CHEMICAL MODIFICATIONS ON CURAUA FIBERS (Ananas erectifolius)
Chemical Product Design and Engineering (CPD&E)
Chemical Product Design & Development - V (CPD&E - 5)
Keywords: enzyme treatment, alkali treatment, lignocellulosic fibers, curaua,composites
A.L.F.S. d’ Almeida1, V.M. Calado1, D.W.Barreto1, JR.M. d’Almeida2.
1Escola de Química – UFRJ – anafampa@yahoo.com.br; calado@eq.ufrj.br; dbarreto@eq.ufrj.br; 2Depto. de Ciência dos Materiais e Metalurgia – PUC-Rio, Rua Marquês de São Vicente 225, 22453-900 Rio de Janeiro/RJ - dalmeida@dcmm.puc-rio.br
Nowadays, a large number of lignocellulosic fibers are being used to reinforce resin matrix composites in many different industrial fields. In the automotive industry, for instance, the interior door panels and cushion seats are already being manufactured with these fibers.
Lignocellulosic fibers such as curaua, sisal, flax, hemp and jute offer benefits as reduction in weight, cost, and CO2 emissions, as well as recycling.
However, lignocellulosic fibers have some drawbacks. One of then is the usual lack of adhesion at the fiber-matrix interface. This weak interface arises due to the hydrophobic character of the common polymeric matrices and the hydrophilic character of lignocelullulosic fibers. To increase the lignocellulosic fiber–polymer interface several chemical and physical treatments like, for example, mercerization (alkali treatment) and acetylation are proposed on the literature.
In this work, the effect of surface treatments, viz. mercerization and a multi enzyme complex, were investigated on curaua fibers by infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA).
Mercerization: The raw fibers were immersed during one hour at ambient temperature in solutions with, respectively, 2 and 5 wt% of NaOH solution. After that, the fibers were washed with flowing tap water and left at rest for 24 hours to remove any residue of NaOH. The water bath was then changed and the fibers were left for more 24 hours in immersion. The pH of this second water bath was observed to be always near 7, indicating that the washing treatment was effective.
Enzyme: A multi-enzyme complex produced from a selected strain of Aspergillus aculeatus was also used to treat the surface of the fibers. This particular enzyme is tailored to extract materials from plant cell walls, including hemicellulose and xylans.
Since the time of treatment varies from plant material to plant material when enzymes are used, the ideal time of treatment was determined at first. For that, the absorbance vs. treatment time curve was obtained using the Somogyi method. This method doses the amount of reducing sugars. In short it consists of soaking a certain amount of the fibers (9 grams) in 300 ml of distilled water with 4.5 pH during 24 hours. This particular pH value was obtained using citric acid as described elsewhere. After that the container with the fibers was placed in a water bath with a temperature ranging from 40 to 50 °C, and 2 ml of the enzyme was then added. The container was continuously shacked and dosing aliquots were extracted at 0 min, every 30 min during the first 5 hours, and at 6, 7, 8 24 and 48 hours of treatment. To neutralize the enzyme the solution was soaked in a water bath at 100 °C during 2 min.
Following the results obtained the raw fibers were treated for 4 hours, neutralized at 100 °C, washed in flowing tap water and air dried.
Scanning electron microscopy shows that all treatments but the 2 wt% mercerization one, promote strong surface modifications on the fibers, removing the outer parenchyma-rich surface layer and exposing the inner fibrillar structure. The thermograms show an improvement in the thermal stability of the modified fibers in relation to the raw fibers. The main peak of DTG curve for the raw fibers occurred at 365 °C, and all treatments increased this temperature. The FTIR shows that the treatments probably removed hemicelulose and others polysaccharides. The treatments with 5% NaOH and enzymes apparently changed on a similar way the surface of fibers. This is an outstanding result since the treatment with enzymes is cleaner than the treatment with NaOH, and, therefore, if it could be used instead of the treatment with NaOH, a more environmental friendly treatment will be available to surface treat curaua fibers.
Presented Thursday 20, 16:00 to 16:20, in session Chemical Product Design & Development - V (CPD&E - 5).
