Bark-based polyols were synthesized through a solvent liquefaction in a polyethylene glycol (PEG)/glycerol cosolvent. Liquefaction reactions were carried out at temperatures of 90, 130, and 160 °C. The bark-based polyols were analyzed for their yield, composition, and structural characteristics using the standard titration method for hydroxyl value, combined with gel permeation chromatography (GPC), Fourier transform infrared (FTIR), and liquid state phosphorus (31P), carbon (13C), and proton (1H) NMR analyses. As the liquefaction temperature increased, viscosity of the polyols became higher with a corresponding broadening of the molecular weight (MW) distributions that also shifted toward higher MW. The liquefaction of biomass induced a high degree of modification to the bark components. These polyols had similar hydroxyl values but differed greatly in molecular structures. The polyol obtained through liquefaction at 90 °C had more secondary alcohols and contained sugars. Meanwhile, sugars were degraded into levulinate and formic esters in the polyols obtained at 130 and 160 °C. None of the polyols had condensed tannins, neither in their polymeric or monomeric state. Instead, aromatic ethers were seen in the carbon NMR spectra and various carboxyl functionalities were observed from the FTIR analysis. These results demonstrated the influence of the liquefaction temperature on the liquefaction behaviors of the bark biopolymers and provided an insight into the physical and structural properties of these bark-based polyols.

Liquefaction is known to be an effective method for converting biomass into a polyol. However, the relationships between bark liquefaction conditions and properties of the resulting foams are unclear. In this study, polyurethane foams (PUF) were made using bark‐based polyols obtained through liquefaction reactions of bark at two different temperatures (90 and 130°C). Through systematic characterization of the PUFs the influence of the liquefied bark and liquefaction conditions on foam properties could be observed. The bark‐based foams had similar foaming kinetics, thermal stability, and glass transition temperatures compared with the PEG‐based control foam. The bark‐based PUF from the polyol obtained at the higher liquefaction temperature showed comparable specific compressive strength to the PEG‐based control foam. Lastly, both bark foams exhibited a high amount of open‐cell content, with the foam made from the lower temperature liquefied polyol having poor cell morphology. This deviation from the controls in the open‐cell content may explain the lower modulus values observed in the bark PUFs due to the lack of cell membrane elastic stretching as a strengthening mechanism. These results demonstrated the influence of the bark liquefaction conditions on foam properties, thereby providing a better fundamental understanding for the practical application of bark‐based PUFs. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40599.

No abstract

No abstract

Bark was liquefied in polyhydric alcohols of various functionality, equivalent weight, and hydroxyl type, and organic solvents of varying polarity to determine how these features impact liquefaction behavior and polyol characteristics. It was found that the liquefaction yield was highly tunable with the use of polyhydric alcohols with primary hydroxyl groups, with low equivalent weight alcohols providing the highest liquefaction yield (59.3%). This showed that the highly polar hydroxyls (primary) and short chains created a highly protic solvent that improved conversion and protected the biopolymers from degradation. This was corroborated by 1 H NMR analysis that indicated a greater amount of sugar degradation products were observed when polyhydric alcohols with secondary hydroxyl groups were used. Regarding organic solvents, ketonic solvents showed the greatest increase in the liquefaction yield. The composition and carbon content analysis of the residues suggested that the highly polar carbonyl group of ketonic solvents like acetyl acetone and cyclohexanone may have hindered condensation side reactions. These results have shown that selection of polyhydric alcohols and organic cosolvents can be quite impactful on the liquefaction yield and the polyol characteristics.