Лесотехнически Университет

Резюме

Mechanical stability – relative reduction of modulus of elasticity and stiffness in bending, of structural particleboards (SPBs) based on modified phenol-formaldehyde resins (PFRs) during long-lasting stay in the open in natural climatic conditions has been determined experimentally. The impact of atmospheric effects by varying climatic factors, such as heating, wetting, freezing, insolation, etc., on strain-strength characteristic of SPBs has been established under field conditions.

To assess the mechanical stability of SPBs during long-lasting stay in the open in natural climatic conditions, respective algorithms and a diagram have been proposed. The traditionally used %, and for the stiffness – %, at a board thickness of 18 ± 2 mm, have been adopted as permissible rate of reduction of the relative modulus of elasticity. SPBs based on PFR modified with aluminium sulphate, in which % for a 10-year period of exposure in the open has been attained, have shown relatively highest weather resistance. For the boards based on PFR and aluminium sulphate, % for a 5-year period of stay in the open, but with respect to stiffness, the permissible duration of exposure is considerably lower – under 1.5 years.

Резюме

A mathematical model (algorithm) and a nomogram for determination of the compression ratio in flat-pressed composites on the basis of urea-formaldehyde resin as a binding agent and addition of paraffin have been presented in the investigation. By means of an algorithm (KD), the compression ratio of the wood mat during its piezothermal treatment is taken into account. As input data, following parameters are included in the algorithm for KD: bulk densities of the input wood raw material and the composite board; the specific weights of the paraffin and the binding agent; the moisture content of the composite board; the percentage of resin and paraffin; the volumetric swelling of wood.

Резюме

The algorithm refers to a nomogram for numerical and graphic determination of stiffness in bending of structural particleboards (SPBs). SPBs are technologically formed composite wood-based products with standardised designation P6 with wide application in construction, furniture manufacturing and interior. As evaluation criterion for the load-carrying capacity of the boards, i.e. for their fitness for use in various structural solutions, serves their strain-strength index stiffness in bending St, defined in technical literature as a product of the inertia moment of the cross-section Jy and the modulus of elasticity in bending Em. For the time being, in engineering calculations, only indirect estimates for this index on the basis of the values for the modulus of elasticity in bending are used.

The algorithm for numerical and graphic determination of stiffness in bending of SPBs is based on:

-   the physical nature of the composite as technologically formed layered material and the simulation modelling of its cross-section as a “double T beam”;

-   the experimentally established empirical dependences of the modulus of elasticity in bending on the bulk densities of the composite board and the wood raw material.