CHAPTER 3: RESULTS AND DISCUSSION
3.1. Research on manufacturing blended rubber materials based on nitrile butadiene rubber and polyvinyl chloride resin
3.1.1. Effect of PVC content on physical and mechanical properties of materials
In composite materials, the composition of the components in the system greatly affects the physical and mechanical properties of the material. To determine the optimal PVC content to replace NBR, we investigated the effect of PVC content on the physical and mechanical properties of the material. The research results are presented specifically in the table below:
Table 3.1: Effect of PVC content on physical and mechanical properties of NBR/PVC blend material
PVC content (%)
Tensile strength (MPa) | Elongation at break (%) | Hardness (Shore A) | |
0 | 23.40 | 560 | 67.5 |
10 | 24.10 | 512 | 68.0 |
20 | 25.39 | 506 | 69.0 |
30 | 25.08 | 480 | 70.0 |
40 | 19.67 | 433 | 71.0 |
50 | 13.32 | 284 | 73.0 |
60 | 14.00 | 240 | 75.0 |
70 | 16.50 | 235 | 78.0 |
80 | 18.60 | 240 | 81.0 |
90 | 21.20 | 245 | 83.0 |
100 | 23.00 | 250 | 85.0 |
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The results obtained above show that when NBR rubber is modified with PVC resin, the mechanical properties of the material are improved when the PVC content is around 20%.
30%. When the PVC content is greater than 30%, the tensile strength and elongation at break decrease sharply, while the hardness increases. The reason for this is that with a certain PVC content, PVC and NBR are compatible with each other, thus increasing the properties.
mechanical properties of the material. On the other hand, when the PVC content increases, the hardness of the composite material also increases, because PVC itself is a fairly hard plastic at room temperature [133]. When the PVC content exceeds 30%, the mechanical properties (tensile strength and elongation at break) of the material decrease sharply, possibly because at this composition range the materials are not compatible with each other, so there is a phenomenon of phase separation and leads to a sharp decrease in the mechanical properties of the material.
3.1.2. Effect of PVC content on swelling in gasoline and oil of the material
3.1.2.1. Effect of PVC content on swelling in A92 gasoline of the material
To evaluate the oil resistance of the material, we conducted a test and determined the swelling in A92 gasoline of the material according to Vietnamese standard TCVN 2752: 2008. The following are the results of the survey on the influence of PVC content on the swelling in A92 gasoline of NBR/PVC material.
Table 3.2. Effect of PVC resin content on swelling in A92 gasoline of NBR/PVC blend material
PVC content (%)
Swelling (% mass) | ||||
After 6 hours | After 24 hours | After 48 hours | After 72 hours | |
0 | 8.19 | 14.90 | 19.10 | 21.44 |
10 | 6.39 | 11.29 | 15.78 | 16.81 |
20 | 5.05 | 8.59 | 11.03 | 11.68 |
30 | 4.25 | 7.35 | 9.31 | 9.52 |
40 | 4.27 | 7.46 | 9.50 | 9.73 |
50 | 4.48 | 7.62 | 9.67 | 9.79 |
60 | 4.56 | 7.72 | 9.81 | 9.95 |
70 | 4.40 | 7.48 | 9.45 | 9.62 |
80 | 4.59 | 7.79 | 9.92 | 9.97 |
90 | 4.47 | 7.58 | 9.61 | 9.72 |
100 | 3.64 | 5.23 | 6.59 | 6.78 |
From the above results, it can be seen that when the PVC content increases, the swelling of the material decreases. At 30% PVC, the swelling reaches a minimum value, then tends to increase when the PVC content continues to increase. After 72 hours of soaking, the sample tends to be saturated and the mass increases more slowly. The above reason can be explained that at 30% PVC content, NBR rubber is compatible with PVC, so the blended material has a tighter structure, thereby reducing the erosion of environmental factors, causing the swelling to decrease.
3.1.2.2. Effect of PVC content on swelling in transformer oil of materials
Based on the research goal of manufacturing blended rubber materials with good physical properties, environmental and grease resistance to meet the requirements for manufacturing products for practical applications, we have oriented to manufacturing technical rubber products for the electrical industry (gaskets, cushions for transformers). Therefore, in addition to surveying the swelling in A92 gasoline, we have conducted a survey of the swelling of the material in transformer oil at normal temperature conditions. The following are the results of the survey on the influence of PVC content in transformer oil of the material.
Table 3.3. Effect of PVC content on swelling in transformer oil of NBR/PVC blend material
PVC content (%)
Swelling (% mass) | ||||
After 120 hours | After 240 hours | After 480 hours | After 720 hours | |
0 | - | - | - | - |
10 | - | - | - | - |
20 | - | - | - | - |
30 | - | - | - | - |
40 | - | 0.15 | 0.18 | 0.20 |
50 | - | 0.27 | 0.30 | 0.32 |
60 | - | 0.29 | 0.31 | 0.33 |
70 | - | 0.32 | 0.35 | 0.37 |
80 | - | 0.35 | 0.37 | 0.39 |
90 | - | 0.33 | 0.35 | 0.30 |
100 | - | - | - | - |
It was found that at all ratios, the NBR/PVC material hardly swelled when immersed in transformer oil for less than 120 hours and with PVC content lower than 40% the material also did not swell when immersed for up to 720 hours, but when denatured with more than 40% PVC, after 240 hours of immersion the material showed swelling. The swelling of the material gradually increased with increasing PVC content and immersion time. However, the swelling increased gradually and did not increase further after immersing the material for more than 720 hours.
3.1.3. Research on environmental durability of materials
To study the environmental (weather) durability of the material, we determined the aging coefficient of the material according to Vietnamese standard TCVN 2229-77 under test conditions at 100 o C for 72 hours in air environment. The results of the survey on the influence of PVC content on the aging coefficient of NBR/PVC material are presented in the graph below:
1
0.95
Aging coefficient
0.9
0.85
0.8
0.75
0.7
0 20 40 60 80 100
PVC content (%)
Figure 3.1. Effect of PVC content on aging coefficient of NBR/PVC blend material
Looking at the graph, it can be seen that the presence of PVC in the material combination significantly improved the thermal oxidation resistance of the material (the aging coefficient of the material increased when the PVC content reached about 20 30%, then decreased slightly and continued to increase).
when PVC content is over 60%). The aging coefficient of the material increases mainly due to the significant increase in tensile strength of the material after heat treatment, although the elongation at break decreases. The causes of the above phenomena can be explained as follows: At a temperature of 100 o C for a long time, a certain amount of PVC is decomposed and this decomposition is accompanied by the separation of HCl, which is an agent capable of reacting with the acrylonitrile group of NBR to form hydrochloride amines. When present
moisture, this substance will hydrolyze into amide and acid groups. Next, these two groups will react with the chloro-allyl group in the PVC chain to form amide and ester crosslinks [72, 106, 107]. When the PVC content is greater than 30%, the aging coefficient of the material decreases, possibly because in such a material composition there is a phenomenon of phase separation and makes the material structure less tight, more susceptible to oxygen and other agents, and more destructive.
Comment:
The above results show that the rubber blend material based on NBR/PVC has the ability to be compatible with each other, especially at PVC content ≤ 30% compared to the total amount of rubber and plastic. In the compatible area, the material has a tight structure and therefore has high mechanical and technical properties, grease and environmental (weather) resistance compared to other ratios. The research results have confirmed that the NBR/PVC material system has a fairly good ability to withstand transformer oil and is suitable for manufacturing products for the electrical industry.
3.2. Research on manufacturing blended rubber materials based on chloroprene rubber and polyvinyl chloride resin
3.2.1. Effect of PVC content on physical and mechanical properties of materials
As we know, chloroprene rubber (CR) and polyvinyl chloride (PVC) are weather-resistant, chemical-resistant and fire-resistant. Of these, CR rubber has good oil resistance but is expensive, while PVC is a popular and cheap plastic, so research on modifying PVC with CR has been of interest since very early on to create materials with technical properties.
high and reasonable price. However, PVC and CR are not compatible with each other [84] , so up to now there have not been many studies and applications of this blend system. However, in order to conduct systematic research, obtain comparative data and put into experimental planning, we have conducted a survey on the influence of the proportion of constituents on the properties of the material. The following are the results of the survey on the physical and mechanical properties of the CR/PVC blend system according to the PVC content as follows:
Table 3.4. Effect of PVC content on physical and mechanical properties of materials
CR/PVC blend
PVC content (%)
Tensile strength (MPa) | Elongation at break (%) | Hardness (Shore A) | |
0 | 15.39 | 408 | 73.0 |
10 | 14.32 | 390 | 74.0 |
20 | 13.1 | 315 | 75.0 |
30 | 11.4 | 230 | 76.0 |
40 | 9.8 | 110 | 77.0 |
50 | 9.15 | 85 | 78.5 |
60 | 9.25 | 90 | 79.5 |
70 | 11.3 | 120 | 81.5 |
80 | 15.8 | 180 | 82.5 |
90 | 19.5 | 210 | 83.5 |
100 | 23.00 | 250 | 85.0 |
From the research results obtained, it can be seen that when CR rubber is modified with PVC resin, the tensile strength of the material decreases significantly, especially when the PVC content reaches 50 60%. When the PVC content continues to increase, the tensile strength increases again. The process of changing the elongation occurs similarly to the tensile strength of the material sample. As for hardness, there is a steady increase when the PVC content increases. The reason for the above phenomenon is that at 50% PVC content, the compatibility of the two components CR and PVC is not good, so phase separation will occur. This leads to a loose structure, resulting in properties
The mechanical properties of the material decrease sharply. As the PVC content continues to increase, the tensile strength tends to increase, while the elongation also increases but not significantly, because the material gradually changes to plastic properties.
3.2.2. Effect of PVC content on swelling in gasoline and oil of the material
3.2.2.1. Effect of PVC content on swelling in A92 gasoline of the material
When CR is modified with PVC, the swelling degree in gasoline of the CR/PVC material system also changes significantly when changing the PVC content added. The following are the results of the survey on the swelling degree in A92 gasoline of the CR/PVC material:
Table 3.5. Effect of PVC content on swelling in A92 gasoline of CR/PVC blend material
PVC content (%)
Swelling (% mass) | ||||
After 6 hours | After 24 hours | After 48 hours | After 72 hours | |
0 | 48.68 | 49.68 | 49.70 | 49.86 |
10 | 44.96 | 47.56 | 48.09 | 48.87 |
20 | 38.02 | 41.43 | 42.82 | 43.25 |
30 | 33.79 | 36.72 | 38.76 | 39.19 |
40 | 27.39 | 32.71 | 33.94 | 34.22 |
50 | 27.46 | 33.36 | 34.72 | 35.28 |
60 | 22.42 | 25.65 | 27.75 | 28.16 |
70 | 15.73 | 19.34 | 21.63 | 22.41 |
80 | 10.86 | 13.89 | 15.08 | 15.87 |
90 | 6.42 | 8.24 | 9.61 | 10.09 |
100 | 3.64 | 5.23 | 6.59 | 6.78 |
From the above results, it can be seen that CR rubber has a higher swelling degree in gasoline than NBR rubber. When the PVC content increases, the swelling degree in gasoline of the material decreases. The reason is that CR and PVC are not compatible with each other and the phenomenon of phase separation occurs in the system, increasing the possibility of eroding the gasoline environment.
However, because the PVC content increases gradually while the CR content decreases proportionally, and the swelling capacity of CR in gasoline is much larger than that of PVC, the swelling capacity of the composite material decreases rapidly with the increase in PVC.
3.2.2.2. Effect of PVC content on swelling in transformer oil of materials Table 3.6. Effect of PVC content on swelling in transformer oil of materials
CR/PVC blend material
PVC content (%)
Swelling (% mass) | ||||
After 120 hours | After 240 hours | After 480 hours | After 720 hours | |
0 | 0.61 | 1.12 | 2.05 | 2.14 |
10 | 0.59 | 1.09 | 2.01 | 2.07 |
20 | 0.55 | 1.03 | 1.99 | 2.02 |
30 | 0.51 | 0.99 | 1.69 | 1.85 |
40 | 0.47 | 0.92 | 1.45 | 1.51 |
50 | 0.58 | 0.99 | 1.59 | 1.73 |
60 | 0.41 | 0.86 | 1.31 | 1.42 |
70 | 0.32 | 0.73 | 1.10 | 1.22 |
80 | 0.25 | 0.55 | 0.84 | 0.90 |
90 | - | 0.33 | 0.45 | 0.52 |
100 | - | - | - | - |
From the above results, it can be seen that the swelling of CR in transformer oil is also higher than that of NBR. When CR rubber is modified with PVC resin, the swelling of the material gradually decreases as the PVC content increases. However, at a ratio of 50% PVC, the swelling phenomenon occurs slightly higher than other ratios, then tends to decrease gradually. When the PVC content is further increased to 80 90% and at this PVC content, the material almost does not swell or swells very little when soaked for a long time.
3.2.3. Research on environmental durability of materials
To study the environmental (weather) durability of the material, we determined the aging coefficient of the CR/PVC blend material according to Vietnamese standard TCVN