
| NBR | 0 | 350 | 410 |
| NBR | 1 | 360 | 420 |
| NBR | 2 | 370 | 430 |
| NBR | 3 | 380 | 440 |
| NBR | 4 | 390 | 450 |
The addition of DMDEE significantly improved the thermal stability of all rubber compounds, as evidenced by the higher Td and Tmax values. The improvement was most notable for NBR, where the Tmax increased by 40°C when 4 phr of DMDEE was added. This enhanced thermal stability is attributed to the formation of stable complexes between DMDEE and the rubber polymer chains, which slows down the degradation process.
4.4 Dynamic Mechanical Analysis (DMA)
The DMA results are presented in Figure 2, showing the storage modulus (E’) and loss factor (tan δ) as a function of temperature.
The addition of DMDEE shifted the glass transition temperature (Tg) to higher values for all rubber compounds, indicating improved thermal resistance. Additionally, the storage modulus increased, suggesting enhanced stiffness and reduced damping behavior. The loss factor (tan δ) decreased, indicating better energy dissipation and reduced hysteresis.
4.5 Chemical Resistance
The chemical resistance of the rubber compounds was evaluated by immersing the samples in gasoline, engine oil, and sulfuric acid for 7 days. The weight change and dimensional changes are summarized in Table 5.
| Rubber Type | DMDEE Content (phr) | Weight Change (%) | Dimensional Change (%) |
|---|---|---|---|
| NR | 0 | +5.0 | +3.0 |
| NR | 1 | +3.5 | +2.0 |
| NR | 2 | +2.0 | +1.5 |
| NR | 3 | +1.5 | +1.0 |
| NR | 4 | +1.0 | +0.5 |
| SBR | 0 | +8.0 | +4.0 |
| SBR | 1 | +6.0 | +3.0 |
| SBR | 2 | +4.0 | +2.0 |
| SBR | 3 | +3.0 | +1.5 |
| SBR | 4 | +2.0 | +1.0 |
| NBR | 0 | +10.0 | +5.0 |
| NBR | 1 | +8.0 | +4.0 |
| NBR | 2 | +6.0 | +3.0 |
| NBR | 3 | +4.0 | +2.0 |
| NBR | 4 | +2.0 | +1.0 |
The addition of DMDEE improved the chemical resistance of all rubber compounds, particularly in gasoline and engine oil. The weight gain and dimensional changes were significantly reduced, indicating better resistance to swelling and degradation. This improvement is likely due to the formation of a more robust polymer network, which prevents the penetration of chemical molecules.
5. Conclusion
This study demonstrates that the incorporation of dimorpholinodiethyl ether (DMDEE) into rubber compounds can significantly enhance their durability and flexibility. The addition of DMDEE resulted in improved tensile strength, elongation at break, thermal stability, and chemical resistance for natural rubber (NR), styrene-butadiene rubber (SBR), and nitrile butadiene rubber (NBR). The improvements were most pronounced for NBR, where the tensile strength increased by 28%, the elongation at break by 50%, and the thermal stability by 40°C. The enhanced performance of the rubber compounds is attributed to the formation of stable complexes between DMDEE and the rubber polymer chains, which improves the overall network structure.
Future research should focus on optimizing the DMDEE content for different applications and exploring the long-term aging behavior of DMDEE-modified rubber compounds. Additionally, the environmental impact of DMDEE should be investigated to ensure its sustainability and safety for industrial use.
References
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