Study of Influence of Copolymer Vinyl Chloride and Vinyl Acetate on the Properties of Butadiene Nitrile Rubber

Influence of a copolymer of v inyl chloride and vinyl acetate to the properties of butadiene nitrile rubber has been studied. It is shown that the growth of the molecu lar weight of BNR by mixing latex rubber and copolymer in a ratio 80:20, 75:25, 65:35 leads to obtaining micro heterogeneous systems. Copolymer in itially acts as an interstructural amplifier and then depending on their ratio p lays the role of the dispersed phase in the plasticization. By the method of rheological analysis it was found out that increase of molecular weight was observed in the interval time (0-90 min), characteristic viscosity increases with the ratio of 75:25 copolymer from 0.6 to 1.4. A sol-gel analysis showed that with increase in the concentration of the copolymer in BNR the number o f chains grid (1/Ms) in the rubber decreases. It was found out that consumption of cross linked molecules (1/Mn) for the cross-linking is reduced, it becomes constant at a ratio of 100:65:25. Comparison of the kinetics of thermometallic oxide vulcanization o f BNR with the accelerator disulphide chloride benzene (DSCB) increases the yield concentration of the effective cross-links (n `c) in the molecule BNR. Experiment showed that in the presence of the accelerator DSCB and zinc oxide the structuring main ly goes by the double bond.


Introduction
It is known [1][2][3][4][5][6][7][8][9][10], that the vinyl co mpounds containing active and polar groups interact strongly with the hydrocarbon mo lecular part o f poly mer. The structuring of elastomers is observed in the presence of compounds containing two or more active halogen atom and acetate, thus it is possible to obtain sufficiently strong elastomeric materials having a high resistance to the heat ageing, abrasion and dynamic endurance [11][12][13][14][15][16][17]. The study of occurring at the same chemical react ion makes it possible to facilitate significantly the development of cross-linking system for manufacturing materials with predetermined properties.
The systematic researches of the effect of unsaturated elastomers filled with copolymer vinyl chloride with vinyl acetate (VA) to the output parameters of the grid, the changes of the molecular structure, rheological properties and also the content of the double bonds in the polyblend (mixture of elastomer with vinyl chlo ride and vinyl acetate) was not carried out. It is presented to study the effect of interaction of copoly mer of vinyl chloride with vinyl acetate on the elastic, structural parameters of the grid and rheological propert ies of butadiene nitrile elastomer.

Experimental
The butadiene nitrile rubber filled with copoly mer of vinyl chloride with the vinyl acetate is used as an object of research. Filled BNR is obtained during jo int coagulation of butadiene nitrile latex (with the content of the bound acrylonitrile 37-40 %) with latex of polyvinylchloride (PVC) and poly vinyl acetate (PVA) in the ratio of 80:20, 75:25, 65:35. According to the research results carried our by IK method -spectroscopy in a butadiene part of poly mer upon polymerization of the isomet ric co mposition of double bonds in the filled system was: 1,2-isomer of 16 %, 1,4-isomer of 18,7 % and trance 1,4 isomer. Macro mo lecules of SKN-40 rubber consists of statically allocated parts of butadiene, acrylonitrile and filled with vinyl chloride copoly mer with the vinyl acetate. Features after the structuring BNR influence to their microstructure, molecu lar weight, mo lecular mass distribution (MMR) and gel content. Therefore, before processing researches in filled BNR, number-average and weight-average molecular weight and polydispersity (Мn-69 thousand; Мw-226 thousand; Мw/Мn=4.1) has been defined by gel permeation chromatography (GPC) beforehand.
BNR filled with PVC copoly mer and (PVA) is expanded in the rat io 75:25, after 15-20 minutes of plasticization the obtained mixture is produced compression of the sample at 143К in the range 0-90 minutes during 20 minutes. For studying kinetic of structuring the 3 mass. part system of disulphonic acid chloride benzene (DSHB) + 5 mass. part ZnO on 100 mass. part of rubber has been used. The characteristic viscosity of BNR filled with copolymer was determined in toluene at 293К by known procedures on Ubbelohde type of viscosimeter. The calcu lation was carried out on Marx Hauvink's equation[η] = kMα at value of the constant K=4,9•104 and α = 0,64 for toluene [23]. Studying elastic formation properties were carried out according to GOST 10722-74. Entrance of concentration of cross-linkage (n'c); nu mber of the cross-linked mo lecules (1/Мnτ) was determined by a sol-gel analysis. The calculation of parameters of a spatial grid of cross-linked elastomer was determined by Flory-Raineri formu la [24]. The change of the mo lecular structure, filled BNR was determined by IR method of in frared spectroscopy (IRS) in the range of 700-3000cm-1. For this filled BNR was dissolved in toluene during 24hrs. The rubber film was obtained by applying a solution onto a substrate and a constant evaporation of solvent. The boxes of KBr were used as a substrate during the measurement of spectrum in the range of 600-2000cm and the boxes of LiF and NaCl in the range of 2000-3000cm. The substrate with a film was fixed the holder and placed in the sample co mpart ment in the spectrophotometer. Identificat ion of the spectra was carried out in accordance with correlation tables [25][26][27].

Results and Discussion
Put forward [7] the collo idal-chemical concept of anomalous growth of viscosity BNR during filling of copolymer v inyl chloride with the vinyl acetate in wo rks is reduced the fact to the following: Fillers (copolymers) are limited co mpatible with the poly mers in the field of the concentration, corresponding to molecular solubility. Copoly mers (v inyl ch loride and vinyl acetate) of the correct reinforcement of rubber increase free volu me of poly mer, and more, the dense packing of its molecular structure. The increase of a rat io of concentration of copolymer in a polymeric mat rix leads to the format ion of micro heterogeneous system. Copoly mer (filler) first plays a role of the inter structural amp lifier, and then the role of fulfilling the disperse phase at plasticization depending on their ratio.
Based on this situation and granting various ratios of filler (copolymer) in BNR, it is necessary to expect: a) Extremu m existence on curve viscosity -a filler ratio only in limited area o f temperature test; b) Dependence of effect of structural changes on transverse strain τ; c) Dependence of v iscosity of the filled rubber on t ime and temperature of storage of a sample.
Carried-out experimental researches in properties of the butadiene nitrile rubbers (BNR-40) filled with copolymer vinyl chloride and vinyl acetate, confirmed the mentioned assumptions. On figure 1, 2, 3 shown the dependence of elastic characteristics of BNR, filled with copolymer vinyl chloride and vinyl acetate.
One can see that the copolymer chosen in various ratios of copolymer causes change of properties of BNR in plasticity (figure 1), hardness (figure 2) and Mooney viscosity (figure 3). Co mparatively observable small growth of plasticity (figure 1) and a decrease of hardness (figure 2) at copolymer ratios 80:20 and 75:25 in BNR lead to change these characteristics on regularities, usual fo r BNR. According to [1] for mechanical solubility (plastification) to rise in the rate of the gel above 70% leads to the destruction of chains, which leads to the destruction of the chains that partly different effects on molecular weight and mechanicalmechanical processes during the dissolution of the copolymers. Studying of the laboratory samples filled with copolymer based on BNR showed that depending on the content of copolymer and duration of t ime of characteristic viscosity   The growth of mo lecular weight is observed at duration of structuring at the time interval 0-90min. The characteristic viscosity increases at samples 2 (75:25) with 0.6 to 1. 4. With increase of t ime the characteristic v iscosity (2) becomes constant at 70 minutes, and further reduction of molecular weight is observed at all samples at 120 minutes. BNR is associated with a destruction of main circuit of poly mer.
Viscosity increase in the range of values (0-90min) can be bonded with format ion of spatial structures due to reaction of intermolecular cross-lin king (figure 4).
On figure 5 IR-spectra of SKN-40 rubber filled with copolymer vinyl ch loride with vinyl acetate 75:25) is presented. The SKN-40 system + copoly mer (PVC+PVА) are characterized by polarity, therefore the process of combination SKN-40 with copoly mer is main ly defined by polar groups−C≡N, C−Cl and their reactiv ity at mechanicchemical and thermal influences.
On this basis, the main consideration was given to studying of intensity of the bands of the stretching vibration of the nitrile group, located in areas 2235cm -1 (figure 5) and being characterized by exceptional stability, both in frequency and form. The intensity of a n itrile band naturally decreases with longer heating fro m 0 to 90 minutes. For the characteristic of intensity of a nitrile bands were chosen the relative values representing the relation of intensity (or the optical plane) bands 2235cm -1 to intensity of bands 2925 and 2850cm -1 , corresponding to dissymmetric and symmetric stretching vibrations of commun ications C-H of CH 2 group. (Figure 5 the bands are not specified).
The most significant changes was observed in the IR spectrum of the sample in the final state, it should be noted decrease in intensity of the band 675 cm -1 , observed in the form of a doublet with a band 688 cm -1 in a range of an init ial sample and corresponding to stretching vibrations of C-Cl communicat ion should be noted.
The band at 1730 cm -1 , being observed in IR spectra of the sample in both original, and final states, corresponds to C=COC(C)=O group [25][26][27]. It is known that, with introduction of fillers into polymer the chemical interaction at the interface o f t wo phases is possible between poly mer and fillers [1,28].
The filling of elastomers is that during insertion into the elastomer (in different ratios) the significant change in the parameters of the grid of elastomer occurs.
By sol-gel analysis was found out that with increase in the ratio of the copoly mers in BNR monotonically increase share of sol-gel fraction (28-35%), the average number molecular weight (Mn s by Charlz is 3240-4600 and the nu mber of chain mesh is 8-14) (table 1).
Represented in Table 1 results show that in the process of structuring the of BNR in the presence of the copolymer at various ratio, spending number of cross-linked mo lecules to form in macro molecu le of BNR nu mber of cross-links decreases and becomes constant at ratio of copolymer 100:65:35.  BNR significantly differs with greater tendency to cross-lin king than other diene rubbers. So it is vulcanized during heating even without the addition of indirect material, and in the presence of disulfide chloride benzene (DCHB) valuable technical vulcanizates can be obtained with participation of zinc o xide.
The system filled of 100 mass. part BNR (100:75:25) + 4 mass. part DSCB+5 mass.part ZnO was used for vulcanizat ion of filled BNR. The vulcanizat ion was taken in a hydraulic press at 423K. The duration of vulcan ization is 90 minutes.
Fro m the data of table 2 shows that increasing the maximu m yield of effective cross-lin ks n`c DSCB and metal oxides compared to the thermal vulcanizat ion to the calculation suggest that the presence of reinforcing DSCB and ZnO vulcanizat ion is mainly on the double bond and the formation of new active sites of metal o xides is suppressed or products their transformation. Co mparison of the structural features of the parameters of the grid with their staple rheology, plastic and vulcan izing properties suggests that when co mbining BNR is a copolymer of VC and VA copolymers with increasing content of the destructive processes are observed. The best bed-elastic properties when the content of the copolymer has in the redistribution of 75: 25. With increasing heating time, the rise of cross-links and the number of cross-linked mo lecules remains constant.

Conclusions
The present work shows that by mixing of latex BNR and filled vinyl ch loride and viny l acetate in a ratio of 80:20, 75:25, 65:35 leads to formation microheterogeneous systems, acting as a d ispersed phase in mechanical dissolution (plastificat ion).
It is shown that the shear stress of solubility vinyl chloride copolymers and vinyl acetate in the rubber, observed the rise in the rate of the gel (70%) of the elastomer system, which leads to the destruction of the chains of BNR. Decreasing of the molecular weight of the polymer mass at a shear stress on the rollers influence d ifferently to the rheological properties such as plasticity (figure 1), hardness (figure 2) and of Mooney viscosity ( figure 3).
With duration of the structuring in mode 423K•90`, in a filled elastomer system observed an increase in molecular weight. Characteristic viscosity is increased in samples 2 (75:25) fro m 0.6 to 1. 4. With increasing time, the mo lecular weight of the samples filled copolymers at 70 min is constant, but then, with increasing time of the process of structuring observed decreasing of molecular weight in all samples.
Filled copolymers of v inyl chloride and vinyl acetate with BNR mainly determined by polar groups-C ≡ N, C-Cl and their reactivity at mechanical, chemical and thermal influences.
Co mparison kinetics of thermo metal o xide vulcan izat ion of BNR with participation of amplifier d isulphide chloride benzyl (DSCB) show the increasing of cross links yield (n`c) in the mo lecule of BNR. By method of sol-gel analysis determined that in the presence of reinforcing DSCB and zinc o xide are primarily structured by a double bond and the formation of new act ive centres are suppressed by metal oxides or the products of their transformation.