Functional lignocellulosic materials prepared by ATRP from a wood scaffold

Wood, a natural and abundant source of organic polymers, has been used as a scaffold to develop novel wood-polymer hybrid materials. Through a two-step surface-initiated Atom Transfer Radical Polymerization (ATRP), the porous wood structure can be effectively modified with polymer chains of various nature. In the present study, polystyrene and poly(N-isopropylacrylamide) were used. As shown with various characterization techniques including confocal Raman microscopy, FTIR, and SEM/EDX, the native wood ultrastructure and features are retained and the polymer chains can be introduced deep within the wood, i.e. inside the wood cell walls. The physical properties of the new materials have been studied, and results indicate that the insertion of polymer chains inside the wood cell wall alters the intrinsic properties of wood to yield a hybrid composite material with new functionalities. This approach to the functionalization of wood could lead to the fabrication of a new class of interesting functional materials and promote innovative utilizations of the renewable resource wood.


Experimental section
Amount of brominated initiator grafted in wood: The estimated amount of grafted brominated initiator (BiBB) in the wood structure is based on the weight gain determined after the first reaction is completed.
After the reaction of wood with BiBB and before the determination of the weight gain, the wood samples are thoroughly washed (in order to remove unreacted chemicals) and dried until a constant weight is observed, to make sure that no traces of washing solvents are present, and that the weight gained after reaction is solely due to BiBB molecules.
The mass of BiBB attached to wood was calculated as follows: Where m t is the mass of the washed and dried treated wood, and m i is the mass of the dried untreated wood.
With m BiBB , one can calculate the number of moles of BiBB attached to wood: = Where M BiBB = 149.99 g/mol (which corresponds to the molecular weight of the BiBB molecule with one Bromine atom less).
The ATRP ratio is then based on n BiBB .

Characterization techniques
Weight percent gain (WPG): the various weight gains (after modification step 1 or 2) were calculated as follow: Where W 2 is the weight of the modified wood samples, and W 1 is the weight of the wood samples before the modification step.
The number of moles of BiBB present in solid wood after the first step is calculated from the weight gain values.
Water uptake (WU): the mass change of the wood samples upon soaking in water was calculated using the following equation: Where W w is the weight of the water-soaked wood samples, and W d is the weight of the dried wood samples.
Water-repellent effectiveness (WRE): the WRE of the modified wood samples was calculated using the following equation: Where WU 1 is the water uptake of the treated sample upon soaking in water, and WU 2 is the water uptake of the untreated wood upon soaking in water.
Swelling (S): the swelling of the wood samples upon soaking in water was calculated using the following equation: Where V 2 is the volume of the water-soaked wood samples, and V 1 is the volume of the dried wood samples.
Anti-Swelling Efficiency (ASE): the ASE of the modified wood samples upon soaking in water was calculated using the following equation: Where S 2 is the swelling of the untreated wood samples, and S 1 is the swelling of the treated wood samples.
Rowell et al. give a comprehensive description of the physical characterizations related to water repellency and dimensional stability of wood. [1]

Results
Step 1: attachment of BiBB to wood samples   Step 2: Polymerization     From a) to d) curves associated to measurements shown in Figure 4, and from e) to h), curves associated to measurements shown in Figure 5.

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Dimensional stability study Figure S9: Plot showing the full water repellency and dimensional stability study on W-PSt samples, with the water-repellent effectiveness (WRE) and the anti-swelling efficiency (ASE).
10 cubes of W-PSt (with a total WPG of 27.3±0.3%) and 10 reference cubes were used for this experiment. Dry cubes are immersed in water, vacuum is drawn for 30 minutes, released for 1 hour, drawn again for 30 minutes and released over 24h. The new weight and dimensions are measured, and the cycles are repeated for a total of 7 days.
The total mass loss was calculated after 7 days in water (difference between the initial dry weight and the dry weight after 7 days), and was found to be 6.7±0.2%.