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Preservatives in Timber Products
W hil e a com prehensi ve revi ew i s beyond the scope of thi s docum ent, a wi de range of treatm ents i s avai l abl e, with varyi ng l evel s of human and envi ronm ental toxi city. Very toxi c chemi cal s have histori call y been i ntroduced i nto our hom es and bui l di ngs i n the cause of timber treatm ent such as DDT, Di el dri n, Pentachl oraphenol , Lindane, Tri butyl ti n oxide and Arseni c. Sci enti fi c understandi ng and publi c sentim ent changes over tim e, and we are usi ng i ncreasi ngly sophi sti cated treatm ents. The US recentl y j oi ned a gr owi ng l i st of countri es i n phasi ng out the use of CCA treated timber (copper chrom e arsenate) for most appl i cati ons (US EPA). Perm ethri n, organi c zi nc com pounds, IPBC, Di chl ofl uani d and Propiconazol e are al l l ess toxi c than the earl i er treatm ents, although true heal th and envi ronm ental im pacts wi ll be apparent onl y after many years of use. Preservatives Used in the treatment of Wood
Low i niti al cost. A new prim er may be requi red for uses l i nseed oi l i nstead of whi te spi ri t, el im i nati ng the greenhouse i m pact of whi te-spi ri t off-gassi ng. cost, pai ntabl e, hi ghly of exc ept as l andfill : hi ghl y shavi ngs and offcuts must be di sposed of as l andfil l. Effecti vel y prohi bi ted i n Japan and som e European countri es, phase-out i n US. Som e research shows si gnifi cant toxi city from contact to treated tim ber to chi l dren under 6 years (Envi ronm ental W orki ng Group 2001) Hi ghl y effecti ve, l ower gen eral l y used for *Appl i cati ons are attri buted ‘Hazard’ l evel s under A ustral i an Standards. These range from ‘H1’ (above ground, i ndoors and protected) to ‘H6’, tim ber perm anentl y i n contact wi th salt water. W indows are typi call y an H3 appl icati on (outsi de but not i n-ground), whil e fences (i n ground contact) typi cal ly an H4. Binder Toxicity
Many wood products today i ncorporate form al dehyde-based gl ues. The IARC has cl assi fi ed formal dehyde as a Category 1 ‘known hum an carci nogen’ (IARC 2008). . In many commonl y used forms formal dehyde wi l l offgas, parti cul arl y i n new products and i n hi gh heat and humi di ty. Inhal ati on of form al dehyde vapors can cause fati gue, respi ratory i rritati on, all ergi c ski n reacti ons and i s a probabl e carci nogen (IARC 2003). Conventi onal i nteri or grade products (pl ywoods, MDF’s, parti cl eboards) typi cal ly use urea-formal dehyde gl ues, whi ch are rel ati vel y unstabl e and offgass consi stententl y over tim e. Accordi ng to the Australi an CSIRO thi s offgassi ng i s not stopped for more than a matter of weeks by pai nti ng, varni shi ng or l ami nate surfaces (Brown, pers. comm. 2003). These m ateri al s are a primary contri butor to form al dehyde em i ssi on concerns i n bui ldi ngs (Brown 2001). Pl ywoods used for exteri or and structural appl i cati ons typi call y use phenol formal dehyde (PF) resi n. PF i s a m ore expensi v e, water-resi stant glue, and a much more stabl e product that offgasses at a m uch l esser rate than UF gl ue. The US Green Bui l di ng Counci l 's LEED Credi t for Com posite W ood on the other hand requi res com posite timber and agrifi bre boards to be free of any added UF products. The recl aim ati on of dem ol iti on tim bers for use and reprocessi ng as recycl ed timber i s prevented du e to the use i n recent decad es of adhesi ve fi xi ngs. W hi l e deconstructabil ity i s fundam ental to reuse and hi gh-val ue recycl i ng, current gl ue & nail practi ces wi ll ensure thi s is i n most i nstances im practi cal, and repai r diffi cul t. It i s cri ti cal wherev er possi bl e to use fi xi ngs that facil itate deconstructi on and hi gh-val ue reuse.



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