屋外ばくろ試験におけるポリエチレン試料の特性変化予測 : 高分子系建築材料の耐久性予測モデル(その1)

抄録

In order to predict service life of polymeric building materials, the application of several mathematical formulations is being discussed recently. As the first approach, the most simple polymer, unstabilized polyethylene film was studied in this paper. This PE sample is specified by "JIS K 7200-1986, Standard Reference Test Specimens for Calibrating a Laboratory Light Exposure Apparatus, SR-LS-PE-8604". Photo-oxidation reaction in PE produces carbonyl groups, which can be quantified by infrared abrsorbtion spectrum. The absorbance ratio, A_r, of carbonyl absorbance to methylene is an index of degradation. A_r=A_<1715>/A_<2030> where, A_<1715> : IR carbonyl absorbance at 1715 cm^<-1> and A_<2030> : IR methylene absorbance at 2030 cm^<-1> From the result of preliminary thermal degradation test of PE specimens, the effect of heat under outdoor exposure test was estimated to be negligible. Samples were exposed outdoor on 0°, 30° and 90° planes facing to south in Tsukuba, Japan, lat. 36°7' 38"N, long. 140°4'39"E, every month from November 1986 to Octber 1988. Collected absorbance ratios were expressed as various functions of fructuating outdoor solar ultraviolet energy and temperature of samples. Among the all these models, Koike and Tanaka's Model, [numerical formula] where, C_u : ultraviolet degradation constant, -, U_v :solar ultraviolet energy in 10 minutes, KJ/m^2, α : power number, ultraviolet degradation constant, -, E_u : activation energy of ultraviolet degradation reaction, KJ/mol, R : gas constant, 8.314×10〜<-3> KJ/mol/K and T_p : temperature of sample observed every 10 minutes, K. produced most acceptable accordance of calculated Ar with observed A_r. Obtained degradation constants and correlation factor, r, between observed and calculated Ar are as follows : number of samples, n=72, C_u=1.29×10^<3>, α=0.0165, E_u=36.2, r= Degradation constants, which produce the least error between observed and calculated Ar, are : number of samples, n=24, C_s=2.66×10^5, γ=0.235, E_s=39.6, r=0.9899 Introducing these values and meteorological data at Asahikawa, Choshi and Okinawa, the absorbance ratios of samples exoosured were estimated and compared with the observed ones.0.9882 The value of α is far more smaller than it has been estimated. This predicts that ultraviolet ray initiates photo-oxidation reaction and that oxigen dispersion dominates degradation rate. The absorbance ratios of samples exposured horizontally could be expressed as a function of meteorological factors, solar radiation energy and ambient temperature in daytime : [numerical formula] where, C_s : solar degradation constant, -, S_p : daily amount of solar radiation energy, KJ/m^2, γ : power number, solar degradation constant, -, E_s : activation energy of degradation reaction, KJ/mol, T_D : average ambient temperature in daytime, K, T_D=(T_6/2+T\9,+T_<12>+T_<15>+T_<18>/2)/4 ; sub-number means observed o'clock, JST (Japan Standard Time)