Colour Modification of Wood by Dry Thermal Treatment Between 90°C and 200°C = A faanyag színének változása száraz hőkezelés hatására 90°C és 200°C között

The colour modification effect of dry thermal treatment was studied in black locust (Robinia pseudoacacia L.), poplar (Populus x euramericana cv. Pannonia), Scots pine (Pinus sylvestris L.), spruce (Picea abies Mill.) and larch (Larix decidua L.) species in the temperature range 90-200 °C. Colour data were presented and evaluated in the CIE L*a*b* coordinate system. All thermal treatments applied altered the wood colour throughout the entire cross section regardless of the treatment temperature. At lower temperatures, wood extractives played a decisive role in colour change. The degradation products of hemicelluloses were the major determinant of the change in lightness at 200°C. Redness change in percentage showed much greater alteration than the yellowness and the lightness change. Spruce presented the greatest chromaticity coordinate (a* and b*) alteration among the investigated species. Changes in redness and yellowness followed the Arrhenius law during the investigated dry thermal treatments confirming that the temperature dependence of these colour parameters is exponential for wood material. Száraz körülmények között végrehajtott termikus kezelés színváltoztató hatását vizsgáltuk akác (Robinia pseudoacacia L.), nyár (Populus x euramericana cv. Pannonia), erdei fenyő (Pinus sylvestris L.), lucfenyő (Picea abies Mill) és vörösfenyő (Larix decidua L.) faanyag esetében 90 – 200 °C hőmérséklet tartományban. A szín adatokat a CIE L*a*b* koordináta rendszerben adtuk meg és értékeltük. Az alkalmazott hőkezelések a faanyag színét, függetlenül az alkalmazott hőmérséklettől, a próbatestek teljes keresztmetszetében megváltoztatták. Alacsony hőmérsékleten az extrakt anyagtartalom volt meghatározó a színváltozásban. A hemicellulózok degradációs termékei határozták meg döntő mértékben a világosság változását 200 °C-on. A százalékosan megadott vörös színezetváltozás sokkal nagyobb mértékű volt, mint a sárga színezet és a világosság változása. A luc faanyaga mutatta a legnagyobb színezeti koordináta-változást (a*és b*) a vizsgált faanyagok közül. A vörös és a sárga színezet változása követte az Arrhenius törvényt a száraz termikus kezelések során mutatva, hogy ezeknek a paramétereknek a hőmérséklet függése exponenciális faanyag esetében

pH-dependent color response of cellulose-based time-temperature indicators impregnated with red cabbage extract

Color-based time-temperature indicators (TTIs) can show the time and temperature changes of an environment with a visually recognizable color change. Made from natural dyes, these TTIs are simple, inexpensive and sustainable. In this study, cellulose-based TTI labels were prepared with red cabbage extract of pH2, pH7 and pH9 to determine how pH alter the response of the labels to time and temperature changes. This study also aimed to determine the relationship between color change and time at different temperatures. The color responses of the labels were followed spectrophotometrically by measuring the CIE Lab color coordinates and by giving the total color difference at 4 °C, 23 °C, 40 °C, 80 and 100 °C after increments of time. The best fitting linear or nonlinear regression models of the CIE Lab coordinates, total color difference and time data as a function of temperature were also determined. The labels prepared with red cabbage extract at different pH behaved differently. Opposite to expectations, the acidic, pink colored labels did not have the highest color stability. Our finding was, that the label prepared with the acidic red cabbage extract is the most suitable as time-temperature label for indicating long-term temperature storage and the label prepared with the neutral red cabbage extract is the most suitable as time-temperature label for indicating short-term storage by color change. According to the results the color changes of the labels are predictable with the fitted models with a correlation coefficient between 0.96 and 1

COLOUR STABILITY OF STEAMED BLACK LOCUST, BEECH AND SPRUCE TIMBERS DURING SHORT-TERM PHOTODEGRADATION

Black locust (Robinia pseudoacacia L.), beech red heartwood (Fagus sylvatica L.) and spruce (Picea abies Karst.) wood samples were treated in saturated steam at 100, 110 and 120 degrees C then irradiated using a UV emitter mercury lamp in order to test their colour stability. Colour change was evaluated and presented in the CIE Lab colour coordinate system. Untreated black locust, beech and spruce specimens as control samples were irradiated using the same mercury lamp. Results revealed that beech produced the greatest colour stability during both steam treatment and the following UV treatment while spruce was the most sensitive species to photodegradation. Steaming reduced the colour change intensity only for black locust during photodegradation. Both redness and yellowness change demonstrate this colour stability increase. Steaming at 120 degrees C resulted in the greatest protection against the colour alteration of black locust caused by photodegradation. The investigated thermal treatments did not change the photodegradation properties of beech and spruce specimens. A considerable increase in colour saturation of the specimens was generated by steaming, and the saturation value further increased during the UV treatment