Polystyrene Sulfonate is Effective for Enhancing Biomass Enzymatic Saccharification Under Green Liquor Pretreatment in Bioenergy Poplar

Background: Water-soluble lignin (particularly lignosulfonate, LS) has been well documented for its significance on enzymatic saccharification of lignocellulose, though the promotion mechanism has not been fully understood. Much attention has been paid to natural lignin or its derivatives. The disadvantage of using natural lignin-based polymers as promoting agents lies in the difficulty in tailor-incorporating functional groups due to their complex 3D structures. To further improve our understanding on the promotion mechanism of water-soluble lignin in the bio-conversion of lignocellulose and to pursue better alternatives with different skeleton structures other than natural lignin, herein we reported a synthetic soluble linear aromatic polymer, sodium polystyrene sulfonate (PSS), to mimic LS for enhancing the efficiency of enzymatic saccharification. Results: The role of PSS played in enzymatic saccharification of pure cellulose and green liquor pretreated poplar (GL-P) was explored by analyzing substrate enzymatic digestibility (SED) under different addition dosages and various pH media, along with LS for comparison. At the cellulase loading of 13.3 FPU/g-glucan, the glucose yield of GL-P increased from 53% for the control to 81.5% with PSS addition of 0.1 g/g-substrate. It outperformed LS with the addition of 0.2 g/g-substrate by 6.3%. In the pH range from 4.5 to 6, PSS showed a positive effect on lignocellulose saccharification with the optimum pH at 4.8, where the most pronounced SED of GL-P was achieved. The underlying mechanism was unveiled by measuring zeta potential and using Quartz Crystal Microbalance (QCM) and Multi-parametric Surface Plasmon Resonance (MP-SPR). The results confirmed that the complexes of cellulase and PSS were conjugated and the negatively superchanged complexes reduced non-productive binding effectively along with the improved saccharification efficiency. The thickness of PSS required to block the binding sites of cellulase film was less than half of that of LS, and the PSS adlayer on cellulase film is also more hydrated and with a much lower shear modulus than LS adlayer. Conclusions: PSS as LS analogue is effective for enhancing the biomass enzymatic saccharification of GL-pretreated poplar. PSS exhibited a severer inhibition on the enzymatic saccharification of pure cellulose, whilst a more positive effect on bioconversion of lignocellulose (GL-P) than LS. In addition, a much lower dosage is required by PSS. The dynamic enzymatic hydrolysis indicated PSS could prolong the processive activity of cellulase. The valid data stemmed from QCM and SPR expressed that PSS bound to cellulases and the as-formed complexes reduced the nonproductive adsorption of cellulase onto substrate lignin more efficiently than LS due to its flexible skeleton and highly hydrated structure. Therefore, PSS is a promising alternative promoting agent for lignocellulose saccharification. From another perspective, the synthetic lignin mimics with controllable structures enable us to reach an in-depth understanding of the promotion mechanism of soluble lignins on enzymatic saccharification.

Polystyrene Sulfonate with Well-Defined Structure as Lignosulfonate Analogue for Promoting Lignocellulose Enzymatic Saccharification

Background: Water-soluble lignin (particularly lignosulfonate, LS) has been well documented for its positive impact on enzymatic saccharification for lignocellulose. Even though, the promotion mechanism of LS hasn’t been fully understood. All researches paid all attentions on the natural lignin or its derivatives. Whereas the structure of natural lignin is too complex and not easily to be tailored functional groups. To further our understanding on the promotion mechanism of water-soluble lignin to enzymatic saccharification for lignocellulose and also to pursue better alternatives with different skeleton structure other than natural lignin or its derivatives, therein we reported a synthetic soluble linear aromatic polymer- sodium polystyrene sulfonate (PSS) with well-defined structure to mimic LS for enhancing the enzymatic saccharification efficiency. Results: At the cellulase loading of 10 FPU/g-glucan, the glucose yield of green liquor pretreated poplar increased from 39.8% for the control to 60.3% with PSS addition of 0.1 g/g-substrate. It outperformed LS with addition of 0.2 g/g-substrate by 4.6%. The underlying mechanism was unveiled using Quartz Crystal Microbalance and the results confirmed that the as-formed complexes of cellulase-PSS, which effectively reduced non-productive binding and eventually improving the saccharification efficiency, were only half thickness and with much lower shear moduli than those of LS. Conclusions: The synthetic lignin mimics with controllable structures offer us more opportunities to understand the promotion mechanism of soluble lignins on lignocellulose enzymatic saccharification.

Natural lignin nanoparticles: a promising nano-crosslinker for constructing fluorescent photoswitchable supramolecular hydrogels

Photoswitchable and photoluminescent ternary supramolecular hydrogels were fabricated by host–guest and ionic interactions between polyacrylic acid, azobenzene guanidine and α-cyclodextrin grafted cellulolytic enzyme lignin nanoparticles.

High ion adsorption densities of site-selective nitrogen doped carbon sheets prepared from natural lignin

Carbon fibers and sheets were prepared from jet-milled natural chitin and cellulose samples, and from natural lignin sample using ice-templating technique, respectively.

Development of anti-photo and anti-thermal high internal phase emulsions stabilized by biomass lignin as a nutraceutical delivery system

β-Carotene was encapsulated in natural lignin-stabilized HIPEs and exhibited good resistance to photodegradation and thermal degradation as well as bio-accessibility.