Identification and Formulation of Polymers: A Challenging

Laboratory Experiment Cite This: J. Chem. Educ. XXXX, XXX, XXX-XXX

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Identification and Formulation of Polymers: A Challenging Interdisciplinary Undergraduate Chemistry Lab Assignment Wanda J. Guedens*,†,‡ and Monique Reynders‡ †

Biomolecule Design Group, Institute for Materials Research, Hasselt University, Campus Diepenbeek, Agoralaan-building D, BE-3590 Diepenbeek, Belgium ‡ Faculty of Sciences, Hasselt University, Campus Diepenbeek, Agoralaan-building D, BE-3590 Diepenbeek, Belgium S Supporting Information *

ABSTRACT: Prior to the recycling process, raising awareness of plastic waste impact, e.g., polluting oceans worldwide, is undoubtedly a first attempt to tackle this pandemic environmental issue. With this in mind, the presented practical session is an effort to entice an interdisciplinary audience of science undergraduates toward a sustainable future. The associated assignment focuses on a collaboration of undergraduate chemistry students and engineering undergraduates with a minor program in chemistry. Acting on an adequate uncluttered mind map of practical guidelines, the students acquire and exchange multiple “good laboratory practice” skills. By this, engineering undergraduates get acquainted with chemicals, e.g., polymers, while future chemists get an impression of how economics is concerned to maintain a balance between economy and ecology, i.e., a circular economy. In a grand finale, the students present their interdisciplinary communication skills via a poster exhibition: “chemistry meets economics”. Moreover, via this interdisciplinary approach the traditional polymer chemistry laboratory session, still a substantial part of the organic chemistry curriculum in the polymer chemistry courses, gets a makeover and will be integrated into a modern, advanced curriculum. KEYWORDS: Second-Year Undergraduate, Polymer Chemistry, Polymerization, Physical Properties, Qualitative Analysis, Synthesis, Testing/Assessment, Problem Solving/Decision Making

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INTRODUCTION

Hereto, the undergraduate chemistry students and the engineering undergraduates with a minor program in chemistry are allocated randomly to mixed groups of three or four participants each. Preliminary to the assignment, the students attend a lecture on polymer chemistry with a focus on industrial processing applications and plastic waste disposal. In particular, manufacturing processes of plastic waste toward semifinished goods on an industrial scale are introduced. Their laboratory assignment starts with creating a plan that outlines their collaboration within the group. During the first group meeting, the students have to come to an agreement in

The continuous search for innovative teaching and learning methods is an utmost priority at Hasselt University.1 For this purpose, the presented laboratory assignment aims to give fresh impetus in teaching traditional polymer chemistry. The study program for engineering undergraduates at Hasselt University2 is focused on a crossover in applied economics and engineering. In a joint assignment, undergraduate chemistry students and engineering undergraduates with a minor program in chemistry work together experimenting and debating on scientific issues starting from their specific backgrounds. Since polymer chemistry is integrated in a course on chemical technology for engineering undergraduates, these students are adequate debate members for undergraduate chemistry students with a complementary view on chemistry: green chemistry meets circular economy. © XXXX American Chemical Society and Division of Chemical Education, Inc.

Special Issue: Polymer Concepts across the Curriculum Received: May 10, 2017 Revised: October 15, 2017

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DOI: 10.1021/acs.jchemed.7b00284 J. Chem. Educ. XXXX, XXX, XXX−XXX

Journal of Chemical Education

Laboratory Experiment

Figure 1. Flowchart for the identification of seven plastic sticks.

a scientific poster. During the grand finale, the collaboration of the group members is validated in a scientific poster presentation for fellow students by peer and self-assessment.

planning and distributing the various tasks according to their skills already acquired. At the start of the practice session, they present their mind map to the coach. As their part in constructing this mind map, the chemistry students have to develop a clear operational flowchart (Figure 1) (based on the protocol available in the Supporting Information). The latter serves as a guidance throughout the experiment for the identification of seven plastic sticks. The flowchart design should be crystal clear so that for engineering students the assignment is unambiguous as well. For the sake of safety, the chemistry students have to follow the procedures for the syntheses of five polymers to the letter, keeping in mind that their fellow students are less experienced in “good laboratory practice” (GLP) skills. On the other hand, the latter are obliged to search for industrial applications of the identified or synthesized polymers covering the entire value chain, i.e., from the tiniest chip to the largest constructions in different industrial branches. After the necessary group discussions, the first half of the practice time (2 hours in total) is spent identifying the seven randomly numbered plastic sticks, i.e., polyethylene (PE), polypropylene (PP), polystyrene (PS), poly(vinyl chloride) (PVC), poly(methyl methacrylate) (PMMA), polyamide (PA), and polycarbonate (PC) on the basis of their own created flowchart. In the second part of the practice session, the students formulate the five different polymers via chain-growth polymerization or condensation polymerization, i.e., PS,3,4 PMMA,5 nylon-6,6,4,6 an alkyd resin,7 and resorcinol−formaldehyde resin,8,9 thereby emphasizing the hazards and precautions. Indeed, not only is the plastic waste an environmental , but also, raw materials for the formulation of polymers can be harmful for the environment as well. After gathering the experimental results and keeping in mind the guidelines (available in the Supporting Information) the students develop

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EXPERIMENTAL PROCEDURE

Materials

The cut-to-size plastic sticks (1.5 cm × 6.0 cm × 0.2 cm) were purchased from VINK BVBA (Heist-op-den-Berg, Belgium): PE300 black (d = 0.98 kg·m−3), PP XT gray ral 7032 (d = 0.98 kg·m−3), PA6 XT natural (d = 1.14 kg·m−3), Lexan PC 9030 clear 112 (d = 1.20 kg·m−3), altuglas PMMA molten clear 112 (d = 1.19 kg·m−3), PVC trovidur EC PVS-U XT gray (d = 1.50 kg·m−3), and vikureen PS white 900 mat/mat (d = 1.05 kg· m−3). The raw materials were purchased from different suppliers: styrene 99% stabilized (Alfa Aesar); benzoyl peroxide ≥97% (dry weight) wetted with ca. 25% water (Alfa Aesar); tetrachloroethylene EMPLURA (Merck); toluene EMPLURA, extra pure (Merck); sodium hydroxide, pellets EMSURE ACS, Reag. Ph. Eur. analytical reagent (max. 0.02% K) (Merck); resorcinol for synthesis (Merck); methyl methacrylate stabilized for synthesis (Sigma-Aldrich); 1,6-diaminohexane for synthesis (Sigma-Aldrich); adipoyl chloride for synthesis (SigmaAldrich); phthalic anhydride for synthesis (Sigma-Aldrich); formaldehyde 36% (39% w/v) stabilized AnalaR NORMAPUR ACS, Reag. Ph. Eur. analytical reagent (VWR Chemicals); glycerol Ph. Eur. (VWR Chemicals). Procedure Identification and Synthesis of a Series of Polymers

At the start of the practice session, the students are instructed to work under the fume hood, complying with the rules for waste disposal. Hereby, special attention is paid to the separated collection of non- and halogenated substances in B




solutions, adipoyl dichloride dissolved in toluene and 1,6diaminohexane, results in the formation of nylon-6,6 (Figure 4). The nylon-6,6 thread can be gently pulled out using a glass stirring rod. Experiment 4. Synthesis of Alkyd Resin (Polyester Resin). Heating 2-benzofuran-1,3-dione (phthalic anhydride) and propane-1,2,3-triol (glycerol) forms a polyester resin (Figure 5). Experiment 5. Synthesis of Resorcinol−Formaldehyde Resin. A mixture of resorcinol, formaldehyde, and sodium hydroxide (the catalyst) is slowly heated in a water bath until the reaction starts. The heat source is then removed, and the mixture is left for a while in the hot water bath to form the resorcinol−formaldehyde resin furthermore (Figure 6).

waste bottles. For their personal protection, a lab coat, safety goggles, face protection and disposable gloves are mandatory (except when working with tetrachloroethylene). The students have to identify seven randomly numbered plastic sticks on the basis of their specific physical and chemical properties. The identification process consists of two nondestructive tests (behavior in water and the scratch test) and four more-or-less destructive tests (fire behavior of the flame, smell of the fumes, solubility in tetrachloroethylene, and the fracture test). Special attention is paid to tackle chemical danger awareness, e.g., the chemical destruction of PVC causes irritating HCl fumes. As the students are provided with just one series of plastic sticks, they are reminded of the chemical and physical destructiveness of some experiments. The behavior in water of the evaluated polymers is based on their difference in density. Those with a lower density than tap water will float, while others with a density higher than tap water will sink. Adding salt to the water will increase the number of plastic sticks floating to the water surface in a specific order. In the fire test, different types of flames can be observed. Moreover, after the flame of burning polymers is extinguished, the smell of the fumes is very typical to each polymer and therefore an additional identification tool. Tetrachloroethylene, C2Cl4, is used as the organic solvent to assess the solubility of the different polymers. The ultimate identification of PP and PE can be done with the fingernail test. Last but not least, the fracture image of the broken plastic sticks is a final identifier. There are three possibilities: a white ductile fracture, a friable, glassy fracture, and no fracture. In the second part of the practice session, the students synthesize five polymers:10−12 PS, PMMA, nylon-6,6, an alkyd resin, and resorcinol−formaldehyde resin. By doing these experiments, the students get acquainted with chain-growth polymerization and polymerization condensation in an interactive manner. As mentioned above, GLP is here of the utmost importance. Experiment 1. Synthesis of Polystyrene. The synthesis of PS is a chain-growth polymerization of styrene with benzoyl peroxide as the initiator. The viscosity of the mixture changes during gentle warming when PS is formed (Figure 2).

Procedure toward a Scientific Poster Grand Finale

After the laboratory practice session, the students analyze their results in an interim group meeting and discuss a roadmap for the development of a scientific poster toward an intramural poster conference. For this assignment, according to best practices available in the guidelines (see the Supporting Information), the chemistry students elaborate the chemical part while the engineering undergraduates with a minor program in chemistry outline possible actions toward a resilient and sustainable polymer industry, and more specifically, how green chemistry and a circular economy for recycling plastics can be tools to challenge resource depletion and increasing pollution of the five oceans worldwide.13

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HAZARDS During the laboratory experiment, the students are obliged to wear a buttoned lab coat, safety goggles, disposable gloves, and face protection. Waste containers are provided for segregated collection of non-halogenated organic solvents, halogenated organic solvents, solid organic waste, and inorganic waste. To stimulate the students’ awareness of the hazards and precaution statements, they have to make an overview of the reagents and the corresponding safety labels. An example can be found in the Supporting Information.

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RESULTS AND DISCUSSION

Identification and Formulation of a Series of Polymers

Because of their difference in density from ca. 900 to 1300 kg· m−3, PE and PP float on tap water while PS, PVC, PMMA, PA, and PC sink.14,15 The last ones emerge in a specific order to the water surface when increasing amounts of salt are added to the water. When the fire test is applied, different types of flames are observed. In the series of polymers, PVC and PC burn to ashes while the flame extinguishes at the same time. Aromatic polymers with many carbon atoms (i.e., PS) burn with a strong sooty flame with a bright yellow light, but all of the aliphatic polymers (i.e., PE, PP, PMMA, and PA) with fewer carbon atoms than the aromatic polymers burn with a light-yellow to blue flame. PE, PP, and PMMA can be distinguished from the others by the falling drops that keep on burning. Moreover, the falling drops of burning PMMA make a specific crackling sound. The smell of the smoke when the flame of the burning polymer is extinguished is very typical for each polymer. The smell of the smoke from polyolefins (i.e., PE and PP) is strongly reminiscent of that of burning candles. Indeed, the chemical characteristics of polyolefins and paraffin, stearin, or wax in candles exhibit good similarities. The sweet smell of styrene, similar to that of tar or coal gas, is an indication that PS

Figure 2. Polymerization of styrene to form polystyrene.

Experiment 2. Synthesis of Poly(methyl methacrylate) (Perspex). For the polymerization of methyl methacrylate with benzoyl peroxide as the initiator, a water bath at 95 °C is used (Figure 3). Experiment 3. Synthesis of Nylon-6,6. Condensation polymerization at the boundary layer between two insoluble

Figure 3. Polymerization of methyl methacrylate to form PMMA at 95 °C. C




Figure 4. Condensation polymerization of 1,6-diaminohexane and adipoyl chloride to form nylon-6,6.

Figure 5. Condensation polymerization of phthalic anhydride and glycerol to form an alkyd resin.

Figure 6. Condensation polymerization of resorcinol and formaldehyde to form a resorcinol−formaldehyde resin.

hazard and precautionary statements for the used raw materials and their personal safety were a theme throughout the entire laboratory practice. Paying attention to safety rules makes the students aware that the formulation of polymers is the first step in the life cycle of plastics with potential pollution of air, soil, and water.16−18

is burning. The smell of melting PMMA is very pleasant since it smells like tasty fruit. On the other hand, the penetrating and irritating smell of hydrogen chloride is definitive coming from PVC. Burning PC smells like phenol, recalling a visit to the dentist, while burning PA, with a protein-like structure, smells like burned horn. In general, plastics are more or less soluble in organic solvents. In particular, of all the polymers to be identified, only PS displays good solubility in tetrachloroethylene and can thereby be distinguished from the other polymers. With the ultimate fingernail test, PP and PE can be differentiated from one another. The scratch of a fingernail on the soft PE stick leaves no trace behind, in contrast to the visible stripe on the harder PP stick. Correspondingly, the fracture test is a final identifier to distinguish PMMA and PS from the other polymers. A glassy fracture is observed in the case of the broken PMMA and PS sticks. Finally, the different groups of students have to summarize their results in a report sheet (available in the Supporting Information) according to the flowchart in Figure 1 and present them to their coach. For the formulation of the five polymers, the students were urged to be very responsible not only for their own safety but also for the safety of their fellow students. A list of reagents (available in the Supporting Information) with the respective

Toward a Scientific Poster Presentation Grand Finale

During the poster conference, the students present their posters in the presence of their fellow students and teaching team. For the students, this event is a good opportunity to evaluate themselves by self- and peer assessment. The process is selfand peer-assessed according the following items: initiative, team work, perseverance, accuracy and completeness, method, and oral language. The product is peer- and teaching-team-assessed according to the following items: layout, structure (i.e., introduction/main text/conclusion/references), written language, content (i.e., the scientific value and implementation of course elements), presentation, and defense (i.e., answers to oral questions). The final score is the mean of the scores given by the teaching team and those obtained by self- and peer assessment. The grand finale poster conference at Hasselt University organized by the teaching team was a real success with no less than 22 poster presentations. For the students it was the D




(3) Wilen, S. H.; Kremer, C. B.; Waltcher, I. PolystyreneA Multistep Synthesis: For the Undergraduate Organic Chemistry Laboratory. J. Chem. Educ. 1961, 38 (6), 304. (4) Williamson, L. K.; Masters, K. M. Macroscale and Microscale Organic Experiments, 6th ed.; Cengage Learning: Belmont, CA, 2011; pp 757−759. (5) Duval-Terrié, C.; Lebrun, L. Polymerization and Characterization of PMMA: Polymer Chemistry Laboratory Experiments for Undergraduate Students. J. Chem. Educ. 2006, 83 (3), 443. (6) Mathias, L. J.; Vaidya, R. A.; Canterberry, J. B. Nylon 6A Simple, Safe Synthesis of a Tough Commercial Polymer. J. Chem. Educ. 1984, 61 (9), 805. (7) Dintzner, M. R.; Kinzie, C. R.; Pulkrabek, K.; Arena, A. F. The Cyclohexanol Cycle and Synthesis of Nylon 6,6: Green Chemistry in the Undergraduate Organic Laboratory. J. Chem. Educ. 2012, 89 (2), 262−264. (8) Lanson, H. J. Chemistry and Technology of Alkyd and Saturated Reactive Polyester Resins. Applied Polymer Science 1985, 285 (9), 1181−1204. (9) Liu, J.; Qiao, S. Z.; Liu, H.; Chen, J.; Orpe, A.; Zhao, D.; Lu, G. Q. Extension of The Stö ber Method to the Preparation of Monodisperse Resorcinol−Formaldehyde Resin Polymer and Carbon Spheres. Angew. Chem., Int. Ed. 2011, 50, 5947−5951. (10) Pavia, D. L.; Lampman, G. M.; Kriz, G. S.; Engel, R. G. Introduction to Organic Laboratory Techniques, 2nd ed.; Thomson Brooks/Cole: Belmont, CA, 2005; pp 394−411. (11) Ophardt, C. E. Condensation Polymers. http://chemistry. elmhurst.edu/vchembook/402condensepolymers.html (accessed October 2017). (12) Lewicki, J. P.; Fox, C. A.; Worsley, M. A. On the Synthesis and Structure of Resorcinol-Formaldehyde Polymeric NetworksPrecursors of 3D-Carbon Macroassemblies. Polymer 2015, 69, 45−51. (13) Stevens, E. S.; Baumstein, K.; Leahy, J.-M.; Doetschman, D. C. Polymer−Plastics Experiments for the Chemistry Curriculum. J. Chem. Educ. 2006, 83 (10), 1531−1533. (14) Hughes, E. A.; Ceretti, H. M.; Zalts, A. Floating Plastics: An Initial Chemistry Laboratory Experience. J. Chem. Educ. 2001, 78 (4), 522. (15) Kolb, K. E.; Kolb, D. K. Method for Separating or Identifying Plastics. J. Chem. Educ. 1991, 68 (4), 348. (16) Lundquist, L.; Leterrier, Y.; Sunderland, P. W., Månson, J.-A. E. Life Cycle Engineering of Plastics: Technology, Economy and the Environment, 1st ed.; Elsevier: Oxford, U.K., 2000. (17) American Chemistry Council. Plastics: Lifecycle of a Plastic Product. https://plastics.americanchemistry.com/Lifecycle-of-aPlastic-Product/ (accessed October 2017). (18) Grant, L. Less Is More: A Lifecycle Approach to Waste Prevention and Resource Optimisation; The Chartered Institution of Water and Environmental Management (CIWEM): London, 2013; http://www. ciwem.org/wp-content/uploads/2016/02/Less-is-More.pdf (accessed October 2017).

crowning glory of their hard work done. Via the mentioned process and product assessment, three winning interdisciplinary teams were awarded with gold, silver, and bronze medals as a boost to increase awareness toward a sustainable future.

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SUMMARY The presented laboratory assignment involves the identification of seven different plastic sticks meant for the polymer processing industry and the formulation of five polymers used as basic materials in processed plastics. Indirectly, the focus on the challenging interdisciplinary collaboration of chemistry undergraduates and engineering students with a minor program in chemistry is an added value to this laboratory experiment as a supporting part of their polymer chemistry and chemical technology courses. Pedagogically, the setup of the assignment goes beyond the experiment. The outcome is presented at a grand finale with a scientific poster presentation where the students exchange their experimental findings. The award-winning teams are selected by objective self- and peer assessment. Conclusively, the teaching team, the third party in the assessment procedure, gets a variety of information, i.e., an assessment of skills of chemistry undergraduates and engineering students with a minor in chemistry as well. Moreover, the described teaching strategy motivates students with quite different points of view and interest in chemistry to cooperate and thus pursue not only their own goals but also their common interest.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.7b00284. The lab assignment (identification of a series of plastic sticks; manual to identify plastic sticks); the lab experiment (identification of seven plastic sticks; synthesis of five polymers); answers to the questions; materials used for the identification of seven plastic sticks and synthesis of five polymers; reagents used for the identification of seven plastic sticks and synthesis of five polymers (list of seven polymers (sticks); list of reagents with hazard and precaution statements); guidelines for making a scientific poster; poster design; assessment of polymer posters (product assessment of polymer posters; process assessment of polymer posters); student observations (PDF, DOCX)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Wanda J. Guedens: 0000-0001-8709-9856 Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Guedens, W.; Reynders, M. Science Outreach Programs as a Powerful Tool for Science Promotion: An Example from Flanders. J. Chem. Educ. 2012, 89 (5), 602−604. (2) Hasselt University. http://www.uhasselt.be/Faculties (accessed October 2017). E


Identification and Formulation of Polymers: A Challenging

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