Maro Publications

Lignin

Notes

From 05/03/2015 through 11/2/2012

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Polymers

Renewable Materials

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Notes

1. Introduction  (Wikipedia)

2. Lignin  Applications (US Patent 8,288,460 )

3. Polylactide-graft-lignin Materials (US Patent 8,993,705 )

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1. Introduction

“Lignin or lignen is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants[1] and some algae.[2] The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum,[3] meaning wood. It is one of the most abundant organic polymers on Earth, exceeded only by cellulose, employing 30% of non-fossil organic carbon,[4] and constituting from a quarter to a third of the dry mass of wood. As a biopolymer, lignin is unusual because of its heterogeneity and lack of a defined primary structure. Its most commonly noted function is the support through strengthening of wood (xylem cells) in trees.[

Global production of lignin is around 1.1 million metric tons per year and is used in a wide range of low volume, niche applications where the form but not the quality is important”

(Wikipedia, Lignin, 11/2/2012)

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2. Lignin  Applications

“Native lignin is a naturally occurring amorphous complex cross-linked organic macromolecule that comprises an integral component of all plant biomass. The chemical structure of lignin is irregular in the sense that different structural units (e.g., phenylpropane units) are not linked to each other in any systematic order. It is known that native lignin comprises pluralities of two monolignol monomers that are methoxylated to various degrees (trans-coniferyl alcohol and trans-sinapyl alcohol) and a third non-methoxylated monolignol (trans-p-coumaryl alcohol). Various combinations of these monolignols comprise three building blocks of phenylpropanoid structures i.e. guaiacyl monolignol, syringyl monolignol and p-hydroxyphenyl monolignol, respectively, that are polymerized via specific linkages to form the native lignin macromolecule.

Extracting native lignin from lignocellulosic biomass during pulping generally results in lignin fragmentation into numerous mixtures of irregular components. Furthermore, the lignin fragments may react with any chemicals employed in the pulping process. Consequently, the generated lignin fractions can be referred to as lignin derivatives and/or technical lignins. As it is difficult to elucidate and characterize such complex mixture of molecules, lignin derivatives are usually described in terms of the lignocellulosic plant material used, and the methods by which they are generated and recovered from lignocellulosic plant material, i.e. hardwood lignins, softwood lignins, and annual fibre lignins.

Native lignins are partially depolymerized during the pulping processes into lignin fragments which dissolve in the pulping liquors and subsequently separated from the cellulosic pulps. Post-pulping liquors containing lignin and polysaccharide fragments, and other extractives, are commonly referred to as "black liquors" or "spent liquors", depending on the pulping process. Such liquors are generally considered a by-product, and it is common practice to combust them to recover some energy value in addition to recovering the cooking chemicals. However, it is also possible to precipitate and/or recover lignin derivatives from these liquors. Each type of pulping process used to separate cellulosic pulps from other lignocellulosic components produces lignin derivatives that are very different in their physico-chemical, biochemical, and structural properties.

Given that lignin derivatives are available from renewable biomass sources there is an interest in using these derivatives in certain industrial applications. For example, lignin derivatives obtained via organosolv extraction, such as the Alcell.RTM. process (Alcell is a registered trademark of Lignol Innovations Ltd., Burnaby, BC, CA), have been used in rubber products, adhesives, resins, plastics, asphalt, cement, casting resins, agricultural products, oil-field products and as feedstocks for the production of fine chemicals.

However, large-scale commercial application of the extracted lignin derivatives, particularly those isolated in traditional pulping processes employed in the manufacture of pulp for paper production, has been limited due to, for example, the inconsistency of their chemical and functional properties. This inconsistency may, for example, be due to changes in feedstock supplies and the particular extraction/generation/recovery conditions. These issues are further complicated by the complexity of the molecular structures of lignin derivatives produced by the various extraction methods and the difficulty in performing reliable routine analyses of the structural conformity and integrity of recovered lignin derivatives. For instance, lignin derivatives are known to have antioxidant properties (e.g. Catignani G. L., Carter M. E., Antioxidant Properties of Lignin, Journal of Food Science, Volume 47, Issue 5, 1982, p. 1745; Pan X. et al. J. Agric. Food Chem., Vol. 54, No. 16, 2006, pp. 5806-5813) but, to date, these properties have been highly variable making the industrial application of lignin derivatives as an antioxidant problematic.

Thermoplastics and thermosets are used extensively for a wide variety of purposes. Examples of thermoplastics include classes of polyesters, polycarbonates, polylactates, polyvinyls, polystyrenes, polyamides, polyacetates, polyacrylates, polypropylene, and the like. Polyolefins such as polyethylene and polypropylene represent a large market, amounting to more than 100 million metric tons annually. During manufacturing, processing and use the physical and chemical properties of certain thermoplastics can be adversely affected by various factors such as exposure to heat, UV radiation, light, oxygen, mechanical stress or the presence of impurities. Clearly it is advantageous to mitigate or avoid these problems. In addition, the increase in recycling of material has led to an increased need to address these issues.

Degradation caused by free radicals, exposure to UV radiation, heat, light, and environmental pollutants are frequent causes of the adverse effects. A stabilizer such as an antioxidant, anti-ozonant, or UV block is often included in thermoplastic resins for the purpose of aiding in the production process and extending the useful life of the product. Common examples of stabilizers and antioxidants include amine types, phenolic types, phenol alkanes, phosphites, and the like. These additives often have undesirable or even unacceptable environmental, health and safety, economic, and/or disposal issues associated with their use. Furthermore, certain of these stabilizers/antioxidants can reduce the biodegradability of the product.

It has been suggested that lignin may provide a suitable polymeric natural antioxidant which has an acceptable toxicity, efficacy, and environmental profile. See, for example, A. Gregorova et al., Radical scavenging capacity of lignin and its effect on processing stabilization of virgin and recycled polypropylene, Journal of Applied Polymer Science 106-3 (2007) pp. 1626-1631; C. Pouteau et al. Antioxidant Properties of Lignin in Polypropylene, Polymer Degradation and Stability 81 (2003) 9-18. Despite the advantages of lignin, for a variety of reasons, it has not been adopted for widespread use as an antioxidant. For instance, it is often problematic to provide lignins that perform consistently in terms of antioxidant activity. Also, the processing of the lignin may introduce substances that are incompatible for use with chemicals such as polyolefins. Additionally, the cost of producing and/or purifying the lignin may make it uneconomic for certain uses.”

[Balakshin et al, US Patent 8,288,460 (10/16/2012)]

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3. Polylactide-Graft-Lignin Materials

US Patent 8,993,705 (March 31, 2015), “Polylactide-Graft-Lignin Blends and Copolymers,” John R. Dorgan, Michael Paul Eyser, and Clay Perbix (Colorado, USA).

As the lignocellulosic biorefining industry emerges as a viable fuels technology, the availability of the assortment of lignins will also expand. Lignin's physicochemical features that attribute to its prospective utilization in determining a value-added product includes a three dimensional aromatic-based structure and an abundance of reactive functional groups in order to manipulate the hydrophobicity of lignin. Both alkali lignin and organosolv lignin were butyrated before being combined with poly(lactic acid) (PLA) via melt blending into composites and solution polymerization into grafted into copolymers. The composites' impact strength and toughness decreased but the modulus and heat distortion temperatures improved. Although the thermomechanical properties weren't desirable, the results paved the road for the continuing research on the grafted copolymers. Gas permeation chromatography, dilute solution viscometry, differential scanning calorimetry, Fourier transform inferred spectroscopy, and solubility tests proved that the different functionalized lignins were successfully synthesized via solution polymerization to form a renewable PLA-graft-lignin copolymer. Although the copolymer is low molecular weight, it has potential to introduce a high value to the otherwise wasted lignin.

Lignin is the second most abundant natural biopolymer on the planet following cellulose, and easily the least utilized despite its great potential as both a filler, and a thermal and mechanical property modifier for other biopolymers. Lignin is found in the rigid xylem cell wall in all vascular plants providing support, acting as a water sealant and as a protector against various biological attacks. As a natural glue, lignin consists of 15-40% of the total material in the plant cell walls. Lignin is composed of an arrangement of 3 different phenyl-propane units (PPU) crosslinked forming a complex structure that varies drastically from plant to plant.

Lignin is industrially separated primarily using the sulfite, kraft, and soda pulping processes. Lignosulfonates today are: burned for energy, used as animal feedstock, agricultural and horticultural applications, additives in concrete, and utilized in lignin-phenol-formaldehyde resins. More than 99% of industrial produced kraft lignin's annual 70+ million tones are burned as a low value fuel in chemical recovery furnaces. The remaining kraft lignin has applications as rubber reinforcers, thermosetting and thermoplastic polymers, phenol-formaldehyde resins, panelboard adhesives, friction materials, and insulation. When lignin is isolated via the organosolv extraction process, it can be used for brake pads, oriented strand board (OSB), PF resins and polyurethane foams and epoxy-resins.

Poly(lactic acid) (PLA) is an aliphatic renewable thermoplastic that is readily biodegradable. Lactic acid is fermented from dextrose, the only natural isomer of cellulose, present in corn, sugar feedstocks, etc. PLA is limited thermally by a low glass transition temperature (softening point) and a low heat distortion temperature. A need exists to elucidate the synthesis and properties of novel polylactide-graft-lignin copolymers with higher impact strength.

As biocellulosic biorefining emerges as a viable fuel technology, there will be an abundance of lignin available. In order to be a successful industry, bioplastics will need to be competitive with plastic made from fossil fuels on a cost-performance basis in order to be widely adopted. Lignin is expected to improve properties in bioplastics and plastics by acting as a toughening agent; improving the connectivity of the network; adding additional stiffening groups to the matrix; acting as a sizing agent between natural fibers and the resin matrix; behaving as a comonomer for the resin; inducing plasticity in the deformation zone at crack tips to improve toughness; acts as a free radical trap to reduce radical scission effects during racture in highly cross linked polymer; improving flame resistance; modifying biodegradability; enhanced photoresistance and thermal stability; expanding fatigue lifetime; and green engineering of materials

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Interested!!
Bookmark this page to follow future developments!.
(RDC 6/5/2012)

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Roger D. Corneliussen
Editor
www.maropolymeronline.com

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Tel: 610 363 9920
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E-Mail: cornelrd@bee.net  

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Copyright 2012 by Roger D. Corneliussen.
No part of this transmission is to be duplicated in any manner or forwarded by electronic mail without the express written permission of Roger D. Corneliussen
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* Date of latest addition; date of first entry is 11/2/2012.