Synthesized and Designed New Modified Poly(vinyl chloride) Structures to Enhance Their Photo-Resistance Characteristics
, Wedad H. Al-Dahhan 1, Hassan Hashim 2 and Emad Yousif 1Round 1
Reviewer 1 Report
The authors synthesized four novel PVC derivative polymers and proved that they can provide some extent of photo resistance when mixing with PVC. The protection was verified by a number of methods. Overall, the effectiveness of the polymers is obvious. However, the authors didn’t compare their results to other stabilizers. It would be important to point out the advantages of the synthesized polymers. Are they nontoxic, environmentally safe, easy to make, or provide better protection?
Some other points:
1. What’s the advantage of PVC modification compared to stabilizing additive?
2. In Scheme 1, when using R group, the aldehyde should be removed. What were shown are the reagents.
3. No addition of pyridine was mentioned in 3.1
4. The authors claimed that 30-35% modification happened from NMR but no spectrum of PVC-ed was shown. Which peaks were used for quantification? Based on the chemical drawing in Table 1 and Figures 1,2 the authors were assuming 50% modification, which cannot explain the ratio of peak 1: peak 3 in Figure 1. Also, the spectrums of PVC-ed/o-OMe and PVC-ed/p-OH were displayed, what about the others?
5. One concern was that inevitable crosslinking would result in aggregation of the polymer and alter the characteristics of the polymer.
6. English needs to be improved.
Author Response
Response to Reviewer 1 Comments
Point 1: The authors synthesized four novel PVC derivative polymers and proved that they can provide some extent of photo resistance when mixing with PVC. The protection was verified by a number of methods. Overall, the effectiveness of the polymers is obvious. However, the authors didn’t compare their results to other stabilizers. It would be important to point out the advantages of the synthesized polymers. Are they nontoxic, environmentally safe, easy to make, or provide better protection?
Response 1: It is known that organotin complexes showed very good photo-stability of PVC when it is used as a photo-stabilizers [12, 14, 16, 18]. Interestingly, the pure organic modified PVC showed almost similar stability according to the weight loss and functional group index experiments. This is quite promising results hence it has been used only organic materials which are less toxic and biodegradable. Therefore, these materials are environmentally safe, provide excellent protection and they are easy to produce.
Point 2: What’s the advantage of PVC modification compared to stabilizing additive?
Response 2: As we mentioned in the first point in this work we did not need to use inorganic materials to stabilize the PVC but pure organic compounds did the same job. Thus it is a new way to protect plastic materials. On the other hand, the modification of PVC materials could open the door for several researches by controlling the percentage of modification and playing with the physical proterties of modified polymer.
Point 3: In Scheme 1, when using R group, the aldehyde should be removed. What were shown are the reagents.
Response 3: It has been corrected thank you.
Point 4: No addition of pyridine was mentioned in 3.1
Response 4: Done.
Point 5: The authors claimed that 30-35% modification happened from NMR but no spectrum of PVC-ed was shown. Which peaks were used for quantification? Based on the chemical drawing in Table 1 and Figures 1,2 the authors were assuming 50% modification, which cannot explain the ratio of peak 1: peak 3 in Figure 1. Also, the spectrums of PVC-ed/o-OMe and PVC-ed/p-OH were displayed, what about the others?
Response 5: In comparison the integration of proton peaks at the aromatic region which is (4) as it should be with aliphatic peaks such as the peak at 1.06 ppm with integration (7) as shown in Figure 1, this peak belongs to CH2 group so the integration should be only two if the modification 100 percent. This is clear evidence that about a third amount of labeled chlorine atoms were substituted. we did not include all NMR spectrums because it would be two crowded however we could send them as supplementary file if you would like.
Point 6: One concern was that inevitable crosslinking would result in aggregation of the polymer and alter the characteristics of the polymer.
Response 6: Yes, you are right but we have considered this issue by using PVC (1 mole) with five moles of ethylene diamine in this process. The two amino groups of ethylene diamine molecule can condense with nearby chlorine atoms to generate cyclic derivatives, but this excess can also reduce the development of crosslinking between distinct polymer chains. Since it has been noted that cross-linking does happen when PVC is treated with ethylene diamine at elevated temperatures for an extended period of time, the reaction was first carried out at room temperature to prevent any cross-linking [21].
Point 7: English needs to be improved.
Response 7: Done.
Reviewer 2 Report
The author reported a modified PVC which is used as photo-stabilizers. PVC with photo-stabilizers exhibits less photo-degradation when exposed to UV light than ordinary PVC. PVC is the second largest manufacturing material after polyethylene. Improving the light stability of PVC is beneficial to its outdoor application. After looking through the paper, I found the experiments were not well designed and studied, the experiments did not provide enough data to prove that the structure and modification percentage of modified PVC meet the expectations. In addition, the micrograph lacks contrast, which cannot strongly explain the photostability of modified PVC. Detailed issues are given as follows.
1. Treating PVC with ethylenediamine at room temperature can prevent crosslinking, but the percentage of modification is too low. The author increased the percentage of modification after increasing the temperature, but did not explain the crosslinking.
2. In 3.2, only the text description of the characteristic peaks of the key groups is given in the FT-IR spectrum analysis, and only the spectra of PVC-ed/o-OMe and PVC-ed/p-OH are given in the 1H NMR spectrum analysis, which cannot strongly prove the structure of the modified polymer. “the signals of both primary and secondary amine are overlapped with water peak between 3.05-3.90 ppm”. This situation cannot explain the existence of signal peaks of primary and secondary amines. In addition, it can be seen from Fig. 2 that there is a certain degree of crosslinking between polyvinyl chloride and ethylenediamine, so it is inaccurate to calculate the percentage of modification using the percentage of nitrogen and chlorine atoms.
3. In the paper, the addition amount of light stabilizer was selected as 5%, but the reason for selection was not explained, lacking data support.
4. When the surface morphology of the film was analyzed in section 3.3.3, the images of PVC-ed/p-OH, PVC-ed/o-OMe, PVC-ed/p-OMe, PVC-ed/o-NO2 before irradiation were missing. The existing results cannot prove that the four PVC additives have different photo stability
5. When comparing the light stability of the four light stabilizers, the paper only explains that the reason why PVC-ed/p-OH has the best photo stability is that “it contains a phenol group which is known as an excellent free radial scanner” and its mechanism has not been further confirmed. The reason of the other three photo stabilizers have poor effects is lacking. In addition, the significance of selecting four different benzaldehyde derivatives was not explained.
6. There are many unprofessional and strange expressions in the paper, which should be modified. Typical example as follows:
“These investigations, which were approved, showed that novel modified Schiff base polymers perform far better as photo-stabilizers than plain PVC.”
“Even though all other additives have shown good stability for PVC films in comparison to pure PVC…”
“…Figure 5c shows the FTIT spectrum of blended PVC film…”
“Equation 2. 2 was used to calculate the…”.
“The weight loss due to photodegraded of PVC films in the presence and absence of additives was calculated using equation 2.3.”
“The calculations were performed for all blank and blended PVC films with a 40 m with addition only 5% …”
Author Response
Response to Reviewer 2 Comments
Point 1: Treating PVC with ethylenediamine at room temperature can prevent crosslinking, but the percentage of modification is too low. The author increased the percentage of modification after increasing the temperature but did not explain the crosslinking.
Response 1: The aim is not to get 100% of modification but to study how it is possible to control the chemical reaction and the percentage of modification. Using an excess of ethylene diamine reduces the possibility of cross-linking which has been explained in Figure 2.
Point 2: In 3.2, only the text description of the characteristic peaks of the key groups is given in the FT-IR spectrum analysis, and only the spectra of PVC-ed/o-OMe and PVC-ed/p-OH are given in the 1H NMR spectrum analysis, which cannot strongly prove the structure of the modified polymer. “the signals of both primary and secondary amine are overlapped with water peak between 3.05-3.90 ppm”. This situation cannot explain the existence of signal peaks of primary and secondary amines. In addition, it can be seen from Fig. 2 that there is a certain degree of crosslinking between polyvinyl chloride and ethylenediamine, so it is inaccurate to calculate the percentage of modification using the percentage of nitrogen and chlorine atoms.
Response 2: The percentage of modification was estimated by comparison the integration of proton peaks at the aromatic region which is (4) as it should be with aliphatic peaks such as the peak at 1.06 ppm with integration (7) as shown in Figure 1, this peak belongs to CH2 group so the integration should be only two if the modification 100 percent. This is clear evidence that about a third amount of labeled chlorine atoms were substituted. we did not include all NMR and FTIR spectrums because it would be two crowded however we could send them as supplementary file if you would like.
Point 3: In the paper, the addition amount of light stabilizer was selected as 5%, but the reason for selection was not explained, lacking data support.
Response 3: The reason for using a low percentage of modified PVC (5%) is to not change the features of PVC at the same time provide good stability.
Point 4: When the surface morphology of the film was analyzed in section 3.3.3, the images of PVC-ed/p-OH, PVC-ed/o-OMe, PVC-ed/p-OMe, PVC-ed/o-NO2 before irradiation were missing. The existing results cannot prove that the four PVC additives have different photostability
Response 4: The four modified PVCs showed very close stability because they have quite similar chemical structures. We have studied the surface morphology of prepared blended films after irradiation and compared it with blank PVC before and after irradiation to demonstrate the influence of stabilizers. As it does not need to study the blended PVC films before irradiation.
Point 5: When comparing the light stability of the four light stabilizers, the paper only explains that the reason why PVC-ed/p-OH has the best photo stability is that “it contains a phenol group which is known as an excellent free radial scanner” and its mechanism has not been further confirmed. The reason of the other three photo stabilizers have poor effects is lacking. In addition, the significance of selecting four different benzaldehyde derivatives was not explained.
Response 5: In comparison, the light stability of the four light stabilizers, it is demonstrated that PVC-ed/p-OH has the best photo stability because it contains a phenol group which is known as an excellent free radial scanner. Thus the free radicals formed due to photo-degradation can be delocalized by the phenol group and reduce its reactivity. At the same time, the PVC-ed/p-OH compound has an aromatic unit that could absorb the UV light and protect the host PVC from degradation. The reason of the other three photo stabilizers have lower effects due to they work only as UV-blockers and not free radical scavengers. In addition, the significance of selecting four different benzaldehyde derivatives was due to its available, cheap, and easy to work with.
Point 6: There are many unprofessional and strange expressions in the paper, which should be modified. Typical example as follows:
“These investigations, which were approved, showed that novel modified Schiff base polymers perform far better as photo-stabilizers than plain PVC.”
“Even though all other additives have shown good stability for PVC films in comparison to pure PVC…”
“…Figure 5c shows the FTIT spectrum of blended PVC film…”
“Equation 2. 2 was used to calculate the…”.
“The weight loss due to photodegraded of PVC films in the presence and absence of additives was calculated using equation 2.3.”
“The calculations were performed for all blank and blended PVC films with a 40 m with addition only 5%
Response 6: They have been corrected thank you.
Author Response File: 
Author Response.pdf
Round 2
Reviewer 1 Report
The authors resolved most of my concerns.
For point 5, I agree that if there is ~1/3 modification, you would have integration of 6 for peak 1, which is reasonable. Following this, you should have integration of 2 for peak 6, and integration of 2 for peak 2 (since there is 2/3 unmodified), totaling up to 4. From Figure 1 the integration for peaks 2,6 is only 3. This indicates that either the peak assignments are incorrect, or there is a mixture of species.
Also, if the authors have more solid evidence for the 1/3 modification ratio, the correct drawing corresponding to this ratio should be drawn. It would be misleading like the authors showed as half modification in Table 1 and Figure 2.
Author Response
Response to Reviewer 1 Comments
The authors resolved most of my concerns.
Point 1:
For point 5, I agree that if there is ~1/3 modification, you would have integration of 6 for peak 1, which is reasonable. Following this, you should have integration of 2 for peak 6, and integration of 2 for peak 2 (since there is 2/3 unmodified), totaling up to 4. From Figure 1 the integration for peaks 2,6 is only 3. This indicates that either the peak assignments are incorrect, or there is a mixture of species.
Also, if the authors have more solid evidence for the 1/3 modification ratio, the correct drawing corresponding to this ratio should be drawn. It would be misleading like the authors showed as half modification in Table 1 and Figure 2.
Response 1: Yes you are right the integration of peaks 2 and 6 should be four all together but as you know it is a polymer and probably undergoes an elimination reaction of a few chlorine atoms. Therefore, it is hard to get very accurate integration values. On the other hand, by using EDX analysis, the nitrogen and chlorine percentages have been estimated the modification percentage which is between 30-35%.
It has been corrected the chemical structure of modified PVC in Table 1 and Figure 2 to show the third percentage of modification.
Reviewer 2 Report
“From the comparison of nitrogen and chlorine percentages, it was estimated the percentage of modification which is between 30-35%.”Here, the calculation of the modification percentage is related to the percentage of nitrogen and chlorine, but the crosslinking leads to the inaccuracy of the calculation.
There are no obvious problems in other parts.
Author Response
Response to Reviewer 2 Comments
Point 1: “From the comparison of nitrogen and chlorine percentages, it was estimated the percentage of modification which is between 30-35%.” Here, the calculation of the modification percentage is related to the percentage of nitrogen and chlorine, but the crosslinking leads to the inaccuracy of the calculation.
There are no obvious problems in other parts.
Response 1: This percentage was estimated depending on the comparison of 1H NMR integration peaks and the percentage of chlorine and nitrogen atoms which were got by EDX analysis technique. To conclude we could say this is approximated percentage and its needs further studies to confirm the exact modification percentage.
