Polymers and their relevance to society

People have always used polymers, especially those that come from plants and animals, such as wood, rubber, cotton, wool, cellulose, and silk. Other polymers are fundamental for biological processes in plants and animals, such as proteins, enzymes, starch, and cellulose. According to IUPAC, polymers are macromolecules which have high relative molecular mass and “the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass” (^{McNaught & Wilkinson, 1997}, p. 2289). And with the contribution of chemistry, alternative materials were found - for instance, new synthetic polymers with adequate properties for daily use in medicine, cosmetics, pharmaceutics, packaging, etc. This strong demand for new polymers was guided by factors such as their durability, tensile strength or resistance to degradation.

In general, plastics and fibers are mixtures of several substances whose main constituent is a polymer. However, there is a vast set of substances added to plastics that grant particular properties to them. Therefore, plastics are inexpensive, long-lasting and resistant, with a low density, flexible or rigid, easily moldable and colored in several designs, and efficient electrical and thermal isolators. These properties, together with polymers’ low production cost, make them so widely used (^{Brinson and Brinson, 2008}). As a consequence, they produce large quantities of non-degradable urban waste, which leads to an environmental problem. Nevertheless, this disadvantage has been the driving factor in boosting the research on biodegradable polymers, whether natural or synthetic (^{Williams and Hillmyer, 2008}; ^{Garrison et al., 2016}).

Polymers in a chemistry curriculum in school year 12

The Chemistry subject in school year 12, as a pre-university course, should present a contemporary vision over relevant aspects in the knowledge of chemistry - defining different scientific views of interpreting the world, so as to proceed in the direction of a more profound interpretation in a higher education level.

^{Cersonsky et al. (2017)} affirm that only 12 states of the USA address polymer-related concepts in pre-university science curricula and that “California is the only state that introduces polymers before high school”. This could be an indicator of the low representation of polymers in Chemistry’s curricula, and so an effort should be done to highlight polymers’ chemistry taught to high school students.

In 2014, in Portugal, new standards were implemented for the school year 12 Chemistry curriculum (^{Fiolhais et al., 2014}). Thus, the curriculum is organized in three domains and its respective subdomains, as presented in Table 1. Regarding this article’s objective, we highlight the domain “Plastic, glass and new materials”, as well as its three subdomains (^{Martins, 2004}; ^{Fiolhais et al., 2014}): 1) “Plastic and polymeric materials” - which aims to portray polymers as a class of materials consisting of macromolecules, distinguishing natural and synthetic polymers; 2) “Synthetic polymers and the industry of polymers” - where students should be able to understand how to obtain synthetic polymers and recognize that their structure determines their properties; 3) “New materials” - aiming for the recognition of some biomaterials and correspondent applications, as well as the advantages and limitations when using sustainable materials. Besides that, it is also important to refer that previous to this course, Organic Chemistry has a residual presence in Portuguese Chemistry curricula. Only nomenclature of alkanes and its derivatives and introductory concepts about functional groups were taught previously in year 12. This Chemistry course for school year 12 has a weekly workload of two classes during the school year, in a total of about one hundred classes, of 90 minutes each. The course program recommends that one of the weekly sessions is presented as a practical laboratory lesson, in an adequately equipped laboratory.

Teaching polymer concepts through inquiry-based approach

In Portugal, the Chemistry program for school year 12 has a national scope and allows for “the free choice of tasks, exploring strategies and teaching methodologies according to the students’ interests and development, an aspect that may be considered as a flexibility method, aiming at a better adjustment to students’ interests and a motivational trigger for the study of Chemistry” (^{Martins, 2004}). Considering this idea of flexibility and adjustment of pedagogic strategies that the Portuguese program allows, teaching polymer concepts in school year 12 Chemistry courses through inquiry-based approach could be an effective possibility (^{Mc Ilrath et al., 2012}).

According to ^{Abd-El-Khalick et al. (2004}), ‘Inquiry’ has become a perennial and central term in the rhetoric of past and present science education reforms. “Students’ profile on leaving compulsory education” (^{Martins, 2017}) and “Essential Learnings - Chemistry, year 12 (^{Direção Geral de Educação, 2018}) are frameworks developed by the Portuguese Ministry of Education that also meets (^{NRC, 2000}; ^{NRC, 2012}) guidelines. Based on that, many researchers (^{Avraamidou and Zembal-Saul, 2010}; ^{Cuevas et al., 2005}; ^{Howes et al., 2009}; ^{Liang and Richardson, 2009}; ^{Smolleck et al., 2006}) mention six essential features of classroom inquiry that apply across grade levels: i) learners address scientifically oriented questions; ii) they plan and carry out investigations to gather evidence; iii) they give priority to evidence in responding to questions; iv) they formulate explanations for evidence; v) they connect explanations to scientific knowledge; vi) and they communicate and justify explanations. NRC describes inquiry as “a multifaceted activity that involves making observations; posing questions; examining books and other sources of information to observe the existing evidence; planning investigations; reviewing the existing evidence in light of experimental evidence; using tools to gather, analyze and interpret data; proposing answers, explanations and predictions; and communicating results” (NRC, 2012) Several studies support the effectiveness of inquiry-based as an instructional approach. ^{Alfieri et al. (2011)}, for example, performed a meta-analysis comparing inquiry to other forms of instruction, such as direct instruction or unassisted discovery, and found that inquiry teaching resulted in better learning. A meta-analysis by ^{Furtak et al. (2012)} incorporated studies using a broad range of terms to describe inquiry-based learning (e.g., mastery learning, constructivist teaching); they reported an overall mean effect size of 5 in favor of the inquiry approach over traditional instruction. Some research has shown favorable results when applying an inquiry-based approach to the teaching of polymers, as one can see in ^{Noiwong and Phinyocheep (2012)} who applied a guided-inquiry laboratory exercise on tensile properties of composite polymers based on natural rubber to 94 secondary students in their Chemistry courses. ^{Mc Ilrath, Robertson and Kuchta (2012)} also had encouraging results when they developed and implemented a lab activity that “intended to provide a new route to introduce students to polymer science through a hands-on, inquiry-based activity in which students synthesize a polymer and investigate its mechanical properties”.

Based on the framework proposed by ^{Pedaste et al. (2015)}, it is recommended that the inquiry-based learning process should begin with an orientation phase, where students not only get an idea about the research topic but are also introduced to the problem to be solved. In the following step, students are supposed to identify the key concept to be studied in the inquiry-based learning process, for which they have different possibilities: through a hypothesis-driven approach or a question-driven approach. Inquiry-based learning begins with orientation, flows from conceptualization to investigation, and usually ends with the conclusion phase. The discussion phase (which includes communication and reflection) is potentially present at all points during inquiry-based learning and connects all the other phases, because it can occur at any time during (discussion in-action) or after inquiry-based learning when looking back (discussion on-action) (^{Pedaste et al. 2015}).

In this article, we present an inquiry-based activity in which part of the orientation and discussion phases were implemented through a role-playing strategy. According to ^{King and Janis (1956)}, role-playing can exert a marked influence on the individual’s private opinion. Besides, the clear verbalization induced by role-playing tends to increase the effectiveness of a persuasive communication. Many examples of role-playing use in science education were found in literature (^{Cook, 2014}; ^{Freire et al., 2016}). This strategy helps students to “expand the diversity of arguments presented and to make a more direct link to real-world discourse” (^{Smythe and Higgins, 2007}) allowing them to develop communication skills and understand the importance and relevance of chemistry within our society. The implemented inquiry-based activity was named “Plastics inside and outside of water” and it was used in order to introduce the subdomain “Plastic and polymeric materials” of the school year 12 of the Portuguese Chemistry curriculum. The activity was divided in two parts: i) a role-playing debate - in which the idea was to increase the students’ awareness related with the fact that the development and the large scale production of plastics promoted a paradigm shift regarding the use of these materials, which, being highly promising, led to an increase in the total plastics mass present in the countries’ urban solid wastes (^{Geyer et al., 2017}) - and (ii) a laboratory component of identification of plastics, based on a simplified scheme for plastics identification.

Centered on that inquiry-based activity, we tried to answer the following questions:

Participants and Setting

This study involved 20 students from school year 12, (13 females and 7 males, with ages ranging from 17 to 18 years old), with pre-university background in science and technology, and three Chemistry teachers - who actively planned, developed and implemented the inquiry-based activity.

The inquiry-based activity was a completely new approach for students since they never had done similar activities before. The interaction with the students took place during two Chemistry classes: one, 45 minutes long (role-playing debate), and another, 90 minutes long (research and laboratory work).

Procedure and materials

Based on the framework proposed by ^{Pedaste et al. (2015)} the inquiry-based activity, named “Plastics inside and outside of water” (see Supplementary Material), was created and falls into two parts: a role-playing debate and laboratory work. In order to make science education relevant to the students, the activity was integrated in a relevant context-based scenario, bridging the gap between learning in school and everyday life (^{Gilbert, 2016}; ^{Stuckey et al., 2013}). Figure 1 presents ^{Pedaste’s et al.(2015)} framework adaptation named “Plastics inside and outside water” inquiry-based activity. The first part is an orientation phase, where students not only get an idea about the topic to be investigated but are also introduced to the general problem to be discussed. The discussion phase (which includes communication and reflection) is also present.

Figure 1  ^{Pedaste’s et al. (2015)} framework adaptation for “Plastics inside and outside water” inquire-based activity 

A set of news from online magazines and newspapers were presented to students with headings such as: “Plastic hands or parts for airplanes, the future is there, with 3D printing” and “What if biodegradable plastics are, after all, a huge lie?”. This first part of the inquiry-based activity was driven by a question, “Should plastics be banned, or should they be used more rationally?” and the idea was to actively involve students in a discussion, based on arguments for and against the use of plastic.

The 20 students were randomly divided into six small groups (3 to 4 students) to collect, structure and organize arguments for and against each of the positions, inspired by the news from online magazines and newspapers quotes. Then the teacher attributed the defense of the “banish plastics” position to three groups and the “use rationally” position to the other three groups. The students spontaneously joined in two large groups according to their positions. Afterwards, the six small groups elected the representatives to defend their position and organize a pros and cons role-playing debate, that was moderated by the teacher.

Following that, the second part of the inquiry-based activity called “Plastics inside and outside of water” was implemented and faced students to the following problematic scenario: […] the school canteen intends to implement a selective collection system that includes the separation of different types of plastics. In this case, it is useful to carry out an analysis of the plastics present on each part of the water bottle in order to obtain its chemical identification. Characterizing properly a plastic can be a useful contribution to promote recycling. Based on that scenario, the challenge launched to school chemistry students was: “How can we identify different plastics present in a water bottle?” Despite Portuguese schools provide drinkable water for free to its students, the purchase of bottled water is a relatively common practice in the educational community. Therefore, the idea of evoking that buying scenario was created to raise awareness about economic, social, and environmental problems related to plastic overuse and the incorrect disposal of these residues, besides the learning goals proposed to this activity. Therefore, students were invited to carry out an initial research in order to know the meaning of the existing recycling codes for plastics and discuss the recycling process of plastics and the final product quality. Once they finished that part, students could start planning a laboratory activity that would allow them to identify different plastics present in a water bottle. For this task, students needed to consider the information of the systematic scheme for plastics previously selected by the teacher. There are schemes for plastics identification which involve a sequence of simple tests, such as density tests, dissolution tests, or heating tests, that identify different types of plastics, including some of the most common ones in packaging (^{Hughes et al., 2001}; ^{Harris and Walker, 2010}; ^{Kolb and Kolb, 1991}). In our case, the scheme should be able to help the students identify, among others, PP (polypropylene), HDPE (high-density polyethylene) and PET (polyethylene ethylene terephthalate) plastics, as they are present in water bottles, as presented in Figure 2.

Figure 2 Types of raw material plastics which form a water bottle, cap and label (^{Chang & Goldsby, 2014}). 

Thus, we selected a simpler scheme involving only density tests (^{Hughes et al., 2001}) that could be used by students working in small groups, without the need for many resources and involving the use of less dangerous procedures and reagents. It is important to note that polymers’ physical properties, such as density, and the chemical structure of the polymers PE-HD, PET, and PP, were unknown to students. They needed to take into account in the activity’s planning. As they finished planning, the students discussed the plan with the teacher, who validated it using some guide questions, such as, “How big is the plastic sample that you are going to cut?, What is the first test that you are going to do? What test would you take next? How many tests are needed to identify PMME?”. When the discussion with the teacher finished, students groups started to perform the activities.

According with the framework proposed by ^{Pedaste et al. (2015)}, in these steps, students should identify the key concept to be studied and the problem to be investigated and solved in the inquiry-based learning process. In this phase they are moving from conceptualization to investigation and at the end they reach the conclusion phase. These phases also have several moments of discussion.

Students’ arguments in favor and against the use of plastics (RQ1)

During the role-playing debate, the arguments for and against the use of plastics were discussed. Their categorization is presented in Table 2. On the one hand, students presented arguments based on features of plastics that constitute the advantages of their use - such as their durability, several designs and colors, flexible or rigid textures, diversity of application contexts, etc. - to underline the existence of these polymers and defend the continuity of its use.

To emphasize these ideas, an example of students’ argument used in this discussion is highlighted: “rational and progressive reduction of the use of plastics because it is: light, flexible and easy to recycle material; important to many sectors of society; economically profitable since it has a low production cost”. On the other hand, arguments were also presented that aim at some pro-activity, such as the need for actions to raise public awareness and regulate the use of plastics.

According to students, it is necessary a clear regulation of the plastics use . As an example, they presented the case of cosmetics industry, that has been sensitive to the consequences that may arise from microplastics, implemented a kind of self-regulation of their practices. We highlighted an example of students’ arguments used to support these claims: “it should be immediately forbidden it’s use in many sectors of activity like in cosmetics. Swabs, bags and other plastic objects should be replaced by others made by biodegradable materials”.

In the case of arguments against the use of plastics, the consequences of the use underlined by students were the enormous waste of plastics and the consequent environmental impact. Alternatives to plastics such as paper - as emphasized by students “Plastics can be replaced by other materials like paper, for example” -, developing glass and new materials have been referred as a promising future alternative to the use of plastic, such as the “replacement of plastic bottles by an algae substrate” was presented by a group of students. These alternatives were framed within a past social history when plastic was absent as a common material.

One of the actions considered necessary is the increase of the production of biodegradable plastics. The vast majority of plastics are produced from fossil fuels with monomers such as ethylene (C₂H₄) and propylene (C₃H₆) and are not biodegradable materials.

As a result, there is successive accumulation of these polymers either in their own sites, in landfills or in the environment. The only way of permanent disposal of these wastes is by thermal treatment such as combustion or pyrolysis. Therefore, the almost permanent contamination of the environment through the accumulation of plastic waste is a growing concern, although, as mentioned by the students, population have not been sensitized to this issue. It is interesting to point out that the category actions required emerged in both position cases: in favor of the use of plastics and against the use of plastics. In each case, they presented apparently different arguments; however, they have a strong overlap among them, such as the case of awareness campaigns.

Even when the class finished, the role-playing debate of arguments for and against the use of plastics continued out of the classroom space.

Students’ engagement in scientific-oriented activity (RQ2)

The class was divided into six working teams. Students researched plastics online, using their smartphones and they were able to find the meaning of the recycling codes 1 through 6 for different types of plastic; the last code, 7 (see Figure in Supplementary Material), raised a greater challenge, and not all students were able to identify it as «Others». Based on the activity text, students understood and debated as a group about how the main raw material used in recycling may affect the quality of the final product - highlighting the fact that, if different plastics are collected and recycled together, the final product will have a low quality and its use will be limited. One of the groups mentioned the possibility that plastics may be contaminated, which will affect their value.

This first research phase was important to explain the use and need of laboratory to identify plastics. A bottle of water contains at least three types of plastic (in the bottle itself, in the cap and in the label). In this activity, students had to use the available lab equipment (scissors; tweezers; two 50 ml beakers; a wash bottle with distilled water; six required solutions (for testing) and they did a systematic analysis or find the identification key - based on density tests: the plastic sample will float or sink on a given solution, depending on its density - in order to plan the identification of the three plastic samples.

Students planned the activity and once it was validated by the teacher, students began their work. The expected results were: bottle - PET (r = 1,39 gcm^-3); cap - PE-HD (r = 0,95-0,97 gcm^-3); and label - PP (r = 0,90-0,91 gcm^-3).

Within this inquiry-based activity, students were challenged to construct a table to record the results obtained, which included information on the analyzed plastic samples. It was expected that year 12 students had experience in construct tables to record the results. However, in order to help their work, some ideas and tips were given by teachers, but students did not follow regularly these instructions. For that reason, data recorded by students wasn’t consistently presented (as shown in Table 3.a). However, Table 3.b demonstrate a good example of students’ records, with an accurate and coherent presentation.

Having correctly identified the type of plastic in the bottle and cap, most of the students affirmed that the results of the bottle label identification (PMP) (r = 0,868 gcm^-3) didn’t match the true material (PP). Only a minority of students reflected more deeply on the analysis of these results, concluding that the misidentification of the label was explained by the ethanol solution 76,8 % (V/V), as it didn’t have the correct concentration for the plastic to sink. The solution had been previously tested by teachers. Nevertheless, since it was stored in a large jar, the vaporization inside probably altered its composition. Some groups didn’t obtain the expected results and were invited to repeat their analysis. The different results were probably caused by a deficient immersion of the plastic, failing to eliminate the superficial tension. The plastic may also have been poorly cut, causing defects where air might have accumulated in small bubbles. A reflection from the students on the activity would have been helpful to understand the causes for the divergent results.

For a quantitative overview of the students’ performance, Figure 3 represents the scores for their answers and records, presented in the activity sheet. Part A concerned research and initial debate on the different types of plastics and how the use of recycled plastics produce new raw materials dictates the final product’s quality (A.1 e A.2). In total, 20 answers from students scored accurately these questions, and most of them had a maximum score.

Figure 3 Students answers assessment in part A and B of the inquiry-based activity “Plastics inside and outside of water” 

Part B was focused on the problem’s resolution in the laboratory. Most of the students had a positive grade when planning and carrying out the laboratorial activity (B.1).

As referred before, students were challenged to construct a table to record the results obtained. Only 5 students built a well-presented table - but most of them, 15 students, presented incomplete or poorly organized records (as the examples shown in Table 3.b), therefore obtaining half the score (B.2). As a follow-up, students were challenged to compare the various results from the other groups (B.3a), and they did effortlessly. In conclusion, four of six groups obtained consistent results. Accordingly, most students obtained the maximum score in this activity phase. Debating the encountered difficulties in plastics identification (B.3b) was a considerable challenge. Thus, the score was very uneven: 6 students had a maximum score, 8 scored in the middle, 5 had less than half points and 1 student had no points at all. This inquiry-based activity was developed to engage students in the scientific-oriented activity. However, as expected, since this is a new dynamic implemented among these students, the results demonstrate that there was a general lack of reflection, indicating the need to work further, aiming to reinforce analytic and critical skills, once these are essential to the development of inquiry-based activities.

Furthermore, due time management issues, only about half the students presented the final activity (B.3c), which consisted of drafting a script (a leaflet or a poster) explaining how canteen users can separate plastics and the reason of its importance (Figure 4).

Figure 4 Examples of posters and slogans of the awareness campaign [(A) Plastics: Did you know that plastic can be recycled? Start now! Look that water bottle. Recycle with us.; (B) Recycle to help the world!] 

Overall, students who participated in this activity presented good and creative work. The records produced by students, as a group, included drawings, or schemes, with messages of encouragement and awareness to recycle the plastics in water bottles. The slogans and images created by them had the quality and creativity one could expect from an awareness campaign (Figure 4).