Bioplastics in the General Chemistry Laboratory: Building a Semester

Article Cite This: J. Chem. Educ. XXXX, XXX, XXX−XXX

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Bioplastics in the General Chemistry Laboratory: Building a Semester-Long Research Experience Alexandra M. Ward and Graeme R. A. Wyllie* Department of Chemistry, Concordia College, Moorhead, Minnesota 56562, United States

J. Chem. Educ. Downloaded from pubs.acs.org by EAST CAROLINA UNIV on 03/14/19. For personal use only.

S Supporting Information *

ABSTRACT: We report here a second semester general chemistry laboratory project themed around chitosan-alginate bioplastics. With increasing awareness of plastic pollution in the environment and the awareness of the importance for materials which are either made from renewable resources or are biodegradable, this topic provides a relevant opportunity to engage students. The semester-long laboratory experience has students working in teams first to complete a series of core experiments which provide a foundational experience in preparing and testing chitosan-alginate bioplastics prior to developing and implementing a project in a direction of their own choosing. The benefit of these student directed research projects can include enhanced engagement and can allow development of skills such as experiment design, data collection and analysis, written and oral dissemination, and critical thinking. We describe here both the core module in bioplastics which has the potential to be incorporated as a self-contained module by interested parties along with the way in which this is expanded to incorporate the student directed projects. KEYWORDS: First-Year Undergraduate/General, Curriculum, Laboratory Instruction, Polymer Chemistry, Collaborative/Cooperative Learning, Hands-On Learning/Manipulatives, Inquiry-Based/Discovery Learning, Materials Science, UV−Vis Spectroscopy, Undergraduate Research

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INTRODUCTION The general chemistry laboratory is traditionally the first undergraduate chemistry laboratory experience for many students; the curriculum usually consists of expository experiments where students carry out verification laboratories following well-defined stepwise procedures. This is commonly where students develop practical laboratory skills in a number of areas such as solution preparation, use of volumetric glassware, creation of calibration plots, titrations, and laboratory safety, while using instruments such as spectrometers. However, laboratory courses should also develop crucial transferable soft skills employers seek such as oral and written communication, teamwork, and critical thinking. Students may have limited opportunity to hone soft skills in traditional expository laboratory experiences, but these can be significantly improved through in-class research experiences,1,2 which deviate from the traditional expository laboratory and often give students the opportunity to be creative and integrate ideas from both lecture and scientific literature, thereby increasing student ownership of their work as well as providing first-hand experience with the messiness that can occur with unscripted laboratory work. Additionally, in-class research experiences can improve the student’s experience compared to the traditional expository experiments, especially if the research project incorporates real world applications or is an extension of ongoing research at the institution.1−3 © XXXX American Chemical Society and Division of Chemical Education, Inc.

We report here the results of the redesign of our second semester general chemistry laboratory around the theme of bioplastics formed from two readily available biopolymers: chitosan and alginate. Students prepare, characterize, and explore the properties of bioplastics in a series of core experiments prior to developing and implementing a research project based on these materials. These low cost experiments were designed to be carried out within the time and resource limitations of a general chemistry laboratory. In addition, the topic of bioplastic showcases a number of aspects of green chemistry,4 specifically the use of renewable starting materials, benign synthetic conditions, and generation of minimal amounts of hazardous waste. The core experiments without the research project could also be utilized as a self-contained four week module on the theme of bioplastics. The selection of chitosan-alginate bioplastics as the basis of a second semester general chemistry laboratory course has been successful in a number of areas; with increasing public awareness of the problems of plastic pollution and the poor degradation characteristics of petroleum plastics, this issue serves as an ideal example of a timely challenge faced by scientists in the real world. The topic is well-suited for the Received: August 15, 2018 Revised: February 26, 2019

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DOI: 10.1021/acs.jchemed.8b00666 J. Chem. Educ. XXXX, XXX, XXX−XXX

Journal of Chemical Education

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session covering the course syllabus and safety (week 0), a single week was devoted to a spectroscopic study of the kinetics of methylene blue degradation,8 which gave students experience in kinetics and refreshed spectroscopy theory and practice (week k). Students were given their choice in forming three-person research teams which remained together throughout the rest of the semester, all of which was devoted to the bioplastic research project. The initial 4 weeks of the bioplastic project comprise the core experiments, which introduce students to the practical aspects of chitosan-alginate bioplastics, and were supplemented by exercises introducing the relevant theory at an appropriate level for general chemistry students. These 4 weeks were also designed to be able to be incorporated as a self-contained module for those not wishing to adopt a semester-long version of this work; all experiments were designed to fit into the constraints of a weekly 3 h laboratory period. The remainder of the semester was dedicated to the student research projects where students develop and execute a project of their choosing related to the theme of chitosan-alginate bioplastics. The results of the student projects are disseminated in the form of both an oral presentation and a written paper. This project was successfully implemented in the spring of 2018 for six separate laboratory sections with approximate enrollment of 15−18 students per section. Online resources (Moodle course management software) were used to facilitate dissemination of data within and among sections allowing students access to larger data sets, and promoting the sharing of work on related research projects across sections. A more detailed overview of the semester can be found in the Supporting Information along with all student handouts, instructor notes, sample results, assessment data, and materials describing a condensed summer school version.

practical considerations of the general chemistry laboratory with respect to student abilities and knowledge, as well as utilization of resources that are commonly available. Furthermore, it provides a rich array of potential directions for student research projects and exposes students to areas such as polymer chemistry, sustainability, and materials science. The selection of bioplastics as the overarching theme of this project coincides with an increased emphasis from the American Chemical Society to teach polymers and materials chemistry, areas traditionally not encountered in general chemistry.5−7

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SEMESTER OVERVIEW General Chemistry at Concordia College is a two semester course in which students take lecture and a 3 h weekly laboratory concurrently. Laboratory setup and other organizational responsibilities are handled by the faculty laboratory coordinator; each laboratory section is taught by a faculty member aided by a student teaching assistant. Due to the fact that incoming students possess a wide disparity in practical skills, the first semester laboratory is designed to ensure all students possess the same fundamental skills at the end of first semester leading into the second semester. Laboratory topics are linked to lecture with the relevant material generally introduced in the lecture and then expanded upon in the laboratory. By the end of the first semester, students are proficient in the basic laboratory skills and learn additional skills such as notebook keeping, formal writing, and safety. The majority of the second semester laboratory course was redesigned to focus on bioplastics (Table 1); this necessitated Table 1. General Chemistry II Semester Overview Week

Laboratory

0 ka 1 2 3 4 5 6−10 11

Syllabus/safety Kinetics of methylene blue Bioplastic I: film preparation/bioplastic terminology Bioplastic II: characterization Bioplastic III: color release Bioplastic IV: tensile strength Formal research proposal presentation Research projects Final presentation/paper due

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CHITOSAN-ALGINATE BIOPLASTICS

Chitosan

Chitin, a homopolysaccharide consisting of monomeric units of N-acetylglucosamine, is the primary component of the exoskeletons of insects and crustaceans. While structurally strong, the potential uses are limited by manufacturing complications and poor solubility. Chitosan, a heteropolymer, is a more functional derivative formed through partial deacetylation of chitin (Figure 1). The determination of the extent of this deacetylation was recently reported on as the basis of a multiweek introductory undergraduate laboratory project.9 If treated with a weak acid such as acetic acid,10−12 or lactic acid,13 the amine moiety in chitosan is protonated, enabling

a k refers to a stand-alone kinetics experiment, separate from bioplastic project.

disconnecting from the material being taught in the lecture sections which remained unchanged by the introduction of the bioplastic projects. In the laboratory, after an introductory

Figure 1. Reaction scheme showing the conversion of chitin to chitosan. In chitosan, the subunit labeled X is N-acetylglucosamine, and the subunit labeled Y is glucosamine. Commonly, 70−90% of the subunits are the deacetylated glucosamine in chitosan. B



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Figure 2. Two chains of chitosan cross-linked by hydrogen bonding (illustrated by the red dotted line).

Alginate has applications in many biomedical areas23 such as implantable devices,24 bone tissue engineering,25,26 tissue sealants,27 drug delivery,26,28 as well as materials based applications such as conductive nanowires.29

hydrogen bond formation with hydroxyl groups on adjacent chains (Figure 2). These weak interactions, known as crosslinking, allow thin chitosan films to be manufactured.11 There has been abundant research into the potential applications of both chitin and chitosan,14−16 more specifically, applications in surgical wound dressing,17 pharmaceutical delivery systems,18 and three-dimensional molds.19

Chitosan and Alginate

Combining both chitosan and alginate in a two-component cross-linked system leads to materials possessing properties different from those of the respective parent systems. In addition to the cross-linking previously discussed, the protonated amine of chitosan can also interact with the carboxylate moiety on the alginate strands (Figure 5). These types of cross-linking interactions lead to the formation of a three-dimensional cross-linked network of chitosan and alginate strands,13,30 with the resulting bioplastic forming the basis of the semester-long project.

Alginate

Sodium alginate is a heteropolymer extracted from various seaweeds and algae. Similar to chitosan, alginate is a polysaccharide composed of two different base units, guluronic and manuronic acid (Figure 3), with the ratio of these dependent on the extraction source.

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CORE EXPERIMENTS The core module (weeks 1−4) was designed to educate students in both the theory and laboratory techniques associated with bioplastics. Experiments on preparation and characterization of chitosan-alginate bioplastics were combined with exercises reviewing the relevant scientific literature studies and items from the related popular press. These exercises are designed to introduce students to not only the chemistry of these materials, but also their significance in the modern world. In the first week of the core experiments, students prepare bioplastic samples following an optimized protocol designed to be carried out in a single 3 h laboratory period. The films cure over the course of the following week and are subsequently characterized. Properties pertaining to release of a doped material, along with tensile strength, are investigated in the following weeks. Chitosan-alginate bioplastic films are prepared by having students combine chitosan and alginate powders in RO (reverse osmosis purified) water followed by a two-step cross-linking procedure which starts with addition of 1% (v/v) lactic acid. The viscous mixture is poured into 10 cm Petri

Figure 3. Two different subunits of alginate, with X being guluronic acid, and Y being manuronic acid.

Addition of a divalent cation, such as calcium, results in formation of strong interactions between guluronic acid units on adjacent chains, with the cation forming the center of the egg-box model.20,21 Addition of sufficient cations forms a cross-linked hydrogel structure (Figure 4) which has the ability to trap additional molecules such as food color between the strands.22 C



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Figure 4. Cross-linking of adjacent alginate strands illustrating the egg-box motif created through the interaction of calcium ions (shown in yellow) and guluronic acid units.

color is seen in the supernatant, indicating the successful incorporation of the blue food color. To measure color release in the laboratory, food color impregnated bioplastic strips are immersed in various solutions, and the absorbance at 631 nm (λmax for Blue No. 1) is measured over time. In a laboratory section, each team was required to carry out three concurrent 2 h color release studies using films immersed in RO water, a sodium chloride solution (the concentration of which varied for different groups in the laboratory section), and a third solution of their choosing. Film swelling and color release were strongly dependent on solution environment; in these directed studies the most robust relationship originated from varying sodium chloride concentrations with the extent of color release increasing as sodium chloride concentration increased, as illustrated in Figure 6. The increased rate of release of the ionic food color molecules from the bioplastic in the presence of increasing salt concentration may be attributed either to changes in the bioplastic structural integrity as calcium ions are replaced by monodentate sodium ions or through changes in the ionic potential of the solution, a process attributable to the Donnan equilibrium.31

dishes, and 0.1 M calcium chloride solution is added to create a hydrogel mixture which will cure over the following week. Coincident with the film preparation, an assignment was distributed that required students to explore current scientific and popular press literature associated with bioplastics. The information gained by students from these assignments was supplemented with a specific handout describing the chemistry of chitosan and alginate, both of which are available in the Supporting Information. The second laboratory period was devoted to film characterization and can also be used for preparing additional films. Characterization was primarily focused on measurement of relevant dimensions (thickness and diameter), mass, and observations on uniformity across the disc. The cured 10 cm diameter ∼0.12 mm thick films often have a thicker rim and are strong but rigid, tending to break under minimal torsional stress, though they can still be cut using scissors to give strips for subsequent testing of color release and tensile strength. Model Pharmaceutical Delivery

As previously discussed, chitosan and alginate are currently being used as drug delivery systems.18,26,28 To better model this within the constraints of the general chemistry laboratory, a pharmaceutical substitute was required and should be inexpensive, nontoxic, and easily quantifiable through common laboratory instrumentation such as UV−vis spectroscopy. Therefore, the compound used was commercial blue food coloring, otherwise known as Blue No. 1. Furthermore, the blue food color is easily incorporated into the bioplastics during film synthesis by addition during the stirring process. After calcium chloride solution decantation, only minimal

Tensile Strength

Investigating practical and material based aspects was a key stipulation behind this study to introduce materials chemistry; students were required to determine the tensile strength of the bioplastic strips using a modification of a standard literary procedure.32 While traditionally strips are cut in a dog-bone shape, the use of superglue instead of clamps to attach samples to the assembly allowed students the easier option of cutting D



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Figure 5. Schematic representation of the chitosan-alginate bioplastic showing the various interactions between chains. Chitosan chains are denoted with the letter C, and alginate chains by the letter A. Hydrogen bonds are shown by red dotted lines and calcium ions highlighted in yellow.

Supporting Information, with the most noticeable result being that the bioplastics possessed a very high tensile strength. Concerns that the superglue would alter the properties of the bioplastics were not realized when it was observed that the strips consistently failed in the middle portion between the metal pieces and not in the region to which superglue was applied. The messy nature of this data offered students an opportunity to work with authentic data and provided experience in data analysis, especially in identifying and removing outliers. Standard characterization of polymers and related materials often relies on techniques not commonly encountered in the general chemistry laboratory, and the determination of the tensile strength of bioplastics provides a valuable example of these techniques. At the end of the core experiments, students have gained familiarity with both the practical and theoretical aspects of chitosan-alginate bioplastics. All student teams were tasked with writing this material up for inclusion in their final paper which was graded and returned with feedback and comments

strips in a rectangular shape. The sample strip was glued to the metal attachment pieces using superglue and then the assembly suspended using fishing line. A spring scale was attached and pulled down until the bioplastic broke; the apparatus is shown in Figure 7. Each team member had a different role in the process: one would support the apparatus, another would pull the spring scale, and the last person would film the spring scale to more accurately determine the point at which the plastic broke. Tensile strength was calculated using eq 1. Class data was compiled and available to all students. tensile strength =

breaking mass (kg) cross‐sectional area (cm 2)

(1)

The samples of the bioplastic generally broke with no visible signs of deformation prior to breaking, though tensile strength was often significantly reduced in cases where the strips were damaged during cutting. Examples of this data are shown in E



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Figure 6. Graph illustrating the color release of Blue No. 1 from bioplastic strips in various sodium chloride solutions.

designed to build upon the core experiments but allowed students the freedom to explore a particular area of interest with the majority of the projects falling into the categories shown in Table 2. Project ideas required approval by the Table 2. Categories and Examples of Student Research Projects Category

Example

Release Uptake Degradability

Color release in hydrochloric acid; release of salicylic acid Commercial dye uptake Film degradation in either potting soil or solutions of varying salinity Changing chitosan and alginate ratios; addition of starch Relationship between thickness and tensile strength

Composition Other

instructor or laboratory coordinator prior to implementation, and as part of the process, a proposal was presented orally to the laboratory section and instructor in week 5. Approved proposals had to take into account peer and instructor feedback before submission to the online class resources. In future years, during proposal submission, students will also have access to the final laboratory reports from previous student teams, which will serve as a body of peer-created and reviewed literature. Additional information on student project guidelines and examples are given in the Supporting Information. In weeks 6− 10, students design, execute, and collect data from their experiments. Access to the laboratory on their projects is restricted to their designated laboratory period. To encourage students to feel they are part of a broader research community, they are required to post weekly in a class forum which is accessible by peers in all sections of the laboratory. Postings are framed around four simple questions: • What was the goal of today’s laboratory period? • What did you actually do in the laboratory today? • What did you learn from today’s laboratory period? • What is the goal for the next laboratory period? This forum is designed to allow students working on related projects, especially those of different laboratory sections, to follow the progress of similar projects and share successes and failures. The role of the instructor also changes significantly to

Figure 7. Example of the assembly used to determine tensile strength.

from the course coordinator well before the deadline of the final report.

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STUDENT RESEARCH PROJECTS Following the core experiments, students spent the remainder of the semester on their research project. These projects were F



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Figure 8. Results of the pre- and postproject survey assessing student familiarity with various topics. The data represents the responses of 90 students; error bars represent the standard deviation for a given question.

Figure 9. Survey questions and results addressing the confidence level of students to follow a procedure or modify a procedure. While the gain in confidence to follow a step-by-step procedure is not large, students have had significant exposure to this type of laboratory in the first semester curriculum. The data represents the responses of 90 students; error bars represent the standard deviation for a given question.

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HAZARDS Students should wear eye protection and follow the appropriate laboratory safety guidelines at all times. The majority of the materials used in this project are nonhazardous and can be disposed of safely down the drain. Standard precautions should be used if students work with hazardous materials such as acids and bases on their research project.

act more akin to that of a research advisor as well as to provide assistance in interpreting complex results and theory. Student work on the research projects culminated in the sharing of their work, in both written and peer reviewed oral format in week 11. The project gave students the opportunity to become familiar with many aspects of the research experience including literature review, experiment design, data analysis, troubleshooting, and multiple forms of dissemination. Additionally, there are many potential directions that the student bioplastics project can take, thereby allowing students to tailor their work to specific interests and increase the potential for engagement. Project cost after initial purchase of chitosan and alginate was also minimal as a majority of materials requested by students were readily available from the department stockroom.

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ASSESSMENT Students were asked to complete an IRB approved pre- and postproject survey. Both surveys contained 17 questions asking students to rank their comfort/familiarity level with a particular topic or the extent of instruction and scripting provided with the laboratory experience. The last question was open ended to allow students to leave additional comments or remarks. The postproject survey also included an additional six questions G



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regarding the usefulness of several resources that were implemented throughout the semester. All responses were ranked on a 1−5 Likert scale with 5 being the most positive response, and 1 being the least. The full survey and averaged responses are available in the Supporting Information. Overall, student responses on all areas surveyed were positive showing increases from the pre- to the postsemester surveys. Traditionally, topics such as polymers and bioplastics are not encountered in general chemistry; through the implementation of this project, strong gains were seen in these topics, as illustrated in Figure 8. One of the primary goals in implementing this bioplastic project was to provide general chemistry students with a research experience which included unscripted laboratory work. Figure 9 illustrates the gains in student comfort level working with three differing types of procedures. The strong gains in the two less scripted examples show the benefits of providing students with a research experience such as this. Finally, it was observed by the faculty that there were palpable increases in student engagement and enthusiasm for the project especially compared to the atmosphere in the first, more expository style, semester laboratories.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.8b00666. Student handouts, instructor notes, and sample data for the core experiments; CAS registry numbers and safety notes for all materials used in this project; instructor notes and examples of student research projects; and survey of student attitudes with full results (PDF, DOCX)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Graeme R. A. Wyllie: 0000-0001-8661-3198 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors would like to thank the Office of Undergraduate Research, Scholarship, and Creative Activity at Concordia College for funding this research and Kelly Noah for her assistance in collecting a portion of the sample data included in the Supporting Information. The authors would especially like to thank the students, instructors, and teaching assistants of the spring and summer General Chemistry II Laboratory courses for their enthusiasm and participating in this project.

CONCLUSION We report here the results of the implementation of a General Chemistry II Laboratory course based on chitosan-alginate bioplastics. The use of bioplastics as a theme coincides with increased public awareness of the environmental concerns associated with traditional plastics and exposes students to areas not normally encountered in general chemistry, namely, polymers and materials science. To create a firm foundation upon which student teams can build for their own research project, a core four week module covering the fundamental practical and theoretical aspects of bioplastics was created. This module, which can also be used as a stand-alone resource, was specifically designed to work within the skill set of the students and the framework of the weekly general chemistry laboratory and also possesses the advantages of both being low cost as well as generating minimal hazardous waste. Following the conclusion of the core experiments, student teams are given the opportunity to develop and implement a multiweek research project of their own choosing within the framework of chitosan-alginate bioplastics. This creates opportunities for the general chemistry students to develop their skills in experiment design, data collection and analysis, and written and oral presentation, something they may not get the opportunity to experience in a traditional expository laboratory course. Overall feedback of the semester-long project from both a formal assessment instrument and anecdotally in the laboratory was extremely positive. Students greatly appreciated the environmental relevance and real world applications of bioplastics, which contributed to the positive student engagement. As seen in the assessment data, students became more confident in their abilities to “think like a scientist”, by becoming more confident in their abilities to adapt procedures, plan and troubleshoot experiments, and utilize different techniques to answer a central question on a week-by-week basis. All of these aspects discussed made for a successful research based project that was able to engage students while accomplishing the teaching goals of the general chemistry laboratory.

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Bioplastics in the General Chemistry Laboratory: Building a Semester

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