Effect of g-radiation on the molecular characteristics of low-density polyethylene V.G. Barkhudaryan * Department of Molecular Physics, Yerevan State University, 1, Alex Manoogian St., 375049 Yerevan, Armenia Received 25 November 1998; received in revised form 12 February 1999; accepted 12 March 1999 Abstract The inﬂuence of g-radiation on the molecular characteristics of low-density polyethylene dependant on the samples’ thickness, the intensity and the dose has been investigated by methods of viscosimetry and light scattering. A remarkable increase of molecular mass by the increase in radiation doses was established. It is linear for the mass-average molecular mass while for the viscosity average molecular mass it is minimum at the initial doses. The origin of this minimum is explained by the change of macromolecular hydrodynamic volume, as it has also been established that the growth of molecular mass at the initial doses is mainly due to the increase of the degree of macro- molecular branching. A dependence of the rate of change of polyethylene molecular characteristics on the samples’ thickness, irradiation intensity and dose was established.  1999 Elsevier Science Ltd. All rights reserved. Keywords: Polyethylene; Radiation; Macromolecular branching 1. Introduction It is known that the noninvertible molecular transforma- tions occur in the polymers by irradiation, resulting in a change of supermolecular structure and, accordingly, the exploitation characteristics of the amorphous-crystalline poly- mers [1,2]. Consequently, the elucidation of the regularities of changes in the molecular characteristics under the inﬂuence of external factors represents a considerable interest for the investigation of previously studied polymers with respect to growth and stabilization. In the present paper we report and discuss the results of viscosity and light scattering investiga- tions of the inﬂuence of g-radiation on molecular character- istics of low-density polyethylene (LDPE) dependent on the samples’ thickness, the irradiation intensity and doses. 2. Experimental LDPE 100, 200, 500 and 1000 mm thick ﬁlms were studied. They were made by the hot-pressing method on the hydraulic press device DP-36 (DDR). Irradiation was carried out on the device RCM-20 in the open air by a standard 60 Co source (taking into account the disintegration of source). The irradiation intensities were 0.1 and 0.4 Mrad h -1 (1 Mrad h -1  2.78 Gy s -1 , 1 Gy  10 2 rad). The temperature on the ﬁlm surface was 40°C. Intrinsic viscosity measurements in Ostwald’s capillary viscometer (the capillary’s diameter 0,64 mm) were performed in cis decalin at 70 + 0.01°C. The efﬂux time of the solvent was 98 s. The solvent and solutions were ﬁltered through a No. 3 glass ﬁlter (at 70°C) before the measure- ments. For the relation of molecular mass and intrinsic vis- cosity (unit of [h] dl g -1 ) the following formula was used [3] h 6:8 × 10 -4 × M 0:675 : 1 Light scattering measurements were performed in cis decalin at 80°C on the light scattering instrument FPS-3 (constructed by the Central Constructional Bureau of Acad- emy of Sciences, USSR) with unpolarized incident light (l  436 nm). Scattering intensities were measured over the angular range 30–150° with benzene as reference (Iu  48.5 × 10 -6 cm -1 ). The refractive index increment (2n/2c) was measured on a Pulfrikh differential refract- ometer in cis decalin at 80°C by using a mercury-discharge lamp with blue light (435.8 nm), giving 2n/ 2c  0.109 cm 3 g -1 . In order to purify the solvent and solu- tions, they were successively ﬁltered through the glass ﬁlters of different sizes (No. 3–5) thermostated at 80°C. The mass-average molecular mass   M w  and mean-square radius of gyration  R 2  1=2 of initial samples were determined Polymer 41 (2000) 575–578 0032-3861/00/$ - see front matter  1999 Elsevier Science Ltd. All rights reserved. PII: S0032-3861(99)00209-8 * Tel.: +7-3742-554-341; +7-3742-524-040; fax: 7-3742-151-800. E-mail address: moleckﬁz@ysu.am; arman@ameria.am (V.G. Barkhudaryan)