Application of Magnesium Hydroxide/Diphenoxy Phosphate in Silicone Rubber Flame Retardant Cable Material
Round 1
Reviewer 1 Report
Reviewer Comments:
In this research work the effects of different flame retardants on the mechanical properties, flame retardant properties, and electrical insulation properties of silicone cable coatings were investigated. The research results show that the flame retardant can be uniformly dispersed in silicone rubber. Meanwhile, the tensile strength, elongation at break, and electrical insulation properties of the silicone rubber containing flame retardants remained at a high level. However author need to elaborate more mechanism behind each property with reference. More related discussion should be included in the discussion section. The Application of this work is interesting. So, I would recommend this manuscript with minor corrections.
Comments:
1. Usage of magnesium hydroxide as flame retardant is not new, authors should mentioned innovative points of this work in last paragraph of introduction
2. Author must also mention the mechanism behind the increase in flame retardant properties? For mechanism schematic figure would be good tool to present your work.
3. Why Carbon Black is very effective?
4. The Figure 8 presenting SEM for sample 14 is different than other samples, why?
5. The authors are suggested to double-check the whole manuscript for grammar errors and typos that need to be corrected.
The authors are suggested to double-check the whole manuscript for grammar errors and typos that need to be corrected.
Author Response
Response to Reviewer 1 Comments:
1) Usage of magnesium hydroxide as flame retardant is not new, authors should mentioned innovative points of this work in last paragraph of introduction
Answer: Thank you for your suggestion. We have added innovative points of this work in last paragraph of introduction.
“Due to the poor compatibility of MH with silicone rubber, it is difficult to disperse uniformly, which may affect the mechanical properties and extrusion performance of the coating.For the compatibility between MH and polymer, certain synergists or phosphorus-based flame retardants can be added to improve the flame retardant properties of the composite while reducing the amount of MH added. Phosphorus and nitrogen flame retardants [27-29] have the advantages of high flame retardant efficiency, low toxicity, and good compatibility with polymer materials. In this experiment, we compounded the synthesized phosphate with magnesium hydroxide for use as a flame retardant for silicone rubber. Using methods such as combustion experiments and thermogravimetric analysis, we initially explored the flame retardant effect of the synthesized flame retardant and the compounding system on the silicone rubber material, expecting to find a formulation with excellent flame retardant properties for silicone rubber.”
2) Author must also mention the mechanism behind the increase in flame retardant properties? For mechanism schematic figure would be good tool to present your work.
Answer: Thank you for your suggestion. We have added the mechanism behind the increase in flame retardant properties.
“Acidic groups such as polyphosphoric acid and phosphoric acid, formed by the de-composition of phosphate under heating conditions, capture the debris from the de-composition of silicone rubber. As can be seen in Figure S2, the uneven distribution of fine bubbles on the surface of the burned material indicates that the diphosphate has good char formation properties.”
“Possible reasons for flame retardant: the water vapor released by the pyrolysis of magnesium hydroxide takes away more heat from the substrate and reduces the surface temperature of the substrate, the foam-like material formed by the thermal decomposition of MDP covers the surface of the material, and prevents the further transfer of heat and oxygen, thus achieving a synergistic flame retardant effect.”
3) Why Carbon Black is very effective?
Answer: Thank you for your suggestion.
The principle of carbon black reinforced silicone rubber can be explained by the "Bonded rubber shell layer structure model" [32]. The strong interaction between the carbon black and the rubber molecules results in the rubber molecules being adsorbed on the surface of the carbon black to form a shell structure. When the rubber is deformed, this shell structure acts as a skeleton in the vulcanized rubber and distributes the stresses evenly, thus increasing the strength of the rubber.
4) The Figure 8 presenting SEM for sample 14 is different than other samples, why?
Answer: Thank you for your suggestion. We re-tested the data for sample 14.
Figure 8 SEM images of six different samples (500x)
- The authors are suggested to double-check the whole manuscript for grammar errors and typos that need to be corrected.
Answer: Thank you for your suggestion. We have checked the whole manuscript.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The manuscript entitled "Application of magnesium hydroxide/diphenoxy phosphate in
silicone rubber flame retardant cable material" can be suitable for publication after addressing the follloing points:
The abstract is poorly organized, with an inappropriate balance of detail, and fails to provide the most crucial information from the article.
The origin country for all utilized materials and instruments should be added in materials section.
In many paragraphs, there is no space between the cited reference and sentences words.
TG in figure 7 should be discussed in detail.
Standard error is missing for figure 4.
In the introduction part the objectives are not very clear and the description (use of modified chitosan, starch and role of crosslinking and plasticizer) is not logical and smooth.
Author Response
Response to Reviewer 2 Comments:
1) The abstract is poorly organized, with an inappropriate balance of detail, and fails to provide the most crucial information from the article.
Answer: Thank you for your suggestion. I have reorganised the abstract.
“Abstract: Deketoxime-type room temperature vulcanized silicone rubber cable materials were prepared using α, ω-dihydroxy polydimethylsiloxane, carbon black, calcium carbonate, magnesium hydroxide, Piperazine bis( diphenoxyphosphat) salt (PBDP) and Melamine diphenoxy phosphate (MDP). The effects of carbon black and flame retardants on the mechanical properties, flame retardant properties, and electrical insulation properties of silicone cable coatings were investigated. The research results show that the products obtained have good mechanical and electrical insulation properties, with tensile strength greater than 3.0 MPa, dielectric strength greater than 22 kV/mm, and volume resistivity higher than 6.5 ×1014 Ω×cm. When 30 parts of Mg(OH)2 : MDP = 2 : 1 were added hundred parts of resin, the flame retardant performance of wire and cable materials can be significantly improved. Under the thermal radiation illumination of 50 kW/m2, the ignition time (TTI) of Mg(OH)2/MDP coating increased by 16 s, and the maximum heat release rate (pkHRR) and total heat release rate (THR) decreased by 29.7% and 68.8%, respectively, compared with the silicone rubber without flame retardant. The silicone rubber coatings prepared are also flame retardant up to the FV-1 level.”
2) The origin country for all utilized materials and instruments should be added in materials section;
Answer: Thank you for your suggestion. We have revised them.
“Electronic universal testing machine (UTM, Shimadzu, AG-IC50kN, Japan)”,
the above drugs were purchased from West Asia Chemical Technology (Shandong, Co., Ltd, China).”
3) In many paragraphs, there is no space between the cited reference and sentences words.
Answer: Thank you for your suggestion. We have revised them.
4) TG in figure 7 should be discussed in detail.
Answer: Thank you for your suggestion. We have revised them.
“Figure 7 shows the thermal weight loss graphs of silicone rubber samples 4, 7, 10, 11, 13, and 14. The silicone rubber (7) without the addition of magnesium hydroxide started to lose weight at 175 °C and ended at 680 °C, with a residual mass of 33.32% for the silicone rubber coating. The initial decomposition temperature of the added flame retardant was delayed in all cases compared to sample 7 without the flame retardant. The thermal decomposition curve of silicone rubber (4) is divided into two intervals. The first interval (230-320°C) is the decomposition of small molecules of the material by heat. The second interval (370-590°C), a strong thermal weight loss occurred, probably due to the decomposition of magnesium hydroxide at 390°C to produce water vapor and high-temperature resistant solid magnesium oxide. Magnesium hydroxide absorbs a large amount of heat during the decomposition process, which can make the initial decomposition of silicone rubber effectively curbed. The residual mass of 36.31% for the silicone rubber coating. The rubber added with MDP (13) started to lose weight at 243 °C and ended at 650 °C, The residual mass of 33.36% for the silicone rubber coating. The thermogravimetric curves of the composites (samples 11 and 14) with the addition of mixed flame retardants of magnesium hydroxide and diphenyl phosphate were similar to those of sample 4, but the material had a lower temperature in the first decomposition interval, while the temperature in the second decomposition interval was higher. The possible reason for this is that the MDP catalyzes the decomposition of the magnesium hydroxide, bringing forward the first decomposition temperature. The heated MDP produces phosphoric acid, which promotes the carbonization of hydroxyl compounds and forms a dense carbonized film on the surface of the film. The carbonized film covering the surface of the substrate prevents heat and oxygen transfer from inhibiting the thermal decomposition of the material until the decomposition temperature of the macromolecules in the rubber is reached. The temperature of the second decomposition interval was delayed. The results of the thermal decomposition experiments showed that the addition of magnesium hydroxide with diphenyl phosphate resulted in better thermal stability performance of the room-temperature vulcanized rubber.”
5) Standard error is missing for figure 4.
Answer: Thank you for your suggestion. We have revised them.
6) In the introduction part the objectives are not very clear and the description (use of modified chitosan, starch and role of crosslinking and plasticizer) is not logical and smooth.
Answer: Thank you for your suggestion. We have revised them.
“Although room-temperature vulcanized rubber has the advantages of a high oxygen index at the combustion limit and a low heat release rate, which can slow down the propagation of flame, silicone rubber itself is combustible and not easily self-extinguished [23, 24], making it difficult to meet the flame retardant requirements of high-voltage transmission lines. Therefore, flame retardants need to be added to room-temperature vulcanized rubber to improve its flame-retardant properties. There are three main ways to improve the flame retardant properties of silicone rubber: adding flame retardants, changing material composition, and blending with other polymer materials. The addition of flame retardants is the simplest and easiest way to improve the flame retardancy of silicone rubber. Magnesium hydroxide (MH) is a more widely used inorganic flame retardant [25, 26]. Mg(OH)2 facilitates the formation of a charred layer on the surface of the material, preventing the entry of oxygen and heat; at the same time, the MgO generated by decomposition is a good refractory material, which can improve the resistance of polymeric materials to flames. Due to the poor compatibility of MH with silicone rubber, it is difficult to disperse uniformly, which may affect the mechanical properties and extrusion performance of the coating.For the compatibility between MH and polymer, certain synergists or phosphorus-based flame retardants can be added to improve the flame retardant properties of the composite while reducing the amount of MH added. Phosphorus and nitrogen flame retardants [27-29] have the advantages of high flame retardant efficiency, low toxicity, and good compatibility with polymer materials. In this experiment, we compounded the synthesized phosphate with magnesium hydroxide for use as a flame retardant for silicone rubber. Using methods such as combustion experiments and thermogravimetric analysis, we initially explored the flame retardant effect of the synthesized flame retardant and the compounding system on the silicone rubber material, expecting to find a formulation with excellent flame retardant properties for silicone rubber.”
Author Response File: Author Response.docx
Reviewer 3 Report
This manuscript reports on the use of magnesium hydroxide and two salts based on acid diphenyl phosphate as a flame retardants in silicone rubber coatings for wires. Authors use numerous experimental techniques to study combustion, thermal decomposition and physical properties of the coatings. However, this paper contains serious flaws and cannot be published in the Coatings.
The goal of this study is not clearly stated. It is logically to assume that authors looked for synergistic effect between Mg(OH)2, PBDS and MDP. Apparently, they didn’t achieve this goal. If there is any effect, it is rather antagonistic than synergistic. See Figure 6. There is no discussion in the paper about synergistic or antagonistic effects between FR additives.
The effect of carbon black on the curing of silicone rubber has been studied and discussed in the paper. But what about effects of Mg(OH)2, PBDS and MDP? Did they affect curing? Flammability performance of the resin can be significantly affected by the degree of cross-linking.
Subchapters 3.2 and 3.3 and Figure 2. Different “quality”? Should it be “quantity” instead?
GB/T10707 test has been followed to assess flame retardant performance of the rubbers. This test consists of part A - LOI test and part B – analog of UL-94 test. What numbers are reported in the line of Sample extinction time in Table 2? Are these average extinction time for 10 flame applications as prescribed by GB/T10707? If so, none of the formulation achieved V-0 rating (FV-0). What about dripping?
Figure S2 and Figure 6 use TPPM and DPPP abbreviations? What are those? It looks like authors didn’t check their manuscript before submitting to the joulnal.
Figure 7. There is huge difference in the thermal stability of different formulations. Especially striking is the difference between non FR formulation formulation 7 and MDP FR formulation 13 with the onset of weight loss at about 400 C. Author’s explanation about charring before onset of weight loss doesn’t make sense. There is no charring without weight loss. What is the thermal stability of MDP? I have never seen melamine salt with onset of weight loss > 400 C.
Authors use “grams” of added carbon black, CaCO3 and flame retardants to identify their formulations. This is not right way to do this. They should use “parts per hundred parts of resin” phr which is independent on the size of the batch.
English is reasonable. Requires some editing.
Author Response
Response to Reviewer 3 Comments:
1) The goal of this study is not clearly stated. It is logically to assume that authors looked for synergistic effect between Mg(OH)2, PBDS and MDP. Apparently, they didn’t achieve this goal. If there is any effect, it is rather antagonistic than synergistic. See Figure 6. There is no discussion in the paper about synergistic or antagonistic effects between FR additives.
Answer: Thank you for your suggestion. We have added innovative points of this work in last paragraph of introduction. Although the synergistic effect of magnesium hydroxide with diphenyl phosphate is not so obvious, we have tried to explain the synergistic effect between them.
“Due to the poor compatibility of MH with silicone rubber, it is difficult to disperse uniformly, which may affect the mechanical properties and extrusion performance of the coating.For the compatibility between MH and polymer, certain synergists or phosphorus-based flame retardants can be added to improve the flame retardant properties of the composite while reducing the amount of MH added. Phosphorus and nitrogen flame retardants [27-29] have the advantages of high flame retardant efficiency, low toxicity, and good compatibility with polymer materials. In this experiment, we compounded the synthesized phosphate with magnesium hydroxide for use as a flame retardant for silicone rubber. Using methods such as combustion experiments and thermogravimetric analysis, we initially explored the flame retardant effect of the synthesized flame retardant and the compounding system on the silicone rubber material, expecting to find a formulation with excellent flame retardant properties for silicone rubber.”
“3.4.1 The ignition time of adding different flame retardants.
The addition of phosphate is effective in extending the ignition time of normal-temperature vulcanized rubber. The reason for this may be that silicone rubber releases substances such as phosphoric acid and polyphosphoric acid during the heat process, which causes the polymeric material to dehydrate carbonization, forming a protective carbon film on the surface of the material and thus delaying the combustion process.”
“3.4.3 Total heat release (THR) with different flame retardants with different flame retardants.
Acidic groups such as polyphosphoric acid and phosphoric acid, formed by the decomposition of phosphate under heating conditions, capture the debris from the decomposition of silicone rubber. As can be seen in Figure S2, the uneven distribution of fine bubbles on the surface of the burned material indicates that the diphosphate has good char formation properties.”
“3.4.4 Vertical combustion test with different flame retardants
Possible reasons for flame retardant: the water vapor released by the pyrolysis of magnesium hydroxide takes away more heat from the substrate and reduces the surface temperature of the substrate, the foam-like material formed by the thermal decomposition of MDP covers the surface of the material, and prevents the further transfer of heat and oxygen, thus achieving a synergistic flame retardant effect.”
“3.5 Thermogravimetric analysis with different flame retardants
he possible reason for this is that the MDP catalyzes the decomposition of the magne-sium hydroxide, bringing forward the first decomposition temperature. The heated MDP produces phosphoric acid, which promotes the carbonization of hydroxyl com-pounds and forms a dense carbonized film on the surface of the film. The carbonized film covering the surface of the substrate prevents heat and oxygen transfer from in-hibiting the thermal decomposition of the material until the decomposition tempera-ture of the macromolecules in the rubber is reached. The temperature of the second decomposition interval was delayed.”
2). The effect of carbon black on the curing of silicone rubber has been studied and discussed in the paper. But what about effects of Mg(OH)2, PBDS and MDP? Did they affect curing? Flammability performance of the resin can be significantly affected by the degree of cross-linking.
Answer: Thank you for your suggestion. We have revised them.
“Table 3 shows that the tensile strength and elongation at the break of the silicone rubber samples with flame retardant additions were slightly lower compared to sample 7 without flame retardant additions. The sample with the addition of diphenyl phosphate has better compatibility with silicone rubber and has better mechanical properties compared to sample 4. Sample 10 had an elongation at a break of 280% and a tensile strength of 3.12 MPa. Sample 13 had an elongation at a break of 297% and a tensile strength of 3.41 MPa. The variation in the mechanical properties of the samples can also be verified in the SEM images. The surface drying times for the samples with flame retardants (4, 7, 10, 11, 13, and 14) ranged from 20.5 to 24.7 minutes and the depth of cure for 24 hours ranged from 3.4 to 3.7mm.”
3) Subchapters 3.2 and 3.3 and Figure 2. Different “quality”? Should it be “quantity” instead?
Answer: Thank you for your suggestion. We have revised them.
4) GB/T10707 test has been followed to assess flame retardant performance of the rubbers. This test consists of part A - LOI test and part B – analog of UL-94 test. What numbers are reported in the line of Sample extinction time in Table 2? Are these average extinction time for 10 flame applications as prescribed by GB/T10707? If so, none of the formulation achieved V-0 rating (FV-0). What about dripping?
Answer: Thank you for your suggestion. We have revised them.
“3.4.4 Vertical combustion test with different flame retardants
Table 2 and Figure S3 shows the vertical burning time of room-temperature vulcanized rubber containing different amounts of flame retardant fillers. During the course of the experiment, it was found that samples 1 and 7 without flame retardant burned continuously, with the flame spreading to the fixture and largely free of residual char and accompanied by the phenomenon of dripping and igniting skimmed cotton. The experimental phenomenon shows that the flame retardant performance of PBDP is lower than that of MDP and Mg(OH)2, while Mg(OH)2 has a synergistic flame retardant effect with MDP. In sample 10 containing PBDP, the after-flame burn time after the ignition was reduced, the sample drip phenomenon, and ignited the skimmer phenomenon. The flame retardant grade of the material is FV-2. The flame retardancy of the samples with the addition of Mg(OH)2 and diphenyl phosphate flame retardant was significantly improved. Sample 4 with 30 phr of Mg(OH)2 was self-extinguishing after the first ignition, and the sum of the two after-flame times was less than 10 s. The flame retardancy of this material reached the FV-0 level. For sample 11 with 20 phr Mg(OH)2 and 10 phr MDP, a protective charcoal layer was observed on the surface of the specimen during ignition. However, due to the presence of the charcoal layer, the second after-flame burn time was slightly longer and the flame retardant rating was only FV-1. Possible reasons for flame retardant: the water vapor released by the pyrolysis of magnesium hydroxide takes away more heat from the substrate and reduces the surface temperature of the substrate, the foam-like material formed by the thermal decomposition of MDP covers the surface of the material, and prevents the further transfer of heat and oxygen, thus achieving a synergistic flame retardant effect.”
Table 2 Flame retardant properties of room temperature vulcanized rubber with different flame retardants
|
Entry |
First after-flame burn time for 5 specimens (t1, i) / s |
Second after-flame burn time for 5 specimens (t2, i) / s |
Total afterflame burning time per specimen ( t1, i + t2, i) / s |
Total afterflame burn time for 5 specimens (tf) / s |
Drip ignition of skimmed cotton |
Flame-retardant grade |
|
1 |
Burn |
Burn |
Burn |
Burn |
Yes |
NR |
|
7 |
Burn |
Burn |
Burn |
Burn |
Yes |
NR |
|
4 |
3/4/2/3/2 |
6/6/5/7/5 |
9/10/8/10/7 |
44 |
No |
FV-0 |
|
10 |
22/16/19/23/20 |
26/25/25/27/34 |
48/41/44/50/54 |
237 |
Yes |
FV-2 |
|
11 |
5/4/5/3/7 |
7/9/11/6/12 |
12/13/16/9/19 |
69 |
No |
FV-1 |
|
13 |
6/6/5/7/7 |
10/9/11/13/14 |
16/15/16/20/21 |
88 |
No |
FV-1 |
|
14 |
14/11/13/13/12 |
13/10/15/17/14 |
27/28/28/30/26 |
6/6/5/7/4 |
No |
FV-1 |
5) Figure S2 and Figure 6 use TPPM and DPPP abbreviations? What are those? It looks like authors didn’t check their manuscript before submitting to the joulnal.
Answer: It is very unfortunate that such an error occurred. We have revised it.
“Piperazine bis( diphenoxyphosphat) salt (PBDP) and Melamine diphenoxy phosphate (MDP)”
6). Figure 7. There is huge difference in the thermal stability of different formulations. Especially striking is the difference between non FR formulation formulation 7 and MDP FR formulation 13 with the onset of weight loss at about 400 C. Author’s explanation about charring before onset of weight loss doesn’t make sense. There is no charring without weight loss. What is the thermal stability of MDP? I have never seen melamine salt with onset of weight loss > 400 C.
Answer: Thank you for your suggestion. We re-tested the thermogravimetric data of sample 13.
“The residual mass of 36.31% for the silicone rubber coating. The rubber added with MDP (13) started to lose weight at 243 °C and ended at 650 °C, The residual mass of 33.36% for the silicone rubber coating.”
7) Authors use “grams” of added carbon black, CaCO3 and flame retardants to identify their formulations. This is not right way to do this. They should use “parts per hundred parts of resin” phr which is independent on the size of the batch.
Answer: Thank you for your suggestion. We have revised them
Table 1 Sample formulations
|
Entry |
PDMS (g) |
Carbon black (phr) |
CaCO3 (phr) |
Mg(OH)2 (phr) |
PBDP (phr) |
MDP (phr) |
|
1 |
100 |
0 |
100 |
30 |
0 |
0 |
|
2 |
100 |
10 |
100 |
30 |
0 |
0 |
|
3 |
100 |
20 |
100 |
30 |
0 |
0 |
|
4 |
100 |
30 |
100 |
30 |
0 |
0 |
|
5 |
100 |
40 |
100 |
30 |
0 |
0 |
|
6 |
100 |
50 |
100 |
30 |
0 |
0 |
|
7 |
100 |
30 |
100 |
0 |
0 |
0 |
|
8 |
100 |
30 |
100 |
20 |
10 |
0 |
|
9 |
100 |
30 |
100 |
10 |
20 |
0 |
|
10 |
100 |
30 |
100 |
0 |
30 |
0 |
|
11 |
100 |
30 |
100 |
20 |
0 |
10 |
|
12 |
100 |
30 |
100 |
10 |
0 |
20 |
|
13 |
100 |
30 |
100 |
0 |
0 |
30 |
|
14 |
100 |
30 |
100 |
10 |
10 |
10 |
Author Response File: Author Response.docx
Round 2
Reviewer 3 Report
Lines 89 and 92. Why drugs? Do you mean chemicals?
Author Response
Response to Reviewer 3 Comments:
1) Lines 89 and 92. Why drugs? Do you mean chemicals?
Answer: Thank you for your suggestion. We have revised them.
“the above chemicals were purchased from West Asia Chemical Technology”
Author Response File: Author Response.docx
