Chapter-6. Film casting

Transcription

1 The present chapter deals with the curing study of polyurethane syrups-iii (described in Chapter-5). The curing study was monitored on a thermogravimetric analysis (TGA) and flame retardant properties of the polyurethane syrups-iii are presented. Film casting Glass plate (10cm 12cm) free from surface imperfections, were cleaned using xylene solvent. The prepared resin was then poured on to one edge of the plate which was left in the vertical position (to spread resin uniformly) at room temperature. Above prepared polyurethane syrups -III were casted into film form. Thermal analysis of polyurethanes cured film 6.1 Experimental TA instrument Model-2960 Thermogravimetric analyzer was used in the present study to record the thermograms of polymer samples. About 5 to 10 mg of the polymer sample was weighed in the boat of a thermo-balance and subjected to heating at a 10 0 C/min heating rate in nitrogen atmosphere. The continuous loss in weight of a sample as a function of temperature gave a TG thermogram, which was used for further data analysis. To study effect of variables on thermal stability of polyurethanes prepared for present investigation, Thermogravimetric analysis (TGA) in the range of C was carried out. The variable accounted were, Cross linking density (NCO/OH ratio) Types of polyols Amount of polyols Types of isocyanate Department of Chemistry, S.P.University Page 147

2 The calculated data of thermograms of polyurethanes i.e. % of weight loss at different temperature (200 0 C, C, C), decomposition temperature range, integral procedure decomposition temperature (IPDT) and the activation energy (E a ) are shown in the Tables 6.1 and 6.2. Department of Chemistry, S.P.University Page 148

3 Table: 6.1 TGA data of Polyurethane Syrups-III based cured film PU-III Code % of Weight Loss at Different Temperature ( 0 C) Decomposition Range ( 0 C) T max a T 50 b Activation IPDT c Energy d ( 0 C) ( 0 C) (Ea) ( 0 C) KJ/Mole -1 B15PUT B16PUT B17PUT B18PUT B19PUT B20PUT B21PUT B15PUT B16PUT B17PUT B18PUT B19PUT B20PUT B21PUT a Temperature for maximum rate of decomposition, b Temperature for 50 % weight loss, c Integral procedural decomposition temperature by Doyle s Method, d by Broido method. Department of Chemistry, S.P.University Page 149

4 Table: 6.2 TGA data of Polyurethane Syrups-III based cured film % of Weight Loss at PU-III Decomposition Different Code Range ( 0 C) Temperature ( 0 C) T max a T 50 b Activation IPDT c Energy d ( 0 C) ( 0 C) (Ea) ( 0 C) KJ/Mole -1 B15PUI B16PUI B17PUI B18PUI B19PUI B20PUI B21PUI B15PUI B16PUI B17PUI B18PUI B19PUI B20PUI B21PUI a Temperature for maximum rate of decomposition, b Temperature for 50 % weight loss, c Integral procedural decomposition temperature by Doyle s Method, d by Broido method. The TGA data of all film are shown thermogram as shown in figures 6.1 to 6.4. Department of Chemistry, S.P.University Page 150

5 Fig: 6.1 TG thermograms of B15PUT1, B16PUT1, B17PUT1, B18PUT1, B19PUT1, B20PUT1, B21PUT1 Department of Chemistry, S.P.University Page 151

6 Fig: 6.2 TG thermogram of B15PUT2, B16PUT2, B17PUT2, B18PUT2, B19PUT2, B20PUT2, B21PUT2 Department of Chemistry, S.P.University Page 152

7 Fig: 6.3 TG thermogram of B15PUI1, B16PUI1, B17PUI1, B18PUI1, B19PUI1, B20PUI1, B21PUI1 Department of Chemistry, S.P.University Page 153

8 Fig: 6.4 TG thermogram of B15PUI2, B16PUI2, B17PUI2, B18PUI2, B19PUI2, B20PUI2, B21PUI2 Department of Chemistry, S.P.University Page 154

9 6.2 Results and Discussion Data indicated by negligible weight loss shows that all the PU syrups- III cured films are stable up to C C irrespective of types and amount of blended (RPR-BCO)-III and urethane linkage. Thermograms indicate that all the PU syrups-iii cured films degraded as not well-distinguished three stages. The degradation in the first stage of polyurethanes may correspond to the breaking of urethane bond and leading the formation of CO 2, alcohols, amines carbon monoxide etc. Te second stage at about C C may be due to the decomposition of ether and ester links. In the case of PU syrups-iii cured film from rosinified phenolic resin and brominated castor oil polyol, the main chain degradation may occur with the formation of as evidenced by the thermal degradation of Lienoliec acid. rate. In the third step finally this cured product degrades completely at slow The percentage of weight loss up to C in aromatic isocyanate based PU syrups-iii cured film is slightly higher compared to aliphatic isocyanate based PU-III cured films because of the instability of aliphatic moiety and increase the crosslinking density the percentage of weight loss decreases. In case of PU syrups-iii cured film as the decrease brominated castor oil % content increase the thermal stability as increase the rosinified phenolic resin. The activation energy of all the PU syrups-iii cured film are in the range of 35 to 90 KJ/mole the polyurethane syrups III prepared from TDI having more thermally stable (i.e. having higher activation energy) than the polyurethane syrup III prepared from IPDI due to its aromaticity, crosslinking density between diisocyanate and blended (RPR-BCO). TG thermograms of cured polyurethanes syrups III films are presented in Figures 6.1, 6.2, 6.3 and 6.4 respectively. Department of Chemistry, S.P.University Page 155

10 6.3 Flame Retardant Polymers Introduction Natural and synthetic polymer materials are being used in ever more areas and under ever more demanding environmental conditions. Obviously, the demand for polymer is expected to increase significantly in the foreseeable future. Fire hazards associated with the use of these polymeric materials, which may cause the loss of lives and properties, are of particular concern among the government regulatory bodies, consumers and manufacturers. As a result, considerable attention has been paid in the last three decades in controlling the inherent flammability of common organic polymers [1, 2]. The use of flame retardants to reduce the combustibility of polymers, and smoke or toxic fume production becomes an important part of the development and application of new materials. Although halogen atoms (e.g. bromine or chlorine) form some of the most widely applied flame retardant materials, in particular for polymers used in composite organic matrices or in electronic equipment, they have obvious disadvantages: not least the potential to corrode metal components and, more pressingly, the toxicity of the hydrogen halide formed during combustion. For this reason, halogen-free flame retardants for polymeric materials have attracted more and more attention from scientists and engineers in recent times [3 5] Halogen-Containing Flame Retardants It s well-known that all kinds of flame retardants act either in the vapour phase or the condensed phase or both of them through a chemical and/or physical mechanism to interfere with the combustion process during heating, pyrolysis, ignition, or flame spread [6 9]. Particularly, halogenated compounds act mostly in the vapour phase by a radical mechanism to Department of Chemistry, S.P.University Page 156

11 interrupt the exothermic processes and to suppress combustion. In spite of the possible threat to the environment and human bodies, various formulations for the flame retardation of both thermoplastics and thermosets consisting of halogen compounds have been developed over decades and are still in use due to the obvious advantages of low-cost, processability, miscibility, and low reduction on the physical/mechanical properties of the flame-retardant systems. The effectiveness of halogen compounds depends on the ease of liberation of the halogen. The nature of the group to which the halogen atom is attached is very important because it determines the carbonhalogen ratio and carbon-halogen bond energy and hence the amount of halogen released during burning [10 12]. In general, aliphatic or alicyclic halogen compounds are more effective than aromatic halogen compounds for most polyolefins burning at low temperature due to the lower carbon-halogen bond energies, and hence relatively easier halogen-release [13]. However, the lower carbon-halogen bond energy limited their wider application in most engineering plastics and polymer materials burning at high temperatures. As the development of flame-retardant materials obtained wide applications in the household areas, the increasing considerations about the safety awareness and environmental issues received extensive attention from the governments and among the public. Halogen-containing flame retardants, particularly the polybromodiphenyl ethers (PBDPE), achieved their bottleneck in their flame-retardant applications due to their high toxic and potentially carcinogenic brominated furans and dioxins formed during combustion [7]. However, numbers of halogen-containing flame retardants which have been restricted on their application or in the disputed state in Europe and United States, including decabromodiphenyl ether (DBDPE), decabromodiphenyl ethane (DBDPEh) tetrabromobisphenol A (TBBPA), brominated epoxy resin (BEP), and hexabromocyclododecane (HBCD), are still broadly utilized as the Department of Chemistry, S.P.University Page 157

12 commercial flame retardants. In this section, the focus mostly on some novel halogen-containing flame retardants and flame-retardant systems Brominated compounds Brominated compounds, mostly commercial, including TBBPA and DBDPE, due to their high bromine content and lower carbon-bromine covalent-bond energies, are widely utilized as flame retardants in both thermoplastics and thermosets. Flame retardancy of the polymeric materials is enhanced while the brominated compounds were added, but the mechanical properties, particularly impact strength, decreased with the increase of the additives. However, the mechanical properties were improved when the flame retardant was treated by a coupling agent [14]. Ou and Li [15] synthesized a novel, semi-aromatic bromine flameretardant as tetrabromophthalate di-2-ethylhexyl ester (TBPDO). Besides its flame retardation, it could considerably increase the impact strength of flameretarded styrenated plastics, including HIPS, ABS, and SMA. In addition, the mixtures of TBPDO with phosphates or brominated oligomers are able to improve the tensile strength and melt flow property for engineering plastics such as PC, PBT, and modified PPO. In addition the brominated samples act as flame retardants [16]. Although polyurethanes are excellent thermal [17] and electrical [18] insulators, they do suffer from a limited and often unsatisfactory level of fire resistance even in the presence of halogen containing fire retardance. The flame retardant activity was found to be greatly enhanced by a number of compounds. This is considered as synergist [19]. As flame retardant antimony oxide is of little value alone, but it displays very pronounced activity when used in conjunction with halogen compounds. Several comparisons of the relative effectiveness of bromine, chlorine [20, 24], fluorine [21] and Department of Chemistry, S.P.University Page 158

13 phosphorus [18, 25, 26, 27] derivatives on the flame retardant activity of some polymers are reported. 6.4 Experimental Flame retardancy of prepared polyurethane syrups-iii based cured films were determined by using ASTM D-2863 procedure (limiting oxygen index, LOI measurement) Analyses were carried out using a Stanton Redcroft analyser. LOI were determined on mm specimen with 3 mm thickness. Analyses were conducted at ambient temperature, with a 40 ml/s gas flow in the quartz column. The oxygen ratio variation in the gas was 0.2%. Table: 6.3 Flame Retardant Proprieties of Polyurethane Syrups-III cured Films data Polyurethane code LOI Flammability B15PUT1 38 F B16PUT1 37 F B17PUT1 36 F B18PUT1 35 F B19PUT1 34 F B20PUT1 33 NF B21PUT1 31 NF B15PUT2 39 F B16PUT2 38 F B17PUT2 37 F B18PUT2 36 F B19PUT2 35 F B20PUT2 34 NF B21PUT2 32 NF Department of Chemistry, S.P.University Page 159

14 Table: 6.4 Flame Retardant Proprieties of Polyurethane Syrups-III cured Films data Polyurethane code LOI Flammability B15PUI1 34 F B16PUI1 33 F B17PUI1 32 F B18PUI1 31 F B19PUI1 30 NF B20PUI1 29 NF B21PUI1 28 NF B15PUI2 35 F B16PUI2 34 F B17PUI2 33 F B18PUI2 32 F B19PUI2 31 NF B20PUI2 30 NF B21PUI2 29 NF The flame resistance of the bromine-containing polyurethanes was evaluated by determining their LOI values. Tables 6.3 and 6.4 lists those values, 29 39, together with the bromine content of the polyurethanes. Since certain LOI values were around 33 (Table 6.3, 6.4 and Reference 17), the polyurethanes flame retardancy was enhanced by incorporating bromine into polymers. Furthermore, polyurethanes exhibited relatively higher LOI values than other samples. Such high values could be due to their richer bromine contents. As previously demon strated, the LOI values of polyurethanes increase with an increasing brominated castor oil content [17]. Observations in this study confirm this event. Department of Chemistry, S.P.University Page 160

15 6.5 Results and Discussion Flammability Halogen, particularly bromine compounds, occupies an important position among the fire-extinguishing and fire retardant agent [22]. The mechanism of the inhibitory action of halogen compounds is believed to be based on the interaction of the halogen with some of the reactive moieties of the flame itself [23] Certain ingredients can be incorporated into the flame retarding systems. Which can combine chemically with the halogen components to increase their residence time in the burning mass [19]. Accordingly in this work, formulation of the formed polyurethane's with bromine which acts as fire retardants improver was used. All the samples containing bromine in their structure are non-flammable while the reverse is true for non-brominated samples. In addition high char yields were associated with the flame retardancy of the polyurethanes, a property that was further demonstrated by the high LOI values of the polyurethanes measured as LOI for materials under study are shown in Tables 6.3 and 6.4. As soon as molecules containing bromine atoms have been introduced LOI are clearly improved. The gain on the value of LOI is nearly 2-3 points, which allows oxygen indices greater than 20 to be obtained. Up to a ratio of incorporated brominated castor oil wt. %. When the aliphatic and aromatic diisocyanate reacts with a blended brominated castor oil-rosinified phenolic resin (wt.%), it is possible to reach a LOI of 39, which becomes very interesting for the fire behaviour of the material. Aromatic polyurethanes have higher LOI than aliphatic polyurethane due to increases the brominated castor oil wt.% and aromatic compound. Department of Chemistry, S.P.University Page 161

16 For aliphatic PU materials, LOI increases with the brominated castor oil ratio increases. In the case of aliphatic PU materials, LOI is maximum when the brominated castor oil ratio is 80 wt.%. Probably for higher brominated castor oil ratio, the material becomes inhomogeneous and has decreasing properties. We also have to notice that during the fire test, the combustion of the specimen is unstable and inhomogeneous. Department of Chemistry, S.P.University Page 162

17 Reference 1. S. Y. Lu, I. Hamerton, Progress of Polymer Science, 27, 1661, (2002). 2. E. D. Weil, S. V. Levchik, M. Ravey, W. M. Zhu, Phosphorus, Sulfur Silicon Relat.Elem., 17,146, (1999). 3. G. Woodward, C. Harrs, J. Manku, Phosphorus, Sulfur Silicon Relat. Elem., 146, 25, (1999). 4. A. M. Aaronson, D. A. Bright, Phosphorus, Sulfur Silicon Relat. Elem., 83, 110, (1996). 5. Y. Z. Wang, X. T. Chen, X. D. Tang, X. H. Du, Journal of Material Chemistry, 13, 1248, (2003). 6. E. D. Weil, W. Zhu, N. Patel, S. M. Mukhopadhyay, Polymer Degradation and Stability, 54,125, (1996). 7. S. Y. Lu, I. Hamerton, Progress of Polymer Science, 27, 1661, (2002). 8. Y. Z. Wang, Flame-Retardation Design of PET Fibers, Sichuan Science and Technology Press, Chengdu, (1997). 9. J. J. Li, X. B. Huang, T. M. Cai, Flame-Retarded Styrene Plastics, Science Press, Beijing, (2003). 10. J. W. Lyons, The Chemistry and Uses of Flame Retardants, Wiley Interscience, New York, (1970). 11. Y. X. Ou, Y. Chen, X. M. Wang, Flame-Retarded Polymeric Materials, National Defense Press, Beijing, (2001). 12. Y. X. Ou, J. J. Li, Flame Retardants: Properties, Preparation and Application, Chemical Industry Press, Beijing, (2006). Department of Chemistry, S.P.University Page 163

18 13. G. Carmino, L. Costa, M. P. Luda di Cortemiglia and references quoted therein., Polymer Degradation and Stability, 33, 131, (1991). 14. F. Lan, N. Chen, L. Cai, J. Zhang, M. Xiang, China Plastics Ind. 27, (1999). 15. Y.-X. Ou, Q. Li, Plastics Science Technology, 1, 24, (1998). 16. L. Chena and Y. Z. Wanga, Polymer Advance Technology, 21, 126, (2010). 17. J. A. Brydson: "Plastics materials", fifth edition, Butterworth, Scientific, London, 271, (1986). 18. A. M. Hassan, M. A. Youssif, A. M. Motawie: "Evaluation of some prepared Fire-resistant plywood coatings". Bull. Fac. Sci. Zagazig Univ., 1, , (1991). 19. M. Lewin, S. M. Atlas, E. M. Pearce: "Flame-retardant Polymeric Materials", Plenum Press, New York and London, 77, (1975). 20. O. Tateshi, H. Noriaki, M. Fumio, S. Noboru, H. Tadayoshi: "Fire-resistant resin composition for metal-clad laminates". JP 63, 215, 711, Chemical Abstract, , (1989). 21. P. Weinhold, European Patent, EP 0, 430, 266, A2, 5, 10, (1991). 22. G. Lask and H.G.Wagner: "8th symposium (international) on combustion", William and Wilkins Co, Baltimore, 432, (1962). 23. W.A. Rosser, et al.: "Mechanism of flame inhibition", Final report, contract No. DA ENG 2863, Department of Agriculture, (1958). 24. H. S. Patel, B. K. Patel, International Journal of Polymeric Materials and Polymeric Biomaterials, 58(6), , (2009). Department of Chemistry, S.P.University Page 164

19 25. Y. L. Chang, Y. Z. Wang, D. M. Ban, B. Yang, G. M. Zhao, Macromolecule Material Engineering, 289, , (2004). 26. T. L. Wang, Y. L. CHO, P. L. KUO, Journal of Applied Polymer Science, 82, , (2001). 27. M. Spirckela, N. Regnier, B. Mortaignea, B. Youssef, C. Bunelc, Polymer Degradation and Stability, 78, , (2002). Department of Chemistry, S.P.University Page 165