The nanostructure of bone has been replicated using a polymer-induced liquid-precursor (PILP) mineralization process. This polymer-mediated crystallization process yields intrafibrillar mineralization of collagen with uniaxially-oriented hydroxyapatite crystals. The process-directing agent, an anionic polymer which we propose mimics the acidic non-collagenous proteins associated with bone formation, sequesters calcium and phosphate ions to form amorphous precursor droplets that can infiltrate the interstices of collagen fibrils. In search of a polymeric agent that produces the highest mineral content in the shortest time, we have studied the influence of various acidic polymers on the in vitro mineralization of collagen scaffolds via the PILP process. Among the polymers investigated were poly-L aspartic acid (PASP), poly-L-glutamic acid (PGLU), polyvinylphosphonic acid (PVPA), and polyacrylic acid (PAA). Our data indicate that PASP and the combination of PGLU/PASP formed stable mineralization solutions, and yielded nano-structured composites with the highest mineral content. Such studies contribute to our goal of preparing biomimetic bone graft substitutes with composition and structure that mimic bone.

Bone is an organic-inorganic composite which has hierarchical structuring that leads to high strength and toughness. The nanostructure of bone consists of nanocrystals of hydroxyapatite embedded and aligned within the interstices of collagen fibrils. This unique nanostructure leads to exceptional properties, both mechanical and biological, making it difficult to emulate bone properties without having a bone-like nanostructured material. A primary goal of our group’s work is to use biomimetic processing techniques that lead to bone-like structures. In our prior studies, we demonstrated that intrafibrillar mineralization of porous collagen sponges, leading to a bone-like nanostructure, can be achieved using a polymer-induced liquid-precursor (PILP) mineralization process. The objective of this study was to investigate the use of this polymer-directed crystallization process to mineralize dense collagen substrates. To examine collagen scaffolds that truly represent the dense-packed matrix of bone, manatee bone was demineralized to isolate its collagen matrix, consisting of a dense, lamellar osteonal microstructure. This biogenic collagen scaffold was then remineralized using polyaspartate to direct the mineralization process through an amorphous precursor pathway. Various conditions investigated included polymer molecular weight, substrate dimension and mineralization time. Mineral penetration depths of up to 100 μms were achieved using this PILP process, compared to no penetration with only surface precipitates observed for the conventional crystallization process. Electron microscopy, wide-angle X-ray diffraction, and thermal analysis were used to characterize the resulting hydroxyapatite/collagen composites. These studies demonstrate that the original interpenetrating bone nanostructure and osteonal microstructure could be recovered in a biogenic matrix using the PILP process.

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In recent years, significant amounts of various lignins became commercially available. Their technical utilization for thermosets such as phenol formaldehyde resins is widely discussed as an added value. However, the comparably low number of reactive sites is still limiting utilization in higher proportions. To overcome this obstacle, lignins can be activated by phenolation prior to resin synthesis. In this study, the applicability and outcome of phenolation was studied for a set of organosolv lignins from hardwood, softwood, and annual plants and was compared to their counterparts from commercial processes, i.e., kraft, sulfite, soda, and hydrolysis lignin. Thus, structural properties of various raw lignins could be linked to the increase of reactive sites upon phenolation. Large differences were found and could mainly be attributed to the number of aliphatic hydroxyl groups in the raw lignins. Highest activation was achieved for hardwood organosolv and softwood sulfite lignins. With ion-exchanged sulfite lignin in H+ form the phenolation could even be performed autocatalyzed to a high extent. In contrast, soda grass and softwood kraft lignin showed weak potential for activation. Additionally, the influence of ash and sulfur content, and the changes in molecular weight were elucidated.

An efficient, nontoxic, and solvent-free oxyalkylation of European beech wood organosolv lignin (OL) has been developed. Two approaches were studied: a direct reaction of lignin with propylene carbonate (PC) and a two-step reaction of lignin with maleic anhydride (MA) followed by oxyalkylation with PC. The structural analysis of lignin polyols was performed by 1 H NMR, 13 C NMR, 31 P NMR, and FTIR spectroscopy. It was demonstrated that PC was able to almost completely oxypropylate aliphatic and phenolic OH groups. Moreover, the carboxylic acid groups of maleated OL were fully oxypropylated by PC. This modification strongly facilitates the generation of a uniform lignin polyol applicable as a biobased component in polyurethanes and polyesters based on cyclic organic carbonates.

The high-value utilization of lignins is the most prominent opportunity to enhance the competitiveness of lignocellulosic biorefineries and reduce dependence on fossil resources. The incorporation of lignin into phenol−formaldehyde (LPF) resins represents a viable route toward this target. Due to its macromolecular nature, lignin could function as a structural backbone in the resin prepolymer. However, the low number of reactive sites with respect to phenol− formaldehyde chemistry hinders effective condensation reactions. Here, we present the effects of the phenolation of organosolv and sulfite lignin on network formation using phenol substitution levels of 20% and 40%. The wood-bonding results of raw and activated lignin-based phenolic resins reveal the superior quality of activated lignins. The wet and dry internal bond strengths of particleboards bonded by the synthesized LPF resins fulfill the European standards for load-bearing boards in humid environment. By comparison of a veneer strip rapid test and particleboard quality, a facile tool for screening resin quality is presented.

A quick and accurate procedure for quantitative evaluation of the different hydroxyl groups in lignosulfonic acids by31P NMR spectroscopy is presented.

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