Synthesis and characterization of novel polymers of sugar- and lignin based rigid, asymmetric monomers

Abstract

Amidst global warming, perturbed ecosystems and an ever-diminishing fossil feedstock, a paradigm shift toward renewable and sustainable plastics have emerged. Significant advances have been made in the past decade and several green polymers have entered the market. Much attention has been focused on the catalytic conversion of lignin, as it represents the largest source of renewable platform chemicals to generate sustainable substitutes to petroleum-based polymers.
This work explores the use of sugar and lignin-based building blocks in synthesis of bio-based monomers with versatile side groups in order to prepare diverse polymers with novel characteristics.
Three different dialdehydes and their corresponding reduced diols were prepared by a base catalysed nucleophilic substitution and reduction with NaBH4 from sugar based 5-CMF and lignin based 4-hydroxy benzaldehyde, vanillin and syringaldehyde. The reaction of vanillin-CMF dialdehyde with pentaerythritol was investigated under acidic condition to produce spirocyclic polyacetals. The thermal instability of the monomer in the acidic environment prohibited the polyacetal formation and resulted in humin formation instead. Copolymerization of the corresponding reduced diol with bio-based 1,6-hexanediol and dimethyl terephthalate by melt polymerization yielded a series of polyesters with 9-34% content of the rigid monomer. Higher amount of incorporation resulted in an increase of the glass transition temperature and decreased melting points. The copolymer containing 9.1% of the rigid diol was semi-crystalline, while the polymers with higher content of the new diol (20-, 29-, 34%) were amorphous. The heat-sensitivity of the new diol resulted in colorization of the products.

Popular Abstract

The idea of sustainable development and wholesome consumption is a cornerstone of today’s academia and firmly integrated in many commercial enterprises and consumer mindsets. The concepts, however, are very much reflective of a 21st century world view and many business sectors lag behind. In particular, we are dependent on non-renewable carbon sources for our energy and plastic material. This year, fossil fuels carry circa 80% of our total global primary energy demand and plastics are ubiquities world-wide. While the harnessing of fossil carbon allowed the west to industrialise at such a rapid pace, it did not turn out to be the eternal source of utility that was once thought. Non-renewable carbon is a strictly finite resource. Even if new reserves are found, the formation rate is only a fraction of the necessary depletion rate to cover energy demands of modern-day life. Expert calculation estimates a complete depletion of coal, natural gas and oil within the coming 50-100 years. Moreover, and perhaps most importantly, the use of carbon for energy concerns produces large amount of greenhouse gases. This has had disastrous consequences for the environment and humans. The process of generating energy through burning hydrocarbons is today directly or indirectly responsible for a total loss of 3.3% of the global GDP in damages and approximately 4.5 million deaths - mostly due to a rapidly changing environment. In a similar fashion, plastics, a cornerstone of our modern-day life, has shown not to be without its faults. A great majority of all plastics made today stem from fossil carbon and it has been discovered in the past few decades to have a severe environmental impact. As recycling has historically been next to nothing, most plastics have ended up in landfills or the ocean. This has been due to the fact that none of the plastics made of non-renewable carbons are completely degradable. Circa 80% of all litter that accumulates on land and in the waters are plastics. Ignoring the purely aesthetic considerations, plastics have been known to leech toxic additives, entangle animals and readily sorb and transport highly damaging persistent organic pollutants. Needless to say, it is imperative that renewable sources of energy and plastics are developed soon, for the sake of our environment and the continuation of modern-day life.
Polymers are substances or materials, which are made by connecting small molecules (monomers), usually one or two different into a really long, large molecule. Natural polymers are cellulose, starch and lignin, while examples for synthetic polymers are Teflon, nylon or PET. An important property of polymers is glass transition temperature. Below this thermal point the polymers are more brittle, while that temperature the polymer becomes more rubber-like. For example, PET has glass transition temperature around 70 °C. That means if we would pour a really hot tea in our bottle, it would become more rubber-like, and bend. Increase of this property also affects the plastic’s physical appearance, processability and recyclability. A common technique to improve the glass transition temperature is to incorporate a more rigid molecule into the commercial polymer. Using this approach cups from modified PET can be filled with almost boiling water was synthetized by Perstorp (Akestra).
In present work six new monomers were prepared from sugar and lignin (cell wall of wood and bark) based molecules to produce novel polymers. The first group of molecules unfortunately turned out to be inadequate, due to their thermal instability, while one of the monomers from the other group were successfully raised into a commercial polymer with up to 34% monomer content, after optimization of the reaction. The reaction successfully improved the glass transition temperature of the resulting copolymer and the desired effect was achieved. The monomers low heat stability unfortunately made the polymerization difficult to execute in high quality. However, after further optimization, the monomers can be effective tools to improve commercial polymers.

• author: Karajos, Andras
• supervisor: Baozhong Zhang; Niklas Warlin
• organization: Department of Chemistry
• alternative title: New plant based derivatives for plastics, in the quest to replace fossil based materials
• course: KEMR45 20192
• year: 2020
• type: H2 - Master's Degree (Two Years)
• subject: Chemistry
• keywords: polymer, green chemistry, biobased, sugar, lignin, glass transition temperature, sustainable, fossil based, analytical chemistry
• language: English
• id: 9031380
• date added to LUP: 2023-06-28 13:31:05
• date last changed: 2023-06-28 13:31:05