Пластмассы, полимерные и синтетические материалы, каучуки, резино-технические изделия, шины и их производство

D. Ch. Sc. Abdikarimov M.N.

Kazakh National Technical University named after K.I. Satpayev, Natural humanities institute named after al Mashani, department «Сhemistry», Е-mail: mn.abdikarimov@mail.ru

Michelson’s equation and the study of destruction processes in condensed phase of burning polymethylmethacrylate in various conditions and geometrical positions

Diffusion combustion of condensed systems particularly of polymeric materials is depend from shape, arrangement and dimension of patterns, concentration of oxidant in sur linear pyrolysis (LP), i.e. at one-sided influence of heated gases stream on cylinder samples of polymethylmethacrylate (PMMA) in various conditions and determination influence of thermal stream, arrangement of patterns on combustion speed and modification of molecular weight in depth of condensed phase.

During the work there was studied processes of linear pyrolysis at combustion of circle plates PMMA with diameter 100 mm and thickness 10 mm, that was burned in the flame of propane-air burner with temperature 1000°C. It was also studied Diffusion combustion of the same patterns with fixation of linear combustion speed and measurement of temperature arrangement. Patterns was burned in vertical position with diametrically opposite directions, with attitude of combustion surface up and down. Temperature field in burning plates of PMMA was determined with the help of chromel-alumel thermocouple (thickness of junction 0.2 mm), which were incompressed to the pattern on the fixed depth. Temperature indications in condensed and gasses phase were fixed on plotter it is also was made dependence of surface temperature from combustion depth in condensed phase. For the temperature of surface was taken temperature of exposure thermocouple junction.

At combustion a pattern of PMMA as bottom-up as top-down trend of curve molecular weight allocation is identical. Thus on the depth of 0.3 mm with combustion top-down molecular weight is 922000, i.e. that is 26.3 % from original molecular weight. On the depth of 0.6 mm molecular weight is 1750000 that is 50 %. Molecular weight on the depth 2.5 mm is equal to identical.

Such drastic change of molecular weight with depth of patterns combustion under the influence of high temperature flame apparently is explain that pattern is not advanced to get warmed to the temperature of substrate because of high speed of burning-0.04 mm/sec and destruction goes on the surface and around the surface but not into the condensed phase deep layer. Gasification depth of the burnt PMMA residua at combustion as from above as from below is 0.75 mm. Despite distinction in speed of burning modification PMMA trend of curve at self burning is identical independently of burning surface arrangement, vials depth of the burnt PMMA residua in this case is 3.5-3.65 mm. Molecular weight of top-down burnt residuum on the depth of 0.4 mm is 228200 which is 6.52 % from the original mass and on the depth of 4.8 mm is 1663000, i.e. 4.75 % from the original.on the depth of 4.8mm molecular weight equal to identical molecular weight of PMMA. At bottom-up combustion molecular weight is state after 4.35 mm. In comparison of curves there was found that at self-combustion of PMMA thermodestruction is deeper to hypogene layers in comparison with forced combustion under the influence of propane-air flame. Evidently it’s explains of slow substrate warming-up at low top-down speed of burning peer 0.0068 mm²/sec and at bottom-up speed of burning is 0.0052 mm/sec.

It is significant that at burning a pattern of PMMA top down is demands considerable inductive period about 2 minutes for inflammation of pattern. At inverse arrangement of pattern time of set fire is about 2 minutes. In all probability, needed induction period for achievement of definite warming-up of the pattern, because polymeric pattern haven’t kindle, before temperature in the depth of condensed phase of PMMA haven’t achieved 70-80^оС. At combustion of pattern bottom-up, probably, head of cone propane-air flame is contiguous with surface of combusted polymer blockade penetration of oxygen from two sides. At inverse arrangement of PMMA pattern liquid and gaseous products of pyrolysis evaporate up, creating auspicious conditions of burning.

Modification of temperature on the depth was calculated by Michelson’s equation, as a whole combustion of PMMA submit this equation. There was rated coefficient of thermal diffusivity by the thermal diffusivity equation, accept that temperature is stable to the time, i.e. in steady-state conditions, speed of burning and temperature of surface was taken from experimental data. Depth of burning was determined as product of burning speed on the burning time. Experimental quantity of burning PMMA in propane-air flame top-down submit Michelson’s equation; coefficient of thermal diffusivity peer 0.0848 mm²/sec and calculated come to 0,09 мм²/с,i.e. very close value.

Reference data: thickness of PMMA is 1.19 g/sm³ ; specific heat-0,35 kkal/g grad; Determined that distribution of temperature with depth at self combustion a pattern of PMMA bottom up at initial part of curve submit Michelson’s equation; experimental meaning of thermal diffusivity coefficient is 0.016 mm²/sec and theoretical meaning -0.09 mm²/sec. At self combustion of PMMA top-down at initial part of curve also submit Michelson’s equation, thermal diffusivity coefficient is 0.0038 mm²/sec and theoretical meaning -0.09 mm²/sec. Seemingly large induction period for ignition of PMMA pattern at self combustion bottom up stipulate for low coefficient of thermal diffusivity conductivity-0.0016 mm²/sec; at self combustion top-down is 0.0038 mm²/sec.

Conclusions:

1. It’s shown that at burning PMMA in propane-air flame speeds of burning and distribution of temperature do not depend on geometrical arrangement of patterns with surface down or inside out.

2. There was calculated coefficients of thermal diffusivity conductivity and shown that large induction period for ignition of PMMA pattern at self combustion bottom up stipulate for low coefficient of thermal diffusivity conductivity-0.0016 mm²/sec;at self combustion top-down is 0.0038 mm²/sec.

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