1re partie Empreinte environnementale du CLT – résultats préliminaires
Dans la présente partie, nous déterminons expérimentalement certaines caractéristiques environnementales quantifiées du CLT en tant que matériau de construction, sans toutefois effectuer une analyse du cycle de vie (ACV) exhaustive. Puisqu’il n’existe aucune documentation comparative sur le CLT, nous utiliserons plusieurs approches pour estimer son empreinte environnementale et pour le comparer au béton. À l’aide des données d’ACV existantes du bois lamellé-collé canadien en tant que valeurs de remplacement, nous examinerons l’empreinte du matériau en soi comparé aux matériaux du béton armé ainsi que des matériaux utilisés dans les bâtiments de moyenne hauteur comparativement au béton. Nous ajusterons ensuite les données de l’ACV du bois lamellé-collé pour qu’elles se rapprochent de celles d’une section de plancher de CLT aux fins de comparaison à une section de plancher en béton équivalente sur le plan fonctionnel. Dans chacun des cas, nous estimons que le CLT surpassera considérablement le béton dans chaque mesure environnementale abordée selon l’ACV.
2e partie Effets potentiels sur la qualité de l’air intérieur de l’utilisation du CLT dans les bâtiments – résultats préliminaires
Cinq produits de bois lamellé-croisé de différentes épaisseurs et lignes de collage ont été testés aux fins d’analyse de leurs composés organiques volatils (COV) comprenant les émissions de formaldéhyde et d’acétaldéhyde afin d’aider les ingénieurs et les constructeurs à mieux choisir les matériaux de construction ayant le moins d’incidence sur la qualité de l’air intérieur. Les émissions ont été évaluées selon la norme ASTM D 5116 et ont été recueillies après que les échantillons aient été exposés dans la chambre d’essais pendant 24 heures.
Aucune corrélation n’a pu être établie entre l’épaisseur du bois lamellé-croisé, les lignes de collage ou la quantité de COV individuels (COVi) émis, comprenant le formaldéhyde et l’acétaldéhyde, ou les COV totaux (COVt). Les cinq produits de CLT ont démontré de très faibles taux d’émissions de COVi et de COVt. La plupart des COV détectés provenaient de composés de terpène de bois résineux utilisés dans la fabrication de bois de construction laminé. Ainsi, lorsque le CLT est employé dans la construction d’un bâtiment, l’effet des COV sur la qualité de l’air intérieur est mineur, voire inexistant.
Lorsqu’on évalue les effets du produit sur la qualité de l’air intérieur, on peut facilement conclure qu’il serait négligeable, sinon nul. Les résultats relatifs aux COVt et aux émissions de formaldéhyde des cinq produits de bois lamellé-croisé après une exposition de 24 heures étaient généralement inférieurs à ceux indiqués dans les systèmes européens de marquage des émissions. En outre, le niveau européen E1 pour les émissions de formaldéhyde des produits de bois, qui est établi à 0,1 partie par million (ppm) ou à 100 parties par milliard (ppb), est de 6 à 20 fois supérieur aux niveaux mesurés pour les produits de bois lamellé-croisé.
D’ici juillet 2012, l’application de la phase 2 des normes du CARB (organisme de réglementation de l’État de Californie) relative à tous les produits composites sera complétée et les limitations d’émissions de formaldéhyde seront établies à des valeurs variant entre 0,13 ppm (130 ppb) pour les panneaux de MDF (panneaux de fibres de densité moyenne) minces et 0,05 ppm (50 ppb) pour le contreplaqué de feuillus avec noyau de composite (HWPW-CC). En comparant ces limitations à celles des produits de bois lamellé-croisé, on peut conclure que ces produits respectent amplement les limitations les plus rigoureuses du CARB, qui sont de 50 ppb.
In this study, various finishing materials used by primary and secondary particleboard and medium-density fibreboard (MDF) manufacturers were subjected to emissions testing in order to determine the most efficient barriers to eliminate (or at least reduce) formaldehyde and other volatile organic compounds (VOC) emissions from MDF and particleboard products.
Since the energy crisis in the early 1970s, there has been a decided trend towards tightly constructed buildings that conserve energy and reduce costs. The downside of these well-intended efforts has been the lowering of interior air exchange rates, to the extent that many chemical contaminants are now being trapped indoors where people spend most of their lives. These contaminants may include volatile organic compounds (VOCs), such as formaldehyde, that have been suggested by some to be among the factors responsible for this air quality deterioration. Wood composite panels, which contain formaldehyde such as particleboard and medium density fiberboard (MDF)are often targeted for strict emission regulations or prohibited altogether, despite the fact that this industry has reduced formaldehyde emissions of raw panels by more than 80% over the past twenty years, thereby actually minimizing indoor air contaminants. Moreover, most consumer products made with composite panels are not used in a raw form, but instead have some type of surface finish over the substrate, that generally acts as a barrier to off-gassing, and subsequently reduces emissions.
In this 2003 research, ten commonly used finishes were evaluated for their effectiveness as emissions barriers for formaldehyde and total volatile organic compounds (TVOC). It appeared that the powder coating is among the most effective barriers for both formaldehyde and VOCs, with more than 90% emission reduction when applied to MDF. A similar efficiency was observed with phenolic, vinyl, melamine paper, aluminium oxide overlay, Syn Décor laminates, thermofoil 12mil, and 2 mils Natural vinyl applied on particleboard panels. Some finishing material showed excellent efficiency towards formaldehyde reduction with, however, a lower VOC emission reduction such as birch finishing etc. Results also suggested an evaluation of powder coatings on particleboard, and, if practical the clear coating and vinyl laminate on MDF to more fully evaluate the impact of the substrate, if any, on emission characteristics of these surface treatments. The evaluation of the other finishing materials which showed an excellent efficiency on a particular type of product such as particleboard also need to be evaluated on the other product such as MDF in order to complete the evaluation of the effectiveness of any given barrier. The paper finish, water based topcoat, and the multiple (3) topcoat wet process appeared to be the less efficient barriers towards either formaldehyde and/or VOCs with, 41% and 28% formaldehyde emission reduction respectively and an increase of VOC emissions by 79% and 57% respectively, suggesting that these barriers may have high solvent contents. A limitation of this trial study was that the formaldehyde and VOC contribution of the surface coating or laminate were not tested by themselves without a substrate. The very limited number of tests conducted for any individual barriers suggests that these preliminary results should be viewed with caution and that more sampling (confirmatory as well as additional coatings/laminates) is necessary to ensure completeness as well as confidence in the data. The inter-laboratory comparison study, showed some discrepancies on both formaldehyde and TVOC results. The techniques used such as one sample face against two faces, the analytical techniques, the air exchange rates could be responsible for some part of these discrepancies and the very limited number of tests did not help improve the reliability of the results.
A very good correlation between ASTM D 5116 and ASTM D 6007 has been established by comparing formaldehyde emission results from the two methods. An R² of 0.94 has been obtained and could be improved by upgrading the database.
The decay tests conducted for a long period of time, some samples were tested for more than 200 days, indicated a net decrease of formaldehyde and VOCs emission over time especially for samples with high initial emission rates. For some low initial formaldehyde emitting samples there was no discernable decrease of emissions over time. Decay emission patterns models varied from sample to sample and some were exponential especially for high initial emitting products and some other were polynomial as reported in the literature. The decaying study showed that VOC emissions decayed favourably other time and some sample products showed almost zero emission after few months. This observation is very encouraging because it indicates that most products before being purchased by the client had emitted more than 60 to 70% of their initial emissions levels, particularly those with high initial emission rates. For those with very emission rates such as those finished with powder coatings, melamine, etc, the decaying is not relevant because their emission levels were already at the detection levels.
Since the energy crisis in the early 1970s, there has been a decided trend towards tightly constructed buildings that conserve energy and reduce costs. The downside of these well-intended efforts has been the lowering of interior air exchange rates, to the extent that many chemical contaminants are now being trapped indoors where people spend most of their lives. These contaminants may include volatile organic compounds (VOCs), such as formaldehyde, that have been suggested by some to be among the factors responsible for this air quality deterioration. Wood composite panels, which contain formaldehyde such as particleboard and medium density fiberboard (MDF) are often targeted for strict emission regulations or prohibited altogether, despite the fact that this industry has reduced formaldehyde emissions of raw panels by more than 80% over the past twenty years, thereby actually minimizing indoor air contaminants. Moreover, most consumer products made with composite panels are not used in a raw form, but instead have some type of surface finish over the substrate, that generally acts as a barrier to off-gassing, and subsequently reduces emissions.
In this year’s research, ten commonly used finishes were evaluated for their effectiveness as emissions barriers for formaldehyde and total volatile organic compounds (TVOC). It appeared that the powder coating is among the most effective barriers for both formaldehyde and VOCs, with more than 90% emission reduction when applied to MDF. A similar efficiency was observed with phenolic, vinyl, melamine paper, aluminium oxide overlay, Syn Décor laminates, thermofoil 12mil, and 2 mils Natural vinyl applied on particleboard panels. Some finishing material such as birch veneer showed excellent efficiency towards formaldehyde reduction with, however, a lower VOC emission reduction. Results also suggested further evaluation of other combinations of substrate and finish need to be considered (powder coatings on particleboard, clear coating or vinyl laminate on MDF) to more fully evaluate the impact of the substrate, if any, on emission characteristics of these surface treatments. The evaluation of the other finishing materials which showed an excellent efficiency on a particular type of product such as particleboard also need to be evaluated on the other product, in this case MDF in order to complete the evaluation of the effectiveness of any given barrier. The paper finish, water based topcoat, and the multiple (3) topcoat wet process appeared to be the less efficient barriers to either formaldehyde and/or VOCs with, 41% and 28% formaldehyde emission reduction respectively and an increase of VOC emissions by 79% and 57% respectively, suggesting that these barriers may have high solvent contents. A limitation of this first study was that the formaldehyde and VOC contribution of the surface coating or laminate were not tested by themselves without a substrate. The very limited number of tests conducted for any individual barriers suggests that these preliminary results should be viewed with caution and that more sampling is necessary to ensure completeness as well as confidence in the data. The next phase of this study will include an inter-laboratory comparison study, further evaluation of the finishes and the effect of sample aging as it relates to emissions.
A very good correlation between ASTM D 5116 and ASTM D 6007 has been established by comparing formaldehyde emission results from the two methods. An R² of 0.94 has been obtained and could be improved by expanding the database.
