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Synthesis of a Biodegradable Bioplastic Alternative to Polypropylene Utilizing a Blend of D-Mannose and Acemannan from Aloe vera

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Authors: Brian Lu and Haripriya Dukkipati
Peer Reviewer: Ashley Yoon
Professional Reviewer: Sidra tul Muntaha
Saint Francis High School 

Abstract

The vast majority of commercial plastic that a general consumer encounters on store shelves, uses on a daily basis, and casually tosses into garbage bins is petroleum-based [1]. However, these materials degrade with much difficulty and originate from less-than-eco-friendly manufacturing processes; as a result, harmful plastic waste accumulates with negative ramifications for living beings in every conceivable ecosystem [3, 4]. In order to address the conundrum of plastic waste buildup, the authors of this study formulated a biodegradable bioplastic using D-mannose and powderized acemannan from dehydrated Aloe vera. This new material was created through acid-catalyzed hydrolysis and dehydration synthesis reactions in the presence of a glycerol plasticizer and a hydrochloric acid catalyst. A Decomposition Test projected that the D-mannose and acemannan bioplastic would fully biodegrade into its smaller molecular components within an average of 1.6 months, as opposed to petroleum-based plastics which would not visibly degrade at all within that timeframe [5]. A subsequent Force Test which simulated wear and tear through routine bending corroborated the hypothesis that the bioplastic at least rivalled commercial polypropylene in durability. Finally, a Water Resistance Test indicated that the new material was significantly more efficient at hydro-degradation than polypropylene. Thus, this study concludes that the D-mannose and acemannan bioplastic is a viable replacement for petroleum-based plastics, with likely applications in a diverse array of products from bottling and packaging to medical instruments.

Introduction

Plastics

Plastics are a category of man-made polymers now nearly ubiquitous among consumer products [1]. From wiring and insulation to dishware and packaging, plastics differ widely in their chemical composition but share a few core properties: their flexibility, non-hazardous nature, chemical inertness, and cost-effectiveness [1]. However, most plastic items obtainable in stores today are made of polypropylene, polyethylene, or other fossil-fuel derivatives and are therefore largely non-biodegradable [1].

Certain chemicals can be mixed into the plastic to tweak its properties toward a desired ideal. One important category of additive is the plasticizer, a substance that increases the flexibility of the plastic by acting analogously to a molecular lubricant and keeping individual polymer chains from entangling or locking together [2]. In this experiment, glycerol functioned as the plasticizer. 

Plastic Waste

Petroleum-based plastics tend to cause twofold environmental harm because of their environmentally unfriendly sourcing and their slow degradation. The extraction of plastic precursors from raw petroleum requires harsh chemicals, and the industrial processes and reactions that turn them into mass-produced plastics often deposit harmful pollutants into the atmosphere and the ocean [3]. Secondly, the nonpolar structure of the hydrocarbon chains that compose most plastics hinders their decomposition in the natural environment. These hydrocarbon chains are insoluble in common polar solutions such as water or the acids in the stomachs of animals, and all the C-H bonds in petroleum-based plastics have the same bond strength, so there are no weaker links for enzymatic or chemical reactions to easily break [4]. Due to these difficulties in degradation, petroleum plastics tend to accumulate as pollutants regardless of their method of disposal, thus leaching into drinking water systems, killing wildlife, and cluttering terrestrial and aquatic ecosystems [5].


Figure 1: Chemical Structure of an Example of a Petroleum-Based Plastic: Polypropylene [6].

Bioplastics and Biodegradability

There are two key improvements to conventional plastic that this study is concerned with: bioplastics and biodegradable plastics. Each of these more eco-friendly types of plastic attempts to solve one of the dual problems of harmful sourcing and slow degradation as explained above. All bioplastics are derived from organic materials, thus allowing for more eco-friendly synthesis, but they do not necessarily have to be biodegradable [7]. For example, corn-based polyethylene is organically sourced, but decomposes extremely slowly because it is chemically identical to existing petroleum-based polyethylene [8]. On the other hand, biodegradable plastics must wholly decompose within 180 days into smaller non-harmful molecules such as water or usable nutrients [9, 10]. Unfortunately, there also exist potential problems with biodegradable plastics—because they are optimized to degrade quickly in natural conditions, toxic or otherwise harmful chemicals might have been used during their production to prolong their shelf-life or to diminish costs [10]. Thus, this study attempts to solve both problems by combining the properties of the two categories of plastics and creating a biodegradable bioplastic.

D-mannose and Acemannan


Figure 2: Chemical Structure of D-mannose [11, 12].


D-mannose is a monosaccharide that is often sold in the form of a white granular powder for use as an over-the-counter diet additive or supplement [12]. It is present in certain types of algae and seaweed, fruits such as apples, and common household plants [12, 13]. According to Zhang, Pan, Quian, and Chen, researchers at the Zhejiang University in China, its extraction can be  cost-effective [13]. D-mannose represents the largest component of this study’s biodegradable bioplastic as measured by percent mass.


Figure 3: Chemical Structure of Acetylated Mannose [14, 15].

Acemannan is a polysaccharide and a polymer of the monosaccharide acetylated mannose, which is itself a version of D-mannose with extra CH3 groups added to its chemical structure [14, 15]. These CH3 groups act as nonpolar regions surrounding an otherwise polar molecule, decreasing acemannan’s interactions with polar molecules such as water [14, 15]. In this study, small amounts of acemannan in the form of dried Aloe vera powder were incorporated into the majority D-mannose bioplastic to increase its water resistance. Aloe vera was selected for this experiment because according to Pinghuai Liu, Deli Chen, and Jie Shi, researchers at Hainan University in China, it contains one of the highest concentrations of acemannan and very little of other unwanted solid compounds, which contributes to ease of extraction [16]. 


Figure 4: Chemical Structure of Acemannan [14, 15].

Table 1: Chemical Composition of Aloe vera Gel [16].

While the extraction of D-mannose and acemannan have been established to be comparatively hassle-free and cost-effective, the D-mannose and acemannan used in this experiment were purchased in powder form because of lack of access to the necessary laboratory equipment for extraction.

Acid Catalyzed Hydrolysis

Hydrolysis refers to the decomposition reaction in which a larger molecule is cleaved into two smaller molecules with the addition of water [17]. When this hydrolysis is catalyzed by a dissociated hydrogen ion from a protic acid, it is called acid catalyzed hydrolysis [18]. For this experiment, acid catalyzed hydrolysis is utilized when the polysaccharide acemannan is broken down into units of acetylated mannose in preparation for polymerization and plasticization. Hydrochloric acid was chosen to catalyze the hydrolysis of acemannan because it always completely dissociates into a hydrogen ion (H+) and a chloride ion (Cl-), thus producing a consistent supply of H+ ions for the acid catalyzed hydrolysis of acemannan [18].


Figure 5: A Proposed Mechanism of the Acid Catalyzed Hydrolysis of Acemannan  [14, 15].

Dehydration Synthesis

Dehydration synthesis—the reverse reaction of acid catalyzed hydrolysis—is a subtype of polymerization that links smaller molecules together in a chain-like structure to form a larger molecule and results in the generation of one water molecule per linkage formed [17]. During the synthesis of the biodegradable bioplastic, dehydration synthesis occurred when the blend of D-mannose and acetylated mannose was polymerized into plastic in the presence of the glycerol plasticizer. In this case, the water generated from the polymerization reaction did not dilute the components of the plastic because it completely evaporated into the surrounding air, as a result of the high temperatures at which the dehydration synthesis was performed.


Figure 6: Polymerization of D-mannose and Acetylated Mannose During the Synthesis of Biodegradable Bioplastic [11, 14].

Objective

The objective of this research project is to synthesize a biodegradable bioplastic from D-mannose and acemannan, to compare its strength against that of polypropylene, and to confirm its viability for everyday use.

Materials for Synthesis of Bioplastic

  • D-mannose
  • Glycerol
  • Aloe vera powder
  • 0.5 M Hydrochloric acid (HCl)
  • 0.5 M Sodium Hydroxide (NaOH)
  • 18 Plastic Petri dishes (6 cm diameter x 1 cm height)
  • Aluminum foil
  • Gram balance
  • Hot plate
  • 2 100 mL Graduated cylinders
  • 1 500 mL Glass beaker
  • 2 Plastic weigh boats
  • Thermometer
  • Magnetic stir bar
  • Forceps
  • Acetone (for cleaning glassware)
  • Permanent marker

Materials for Preparation of Polypropylene Control

  • Polypropylene bottle caps
  • 1 500 mL glass beaker
  • Fume hood
  • 3 glass Petri dishes (6 cm diameter x 1 cm height)
  • 12 Plastic Petri dishes (6 cm diameter x 1 cm height)
  • Gram balance
  • Hot plate
  • Thermometer
  • Forceps
  • Acetone (for cleaning glassware)
  • Permanent marker

Materials for Decomposition Test

  • 6 Gardening pots (15 cm diameter x 16 cm height)
  • Potting soil
  • Ruler
  • Camera

Materials for Force Test

  • String (0.3 cm thick)
  • Bench vise
  • Flat surface
  • Plastic bucket
  • Assorted weights
  • Gram scale
  • Ruler

Materials for Water Resistance Test

  • Stopwatch
  • 6 Plastic cups (8 cm diameter x 12 cm height)
  • Distilled water
  • Gram scale

Methods

Synthesis of Bioplastic

Each of the 18 plastic Petri dishes was labeled from P1 to P18 with the permanent marker. The interior of each Petri dish was lined with aluminum foil to prevent any molten bioplastic from fusing with or deforming the plastic Petri dishes. The biodegradable bioplastic was synthesized in six batches of three samples each to reduce the variability between individual samples. Only three foil-lined Petri dishes were used for each batch of plastic; the remaining 15 were set aside temporarily.

To begin the synthesis of one batch of plastic (three samples), the gram balance was used to measure out 33.01 grams of D-mannose in a plastic weigh boat, 0.83 grams of Aloe vera gel powder in a second plastic weigh boat, 0.70 grams of 0.5 M HCl in a graduated cylinder, 0.70 grams of 0.5 M NaOH in a second graduated cylinder, and 4.30 grams of glycerol in a 500-mL glass beaker. The beaker of glycerol was set on the hot plate, and the magnetic stir bar and thermometer were placed into it.

Next, the hot plate was turned on to a heat setting of 5/10 and a stirring speed of 5/10 (the hot plate was capable of reaching a temperature of 210 degrees Celsius at its maximum heat setting). The D-mannose was gradually mixed into the glycerol and heated until the mixture resembled a thick clear-white paste. The HCl and Aloe vera powder were then added, immediately resulting in bubbling. In this step, the HCl catalyzed the hydrolysis of the acemannan within the Aloe vera powder into acetylated mannose [18]. Simultaneously, the heat energy provided by the hot plate initiated the dehydration synthesis polymerization of the D-mannose and the acetylated mannose [17]. In the presence of the plasticizer glycerol, the long polymer chains of D-mannose and acemannan became a plastic [2]. This mixture was continuously heated and stirred until it reached a temperature of 105 degrees Celsius. When the mixture began to froth vigorously, the NaOH was added to neutralize the still present H+ ions and prevent the creation of an acidic bioplastic, causing a thinning of the paste and more frothing.

Once the bubbles finally subsided, demonstrating that all excess water produced by dehydration synthesis polymerization and acid-base neutralization had been evaporated from the molten bioplastic mixture, the glass beaker was removed from the hot plate with heat-resistant gloves and forceps. The magnetic stir bar was retrieved from the beaker with the forceps. The contents of the beaker were swirled manually with the forceps for 30 seconds to cool, and distributed as equally as possible among the three foil-lined Petri dishes. The molten bioplastic was then moved to a cool, dry location to set for several days. Once the bioplastic samples solidified, the foil was peeled away and discarded.

The glassware, the magnetic stir bar, the thermometer, and the forceps were all cleaned with acetone and distilled water to remove all bioplastic residues and then dried. The above procedure was then repeated to produce additional batches of three bioplastic samples at a time until a total of 18 samples of bioplastic were synthesized.

Preparation of Polypropylene Control

Before the polypropylene was melted and remolded into cylindrical samples that were the same size and shape as the bioplastic samples, the hot plate and three glass Petri dishes were placed in a well-ventilated fume hood because polypropylene produces noxious fumes when heated [1]. Each of 12 plastic Petri dishes was labeled from C1 to C12 with the permanent marker and set aside. 

The polypropylene was prepared in four batches of three pieces. 26.76 grams of polypropylene bottle caps were measured out for each batch of three; caps were broken by hand to approximate this amount as closely as possible. This required amount of polypropylene was determined through a stoichiometric calculation, solving for the mass of polypropylene given its density and the desired volume of synthesized bioplastic (so that the bioplastic samples and polypropylene controls could be identical in diameter and thickness). The appropriate amount of polypropylene was placed into a 500-mL glass beaker, along with a thermometer. The beaker was placed on a hot plate, and the fume hood was powered on to ensure proper ventilation of the harmful fumes that would be produced by molten polypropylene. The hot plate was then adjusted to a heat setting of 9/10. No stirring was necessary. The polypropylene was heated at approximately 200 degrees Celsius for 25 minutes until it fully melted.


Figure 7: Setup of Fume Hood, Including Hot Plate, Beaker, and Thermometer.

Once the polypropylene completely liquified, the beaker was swirled manually with the forceps for 30 seconds to cool its contents. The molten polypropylene was distributed as equally as possible among the three glass Petri dishes and was allowed to set for several days. When each polypropylene sample cooled and solidified, it was transferred into the corresponding plastic Petri dish. A knife or other sharp tool was necessary to pry the polypropylene samples out of the glass Petri dishes.

         The glass Petri dishes, glass beaker, thermometer, and forceps were all cleaned with acetone and distilled water to remove polypropylene residues, then dried. The above procedure was then repeated to produce additional batches of three polypropylene samples until a total of 12 samples of polypropylene were prepared.

Random Assignment

Out of the 18 bioplastic samples and 12 polypropylene samples, three samples of bioplastic and three samples of polypropylene were randomly assigned using a random number generator to each of the three tests: Decomposition Test, Force Test, and Water Resistance Test. This random assignment minimizes the skewing effects of any hidden or confounding variables. Moreover, any samples with visible cracks or other major physical flaws were excluded from testing to prevent incorrect conclusions due to variations in structural integrity, exposed surface area, etc. In total, nine of the 18 bioplastic samples and nine of the 12 polypropylene samples were chosen for the tests; the unused samples were set aside and not tested.

The random assignments used in this study are depicted below:



Table 2: Random Assignment of D-Mannose Bioplastic Samples and Polypropylene Samples to the Decomposition Test, Force Test, and Water Resistance Test.

Decomposition Test

Three samples of bioplastic (P8, P16, and P18) and three samples of polypropylene (C3, C4, and C11) were selected, as assigned in Table 2 above. Six gardening pots, each with a 15 cm diameter and 16 cm height, were filled halfway (eight centimeters high) with potting soil. Each pot was labelled according to the sample to be contained inside. Each sample’s initial diameter and thickness were measured and recorded. A camera was used to take pictures of each sample in order to record its shape prior to decomposition. To start the Decomposition Test, each sample was buried in its corresponding pot about two centimeters below the soil’s surface; it was ensured that none of the samples were directly visible. The pots were then placed in a row in a room-temperature room.

         Each sample was dug up and inspected daily. Any excess dirt clinging to the sample was lightly brushed off with a gloved finger as much as possible. The diameter and thickness of each plastic was measured with a ruler to record the day-to-day progression of the decomposition. Then, each sample was re-buried in the correct pot of soil in its original position (two cm below the soil’s surface). This procedure was repeated each day for a total of 35 days.

Force Test

The diameter and thickness of each plastic sample was first measured with a ruler to allow for later calculation of the force-bearing cross-sectional area. A bench vise was set up on the edge of a flat surface such as a table. Three samples of bioplastic (P10, P11, and P15) and three samples of polypropylene (C1, C5, and C10) were selected for the Force Test, as assigned in Table 2 above. The gap in the bench vise was adjusted to a width of two centimeters and the plastic sample was placed across it. Each end of a 100 cm length of string was then tied to a plastic bucket. The string was hung across the middle of the cylindrical sample so that the vertical cross-section containing the diameter of the sample supported the entire weight of the string and bucket. In Figure 8 below, the Petri dish models where a sample was placed during a real trial of the Force Test.


Figure 8: Setup of Force Test.

Assorted weights were then placed into the bucket, applying stress in a plane perpendicular to the circular base of each sample. The samples were supported on opposite ends by the edges of the bench vise and a force was applied across the sample’s midsection, simulating the forces experienced by plastic when bent through everyday use. More and more weights were added until the sample snapped into two pieces. When it did, the total mass of the string, bucket, and weights required to break the sample was measured with the gram balance and recorded. The above procedure was repeated until all three chosen samples of bioplastic and polypropylene had been tested. Then, the average mass supported per square centimeter of cross-sectional area was computed for each plastic type and compared.

Water Resistance Test

         Three samples of bioplastic (P5, P6, and P14) and three samples of polypropylene (C6, C7, and C9) were selected for the Water Resistance Test, as assigned in Table 2 above. Each sample’s initial mass was measured with a gram balance and recorded. Six plastic cups (all with an eight centimeter diameter and 12 cm height) were prepared by filling each with distilled water until the water was two centimeters deep. Each cup was labelled according to the sample to be contained inside. Next, the samples of bioplastic and polypropylene were submerged in their respective cups. A stopwatch was immediately started.

After five minutes had elapsed, each plastic sample was retrieved from the water, excess water was removed by gently dabbing the sample with an absorbent paper towel, and the sample’s mass was measured again with the gram balance and recorded. Then the sample was re-submerged. The above procedure was repeated again 15, 25, 35, 60, 120, 180, 240, 360, and 480 minutes after the six samples were initially submerged.  These specific times were chosen in order to develop a more accurate model of water’s effects on the bioplastic and the polypropylene samples over both the short-term and the long-term.

Results

Measurements of Plastic Samples

After all the bioplastic samples had set (with the aluminum foil peeled off) and all the polypropylene samples had solidified, the mass of each sample was measured with a gram balance and recorded to provide a baseline for comparison with the results of the Decomposition Test, Force Test, and Water Resistance Test. A picture of each sample was also taken with a camera to record initial observations. All of the synthesized bioplastic samples were noted to be translucent, hazel in color, and malleable enough to be bent or shaped without shattering; additionally, they clung to the aluminum foil even after hardening. In contrast, the polypropylene samples were opaque, black (perhaps due to a dye already present in the bottle caps that were melted down), rigid, and smooth.


Figure 9: The 12 Control Polypropylene Samples.


Figure 10: The 18 D-Mannose and Acemannan Bioplastic Samples.

Table 3: Initial Mass Measurements Obtained After the Synthesis of Bioplastic and Preparation of Polypropylene Control.

Results of Decomposition Test – Polypropylene Control


Figure 11: Polypropylene Diameter Over 35 Days of Decomposition.

Figure 12: Polypropylene Thickness Over 35 Days of Decomposition.

Figure 13: Polypropylene Volume Over 35 Days of Decomposition.

This Decomposition Test was intended to measure and compare the decomposition of the samples of controlled polypropylene and the samples of synthesized bioplastic. The controlled polypropylene samples (C3, C4, and C11) did not significantly decompose to any degree over the 35-day testing period of the Decomposition Test. The measured diameter of sample C4 actually decreased on day 17 as shown in Figure 11. However, it was deduced that this reduction in diameter was not due to decomposition of the polypropylene, but rather cracking and chipping that was initially present in the sample and which worsened with frequent handling. The diameter, thickness, and volume of each sample remained approximately constant throughout the entire test as displayed in Figures 11, 12, and 13.

Using Microsoft Excel, the degree-5 polynomial of best fit was generated and plotted for each controlled polypropylene sample in the graph of polypropylene volume (Figure 13). These polynomials can be extrapolated to predict that C3 would require 428505 days (1173.98 years), C4 would require 198975 days (545.136 years), and C11 would require 399750 days (1095.20 years) to completely decompose and reach a volume of zero. These projections that were generated from the collected data and the calculated volume of each cylindrical sample serve to corroborate the known fact that petroleum-based plastics like polypropylene are non-biodegradable and often require exorbitant lengths of time to fully decompose [5].

Results of Decomposition Test – Bioplastic


Figure 14: Bioplastic Diameter Over 35 Days of Decomposition.


Figure 15: Bioplastic Thickness Over 35 Days of Decomposition.


Figure 16: Bioplastic Volume Over 35 Days of Decomposition.

In contrast to the polypropylene control, the diameter and thickness of each of the three bioplastic samples (P8, P16, and P18) decreased steadily until Day 10, then gradually levelled off after around Day 20. Some exceptions to this trend existed; for example, the measured thickness of sample P18 actually increased on the eighth day due to an unusually thick coating of dirt which was difficult to fully remove without damaging the sample itself. The diameter of the samples decreased at an average rate of 0.075 cm/day (calculated from Figure 14) and their thickness decreased at an average rate of 0.002 cm/day (calculated from Figure 15). As a result, the samples’ calculated volumes decreased at an average rate of 0.060 cm3/day (calculated from Figure 16). Within ten days, the tested bioplastic samples had decomposed to less than one-half of their initial volume as calculated from the initial measurements of diameter and thickness. By the conclusion of the Decomposition Test, the bioplastic samples had each decomposed to less than one-eighth of their original volume.

Using Microsoft Excel, the degree-5 polynomial of best fit was also generated and plotted for the volume graph of each bioplastic sample in Figure 16 above. While none of the bioplastic samples completely decomposed during the 35 days of the Decomposition Test, the extrapolations generated in Microsoft Excel predicted that P8 would completely decompose within 43.56 days, P16 would completely decompose within 57.92 days, and P18 would completely decompose within 48.16 days. Because these three bioplastic samples are projected to fully degrade in an average of approximately 50 days (well within the time limit of 180 days), the D-mannose bioplastic synthesized in this study qualifies as biodegradable [9, 10].

Results of Force Test


Table 4: Raw Data of Force Test - Polypropylene Samples.

Table 5: Raw Data of Force Test - Bioplastic Samples.

This Force Test simulated the forces arising from bending through everyday use and compared polypropylene and the synthesized bioplastic based on the amount of stress that each could sustain before snapping in two. While the thickness of each polypropylene sample correlated strongly with the amount of force it could withstand, all of the bioplastic samples in this test tolerated roughly the same amount of force. After controlling for the differently sized cross-sectional areas (diameter x thickness), it was found that the bioplastic samples supported an average of 14.20 Newtons of force per square centimeter of force-bearing area more than the polypropylene control did. 

In other words, if a bioplastic sample and a polypropylene sample of exactly the same diameter and thickness were simultaneously bent, data suggests that the polypropylene would snap first. These results demonstrate that the synthesized bioplastic is capable of withstanding a quantity of stress at least comparable to the amount that polypropylene can handle. This bioplastic therefore has the potential to be an effective polypropylene substitute and could be used for commercial purposes such as creating durable tubing, rods, and bottlecaps.

Results of Water Resistance Test


Table 6: Raw Data of Water Resistance Test.

Figure 17: Comparing Hydro-degradation of D-mannose Bioplastic and Polypropylene.

This test compared the water resistance of the synthesized bioplastic and the polypropylene control, which is necessary because plastics commonly come into contact with or are used as containers for water and other liquids. The bioplastic samples used in this test (P5, P6, and P14) experienced a precipitous decrease in mass during the first 15 minutes of submersion in distilled water, but then settled at slightly less than half of their initial mass. The polypropylene samples were not significantly affected by the water at all. 

This large difference in hydro-degradability can be attributed to differences in the chemical structures of the monomers that make up the bioplastic and the polypropylene. The D-mannose subunits are polar and hydrophilic (the acetylated mannose is less so as explained in the Introduction, but still hydrophilic), while the propylene subunits are entirely non-polar and hydrophobic [6, 11, 14, 15]. Moreover, as sugars, all forms of mannose are highly soluble in water; when the synthesized bioplastic is initially immersed in an aqueous environment, it is likely to decrease in mass as the D-mannose and acetylated mannose rapidly enter solution [11, 12]. However, this dissolution reaction reaches equilibrium after some time, so the rate of reduction in mass decreases as the solution nears saturation. On the other hand, polypropylene is much less soluble in water than mannose, so its solid mass at equilibrium would be much larger than the solid mass of the synthesized bioplastic at equilibrium (in other words, much less of it dissolves) [6].

Discussion

Conventional petroleum-based plastics such as polypropylene require almost a millennium to decompose, precipitating the accumulation of harmful waste products and contaminants across the planet and its oceans [5]. The increasingly widespread reliance on disposable plastics in an assortment of fields, such as industrial manufacturing and medicine, intensifies humanity’s need for more biodegradable alternatives [1].

The objective of this study was to develop a biodegradable bioplastic alternative to petroleum plastics and assess its viability for common uses. In order to accomplish this, a blend of D-mannose and water-resistant acemannan from Aloe vera powder was plasticized in the presence of glycerol, a non-toxic and all-natural food preservative and sweetener. The results of the Decomposition Test and Force Test demonstrated that the synthesized bioplastic would decompose within an average of approximately 50 days and was capable of withstanding at least as much stress from bending as commercial polypropylene. Moreover, the water resistance test indicated that the bioplastic was also more hydro-degradable than polypropylene. Because the synthesized bioplastic is at least as durable as polypropylene, yet is both biodegradable and hydro-degradable, it can be considered a practical alternative to commercial plastics that is viable for everyday use.

Despite humanity’s best intentions and increased efforts to be more “green” in recent years, plastics still commonly pollute oceans and other ecosystems to this day [5]. Even in the worst case scenario where the bioplastic developed in this study becomes pollution or waste, it will still have a less negative impact on the environment than polypropylene would. If buried underground in a landfill, as simulated by the Decomposition Test, the bioplastic would likely decompose in a mere 50 days (as opposed to centuries for polypropylene) and return to its non-toxic components of D-mannose and acemannan, thus posing much less risk to terrestrial ecosystems and organisms [5, 9, 10]. If disposed in an aqueous environment, the synthesized bioplastic would also decompose rapidly into its non-toxic constituents due to its high hydro-degradability, causing minimal harm to marine life [10, 19]. On the other hand, petroleum-based plastic does not easily degrade within any part of the natural environment, so it has a higher probability of negatively impacting wildlife [1, 19]. For example, animals in terrestrial and aquatic ecosystems often confuse plastic for nutritional sustenance and ingest bits of it, mistakenly thinking it is a food source [19]. Worse, if these harmful materials are slow to degrade like polypropylene, they can build up in the digestive tracts of organisms and get in the way of nutrient absorption, causing drawn-out and painful deaths [19].

Limitations to this study include a lack of access to equipment for the Force Test. Tensile testing, a standard procedure within materials science that analyzes the levels of tension a material could withstand before structural failure, could not be performed without expensive industry instruments. An alternative setup for the Force Test had to be utilized, instead operatively defining strength as the quantity of stress withstood. In addition, there was also some inevitable lab error. During the Decomposition Test and Water Resistance Test, human error was compounded by the impossibility of completely removing all excess soil or water from the samples, thus resulting in incorrectly increased measurements of the dimensions and the mass for all samples involved in these tests. When pouring the molten bioplastic into the Petri dish molds, some of the liquid mixture inevitably clung to the side of the beaker due to the molten bioplastic’s viscosity. This phenomenon resulted in samples that were thinner than expected and thus might have caused the bioplastic samples to snap more easily or dissolve more easily in water due to the larger surface area to volume ratio.

Based on the results of this study, the hydro-degradability of the synthesized bioplastic should be more carefully modulated in the future because the three bioplastic samples that were analyzed lost more than half of their initial mass within the eight hours of the Water Resistance Test. Moreover, D-mannose bioplastics could be synthesized with varying levels of flexibility, durability, and strength for different applications from wiring insulation to medical instruments to environmentally friendly packaging. Due to their remarkable properties, D-mannose bioplastics have the potential to revolutionize the materials industry without compromising the planet we share. 

Acknowledgements

We would like to thank Ms. Jennifer Thomas at Saint Francis High School for providing the use of her lab space, lab equipment, and fume hood. This study would not have been possible without her encouragement, guidance, and resources.

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