Influence of Degree of Polymerization of Cellulose and Hemicellulose on Strength Loss in Fire-Retardant-Treated Southern Pine

Abstract

Southern pine boards, both untreated and treated with a fire retardant, were exposed to either a room temperature or high temperature (66°C (150°F)) environment. Strength properties were measured after 1 and 1-1/2 years of exposure, respectively. The degree of polymerization and the chemical composition of αcellulose isolated from the exposed wood were measured. Little relationship was found between degree of polymerization and strength. However, a strong relationship was found between the amount of mannan in the α-cellulose isolated from the wood and the modulus of rupture and the work-tomaximum load of solid wood. This correlation leads to the conclusion that hemicellulose plays an important role in determining the strength of wood.

Strength properties of thermally modified softwoods and its relation to polymeric structural wood constituents

“…They suggest that mechanical properties, which relates to internal stress and strain, are simply functions of chemical bond strength: covalent and hydrogen intrapolymer bonds (molecular level); covalent and hydrogen interpolymer bonds and cell wall layer bonds (microscopic level); and fiber-to-fiber bonding with the middle lamella acting as the adhesive (macroscopic level). According to Sweet and Winandy [45] wood fibres can be regarded as a composite material and a single micro fibril or a group of microfibrils cannot entirely account for the strength of an entire wood fibre. The chemical-mechanical linkages between cellulose microfibrils and the lignin-hemicelluloses matrix allow load sharing among the microfibrils.…”

“…An increased cross linking of the lignin polymer network could be another reason for this improvement. Lignin acts as a stiffener of the cellulose microfibrils/fibrils [45] and an increased cross linking of this polymer appears to prevent or limit movement perpendicular to the grain (which occurs during compressive loading parallel to the grain). Furthermore, lignin is the main component of the middle lamella [15] and an increased cross linking of the lignin polymer network improves the strength of the middle lamella which subsequently affects the strength properties of the cell wall.…”

“…There appears to be a relationship between the decrease of the bending strength and the degradation of the hemicelluloses [23,29,52] and it has been suggested that changes in the hemicelluloses content and structure are primarily responsible for the initial loss of the bending strength [45,54], since hemicelluloses are the most thermal-chemically sensitive component of wood [25]. Raising the effective treatment temperature and/or increasing the treatment time during the hydro-thermolysis stage resulted in a further decrease of the bending strength (Figs.…”

“…It is however rather hypothetical whether a polymer of such short DP and situated around the (amorphous) cellulose microfibrils, can contribute in this way to the strength of wood fibres. It appeared that cellulose and lignin were not affected until strength losses exceeded 30-40% [45,54], since no depolymerisation or degradation products of these polymers were observed. However, the possibility of rearrangements of the molecular structure of cellulose and/or lignin, and its effects on the strength properties of wood, were not considered (e.g.…”

Use of maize cob for production of particleboard

“…While studying the chemical composition of Pinus oocarpa cultivated in the cerrado, Morais, Nascimento and Melo (2005) found 11.47% of extractives, 25.18% of lignin and 1.26% of ash. Higher lignin contents are desirable for particleboard production, this component having a very condensed structure and irregular aspect which provides high rigidity to the relevant material, acting as a buffer of cellulose microfibrils, limiting parallel to grain movement and increasing mechanical strength against external forces (SWEET;WINANDY, 1999).…”