Comparative analysis of wheat straw paperboards prepared after biomechanical and semichemical pulping

A series of industrial and laboratory parameters has been determined in paper handsheets prepared from wheat straw after conventional semichemical pulping and after biomechanical pulping including solid-state fermentations with Pleurotus ostreatus or P. floridanus. The effects of two different refining degrees, as well as of different doses of wastepaper added to straw pulps, were examined using factorial designs to assess the effect of the biological pretreatments. In general, the most noticeable effects of biomechanical pulping were not found in the relative concentration of the major chemical constituents, but in the surface properties of the lignocellulose matrix, which were reflected in the infrared spectra and in parameters such as water repellency, or in the fiber arrangement patterns revealed in thin sections of the handsheets. Multiple regression models and factor analyses suggested that classical industry parameters (iSCT, iCMT, Gurley porosity and burst index) can be expressed as single or polynomial functions of laboratory parameters, mainly hydrolyzable hemicellulose, water drop penetration time, water-holding capacity, bulk density and the 1720/1510 cm−1 intensity ratio in the infrared spectra. In general, the first three parameters were the best to distinguish biomechanical from semichemical paper. The Klason lignin content had no significant bearing on the correlation models involving the other industry or laboratory parameters.