More than 70 % of wood derivative products use some kind of adhesive, with the increased replacement of wood products by its derivatives generated an increase of synthetic adhesives consume [1].
Normally, the panels binding process to produce furniture is made with thermosetting resins, such as urea-, phenol-, or melamine-formaldehyde and isocyanate [2]. These resins comes from petroleum and has solvent in its compositions, as volatile organic compound, VOC’s, toxic, carcinogenic and mutagenic substances [3].
Among the synthetics adhesives, the most used by Brazilian’s wood and furniture industry, stand out poly (vinyl acetate) adhesives, PVA, besides the polyurethane ones [1]. The furniture industries use contact adhesives that may provide to its workers leukemia and nasal cancer development risk, apart from instant abortion on women case [4].
These adhesive solvents can be skin absorbed and make it infections susceptible. Also can cause irritations and allergic reaction on sensitive people. When inhaled can cause headaches, fatigues, nausea, eyes irritations and in its respiratory systems or mental and visual disorders [5].
The polyurethane derived from castor oil is extract from Ricinus communis and do not have VOC’s in its composition [6]. The castor bean (R. communis) is a tropical plant with great oleo chemical potential that can provide polyols from its fatty acids [7]. The castor bean seed’s most important constituent is ricinoleic acid, which also is the castor oil biggest component. The hydroxyl groups provide alcohol characteristics to the oil that are relatively stable under different pressure and temperature conditions [8]. Polyurethane can be used in structural applications, as well as indoor and outdoor environments and is weather resistant [9].
Azevedo et al. [10] did a thermo-mechanical characterization polyurethane derived from castor oil by instrumented nanoindentation test and ones concluded that the Berkovich pyramidal tip hardness was 0.14 GPa. The modulus of elasticity, with spherical tip, was 2.4 GPa, using Hertz methodology. The viscosity, also measured by spherical tip, was (22 ± 2) × 1012 Pa s. The temperature of initial mass loss was 250 °C and the glass transition temperature was 76 °C.
Campos and Lahr [11] studied MDF panels, with Eucalyptus and Pinus fibers, resistances properties with 8, 10 and 12 % of urea-formaldehyde, polyurethane derived from castor oil bi-component and inorganic resin. The Eucalyptus and Pinus panels with 12 % of PU obtained the best results for both internal adhesion (0.91 and 0.89 MPa) and flexion resistance (29.4 and 28 MPa).
Fiorelli et al. [12] developed sugarcane bagasse panels with polyurethane derived from castor oil and investigated its physical and mechanical characteristics. The results indicate a high-density material and suitable for industrial use.
Silvia et al. [13] evaluated, with European standard EMB/IS-2: 1995 support, the mechanical properties of Pinus fibers panels with polyurethane derived from castor oil (PU) and concluded that with 6 % of PU proportion provided mechanical properties compatible to the standard requirements.
Campos et al. [14] evaluated MDF panels of Pinus caribaea var. hondurensis fibers with polyurethane derived from castor oil, according to the European standards. Its physics and mechanics properties showed superior values than standard’s established. With 731 kg/m3, 12 % of thickness swelling and 30.7 % of water absorption, 2754 MPa for MOE and 27.2 MPa for MOR, the internal adhesion was 0.79 MPa. Indicating the adhesive is promising in MDF production.
Substrate adhesion is a physic-chemical phenomenon that provides a tension transfer mechanism between two pieces by molecular process and involves both mechanicals theories of polymer diffusion and chemical adhesion [15]. In these models, a good adhesion requires a good substrate’s surface wettability by the adhesive as well as its penetration on the surface pores. Its solidification and its flexibility are also required to reduce the tension effects caused by exertion [16].
The tendency to replace formaldehyde-based adhesives due to its harmful effects in both environment and human health, led the efforts in ecofriendly adhesives research. As PVA, the polyurethane derived from castor oil showed satisfactory results on fiber composites [17] and plywood manufactory [3]. Researches between MDF and polyurethane derived from castor oil interaction are scant, generating a need to study its properties. The aim of this paper is to evaluate the mechanical resistance of glued joint with polyurethane derived from castor oil in MDF panels.