Amylose/cellulose nanofiber composites for all-natural, fully biodegradable and flexible bioplastics.

Thermoplastic, polysaccharide-based plastics are environmentally friendly. However, typical shortcomings include lack of water resistance and poor mechanical properties. Nanocomposite manufacturing using pure, highly linear, polysaccharides can overcome such limitations. Cast nanocomposites were fabricated with plant engineered pure amylose (AM), produced in bulk quantity in transgenic barley grain, and cellulose nanofibers (CNF), extracted from agrowaste sugar beet pulp. Morphology, crystallinity, chemical heterogeneity, mechanics, dynamic mechanical, gas and water permeability, and contact angle of the films were investigated. Blending CNF into the AM matrix significantly enhanced the crystallinity, mechanical properties and permeability, whereas glycerol increased elongation at break, mainly by plasticizing the AM. There was significant phase separation between AM and CNF. Dynamic plasticizing and anti-plasticizing effects of both CNF and glycerol were demonstrated by NMR demonstrating high molecular order, but also non-crystalline, and evenly distributed 20 nm-sized glycerol domains. This study demonstrates a new lead in functional polysaccharide-based bioplastic systems.

Phenolic cross-links: building and de-constructing the plant cell wall.

Covering: Up to 2019Phenolic cross-links and phenolic inter-unit linkages result from the oxidative coupling of two hydroxycinnamates or two molecules of tyrosine. Free dimers of hydroxycinnamates, lignans, play important roles in plant defence. Cross-linking of bound phenolics in the plant cell wall affects cell expansion, wall strength, digestibility, degradability, and pathogen resistance. Cross-links mediated by phenolic substituents are particularly important as they confer strength to the wall via the formation of new covalent bonds, and by excluding water from it. Four biopolymer classes are known to be involved in the formation of phenolic cross-links: lignins, extensins, glucuronoarabinoxylans, and side-chains of rhamnogalacturonan-I. Lignins and extensins are ubiquitous in streptophytes whereas aromatic substituents on xylan and pectic side-chains are commonly assumed to be particular features of Poales sensu lato and core Caryophyllales, respectively. Cross-linking of phenolic moieties proceeds via radical formation, is catalyzed by peroxidases and laccases, and involves monolignols, tyrosine in extensins, and ferulate esters on xylan and pectin. Ferulate substituents, on xylan in particular, are thought to be nucleation points for lignin polymerization and are, therefore, of paramount importance to wall architecture in grasses and for the development of technology for wall disassembly, e.g. for the use of grass biomass for production of 2nd generation biofuels. This review summarizes current knowledge on the intra- and extracellular acylation of polysaccharides, and inter- and intra-molecular cross-linking of different constituents. Enzyme mediated lignan in vitro synthesis for pharmaceutical uses are covered as are industrial exploitation of mutant and transgenic approaches to control cell wall cross-linking.

Sustainable production of cellulose nanofiber gels and paper from sugar beet waste using enzymatic pre-treatment.

Removal of non-cellulosic polymers from vegetable pulp to obtain cellulose nanofibers (CNF) is normally achieved by chemical pre-treatments which requires several washing steps. In the present study, it is demonstrated how incubation of sugar beet pulp at pH 9, followed by treatment with polysaccharide-degrading enzymes and subsequent bleaching can be done in a one-pot procedure to make CNF. The new method consumes 67% less water and removes non-cellulosic polysaccharides with similar efficiency as a chemical method. In addition, CNF produced by the new method contained slightly more pectin and formed gels with 2.7 times higher storage modulus. Nanopapers cast from chemically- and enzymatically produced CNF showed similar mechanical properties. However, without the pH 9 incubation step, the enzymes accessibility to cell-wall polymers was limited resulting in lower gel and paper strengths. In conclusion, the new method offers a sustainable route for producing high quality CNF from sugar beet waste.

Nanofibers Produced from Agro-Industrial Plant Waste Using Entirely Enzymatic Pretreatments.

Cellulose fibers can be freed from the cell-wall skeleton via high-shear homogenization, to produce cellulose nanofibers (CNF) that can be used, for example, as the reinforcing phase in composite materials. Nanofiber production from agro-industrial byproducts normally involves harsh chemical-pretreatments and high temperatures to remove noncellulosic polysaccharides (20-70% of dry weight). However, this is expensive for large-scale processing and environmentally damaging. An enzyme-only pretreatment to obtain CNF from agro-industrial byproducts (potato and sugar beet) was developed with targeted commercial enzyme mixtures. It is hypothesized that cellulose can be isolated from the biomass, using enzymes only, due to the low lignin content, facilitating greater liberation of CNF via high-shear homogenization. Comprehensive Microarray Polymer Profiling (CoMPP) measured remaining extractable polysaccharides, showing that the enzyme-pretreatment was more successful at removing noncellulosic polysaccharides than alkaline- or acid-hydrolysis alone. While effective alone, the effect of the enzyme-pretreatment was bolstered via combination with a mild high-pH pretreatment. Dynamic rheology was used to estimate the proportion of CNF in resultant suspensions. Enzyme-pretreated suspensions showed 4-fold and 10-fold increases in the storage modulus for potato and sugar beet, respectively, compared to untreated samples. A greener yet facile method for producing CNF from vegetable waste is presented here.