Colorimetric and vibrational spectroscopic characterization of weathered surfaces of wood and rigid polyvinyl chloride–wood flour composite lumber

Rigid polyvinyl chloride–wood flour composite lumber containing either pine or maple wood flour and pine and maple lumber was subjected to accelerated weathering according to the ASTM Standard G 53 protocol. Non-weathered and weathered surfaces of all specimens were analyzed using colorimetric methods, reflectance infrared Fourier transform and Raman spectroscopic techniques. In the FT-IR spectra, conjugated ketones (1,744 cm^?1) of lignin as evidenced by their skeletal vibrations (1,560–1,500 cm^?1) and stretching (1,440–1,500 cm^?1) were reduced in weathered specimens. Cellulose was largely unaffected by weathering. C–O bending vibrations at 1,040 cm^?1 from holocellulose in pine specimens and intensity bands at 1,125–1,090 and 1,360 cm^?1 (C–O stretching and O–H bending from cellulose) in the maple and wood–plastic composite (WPC)-maple specimens were unaffected. A band at 1,650 cm^?1 became prominent after weathering of both pine and maple WPC specimens which is due to C=C–C=C stretching vibration of weathered PVC portion of the specimen. Raman shifts at 530 and 840–900 cm^?1 are attributed to C–O and C–C–O stretching in cellulose (remain unchanged). The role of extractives in weathering of pine is shown by the disappearance of Raman shifts at 392 and 434 cm^?1 (C=C deformations in pine extractives) in weathered pine. One-Way ANOVA, between-group designs showed significant effect on brightness (L*), redness (a*) and yellowness (b*) for all treatments.