Crosslinked Polymers from Pyrolysis of Lignocellulosic Biomass

Abstract

Present research is aimed at the development of crosslinked polymers from biomass pyrolysis oil. Crosslinked polymers are high performance materials employed in a wide range of applications and are most commonly derived from petrochemicals. With the increasing depletion of petroleum and the climate change, the focus is shifted toward biomass-based polymers. Biomass has a great variety due to a vast number and types of plant species. Moreover, lignocellulosic biomass offers challenges for the development of materials due to its complex chemical nature. Pyrolysis of biomass efficiently breaks down biomass components to simpler organic compounds with differing functionalities which can be used for the development of novel monomers and polymers. For the current study, bio-oil was obtained from the fast pyrolysis of lignocellulosic biomass. Gas-chromatography-mass spectroscopy (GC-MS) was carried out for detection of compounds in the bio-oil. The hydroxyl number was measured using 31P-Nuclear magnetic resonance (31P-NMR) spectroscopy. Different monomeric structures were synthesized from bio-oil by reacting with specific reagents. In chapter two, bio-oil was co-reacted with phenol and formaldehyde to produce bio-novolac resin. Glycidylation was performed on α-resorcylic acid to product another bio-based epoxy – GDGB. Semi-interpenetrating polymer networks (semi-IPN) of bio-novolac and GDGB were developed by crosslinking GDGB in immediate presence of bio-novolac. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were used for measuring glass transition temperature, storage modulus, loss modulus, tan δ and active chains density. In chapter 3, bio-oil and bio-novolac were glycidylated to form epoxidized bio-oil and epoxidized bio-novolac monomers which were crosslinked by an amine hardener – Jeffamine T-403. The thermo-mechanical performance of bio-oil-derived epoxy and novolac polymers was comparable to their conventional analogues. In chapter 4 cyanate esters were produced from bio-oil organic phase and from bio-oil-derived biphenol (ORG-biphenol). Crosslinked cyanate esters from ORG-biphenol yielded higher glass transition temperature than bisphenol-A-cyanate ester. In the final chapter, the aqueous phase of bio-oil was used for monomer synthesis. Methacrylation reaction was performed on bio-oil aqueous phase to produce a mixture of methacrylic monomers. Methacrylated aqueous bio-oil and acrylated epoxidized soybean oil were copolymerized to form crosslinked thermoset materials with sub-ambient glass transition temperatures. Soxhlet extraction with refluxing dichloromethane was used for assessing mass retention of crosslinked materials. Morphology of the polymers was observed with scanning electron microscopy (SEM). Bio-oil based crosslinked polymers developed in this research study are sustainable and can be potentially applied in the fields of composites, coatings, adhesives, elastomers and packaging.

Keywords: Bio-oil, crosslinked polymers, BioNovolac, epoxy resins, cyanate esters, polyacrylates