Abstract
Ethanol organosolv alfa grass lignins were extracted in the presence of sulfuric acid or Lewis acids (Sc(OTf)3, FeCl3) as catalysts and subjected to a comprehensive structural characterization by solid state 13C NMR, GPC, MALDI-TOF, and ASAP-MS/MS. The impact of the severity of the treatment and of the nature of the acid catalyst on the recovered lignin structure was investigated. The lignins isolated at high severity were highly recondensed and partly composed of regular structures composed of furan-like rings. The alfa (Stipa tenacissima L.) organosolv lignins were used for the preparation of formaldehyde-free adhesives which were characterized by TMA and used for the preparation of particleboard without any addition of synthetic resin. It has been demonstrated for the first time that: (1) the addition of 10% to 30% of organosolv alfa lignin in a tannin-based adhesive improved the adhesive performance; and (2) the conditions of the lignin extraction strongly impact the lignin-based adhesive performances. The highly recondensed lignin extracted with sulfuric acid as a catalyst allowed the production of resins with improved performances. Formulations composed of 50% glyoxalated alfa lignin and 50% of Aleppo Pine tannins yielded good internal bond strength results for the panels (IB = 0.45 MPa) and satisfied relevant international standard specifications for interior-grade panels.
Highlights
The production of environmentally friendly wood adhesive has been a topic of interest since1970s [1,2]
We described a lignin based adhesive composed of 40% of miscanthus organosolv lignin and of 99.5% of renewable materials [6]
We previously studied the effect of the severity of an ethanol organosolv pretreatement on the chemical structure of the extracted lignin
Summary
The production of environmentally friendly wood adhesive has been a topic of interest since1970s [1,2]. The production of environmentally friendly wood adhesive has been a topic of interest since. Tannins-based formaldehyde-free adhesives have been successfully described and used for interior and exterior wood bonding. The production of tannin-based adhesives is limited by the relatively limited supply of tannins. The industrial development of such green wood adhesives depends on the availability of low-price, high quality, and reactive biopolymers. Lignin is one of the most abundant natural and renewable polymers and is currently a co-product of pulp industries. The occurrence of large volumes of low value lignin has made it a potentially attractive material for adhesive production. Utilization of lignin as a partial substitute or extender for phenolic wood adhesives has been extensively described [3,4,5,6]. In contrast with the Polymers 2016, 8, 340; doi:10.3390/polym8090340 www.mdpi.com/journal/polymers
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