Veggie (Scrap) Tales – Are plant-based polymers the answer to our plastic conundrum?

By Molly Sung, Secretary for the GCI

Plastic is one of the most ubiquitous materials on the planet. Everything from our toothbrushes, to pens, take-out containers, or parts used in the automotive or aeronautic industries are made from plastic. What started off as a convenient and cheap alternative to traditional materials has become a global reliance – and it’s taking its toll.

Traditional plastics are petroleum-based – and as we know, petroleum is a non-renewable resource and its extraction, processing, and use contributes to environmental pollution and climate change. When plastic bags were first gaining popularity in the 1950s and 60s, one of the selling points of using plastic bags was that they were more durable and long-lasting than paper,1 but that’s also exactly the problem. Plastic doesn’t degrade easily like paper does, so it starts to accumulate. This accumulation in landfills and, unfortunately, our waters has spurred research in the development of plastics that can break down over time.

An example of a biodegradable plastic is polylactic acid (PLA). The starting material, lactic acid, can be obtained through fermentation of crops such as sugarcane or corn, which can undergo condensation to form short chains (oligomers). Next, these oligomers undergo depolymerization to form lactide, a cyclic ester, which is then polymerized with the help of a catalyst to give PLA, shown in Figure 1.2

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Figure 1. Synthesis of polylactic acid (PLA), a biodegradable plastic, from lactic acid.

PLA performs comparably to the popular commercial plastic polyethylene terephthalate (PET, labelled with the “1” inside the recycling symbol). It is currently used in food packaging (such as disposable cups), as medical implants,2 and has also found renewed popularity as a common filament for 3D printing, but it’s not without its problems. The monomer, lactide, can have varying stereochemistry which influences the final polymer product and the mechanical properties of the plastic. Significant strides have been made in this area of research, but possibly the biggest barrier to using PLA is the competition with the food industry for the starting material. This is incidentally the same problem many first-generation biofuels ran into. But what if we could take food waste and turn it into usable plastics?

While there are some technologies being developed to use non-food materials like cellulose as a bioplastic, many of these methods require fairly harsh reactions. A gentler, water-based approach to make a cellulose-based plastic was recently reported by a research team from the Italian Institute of Technology and the University of Milano-Bicocca in the journal Green Chemistry.3

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Figure 2. Image of the bioplastic films made from different vegetable powders: (A) carrot, (B) parsley, (C) radicchio, (D) cauliflower. Reproduced from Perotto et al. [3].

This new technique uses waste from the food-industry, including carrot, cauliflower, radicchio, or parsley waste. The vegetable matter must first be dried and ground into a micronized powder, but otherwise no further processing or purification is required to make the veggie waste usable in this process. To make the plastic films, the researchers simply mixed the vegetable powder with a weakly acidic solution (5 % HCl w/w) at 40 °C, then removed any residual acid through dialysis and let the suspension dry in a petri dish for 48 hours. This process has a 90 % conversion of the vegetable waste into bioplastic (by weight) and the product has very promising mechanical properties (Figure 2).

In particular, in measuring the elasticity and tensile strength of the bioplastic films, it was found that the carrot film had comparable properties to polypropylene (commonly used for rigid plastic containers – otherwise referred to as number “5” plastics).

The researchers also tested important factors for plastics being considered for food storage applications. First, they studied whether the films would interact with water. The parsley film was found to absorb water fairly readily. Conversely, the carrot filmed exhibited hydrophobic behaviour – an uncommon characteristic for vegetable-derived plastics. This hydrophobic behaviour means that the moisture from food is unlikely to soak through the plastic film or structurally damage it.

One very interesting property of the radicchio waste is that it is rich in anthocyanins. Anthocyanin is what gives radicchio, red cabbage, and beets their vibrant red colour. More importantly, anthocyanins are known anti-oxidants and materials rich in these anti-oxidants are currently being investigated as food-packaging materials that extend the shelf-life of food.4 Unfortunately, these vegetable films tested to be fairly permeable to oxygen, which would offset any benefit from the antioxidant-rich radicchio film. However, the researchers showed that if the vegetable waste was blended with polyvinyl alcohol (PVA), the oxygen permeability can be reduced significantly and was even an improvement on the pure PVA.

Lastly, and very importantly, the researchers tested for the biodegradability of the films. To test the rate of biodegradation, the researchers submerged the carrot film in seawater to measure the rate of oxygen consumption by the seawater organisms responsible for the biodegradation of the film. They found that the film decomposed fairly quickly in 15 days.

These scientists have now demonstrated a very mild process in the synthesis of bioplastics that have mechanical properties similar to one of the most common commercial plastics. They have also made a plastic that, because of the presence of anthocyanins, may have applications in food storage that can help reduce food-waste.

What is especially promising about these bioplastics is how little purification of the vegetable waste is required to make them; however, there are improvements to be made. A major obstacle these materials will face is their performance in wet or humid environments as well as scaling up to an industrial process. It is clear that we need more sustainable materials and these vegetable waste plastics present an exciting new avenue towards biodegradable bioplastics.

 

References

  1. Laskow. How the Plastic Bag Became So Popular. The Atlantic [Online] 2014. https://www.theatlantic.com/technology/archive/2014/10/how-the-plastic-bag-became-so-popular/381065
  2. Gupta et al., J. Prog. Polym. Sci. 2007, 32, 4, 455-482. DOI: 10.1016/j.progpolymsci.2007.01.005
  3. Perotto et al., Green Chemistry, 2018, 20, 804-902. DOI: 10.1039/C7GC03368K
  4. N. Tran, et al., Food Chemistry, 2017, 216, 324-333. DOI: 10.1016/j.foodchem.2016.08.055

 

Figure from Perotto et al. 2018 reproduced with the permission of the Royal Society of Chemistry.

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Glycoside Hydrolases: A Doorway to Alternative Energy

Glycoside Hydrolases: A Doorway to Alternative Energy

By Namrata Jain, GreenChem UBC (Invited post!)

Biofuels, in particular bioethanol, are widely accepted as carbon-neutral fuels1, meaning they have no net greenhouse gas emissions; the amount of carbon dioxide produced during their combustion equals the amount fixed from the atmosphere while the plants grow. These fuels provide an alternative to the current outrageous usage rate of fossil fuels. Plant biomass, a renewable and abundantly available natural resource, is used as the main source for bioethanol production.

In order to produce bioethanol, polymeric plant carbohydrates (polysaccharides) must be broken down into the corresponding monosaccharides, followed by fermentation via yeasts. Typically, starch-rich crops such as corn and sugarcane are the most heavily used as carbohydrate sources.

However, since utilization of these starchy sugars in bioethanol production competes with their use as food crops, there has been a recent shift towards utilization of lignocellulosic biomass.1 Lignocellulosic biomass includes cellulose and hemicelluloses present in non-edible parts of plants, and hence reduces dependence on edible, starch-rich crops.

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Figure 1. Structure of a plant cell wall, highlighting xyloglucan, a particular hemicellulose of interest. [2]

Lignocelluloses form an important part of the plant cell wall (Figure 1) and are composed of cellulose, hemicelluloses (such as xyloglucan), and polyaromatics called lignin. These polymers are tough and more difficult to break down to release monosaccharides, as compared to starch. Nevertheless, lignocelluloses are the most abundant biological material on earth and are an untapped resource.1

The complete utilization of this biomass, however, is hindered by the structural complexity of plant cell walls, arising from the heavy crosslinking between hemicelluloses, celluloses, and lignin within, making it difficult to access the degradable polysaccharidic components. Hemicelluloses, such as xyloglucan (Figure 2A), can make up 15-50 % of these lignocellulosic materials and have been the focus of research for optimization to use as a biofuel.

To efficiently break down the lignocelluloses, many types of enzymes are needed. Glycoside hydrolases, one such group of carbohydrate active enzymes, have proven to be very efficient in the hydrolysis of many complex polysaccharides.3 However, more details about the chemical structure of the enzymes, as well as a reliable way of comparing the kinetic activity of various enzymes has been of interest to researchers in the field.

One of the ways of quantifying the kinetic details of such enzymes is by designing chemical probes such as one shown in Figure 2B. Such probes are chemically very similar in structure to the polysaccharide of interest (eg. Figure 2A), and hence can subtly fit into the active site of the enzyme and manipulate its rate of catalysis in a controlled and quantifiable way, making comparisons between enzymes’ kinetics possible.

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Figure 2. Structures of (A) xyloglucan; and (B) xyloglucan oligosaccharide based probe.

These probes can also assist in the crystal structure formation of the enzyme providing key details about the nature of interactions between the enzyme and corresponding polysaccharide and the specific amino acids responsible for its catalytic activities (Figure 3).

The Brumer group at the University of British Columbia4 has recently designed one such probe (Figure 2B) specific for xyloglucan active enzymes (xyloglucanases) by chemically modifying a xyloglucan-derived heptasaccharide. This probe was able to provide valuable information about the kinetics, specificity, as well as structural details of a newly discovered xyloglucanase PbGH5, which is secreted by a microbe residing in the intestinal system of ruminants such as cows.

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Figure 3. Crystal structure of the characterised endoxyloglucanase in complex with the inhibitor. [4]

As more research goes into the design and improvement of such probes, we would be able to develop novel enzyme cocktails that can make bioethanol production more economically and practically viable, leading to gradual decrease in our dependence on fossil fuels for our energy needs.

 

References:

  1. Scheffran J. The Global Demand for Biofuels: Technologies, Markets and Policies. In: Biomass to Biofuels: Strategies for Global Industries. Blackwell Publishing Ltd.; 2010:27-54. doi:10.1002/9780470750025.ch2.
  2. https://en.wikipedia.org/wiki/Cell_wall#Plant_cell_walls
  3. Henrissat B, Davies G. Structural and sequence-based classification of glycoside hydrolases. Curr Opin Struct Biol. 1997;7(5):637-644. doi:http://dx.doi.org/10.1016/S0959-440X(97)80072-3.
  4. McGregor N, Morar M, Fenger TH, et al. Structure-function analysis of a mixed-linkage β-glucanase/xyloglucanase from key ruminal Bacteroidetes Prevotella bryantii B14. J Biol Chem. 2015;291(3):1175-1197. doi:10.1074/jbc.M115.691659.

Greener Alternatives in Organic Synthesis Involving Carbonyl Groups: Dethioacetalization and Iron-Catalyzed Transfer Hydrogenation

By Diya Zhu, Member-at-Large for the GCI

A carbonyl functionality is a functional group composed of a carbon atom double-bonded to an oxygen atom (C=O). It is ubiquitous in nature as well as widely employed and studied in all areas of chemistry. In this blog, we will explore two common synthetic processes involving carbonyl groups with greener alternative reagents.

Dethioacetalization with NH4I

Carbonyl-containing compounds are abundant in nature, expressing a wide range of functionality. As targeted in many natural and non-natural product syntheses, the protection and deprotection of the carbonyl functional groups are critical and often require multiple steps. Common carbonyl protecting groups are dithianes and dithiolanes due to their easy accessibility and high stability under acidic/basic conditions. The traditional dethioacetalization is generally performed utilizing heavy-metal salts such as mercury(II) chloride, silver(II) nitrite, ceric ammonium nitrate, and selenium dioxide, of which the resulting waste is very toxic to the environment.1

From 1989 to 2005, serval hypervalent iodine compounds such as bis(trifluoroacetoxy)-iodobenzene (BTI), Dess-Martin periodinane (DMP), and o-iodoxybenzoic acid (IBX) have been employed as dethioacetalization reagents due to their low toxicity, high selectivity, and metal-ion free nature. While these reagents have a smaller environmental impact, they are still required in excess amount, which is economically wasteful.2, 3

Finally, in 2011, Ganguly and Mondal reported a mild, efficient, and greener dethioacetalization protocol using a catalytic amount of ammonium iodide with hydrogen peroxide.3 In this work, the deprotection was carried out with 10 mol% of nontoxic ammonium iodide and 30% hydrogen peroxide as the terminal oxidizer in an aqueous medium in the presence of sodium dodecylsulfate (SDS). This protocol (Figure 1) shows a high yield (>90%) deprotection of 1,3–dithianes and dithiolanes of activated aromatics and even deactivated and sterically encumbered substrates. The high tolerance, low environmental impact, mildness, operational simplicity, high throughput, and generality of the protocol make it an intriguing alternative.

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The greener dethioacetalization protocol by Ganguly and Mondal. [3]

Iron-catalyzed transfer hydrogenation with formic acid

Various catalyst systems for the reduction of carbonyl compounds have been established, such as Meerwein–Ponndorf–Verley (MPV) reduction.4 However, only a handful of protocols were reported for the transfer hydrogenation of aldehydes due to the difficulty in controlling the chemoselectivity in the process.

In these conversional protocols of transfer hydrogenation, many side-reactions (for example, aldol condensations) take place after deprotection by the base. The heavy-metal catalysts (such as rhodium, iridium, and ruthenium complexes) are expensive and often poisoned by the substrates, resulting in non-recyclable catalysts and many side-products. In addition, the hydrogenation of carbon-carbon double bonds (C=C) and aldehydes compete, resulting in poor chemoselectivity.5,6 Due to these drawbacks, there was a significant desire for more efficient and environmentally benign catalytic systems.

In the last decade, iron catalysts have received much attention due to their nontoxic, abundant, and inexpensive qualities. In 2013, Beller and his colleagues published an efficient iron-based catalyst system for the highly selective transfer hydrogenation of aldehydes under mild conditions.6 In this system, they suggested that iron-tetraphos complexes [(Fe(BF4)•6H2O and P(CH2CH2PPh2)3) are able to catalyze a wide range of substrates such as aromatic, aliphatic, and α,β-unsaturated aldehydes to the corresponding alcohols in excellent yields (>99%). Without the presence of a base, formic acid is used as a cheap, environmental friendly, and easy to handle hydrogen source. In addition, no significant amounts of side products were observed.

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The iron-catalyzed transfer hydrogenation with formic acid. [6]

In addition to these two examples, many chemical companies promote the idea of green chemistry and offer more green choices to reduce environmental impact without compromising the quality and efficacy of research.7

 

References:

  1. J. Corey, B. W. Erickson, Journal of Organic Chemistry 36 (1971), 3553; E. Vedejs, P. L. Fuches, Journal of Organic Chemistry 36 (1971), 366.
  2. S. Kirshnaveni, K. Surendra, Y. V. D. Nageswar, K. R. Rao, Synthesis 15 (2003), 2295. DOI: 10.1055/s-2003-41055
  3. C. Ganguly, P. Mondal, Synthetic Communications 41 (2011), 2374. DOI: 10.1080/00397911.2010.502995
  4. Gladiali, E. Alberico, Chemistry Society Reviews 35 (2006) 226. DOI: 10.1039/B513396C
  5. S. M. Samec, J.-E. Bäckvall, P. G. Andersson, P. Brandt, Chemistry Society Reviews 35 (2006), 237. DOI: 10.1039/b515269k
  6. Wienhöfer, F. A. Westerhaus, K. Junge, M. Beller, Journal of Organometallic Chemistry 744 (2013) 156. DOI: 10.1016/j.jorganchem.2013.06.010
  7. Sigma Aldrich Alternative Product Page. http://www.sigmaaldrich.com/chemistry/chemistry-products.html?TablePage=119262253 (accessed Oct 15, 2017).
Ecocatalysis: Harnessing Phytoextraction for Chemical Transformations

Ecocatalysis: Harnessing Phytoextraction for Chemical Transformations

By Karlee Bamford, Treasurer for the GCI

What is ecocatalysis? I had never heard this term before until reading a recent publication from Grison and coworkers in the RSC journal Green Chemistry entitled “Ecocatalyzed Suzuki cross coupling of heteroaryl compounds”.1 In this work, the authors perform the familiar Suzuki cross-coupling of arylboronic acids (Figure 1) with heteroaryl halides. However, they use a thoroughly unfamiliar palladium catalyst: the common water hyacinth (Figure 2).

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Figure 1. The general reaction for Suzuki cross-coupling  (Ar = substituted phenyl, thiophene, or indole groups).

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Figure 2. The common water hyacinth (Eichhornia crassipes). Credit: Richard A. Howard, provided by Smithsonian Institution, Richard A. Howard Photograph Collection (Montréal, Canada). [2]

In broad terms, ecocatalysis is the use of plant-derived, metal-based catalysts in chemical reactions. If it were not for the author’s graphical abstract illustrating the plant body performing catalysis, I would have assumed that this was a more standard bioinorganic paper featuring a plant extract as catalyst. While the propensity of certain plants and microbiota to uptake (“phytoextract”) particular contaminants has long been used in waste water purification, for example in the uptake of inorganic phosphates (e.g. [PO4]3-),3 ecocatalysis represents a clever progression from plants being used in chemical sequestration to chemical transformation.

Plants currently used in phytoremediation, that is, the removal of contaminants such as heavy metals from anthropogenically polluted environments, could clearly be used in the production of ecocatalysts.4 One current use for such metal-laden plants is in phytomining as so-called bio-ore.5 This metal extraction process ultimately results in the majority of the plant bio-mass being wasted through the energy-consumptive process of incineration, whereas an ecocatalyst such as EcoPd requires that same bio-mass as a kind of ligand support.

Grison and colleagues report reaction times, conditions, and yields (typically >90 %) for their “EcoPd” catalyst that are competitive with typical Suzuki cross coupling experiments and catalysts, both homogenous and heterogeneous. Remarkably, the primarily root-based EcoPd catalyst can be reclaimed and reused without loss of activity, as the authors demonstrated in a control study that involved recycling the catalyst four times over. Finally, the palladium content of the used catalyst can be quantitatively recovered by rhizofiltration, that is, by returning the elemental palladium obtained in post-synthesis work-up to a new plant specimen for metal uptake. In practical terms, this involves filtering the post-synthesis solution, dissolving the isolated solids with aqua regia, and diluting the resultant palladium-containing solution with water before reintroducing it to the roots of E. crassipes.

Ecocatalysis is an entirely new and emerging field of chemistry (circa 2013) being pioneered by Grison and coworkers at The Laboratory of Bio-inspired Chemistry and Ecological Innovations (University of Monpellier) in France. Their research has furnished several other noteworthy ecocatalysts (EcoM’s) featuring nickel (EcoNi),6 zinc (EcoZn),7 manganese (EcoMn),8 copper (EcoCu),9 which have proven effective in Biginelli, Diels-Alder, reductive amination, and Ullmann reactions, respectively.

This new approach to catalysis is not only charmingly novel – at least to a non-bioinorganically-minded chemist such as myself – but it also offers a real solution to the problematic dependence of catalysis on pure precious metals. The plants themselves provide a means for both harvesting and using low-abundance metals in a format that does not require complicated ligand design and is consistent with homogenous catalysis. Clearly, EcoPd and other such EcoM may not be suitable replacements in every metal-catalyzed transformation, but they nonetheless provide a new avenue for recycling precious metals and realising catalyst sustainability.

The range of possible ecocatalysts is, in my mind, astounding. Plant species that are known to preferentially accumulate heavy metals, known as accumulators and hyperaccumulators, are greater than 500 in number and sequester metals from across the p- and d-block of the periodic table, each to varying extents.10 As the tolerance and preference for certain transition metals is in part gene-regulated,11 it is conceivable that genetic modification and controlled environmental conditions could in the future yield heavy metal-specific plant species for sequestration and, perhaps, subsequent ecocatalysis.

 

References:

  1. G. Clavé, F. Pelissier, S. Campidelli and C. Grison, Green Chemistry, 2017, DOI: 10.1039/c7gc01672g.
  2. Used with permission from Larry Allain, hosted by the USDA-NRCS PLANTS Database.
  3. J. Lv, J. Feng, Q. Liu and S. Xie, Int. J. Mol. Sci., 2017, 18.
  4. C. Grison, Environmental Science and Pollution Research, 2015, 22, 5589-5591.
  5. R. R. Brooks, M. F. Chambers, L. J. Nicks and B. H. Robinson, Trends in Plant Science, 1998, 3, 359-362.
  6. C. Grison, V. Escande, E. Petit, L. Garoux, C. Boulanger and C. Grison, RSC Adv., 2013, 3, 22340.
  7. V. Escande, T. K. Olszewski and C. Grison, Comptes Rendus Chimie, 2014, 17, 731-737.
  8. V. Escande, A. Velati, C. Garel, B.-L. Renard, E. Petit and C. Grison, Green Chemistry, 2015, 17, 2188-2199.
  9. G. Clavé, C. Garel, C. Poullain, B.-L. Renard, T. K. Olszewski, B. Lange, M. Shutcha, M.-P. Faucon and C. Grison, RSC Adv., 2016, 6, 59550-59564.
  10. H. Sarma, Journal of Environmental Science and Technology, 2011, 4 118-138.
  11. S. Jan and J. A. Parray, Approaches to Heavy Metal Tolerance in Plants, Springer Singapore, Singapore, 2016.

Green Chemistry at CSC2017 – The 100th Canadian Chemistry Conference and Exhibition

By Kevin Szkop and Alex Waked

This year, the GCI partnered with the Chemical Institute of Canada (CIC), the organizing body of the CSC2017, to be closely involved in various aspects of Canada’s largest chemistry meeting.

In collaboration with GreenCentre Canada and CIC, the GCI organized a Professional Development Workshop as part of the CSC2017 program. This event consisted of four components:

The green chemistry crash course, led by Dr. Laura Reyes. Laura is a founding member of the GCI, and is now working in marketing & communications with GreenCentre Canada.

A case study, led by Dr. Tim Clark, Technology Leader at GreenCentre Canada. The case study gave attendees a unique opportunity to learn about some projects that GreenCentre has been developing and in collaboration with peers, learn how to find applications for new intellectual property (IP) and how to make contacts within relevant companies.

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Dr. Tim Clark leading the GreenCentre Canada Industry Case Study

Career panel discussion, sponsored by Gilead, featuring members of academia and industry.

A coffee mixer for an opportunity for informal networking.

 

Supplementary to the Professional Development Workshop, the GCI organized a technical session, co-hosted by the Inorganic, Environmental, and Industrial sections of the conference. This new symposium, entitled “Recent Advances in Sustainable Chemistry”, brought together students, professors, industry, and government speakers to showcase a diverse and engaging collection of new trends in green and sustainable chemistry practices across all sectors of chemistry. Highlighted talks included Dr. Martyn Poliakoff from the University of Nottingham, also a CSC2017 Plenary Lecturer, Dr. David Bergbreiter from Texas A&M University, and Dr. William Tolman from the University of Minnesota.

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Dr. Martyn Poliakoff teaching the audience about NbOPO4 acid catalysts found in Brazilian mines

Dr. Bergbreiter’s lecture was an engaging one. His enthusiastic approach to the use of renewable and bio-derived polymers as green solvents was captivating to both industrial and academic chemists.

Dr. Martyn Poliakoff, a plenary speaker at the conference, gave a phenomenal talk during the first day of the symposium. His charismatic style complimented perfectly the cutting-edge research ongoing in his group at the University of Nottingham. Particularly interesting was the use of flow processes in tandem with photochemistry to yield large quantities of natural products useful in the drug industries.

Dr. Tolman’s talk was of interest to essentially anyone working in an academic environment, especially for student run groups, like the GCI, with both academic interests as well as safety awareness initiatives. In the first part of the talk, synthetic and mechanistic studies of renewable polymers were discussed. The second part shifted focus to student-led efforts to enhance the safety culture in academic labs, which stood out from most of the other talks in our symposium.

One highlight was a group of graduate students at the University of Minnesota organizing a tour of Dow Chemicals to observe the work and safety codes in an industrial setting, which they used as a lesson to bring back to their own research labs. This caught the eye of most of the GCI members, which inspired us to organize a similar day trip in the future.

In further efforts to make our symposium accessible to undergraduate and graduate students, the GCI partnered with GreenCentre Canada to award five Travel Scholarships to deserving students from across Canada to provide financial aid to participate in the conference.

We thank all of our speakers, both national and international, for their participation in the program. It was a great success!