Impact of residual extractives on the thermal stability of softwood Kraft pulp

Abstract

Wood extractives are known to cause problems during the production of pulp and paper and to impact their mechanical properties. In the present work, we systematically explored whether minute residual amounts of extractives that reprecipitate on the fiber surface in the final stages of the pulping process would lower the thermal resilience of softwood Kraft pulp. Pulp samples subjected to different extraction methods were characterized by means of thermogravimetric analysis. The compound classes constituting the respective extracts were identified and quantified via gas chromatography-mass spectrometry/flame ionization detector (GC-MS/FID) and the influence of the individual compound classes on the thermal stability of the samples was investigated separately. Soxhlet extraction with an ethanol/toluene solvent system clearly led to increased thermal stability. Besides fatty acids and resin acids also sterols and sterol esters that do not carry carboxylic acid functionalities contributed to the deterioration of the thermal pulp properties. Lateral order indices derived from Fourier transformed infrared spectra and crystallinity indices derived from solid-state 13C nuclear magnetic resonance spectra indicate that upon thermal degradation, the presence of even minute amounts of extractives leads to an increased degree of supramolecular disorder. Moreover, the characterization of the samples’ carbohydrate composition by means of acidic hydrolysis showed a tendency towards facilitated pyrolysis of the hemicelluloses if extractives were present in the pulp.

The Components’ Roles in Thermal Stability and Flammability of Cork Powder

“…This fact implies that extractives can act as a catalyst by reducing the decomposition temperature of untreated cork and promoting the thermal decomposition of other components. Similar behavior was also observed for the contribution of extractives to the wood thermal degradation [ 58 , 59 , 60 ]. However, this effect contradicts the role of extractives in thermal stability improvement of cork in oxidative atmosphere [ 7 ].…”

“…The removal of extractives from cork shifted the decomposition temperature, at a 5% of mass loss, from 260 • C to 280 • C and led to the formation of a more thermally stable residue between 500 • C and 800 • C. This fact implies that extractives can act as a catalyst by reducing the decomposition temperature of untreated cork and promoting the thermal decomposition of other components. Similar behavior was also observed for the contribution of extractives to the wood thermal degradation [58][59][60]. However, this effect contradicts the role of extractives in thermal stability improvement of cork in oxidative atmosphere [7].…”

“…Materials 2023, 16, x FOR PEER REVIEW 9 of 18 decomposition of other components. Similar behavior was also observed for the contribution of extractives to the wood thermal degradation [58][59][60]. However, this effect contradicts the role of extractives in thermal stability improvement of cork in oxidative atmosphere [7].…”