CC BY
12
ISSN 2522-1841 (Online) AZERBAIJAN CHEMICAL JOURNAL № 1 2023 129
ISSN 0005-2531 (Print)
UDC 678.028.296.2
FEATURES OF THE STRUCTURE AND PROPERTIES OF COMPOSITIONS OF MODIFIED ISOPRENE RUBBER WITH CHLORIDE-CONTAINING AND EPOXY
COMPOUNDS
Sh.M.Mammadov, S.A.Rahimova, R.F.Khankishiyeva, P.I.Ismayilova, I.T.Movlayev*, J.Sh.Mammadov
*Azerbaijan State University of Oil and Industry Institute of Radiation Problems, Ministry of Science and Education of the Republic of Azerbaijan
shiraz.mamedov@gmail. com
Received 25.05.2022 Accepted 27.09.2022
The effect of HCPX and EC as a stitching agent during thermal vulcanization of modified isoprene rubber (SKI-3- PVA) 80:20 in the presence of zinc oxide was studied. Studies of structural changes occurring in vulcanizates based on SKI-3-PVA under the influence of heating have been carried out. Based on the data of IR spectroscopy and the gel fraction, the rate of reactions with hexachloroparaxylenes (HCPX) between the studied low molecular weight compounds was studied. Considerations are made about the nature of the vulcanization action of the studied structuring systems and the features of their influence on the parameter of the spatial network and the physical and mechanical properties of vulcanizates. The effect of heating time on the content of total and combined chlorine in samples containing HCPX and ZnO was studied. The number of stitched HCPX molecules per cross-link was calculated.
Keywords: isoprene rubber, polyvinyl alcohol, crosslinking, hexachloroparaxylene, vulcanization, strength, gel fraction.
doi.org/10.32737/0005-2531-2023-1-129-134 Introduction
Isoprene rubbers (SKI) have a valuable set of physicochemical properties that determine a wide range of their practical use. However, these polymers are relatively easily destroyed by the action of external factors at high temperatures [1-3].
In recent years, high and low molecular weight compounds [4,5,6] have been widely used as modifying agents for isoprene rubber (SKI-3) to eliminate these factors.
Organic stitching accelerators in elastomer mixtures perform diverse functions [6]. The resulting vulcanizates may contain a variety of different cross-links. To increase the yield of stitching products and increase the rate of chemical reactions occurring in this case, various organic stitching agents (OCA) [7], including hexachloroparaxylene and derivatives of chlorine-containing dicarboxylic acids, have been proposed.
The action of polyhalogen derivatives of aliphatic and some aromatic compounds has been most extensively studied [8].
However, the effect of polyhalomethylyl-substituted (PHMSS) compounds of the aromatic series has not been studied enough. It was of interest to study the process of vulcanization of modified isoprene rubber (SKI-3-PVA; 80:20) with the participation of chlorine-containing and epoxy compounds in the presence of zinc oxide.
Experimental part
Modified isoprene rubber (SKI-3) with polyvinyl alcohol (SKI-3 - PVA) was used as an object of research.
Modification of SKI-3 with polyvinyl alcohol was carried out on rollers, the content of SKI-3 was 80, polyvinyl alcohol 20 wt.p. per 100 wt.p. rubber.
Hexachloroparaxylene (m.p. 120-1300C) and epoxy resin ED-5 (epoxy dianoic) were used as an accelerator.
On laboratory rollers, after thorough mixing of the modified SKI-3 (SKI-3- PVA) for 3-5 min, elastomer mixtures were prepared containing (per 100 wt.p. rubber) 3.0 wt.p. HCPX, 1.5 wt.p. sulfur, 5.0 wt.p. zinc oxide, 4.0 wt.p. epoxy resin ED-5. Then the samples were molded in an electric press at 1500C in the form of plates with the thickness of 0.3 mm. The heating duration was 20-40 min [10].
The structures of vulcanizates were studied using sol-gel analysis. The number of cross bonds (cb) and their yield were determined by the method of equilibrium swelling in the solvent toluene [11].
Changes in the molecular structure of the samples were studied by IR spectroscopy [12-13].
Results and discussion
In the SKI-3-PVA+HCPX system, both components are polar compounds, and the process of their combination is mainly determined by the presence of polar COO and C-Cl groups and the reactivity of these groups under mechanochemical and thermal effects. In the IR spectra, the intensity of the band of the stretching vibration of the C-Cl group located in the region of 730 cm-1 decreases with increasing stitching time in an electric press (from 0-40 min). To characterize the intensity of this band, we used the ratio of intensities (or optical densities) of 730, 760, and 810 cm-1, corresponding to asymmetric and symmetric stretching vibrations of the C-H bonds of the CH2 group (Table 1).
As can be seen from the data in Table 1, in most cases, the /730 /830 ratios decrease during the vulcanization of samples in an electric press. In the absence of HCPX, changes in relative intensities occur to a much lesser extent and without a definite pattern.
In the IR spectrum of the vulcanizate, there was also a decrease in the intensity of the band at 1610 and 675 cm-1 (a doublet from the band at 1610 cm-1 in the spectrum of the initial sample) corresponding to the stretching vibration of the COO bond of the SKI-3-PVA molecule and the appearance of a new
absorption band in the region of 1690 cm-1. In the IR spectrum of both the initial sample and the vulcanizate, there are bands at 1730 cm-1 corresponding to the carbonyl group; it appears during the modification of SKI-3 and PVA.
When the heterogeneous system SKI-3-PVA+HCPX is heated, the intensity of the bands at 967 and 1340 cm-1 decreases, which are caused, respectively, by out-of-plane and bending vibrations of the C-H bond in the CH=CH group [12]. In addition, there is a significant change in the structure of SKI-3-PVA: The appearance of double bonds of various configurations. The distribution of double bonds in the elastomer was calculated from the optical densities of the absorption bands at 960 cm-1 (1.4 trans double bonds) and 912 cm-1 (1.2 double bonds): 20% bonds 1.2, 60% bonds 1.4-trans and 20% bonds 1,4-cis [13].
Similar changes in the spectrum are observed with epoxy resin. Judging by the stitching rate, the most active of the studied crosslinking systems for the modified SKI-3 is the system containing HCPX, ZnO and EC (Table 2).
As expected, the gel content noticeably grows with increasing vulcanization time (Figure 1).
The high content of gel in the system indicates that the studied HCPX and EC take part in the stitching process [14, 15]. For all systems, the formation of effective cross-links increases with a growth of the duration of vulcanization (Figure 2).
As can be seen, in the SKI-3-PVA+HCPX+ZnO+ES system, the stitching rate is higher than in other systems (3,4). This is due to the higher activity of the HCPX and SE compound. With a long vulcanization time (50 and 60 minutes), the number of cross-links decreases.
Thus, the presence of chemical interaction of polyfunctional macromolecules SKI-3-PVA and HCPX in the presence of epoxy compounds and zinc oxide under thermal and thermomechanical effects was established.
Table 1. Influence of the duration of vulcanization of samples in an electric press (150°CX40') on the relative intensity of the stretching vibration band of the C-Cl group (/=730 cm-1)_
Indicators Heating duration, min
10 20 30 40
/730 64.1 62.3 97.5 87
/780 127 123 145 124
/810 0.501 0.490 0.471 0.450
/830 0.785 0.710 0.705 0.670
/730 /830 0.610 0.580 0.560 0.550
Table 2. The influence of the stitching system on the ability of elastomeric mixtures (SKI-3-PVA) to premature vulcanization (Mouni viscometer at 100"C)_
Stitching system t5, min t35-t5, min
SKI-3 + Sulfur+Captax (known) 6.5 7.6
SKI-3 -PVA+HCPX+ZnO 5.1 6.2
SKI-3 -PVA+HCPX+ZnO+ES 4.2 5.8
SKI-3 -PVA+HCPX 6.2 7.0
G,%
Время прогрева т, мин
Fig.1. Kinetics of gel formation in the system:
1 - SKI-3+Sulfur+Captax+ZnO (known)
2 - SKI-3 -PVA+HCPX+ZnO+ES
3 - SKI-3 -PVA+HCPX +ZnO
4 - SKI-3 -PVA+HCPX
Время прогрева т, мин
Fig.2. The dependence of the concentration of effective cross-links on the time of vulcanization in systems
1 - SKI-3 -PVA+HCPX+ZnO+ES
2 - SKI-3 -PVA+HCPX+ZnO
3 - SKI-3 -PVA+HCPX
It is known that the stitching of isoprene rubber (SKI-3) by chlorine-containing compounds is activated by metal oxides [16,17]. We have studied the effect of heating time on the content of total and bound chlorine in samples containing HCPX and ZnO, and calculated stitched HCPX molecules per crosslink (Table 3). As can be seen from the data in table 3, the amount of total chlorine decreases as much with an increase in the stitching time, and the amount of combined chlorine that interacted with zinc oxide to form chlorides increases. The amount of HCPX attached to the elastomer also increases. The subsequent decrease in the content of HCPX in the toluene extract of the vulcanizate is evidenced by the fact that it almost completely disappears. The number of HCPX molecules per cross-link decreases with increasing heating time.
Based on the theoretical prerequisites, experimental data, and the colloid-chemical concept of the mechanism of formation of
stitched elastomers with HCPX [14], the mechanism of action of the stitching agents studied by us can be explained as follows. The stitching of SKI-3-PVA with the help of HCPX under thermal and thermomechanical action in the absence of an activator (ZnO) probably occurs through decomposition of HCPX with detachment of chlorine from trimethyl groups. The resulting radical accentuates hydrogen from elastomer molecules, forming macroradicals that are able to interact with each other [8].
The chemical interaction of the functional groups of SKI-3-PVA and HCPX macromolecules under thermal and thermomechanical exposure is confirmed , in addition to spectroscopic data and to the results of sol-gel analysis, by a growth in the physicomechanical properties of SKI-3-PVA+HCPX+ZnO+ES compositions compared to sulfur vulcanizates of isoprene rubber SKI-3 (Table 4).
Table 4. Physical and mechanical properties of vulcanizates based on modified SKI-3-PVA with various stitching agents
Table 3. Influence of the duration of vulcanization and the type of stitching agent (HCPX) on the chemical composition of the SKI-Z-PVA vulcanízate (ZnO content 5.0)_
Stitching system Vulcanization period, min Content, % The number of cross-linked molecules 1/Мс, mol/sm3
Total chlorine Bound HCPX in toluene extract
SKI-3 -PVA+HCPX+ZnO 10 88 15.8 9.8 5.2
20 72 25.3 8.7 4.1
30 58 31.3 traces 2.9
40 45 34.1 traces 1.8
Indicators Stitching systems
SKI-3+Sulfur+Captax (known) SKI-3 -PVA+HCPX+ZnO+ES
Conditional tensile strength, MPa 23 25
Relative extension, % 360 290
Residual elongation, % 12 10
Rebound elasticity,% 34 41
Shore A hardness, conv. units 58 52
Conclusion
The data obtained are of interest for predicting the processes of combining isoprene rubber (SKI-3) with high molecular weight compounds (HC) of sorption and diffusion in them of low molecular weight compounds used in the stitching of macromolecules.
In quasi-binary stitched heterogeneous mixtures of elastomers, the intensity of interfacial interaction, the formation of a chemical C-C bond should be determined by the micro and supramolecular structure of both components. In the modified SKI-3-PVA, the total content of 1.4 and 1.2 units is 2 times less. The difference in the degree of stitching of the modified rubber is shown. In the SKI-3-PVA+ZnO+HCPX+ES system, their combination is determined by the presence of polar COO and CCl of these groups under mecha-nochemical and thermal effects.
For mixtures of SKI-3 -PVA+ZnO+ HCPX+ES, a higher rate of release of the gel fraction during vulcanization is observed. The formation of the interfacial layer is affected by the content of polar units of SKI-3-PVA and those containing a diene on the yield of crosslinks and stitched molecules.
References
1. Mamedov SH.M. Synthesis of processing and vulcanization of butadiene nitrilrubbers. Lap Lambert Academic Publishing, 2015. 355 p.
2. Runt I, Fitzgerald I. Structural-chemical modification of polybutadiene containing polymers. Macromolecule 2016. V. 30. № 8. P. 2431-2437.
3. Jois I.R. Modification of polybutadiens, J. Macro-mol Scis. 2014. V. 16. № 3. P. 443-455.
4. Giishin B.S. New prinsipis of physical modification of elastomers. Kauntsch und Gummi Kustst. 2015. № 3. P. 222-227
5. Petrov O.V. Modifikaciya kauchukov epoksid-nymi soedineniyami kauchuk i rezina. 2017. № 5. S.11-20.
6. Weinstein A.H. Incorporation of antioxidant groups in to polybutadiens. J. Rubb. Chem. Technology. 2017. V. 50. № 4. P. 641-648.
7. Poluektov P.T., Gopsovskaya F.T. Epoksidiro-vanie izoprenovyh kauchukov v prisutstvie oksida metallov. Vysokomol. Soed. Seriya A.2010. T. 51. № 4. S. 583.
8. Tutorskij I.A. Himicheskaya modifikaciya poli-merov. 2-e izd. M.: Nauka, 2012. S.347
9. Averina T.G., Mirinova V.V. Primenenie epoksid-nyh soedinenij v kachestve modifyciruyushchej dobavki. Proizvodstva shin. RTI i ATI. 2014. № 5. S. 6-9.
10. Kuznecov E.V., Budarina S.A. Praktikum po fizike i himii polimerov. L.: Nauka, 2010. S. 287.
11. Mamedov SH.M., Opredelenie strukturnye parametry setki vulkanizatov kauchuka i reziny, 2014. № 8. S.13-17.
12. Bellami L., Infraspektry slozhnyh molekul, IL. M. 1989, s.375
13. Nelson V. Opredelenie strukturu slozhnyh molekul kauchukov. L.: Nauka, 2013. S.217
14. Pol D. Mezhfaznye dobavki sposobstvuyushchie sovmestimost' v smesyah polimerov. M.: Mir, 2011. S.39.
15. Van Krevelen D.V. Svojstva i himicheskie stroenie polimerov. M.: Himiya, 2006. S. 414.
16. Xuefei Wang, Lingling Wu, Haiwen Xu, Tongliang Xiao, Huaming Li, Jun Yang, Modified silica-based isoprene rubber composite by a multifunctional silane: Preparation and its mechanical and dynamic mechanical properties. Polymer Testing jour. V. 91. November 2020. P. 384.
17. Young Win Kim, Saravanan Nagappan, Ildoo Chung, Vulcanization behavior and mechanical properties of isoprene-modified silica reinforced butyl rubber composities. Molecular Crystals and Liquid Crystals. 2020. V. 707. P. 46-58.
XLORId TORKiBLi УЭ EPOKSi BiRLO§MOLORi iLO MODiFiKASiYA OLUNMU§ iZOPREN KAUÇUKUNUN QURULUS XÜSUSiYYOTLORl УЭ KOMPOZiSiYANIN XASSOLORl
§.M.Mammadov, S.A.Rahimova, R.F.Xankiçiyeva, P.i.ismayilova, i.T.Mövlayev, C.§.Mammadov
Sink oksidin içtiraki ils modifikasiya olunmuç izopren rezin (SKI-3-PVA) 80:20 termiki vulkanlaçmasi zamani HCPC va EB-nin tikici agent kimi tasiri tadqiq edilmiçdir. SKI-3-PVA asasinda vulkanizatlarda qizdirmanin tasiri altinda baç veran struktur dayiçikliklarinin tadqiqi apanlmiçdir. iQ-spektroskopiya va gel fraksiyasinin malumatlari asasinda tadqiq olunan kiçik molekullu çakili birlaçmalar arasinda heksaxloroparaksilenlarla (HCPC) reaksiyalarin sürati ôyranilmiçdir. Tadqiq olunan struktur sistemlarinin vulkanizasiya tasirinin xarakteri va onlarin faza torunun parametrina va vulkanizasiyalarin fiziki-mexaniki xassalarina tasirinin xüsusiyyatlari haqqinda fikirlar aparilir. Tarkibinda HCHP va ZnO olan nümunalarda qizdirma vaxtinin ümumi va birlaçdirilmiç xlorun tarkibina tasiri ôyranilmiçdir. Har bir cargali alaqaya göra tikici HCPC molekullarmrn sayi hesablanmiçdir.
Açar sözlzr: izopren kauçuk, polivinil spirt, heksaxloroparaksilen, tikilma, vulkanla§ma, möhkamlik, gel fraksiya.
ОСОБЕННОСТИ СТРУКТУРЫ И СВОЙСТВ КОМПОЗИЦИЙ МОДИФИЦИРОННОГО ИЗОПРЕНОГО КАУЧУКА С ХЛОРСОДЕРЖАЩИМИ И ЭПОКСИДНЫМИ СОЕДИНЕНИЯМИ
Ш.М.Мамедов, С.А. Рагимова, Р.Ф. Ханкишиева, П.И.Исмайлова, И.Т.Мовлаев, Дж.Ш.Мамедов
Изучено действие ГХПК и ЭС в качестве сшивающего агента при термической вулканизации модифицированного изопренового каучука (СКИ-3-ПВС) 80:20 в присутствии оксид цинка. Проведены исследования структурных изменений, происходящих в вулканизатах на основе СКИ-3-ПВС под воздействием прогрева. На основании данных ИК-спектроскопии и гель фракции изучено, скорость протекания реакций гекса-хлорпараксилолом (ГХПК) между исследуемыми низкомолекулярными соединениями. Высказано соображения о природе вулканизационного действия изученных структурирующих систем и особенности их влияния на параметр пространственной сетки и физико-механические свойства вулканизатов. Изучено влияние времени прогрева на содержание общего и связанного хлора в образцах, содержащих ГХПК и ZnO. Рассчитано число сшитых молекул ГХПК, приходящихся на одну поперечную связь.
Ключевые слова: изопреновый каучук, поливиниловый спирт, сшивание гексахлорпараксилол, вулканизация, прочность, гель фракция.
