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N.M. Garz on-Barrero et al. / International Biodeterioration & Biodegradation 115 (2016) 266e276 273
Table 5
The degree of mold growth probabilities for the evaluation of surface coating and time of incubation in the accelerated test (ASTM D3273-2012).

probability of obtaining a rating of 10 during the first 7 days of in relation to the cMDP after equal conditions of exposure.
exposure, and 9% presented a rating of 9. Still, in the first week, the According to Stark et al. (2004), water also acts as a degrading
non-coated materials presented a 25% probability of presenting a factor and accelerates the oxidation reaction causing wood fiber
rating grade of 3 for colonization which continued to progress until swelling. The degradation of the hydrophobic components (such as
reaching a rating grade 0 at 28 days of incubation. lignin) on the composite surface leads to increased amounts of
The scanning electron microscopy images show the differences cellulose (hydrophilic component) on the surface, which causes the
between the surfaces of the two non-coated materials (BCP and composites to be more susceptible to moisture absorption. The
MDP). The ncBCP test samples presented a surface with exposed uncoated materials showed higher values of thickness swelling and
fibers, involved in some areas by castor oil based polyurethane consequently showed lower values in their corresponding me-
resin as an adhesive in the process of pressing the boards (Fig. 5a). chanical properties.
After 28 days of incubation, an intense surface colonization of mold The surface coating in both materials protected them from
with the presence of hyphae groups (Fig. 5b) was observed in these inferior results of modulus of elasticity, modulus of rupture and
same ncBCP test samples. thickness swelling. However, the exposure to natural weathering
Fig. 5c presents images of MDP without coating before the was more aggressive and severe in comparison to the accelerated
accelerated test. In Fig. 5d, after incubation for 28 days, surface mold growth test. This could be explained by the combination of
colonization with great presence of hyphae groups in large mycelia meteorological factors (precipitation, solar radiation, temperature
was detected, indicating the susceptibility of this material to the and relative humidity) present in natural exposure, which influence
fungi colonization. the deterioration of the sugarcane bagasse fiber and wood particles,
as seen through the analyzed micrographs. Studies were not found
in the literature related to mechanical performance after acceler-
3.2.3. Mechanical and physical properties
Table 6 shows the results of thickness swelling and the me- ated tests for mold growth.
chanical properties of the modulus of elasticity and the modulus of The performance obtained for the modulus of rupture in coated
rupture in bending test. The thickness swelling was caused by the sugarcane bagasse materials had a lower reduction in the values
after natural exposure, 7.5 MPa (cBCP), compared to the non-coated
internal expansion of the fibers of the composite. Therefore, the
lower thickness swelling registered in the case of coated cBCP ones, 3.5 MPa (ncBCP). Similar behavior in flexural tests was found
by Korai et al. (2013) in commercial medium density fiber (MDF)
material can explain the best results for MOE and MOR properties