Characterizing Wood Components as Network Polymers by Dynamic Mechanical Analysis

The characterization of structure-property relationships in wood components, such as lignin, is a critical aspect of utilization. This point has been emphasized recently with concerns directed toward the application of natural products as wood bonding agents. Dynamic mechanical analysis is a valuable technique for the study of these relations because of its sensitivity to variations in polymer structure

Multiphase Materials With Lignin. VI. Effect of Cellulose Derivative Structure on Blend Morphology with Lignin

Polymeric blends of lignin with ethyl cellulose (EC) and cellulose acetate/butyrate (CAB) were prepared by solution casting from dioxane. Fracture surface analysis by scanning electron microscopy revealed phase separation when the lignin content exceeded 10% for blends with EC and 5% in the CAB system. While this phase behavior is as predicted for the EC blends, a greater level of compatibility had been expected for the CAB blend system. Results from both differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) suggest that the observed phase separation may be a consequence of supermolecular structure development rather than immiscibility. In the case of the EC/lignin blends, the observed Tg of lignin was 25 C and 35 C higher than that of the pure component for the 40 and 50 wt.% blend, respectively; and CAB/lignin blends produced conflicting results by DSC and DMTA. Where DSC revealed single Tg's for all blends with up to approximately 20% lignin, and dual transitions for all other compositions, DMTA data reflected single relaxations with variable Tg's throughout. This discrepancy is tentatively explained through the formation of liquid crystal mesophases in the cellulose derivative/lignin blends during solvent evaporation

Fiber Surface Modification by Steam-Explosion: Sorption Studies With Co-Refined Wood and Polyolefins

Steam-explosion was investigated as a reactive processing method to create a modified wood fiber by simultaneously co-refining wood chips and polyolefins (polyethylene and polypropylene). Sorption studies, along with infrared spectroscopy, were utilized to determine changes in physical and chemical properties to assess the degree of modification. From the isotherm sorption studies, it was found that co-steam-exploded wood fiber had reduced weight gain for the swelling region of the isotherm as compared to steam-exploded fiber without polyolefin (normalized by fiber mass). The reduction in weight gain for the co-steam-exploded samples was a function of polyolefin loading and polyolefin type. Additionally, the sorption rate of the fibers was reduced for the co-steam-exploded wood with polypropylene (in oxygen gas-deficient reaction conditions). With polyethylene, however, the rate of sorption increased for the co-steam-exploded mixtures. This phenomenon arose from an increase in the initial diffusion constant for all the materials. Although co-steam-exploded wood and polypropylene had a similar increase in diffusion constants, a difference of polyolefin interaction with wood fiber is attributed to slowing the rate of moisture penetration into the fiber for the iPP sample (in oxygen gas-deficient reaction conditions). The increase in diffusion constant for all co-steam-exploded material indicates modification within the cell wall. The proposed agents for interior cell-wall modification are oxidized polyolefin degradation products that migrate into the cell wall during processing

Synopsis

Polymer blends of hydroXYpl"Opyl cenul ~ (HPC) and organ~lv lignin (OSL) were prepared by mixing in solutions of both pyridine and dioxane, and casting 88 fibD8, and by mixing in the melt followed by extrusioo. All preparations exhibited partial miscibility 88 evidmced by a aingle T. up to a compositioo of 40 wt % lignin above which phase aeparatioo was detected. Dioxan~t and injectioo-molded bl_ds were distinguished from the pyridine-cast materiaJs by a positive T. deviatioo from additivity, an approximatioo which adequately dM<:ribed the latter. This ~tive deviatioo in T. is attributed to the formatioo of a liquid-cryatai mesophase with a nIIultant reduction of amOl'phous HPC available fOl ' interactioo with the lignin componmt. This explanatioo is supported by a rapid rise in modulus (- IfKJ%) and tenaile 8trmgth with very low lignin contSlt, and by an aBSociated sharp decline in ultimate eloogatioo. The developmmt of morphological f~tur-. 88 obesved by scanning electron micr(S»PY provide further ' substantiation of this hypothesis

Comparative analysis of inactivated wood surfaces

The changes in surface chemistry, wettability, and adhesion of inactivated wood surfaces, including yellow-poplar (Liriodendron tulipifera) and southern pine (Pinus taeda), were studied. Surface inactivation, which is induced by exposure to high temperature, causes poor adhesion. The comparative characterization of the surface was done by X-ray photoelectron spectroscopy (XPS), sessile drop wettability, and fracture toughness of adhesive bonds. Additionally, several chemical treatments were utilized to improve wettability and adhesion of inactivated wood surfaces. The results showed that wood drying caused modification in wood surface chemistry. The oxygen to carbon ratio (O/C) decreased and the C1/C2 ratio increased with drying temperature. A low O/C ratio and a high C1/C2 ratio reflected a high concentration of extractives and lignin on the wood surface. Contact angle decreased with time and increased with the temperature of exposure. A dependence of wood species was evident. The southern pine was most susceptible to inactivation particularly when bonded with PF adhesive. Yellow-poplar surfaces showed little inactivation when exposed to drying temperatures up to 187°C. The chemical treatments improved the wettability of inactivated wood surfaces, but an improvement in adhesion was not evident for specimens bonded with PVA. Sodium hydroxide (NaOH) was the most effective in restoring bonding ability of inactivated wood surfaces bonded with PF adhesive. The maximum strain energy release rate (Gmax) of specimens treated with NaOH increased by a factor of three when compared with inactivated specimens

Pulp-and Paper-Making Potential of Peanut Hull Waste in Blends with Softwood Pulp

The use of peanut hulls as a raw material source for the manufacture of cellulose fiber products was evaluated by abbreviated kraft and soda pulping processes. Several types of experimental paper products were made from the unbleached and partially bleached pulps. Breaking lengths and tear factors were determined for handsheets made with peanut hull pulp alone and with mixtures of peanut hull and softwood pulp. Some hand-sheets blended from peanut hull and wood fibers were stronger than those made from pure wood pulp. In view of the results obtained, it appears feasible to employ peanut hull waste to extend the fiber raw material basis of pulping processes without sacrificing paper quality

Site-Selective Growth of Colloidal Crystals with Photonic Properties on Chemically Patterned Surfaces

Microscopically structured colloidal crystals have been self-assembled by capillary forces onto chemically patterned surfaces. It was shown that the wetting meniscus on substrates patterned with hydrophobic and hydrophilic regions acts in this process as self-removing crystallization template. By this method closed-packed structures with a well defined and intense band gap in the visible range are obtained