Millions of tons of lignin—a biopolymer that strengthens the cell walls of plants—are produced each year by the pulp and paper industry. Although lignin production is widescale, lignin is considered a waste product with no commercial application due to its complexity as a non-uniform material. Incorporation of lignin into commercially important polymers remains a challenge in both pure research and applied industrial environments; yet if we could understand and use this material in a predictable manner, it would have a myriad of applications. Fortunately, a 2018 study in ACS Sustainable Chemistry & Engineering has revealed how to prepare and characterize different copolymers of lignin and polylactide (PLA).
Tag Archives: polymers
Researchers uncover how to make better polymers from pulp and paper waste
Posted in Science Communication
Tagged biodegradable, biopolymers, chemistry, copolymer, copolymers, green, green chemistry, lignin, materials, Materials Chemistry, melt, Outreach Project, PLA, polymers, Public Engagement, UBC
Plastic replacements: some new conSQUIDerations
The amount of plastic that has been produced to date now exceeds 8300 million metric tonnes (Mt). To put this into perspective, the average blue whale weighs approximately 180 Mt, thus 46 million blue whale’s worth of plastic has been produced since humans started commercializing plastics in 1950. Our society had become extremely dependent on plastic products and synthetic (petroleum- based) textiles which cause serious consequences such as microplastic and microfiber pollution as I’ve discussed in previous blog posts.
Figure 1. Size reference for blue whales. Wikipedia Commons
Bioplastics have more recently taken the stage as a potential avenue for replacing petroleum-based plastics. Biologically based polymers have structural elements such as helices, β-turns, β-sheets and coils which provide structural integrity and resilience and can replicate the desirable polymeric interactions in plastics. Additionally, a lot of new material is being developed based on the protein polymers that are naturally occurring in biological systems (including ourselves).
Figure 2. Fibrous protein polymers have molecular architecture that can include (i) helices and coils, (ii) β-turns and β-spirals, and (iii) β-sheets. Source
Video 1. SRT- coated fabrics that self-heal in water.
Squid ring teeth (SRT) are an especially promising candidate for making functional fibres and films due to its strength, conductivity and self-healing properties. The SRT are located inside the suction cups of the tentacles of squids and are composed of a naturally occurring protein complex. Fortunately, it is not necessary to harvest squid to obtain the SRT proteins as they can be biosynthetically produced since having their genome sequenced. The SRT-inspired monomer is repeated to create a polymeric chain and the resulting protein that is produced is named accordingly as tandem repeat (TR) proteins.
Figure 3. The Squid ring teeth of a giant squid. Wikipedia Commons
Figure 4. Optical images of squid ring teeth (SRT) and the six common squid species they originate from. Source
Films produced with SRT proteins consist of disordered domains that provide elasticity and flexibility to the materials in addition to ordered domains such as β-sheets that provide mechanical strength. One study designed four TR proteins denoted as TR-nX where X was the number of repeat units within the molecule. They measured the mechanical force of these four TR proteins and found that the ultimate strength of the protein’s scale linearly, with TR-n25 reaching an ultimate strength of 40 MPa. As seen in Figure 4 below, there is a limitation of the study due to sample size. The error bars of the TR-n12 and TR-n25 overlap, so it is not possible to say there is a statistically significant difference from each other.
Figure 4. Mechanical testing of fully hydrated TR proteins (inset shows 1/n dependence) Source
Additionally, SRT protein films have been suggested as a potential solution to the issues related to the release of microfibers into the water from washing. A cloth made from polyester was coated with an SRT protein film and was found to dramatically increase the cloths resistance to abrasion (and microfiber release) compared to cloths that were not coated with SRT protein films.
While there is still a lot of further research to be done, SRT-based proteins are a promising avenue for making our world a little bit less plastic.
~Isla
Posted in Biological Sciences, Science Communication
Tagged biological chemistry, chemistry, microplastic, plastic, pollution, polymers, protein, squid, technology
Photoactivated Self-healing Copolymers- It’s Lit
A scratch on your car may no longer need a trip to the auto-shop. Simply applying heat or light could remedy this issue. This idea could soon be a reality using vitrimers, a new class of plastics that have thermal and chemical stability, but can also be self-healing on a small scale and fully recyclable on a larger scale.
Taylor Wright from Dr. Wolf’s group at UBC. Source
In 2018, at the University of British Columbia, Taylor Wright under the supervision of Dr. Michael Wolf investigated the photoactive self-healing properties of vitrimeric copolymers.
Photoactive materials undergo physical and chemical changes in response to illumination. The development of responsive materials to both heat and light were explored for the first time through the incorporation of functional molecular groups into the polymeric backbone of these systems.
Wright and Wolf’s focus on the molecule’s response to light also offered a new aspect into vitrimeric research compared to the previous studies, that exclusively focused on the vitrimers’ response to heat.
Figure 1. Comparison of thermoplastics and thermosets upon heating. Source
So what exactly are vitrimers? Vitrimers are a new class of polymeric material that was first created in 2011 by a Polish physicist, Dr. Ludwik Leibler. By combining characteristics of thermosets and thermoplastics, Leibler was able to develop a material that is strong and durable, yet moldable and recyclable.
Thermoplastics are made of plastics linked by intermolecular forces. They can be easily molded and shaped under heat, then cooled down to produce the final structure. This allows for ease when it comes to processing. Additionally, this property allows them to be recycled to produce new products.
Conversely, thermosets involve irreversible cross-linking, connecting the backbones of the polymer chains with molecular bridges. This results in enhanced chemical and heat resistance, making the material less susceptible to stress-cracking. However, due to their cross-linked bonds, these materials do not melt upon exposure to heat, unable to remold and recycle.
Vitrimers combine the best properties of both materials; structural integrity is improved through cross-linking, as well as self-healing and fully recyclable properties.
Figure 2. The molecular structure of the photoactivated vitrimeric copolymer created by Wright and Wolf. Source
As seen above in Figure 2, the vertical wiggly line splits the system into the two unique parts that make this a copolymer. The left side shows the aromatic anthracene molecule that crosslinks into a dimer in response to UV radiation. The amine on the right side behaves like a more traditional vitrimer and responds to heat to form reversible exchanges.
Originally, their aim was to create a single polymeric system that responds to both heat and light simultaneously. However, during their research, they found that amines directly bonded to the anthracene molecules simply do not engage in the bond exchange process. They believed the electronics of the ring alters the behaviour of the molecule in comparison with non-aromatic amines.
Studying the photodimerization and thermally exchangeable functionalities of the copolymer based on the vinylogous urethane vitrimer, the self-healable properties can be seen in the video above. Self- healing polymers are a class of materials that enable the repair of micro-scale damage in the coating, ultimately restoring the passive state of the metal substance. This enables reprocessability or longer lifetimes in cross-linked polymeric materials. The systems containing anthracene undergo self-healing through reversible reactions, allowing monomers and polymer chains to link and unlink.
Figure 3. Polymer sample, P2, mounted on a glass slide. A scratch from a razor blade can be observed. Source
Wright and Wolf tested the modification of surface properties by using a razor blade to scratch a polymer sample (that Wright denoted as P2), that was mounted on a glass slide. By using optical microscopy, the scratches were observed as dark lines crossing the sample, as seen below in Figure 4. The scratches were seen to decrease in width and ultimately close during heating through a series of expansions and contractions of the material, which can be seen in the video above.
Figure 4. Optical microscope image of (a) sample P2a initial scratch, (b) P2a after heating (c) sample P2b initial scratch, (d) and (e) P2b after heating. Black scale bar is 300 μm. Source
These specific Wright and Wolf vitrimeric copolymers will not be scaled up for commercial use, due to the difficulties of incorporating the two components of the copolymer together. However, the general idea of vitrimeric materials has “almost limitless applications”. For example, they can be incorporated into products that have a long lifetime, such as shipping materials and plastic stadium seats which can be recycled into new products once they start to deteriorate.
Additionally, Wright is currently working on vitrimers that start as a viscous liquid, much like thermoplastics, that can be easily molded and processed. This possible advancement will provide more flexibility with processing the starting material and ease in the synthesis process.
~Brina, Isla and Taiki (Group 4)
Posted in Science Communication
Tagged chemistry, Outreach Project, plastic, pollution, polymers, science, technology
