Long Term Durability Of Wood-Flour-Polypropylene-Elastomer Composites
Journal of the Mechanical Behavior of Materials
Investigations on the long-term durability of wood flour-propylene-elastomer composites at static loading and high stresses are reported. This is an extremely important characteristic that makes possible the fairly accurate prediction of the service life of polymeric articles. The long-term strength is investigated under conditions of uniaxial tension of polypropylene, elastified with 10% polyisoprene, and polypropylene, filled with 5% and 10% wood flour. It was established that the elastomer
... hat the elastomer and the filler change the fracture mechanism of the polymer in opposite directions. This result oriented the work towards investigations on the durability of polypropylene, elastified with polyisoprene and filled with wood flour simultaneously. The presence of polyisoprene in the wood flour-filled polypropylene increases the elasticity of the composition, and at the same time retards the processes of ageing. Long Term Durability OfWood-Flour-Polypropylene-Ela durability of wood flour-polypropylene-elastomer composites (WFPPE) under the action of static loading and high stresses. OBJECTS AND METHODS OF INVESTIGATION The investigations were carried out on PP, type "Buplen-6631", produced by Nephtochim, Bourgas, Bulgaria. The investigated polypropylene has the following parameters: MFI = 2.67 g/10 min; yield point = 30 MPa and Izod impact strength -30 J/m. The elastifying modifier was stereo-regular 1,4-cis polyisoprene rubber "Ski-3", a Russian product. In our previous investigations this elastomer exhibited good elastifying action on PP 191. The elastomer was plasticized in advance on a two-roll mill with friction coefficient =1.1, still Mooney plasticity = 15.5. The filler is coniferous wood flour, produced by the Maritsa company, Bulgaria with a grain size in the range of 140 -160 μηι. Mixing of WF and PI is carried out on a two-roll mill. The mixture is drawn in sheets and is granulated by cold cutting, after which it is mixed with PP in a special mixing extruder /10/, providing dispersing homogenization of the components in the polymer matrix. The samples are blanked from pressing plates, prepared under the following conditions: Τ = 180°C, pre-pressing time = 8 min, pressing time = 8 min and cooling rate = 20°C/min. Their shape and size conform to the requirements of ISO-527. The determination of the long-term strength at static loading is carried out in chambers at a constant temperature, Τ = 10 ± 2°C. The samples are suspended on a metal frame, and loading is accomplished with metal weights, ensuring uniform distribution of the load. Testing of the samples under super-high stresses is carried out with specially designed equipment /ll/, in which the force is created electrodynamically, and the time to fracture is measured with an electronic timer with an accuracy of 10" 8 s. The equipment is placed in a chamber, maintaining constant temperature. The microscopic investigations are conducted with a scanning electron microscope, Olympus-BH2-BHSP. The X-ray structural analyses are made with Philips equipment with iron radiation. The thermal and mechanical analysis performed on UIP-70M. RESULTS AND DISCUSSION It is known that the long-term durability of polymers is determined by measuring the time interval between the onset of loading and the fracture of the specimen. Under real operating conditions, the articles are most frequently subjected to constant loads for a certain period of time. For this reason the present work reports on investigations of the long-term durability of WFPPE composites, containing PP, PI and WF, at static loading under conditions of uniaxial tension.