EFECTUL SUBSTANTELOR EXTRACTBILE SOLUBILE IN APA ASUPRA UNOR PROPPRIETATI FIZICE SI MECANICE LA TREI SPECII DE FOIOASE TROPICALE

Charles ANTWI-BOASIAKO
Dr., Head of Department of Wood Science &Technology - Faculty of Renewable Natural Resources
Kwame Nkrumah University of Science &Technology, Kumasi-Ghana
Tel: +233-243771376. Fax: +233-51-60137.
E-mail: cantwi-boasiako.frnr@knust.edu.gh

Jane ANTWIWAA BIMPONG
BSc. - Faculty of Renewable Natural Resources
Kwame Nkrumah University of Science &Technology, Kumasi-Ghana
Tel: +233-242153317. Fax: +233-51-60375.
E-mail: preciouzjay@yahoo.com

Rezumat:
         Interactiunea lemnului cu mediul inconjurator umed duce la scurgerea substantelor extractibile, ce influenteaza durabilitatea naturala a acestuia. Acest studiu examineaza influenta extractibilelor solubile in apa asupra unor proprietati fizico-mecanice, la trei specii de foioase cu importanta economica (Milicia excelsa (Welw.) C. Berg., Sterculia rhinopetala K. Schum. and Piptadeniastrum africanum (Hook.f.) Brenan). Cincizeci de epruvete din lemn de duramen (2×2×2cm, 2×2×10cm si 2×2×6cm, respectiv pentru masa volumica, contragere si rezistenta la compresiune [BS 373, 1957]), selectate pe diametru, la inaltimea pieptului, din fiecare specie, au fost fierte in apa, 20 de ore la 1000C (pe baie de apa). Cincizeci de epruvete netratate, din fiecare specie au servit ca probe martor. Greutatea specifica pentru ambele tipuri de epruvete, supuse extractiei si martor, a variat astfel: M. excelsa > S. rhinopetala > P. Africanum, iar pentru cele supuse extractiei aceasta s-a redus. Contragerile au fost evaluate astfel: volumice > tangentiale >radiale pentru fiecate tip de cherestea, cu media variind astfel: S. rhinopetala > P. africanum > M. excelsa. In general, pentru epruvetele supuse extractiei contragerea a fost mai mare decat pentru epruvetele martor. Raportul dintre contagerea tangentiala si contragerea radiala (T/R), folosit frecvent pentru evaluarea stabilitatii dimensionale a lemnului, a variat intre 1,35 si 1,67 si s-a incadrat in intervalul acceptat de 1,4 - 2,0. Epruvetele supuse extractiei au avut valori mai mari si pot fi clasificate ca fiind mai putin stabile decat epruvetele martor. Rezistenta la compresiune a epruvetelor a variat astfel: P. africanum > S. rhinopetala > M. Excelsa, epruvetele martor avand valori mai mari decat cele supuse extractiei. Indepartarea extractibilelor solubile in apa a dus la cresterea contragerii la toate epruvetele din fiecare specie, si la scaderea greutatii specifice si a rezistentei la compresiune.

Cuvinte cheie: rezistenta la compresiune, stabilitatea dimensionala, contragerea volumica, extractibile solubile in apa.

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