Development of a One-Step Process for Production of Foam Core Particleboards using Rigid Polyurethane Foam
A simulated one-step process has been developed for the production of foam core particleboards using rigid polyurethane as the core layer. The results showed that the different techniques used for surface layer separation (unresinated particles and sprayed water) and foam injections (open system and closed system) had no influences on panels’ characteristics. Mechanical properties (e.g., bending strength and internal bond strength) were mostly influenced by the surface layer thickness, while the water absorption and edge screw withdrawal were influenced by the foam cell structure. The use of sprayed water for surface layer separation doubled the formaldehyde emission (FE) of the panels. The addition of urea (based on 10% of the dry resin) to the sprayed water had a positive effect of reducing the final FE. Furthermore, increasing the surface layer thickness had a positive, linear relationship with FE.
Absorption of water by polyurethane foam. modelling and experiments
Abstract Polyurethane (PU) foams are made of small cells, regular in shape, which result from the presence of a gas acting as a blowing agent during its formation (carbon dioxide or fluorocarbon). When the PU foam is in contact with water, a matter transfer is observed, water diffusing into the foam. The presence of the blowing agent in the cells is responsible for hindered diffusion of the water. The same PU foams are immersed in water and dried; the process of absorption-desorption repeated many times shows a change in the diffusivity for the following stages of absorption. The diffusivity is considerably lower for the first absorption than for the following absorptions. Moreover, a finite coefficient of matter transfer is observed for the first absorption, while this coefficient is very high with the following absorptions.
MATERIALS RESEARCH ON EPS20 AND EPS15 UNDER REPRESENTATIVE CONDITIONS IN PAVEMENT STRUCTURES
This article deals with the investigation of the mechanical characteristics of EPS with bulk densities of 15 km/cu m (EPS15) and 20 kg/cu m (EPS20) under different hydro-thermal condiitons. In the experiments, the EPS is tested under the expected loading, moisture and temperature conditions defined as critical. It is a guarantee that EPS will show at least an equally good mechanical behaviour in real sub-base conditions under real traffic loading. In the second section, details are given about EPS20 and EPS15 specimens on which the experiments were carried out. The third section deals with hydro-thermal research on EPS. Water absorption of EPS is stimulated by means of immersion, immersion together with exposing to underpressure, and exposing to freeze-thaw cycles. The purpose of the experiments is twofold: firstly, to obtain information on the water absoprtion of EPS under different conditions and, secondly, to prepare samples for further mechanical research. In the fourth section, determination of the dynamic moduli of elasticity of EPS20 by means of propagation velocity of a wave through a prismatic sample is described. The fifth section describes compression tests on cylindrical specimens of EPS15 and EPS20. Compression was performed with different strain rates on the specimens with varied moisture contents. The linear elastic region, evolution of the EPS material modulus and the stress and strain values corresponding to beginning of permanent deformations were determined by results analysis. The experiments were performed at low temperatures too. The minimum test temperature was -13.9 degrees C. Different strain rates, various test temperstaures (only EPS30) and specimen conditions were used to determine the effects, if any, of these test conditions on EPS15 and EPS20 material behaviour. In the scope of uniaxial cyclic loading tests described in the sixth section, samples have been exposed to combined static and dynamic loading. In the seventh section, creep in the EPS sub-base is investigated under static stresses, which represent dead weights of thin and thick overlaying layers above an EPS sub-base. Finally, in the last section, overall conclusions for this research on EPS15 and EPS20 are drawn. (A)