Biomass Fundamentals

Module 14: Lignin II:Specialty Applications

A capstone course for

BioSUCCEED:

Bioproducts Sustainability: a University Cooperative Center of Excellence in EDucation

The USDA Higher Education Challenge Grants program gratefully acknowledged for support

This course would not be possible without support from:

USDA

Higher Education Challenge (HEC) Grants Program

www.csrees.usda.gov/funding/rfas/hep_challenge.html

What is “lignin?”• The amorphous glue that

binds carbohydrate bundles• A complex, polydisperse

(weight average MW/Number average MW measure of distribution of individual MWs) polymer

• A source of endless discussion for the exact nature of its biosynthesis in plants (enzyme controlled vs. random radical coupling)

• C9 polypropylphenol derivative O

O

OHOCH3

O

O

H3CO H2COH OH3C

CH2OH

OCH3

O

OH3C

OH3C

O

OCHOH

CH2OH

OH

CH2OH OCH3

OCH3

OH3C

OH3COCH3

O

OH3C

OO

O

CHOH

CH2OH

O

CHOH

CH2OH

O

O

CH2OH

CHOH

CH2OH

O OH3C

OCH3 O

CHOH

CH2OH

O

OH

CHOH

CHOH

OCH2OH

CHOH

H2COHO

OH3C

OCH3

OCHOH

CH2OH

OH OH3C

OH

CH2OH

OCH3

OCH3 O

CHOH O

OCH3

CH2OH

OO

OCHOH

CH2OH

OH3C

CH2OH

CHOH

O

O

OH3C

HOCH2OH

CHOH

O

CH2OH

O

OH3C

CHOH

O

OCH3 OH

OO CH2OH

CH2OH

CHOH

Lignin Biosynthesis

Structures of Lignin Precursors

Flavonoids: Chemical Offshoots of Lignin Biosynthesis

• 15 carbon atom compounds (C6-C3-C6) – over 4000!

• Polyphenol• Phytochemicals (phenolic acids,

stilbenes, polyphenols)• Antioxidants• CV health: reduce agglomeration

of platelets in endothelia• Assist lignification of cell walls in

plants in response to injury• Antimicrobials

Biologically Active Isoflavonoid• Rotenone comes from

Derris root and Lonchocarpus species

• Insecticide• Fish poison• Topical treatment of

head lice, scabies, and ectoparasites

Rheological Properties of Lignin• Schematic illustration of

secondary cell wall of spruce tracheids

• Between ordered cellulose fibrils is the lignin-hemicellulose matrix

• Various vibrational studies (static & dynamic FT-IR) of lignin functional groups suggest lignin is ordered in plane with the plane of cell wall surface

• Distribution, however, is not ISOTROPIC in fiber wall

Rheological Properties of Lignin, Part Deux

• Monolignols couple/polymerize under environmental constraints along fiber axis to ordered polysaccharide matrix

• Polysaccharides templates*?• A high response in a 90° out-of-phase spectrum with lignin

peaks indicates a more viscoelastic behavior for lignin over carbohydrates – also can move freely in matrix unperturbed by carbohydrates

*

Lignin in Composite/Industrial Applications

• Lignosulfonates• Extrusion moldings• Fuel• Fertilizer/agricultural adjuvant• Potential raw material for fine chemical

production

Lignin as a Medical “Tissue”• Wood and bone possess unique structural

motifs that fulfill requirements of support & transport of nutrients

• Is it possible, therefore, to use wood as a implantable material?

• Can it be used, for example, as a femoral replacement?

Technical Hurdles to Address• Toxicity• Compatibility• Adsorption• Functionality• Mechanical Properties

What is Bone?• Ceramic-polymer composite• Calcium phosphate (hydroxyapatite) and collagen• The apatite has different metal ions that adjust

solubility and availability of mineral elements to rest of body

• Small apatite platelets crystallize in preferred locations on collagen

Ultrastructure of Bone

Attempts to Mimic Bone• MOE: *Hydroxyapatite + polyethylene – middle ear

implants, maxillofacial reconstruction, & bone repair; possesses MOE similar to bone

• Porosity: Porites (coral species) have similar pore size & interconnectivity; CaCO3 (aragonite in coral) hydroxyapatite by hydrothermal process

• Hierarchical Structure: tendon, muscle, WOOD, and bamboo

*

van Leeuwenhoek’s Famous Comment

When he first recognized the Haversian canals in bone in 1693, hemade reference to other hierarchical structures:

Structure & Function of Wood• Wood is a polymer of 20-30%

lignin and the virtual remainder carbohydrates

• Tracheid (osteocyte in bone) is “cell”

• Tracheids consists of 5-30 nm wide microfibrillar elements composes of cellulosic strands (2.5 nm diameter)

• Wood is porous and operates on negative pressure osmotic gradients in lumens and valves in pits – transport in bone is positive pressure from circulation of nutrients

Morphological Structure of Juniperus communis

A: annual rings; B: rays & pits; C: pirs in a ray connecting adjacent tracheid; D:Helical texture of spiraling cellulose strands outside a tracheid

Bone & Wood• Collagen is bone’s counterpart to wood’s

cellulose• Alternating fibrillar orientation in the

various lamellae in bone and wood imparts strength & toughness

• Pore networks differ only in size and connectivity

Material Property Chart for Orthopedics

Histological Section of Juniper Wood

A: cortical bone after 3 mos.

B: cortical bone after 6 mos.

C: trabecular bone after 6 mos.

D: Cortical bone after 1.5 years

E: cortical bone after 3 years

Conclusions from Medical Study• No infection, serendipitously due to wood oils• Boiling wood to remove excess oil and any

microorganisms lowered MOE, better mechanical fit to wood (see chart)

• Wood well tolerated by body – surrounded by bone

• Even bone growth into open pores and artificial microchannels (a priori machining) for improved integration