Binderless fiberboard production from Cynara cardunculus and Vitis vinifera

Resumen

Binderless fiberboard production from Cynara cardunculus and Vitis viniferaTwo lignocellulosic materials, Cynara cardunculus and Vitis vinifera, were pretreated and used to produce fiberboards without synthetic adhesives. The lignocellulosic materials were steam exploded through a thermo-mechanical vapor process in a batch reactor. After pretreatment the materials were dried, ground and pressed to produce the boards. The effects of pretreatment factors and pressing conditions on the chemical and physicomechanical properties of the fiberboards were evaluated and the conditions that optimize these properties were found. Response surface methodology based on a central composite design and multiple response optimization were used. The variables studied were: pretreatment temperature, pretreatment time, pressing temperature, pressing pressure, and pressing time. Binderless fiberboards produced from Cynara cardunculus stalks at the optimum conditions found fulfilled the European standards for boards of internal use. Nevertheless, binderless fiberboards produced from Vitis vinifera prunings at the optimum conditions found for this material did not completely met the European standards; modulus of rupture and internal bond values for these boards were lower than required minimums.Simultaneously, commercial Kraft lignin was reacted in an alkaline medium to enhance its adhesive properties. Chemical changes in reacted Kraft lignins that include ash content, Klason lignin, acid-soluble lignin and sugars were determined, as well as, structural characteristics of these lignins in terms of phenolic hydroxyl, aliphatic hydroxyl, methoxyl, carbonyl, Mw, Mn and polydispersity. The effects of reaction temperature and reaction time on lignin properties were studied using response surface methodology, and optimal reaction conditions were found.Two different types of Kraft lignin were used, alkali treated Kraft lignin and crude acid-washed Kraft lignin, as additives to enhance the physicomechanical properties of binderless fiberboards produced from Vitis vinifera to reach and overcome the European standards completely. At the end fiberboards produced with 20% of Vitis vinifera fibers replaced by crude acid-washed Kraft lignin were able to meet the European standards completely.This research work was an effort to reduce our dependency upon petroleum derivates, to diminish deforestation and to increase the use of renewable and biodegradable materials with the intention of preserving the environment and to encourage a sustainable development of our society.