Effect of Storage Time of Biodegradable Plastic Porang Starch with Glycerol Plasticizer on Mechanical and Thermal Properties

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CrossMark RESEARCH ARTICLE | MAY 15 2023

Effect of storage time of biodegradable plastic porang starch with glycerol plasticizer on mechanical and thermal

properties 

Awan Maghfirah; Susilawati; Lisa Sahara; ... et. al

AIP Conference Proceedings 2595, 030002 (2023) https://doi.org/10.1063/5.0123884

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Effect of Storage Time of Biodegradable Plastic Porang Starch with Glycerol Plasticizer on Mechanical and Thermal

Properties

Awan Maghfirah

^{1, a)}

, Susilawati

¹

, Lisa Sahara

¹

, Nurul Istiqomah

¹

, Pindi Priscila

¹

1University of North Sumatra, North Sumatra, Indonesia.

a)Corresponding author: [email protected]

Abstract. The increasing use of synthetic plastics has a negative impact on the environment because it cannot be degraded by nature. The current work investigates the effect of storage time of biodegradable plastic porang starch with glycerol plasticizer on mechanical and thermal properties. The effect of the storage time of biodegradable plastic on the mechanical properties of tensile strength and elongation is decreasing every week but still meets the standards at all concentrations of glycerol plasticizer up to four weeks of storage with tensile strength values of 7,137 MPa, 4,541 MPa and 2,657 Mpa and elongation values 58,574%, 47,324 %, 74,699%. The effect of storage time on the thermal properties of TGA-DTA analysis in the third and fourth weeks of thermal stability began to decrease with a total mass reduction of 9,934 mg and 9,954 mg, respectively. The degradation ability test showed a decrease in mass every week. SEM and FTIR test analyzes were also carried out. The results showed that biodegradable plastic porang starch is suitable for packaging applications because it still meets the standards until the fourth week of storage time.

INTRODUCTION

Plastic is a material that is widely used, because it has a low price and is relatively strong and light. Plastic consumption in developing countries is reported to be more than the world average, this is due to economic development and higher rates of urbanization. Developing countries including China, Indonesia, Vietnam, the Philippines and Sri Lanka are reported to produce more than 50% of global plastic in the marine environment.

Although the technology to deal with plastic waste has been improved, the increase in the world's human population has resulted in an increase in the demand for higher plastic production and ultimately an increase in the amount of plastic waste. Plastic waste has several impacts on ecosystems and human health because it cannot be decomposed by nature [1].

Based on these problems, have produced alternative plastic materials obtained from materials that are easily available, available in nature, cheap and can be degraded by nature, namely biodegradable plastic. Biodegradable plastics are plastics that can be broken down by the activity of microorganisms into the final product of water and carbon dioxide gas [2]. World plastic production in 2018 reached nearly 360 million tons, the production capacity of biodegradable plastic in 2018 was only 2.01 million tons or 0.56% of world plastic production. Increased production of biodegradable plastics can reduce dependence on conventional plastic base materials, namely fossil-based resources turning into natural-based resources [3]. Previous research by Zoungranan et al in 2020 [4] with the title "Influence of natural factors on the biodegradation of simple and composite bioplastics based on cassava starch and corn starch"

still focused on the ability of biodegradable plastics to degrade. Therefore, it is necessary to conduct research which in addition to focusing on the ability of biodegradable plastic to be degraded, it must also focus on mechanical and thermal analysis so as to produce biodegradable plastic which is not only biodegradable but also strong and heat- resistant like conventional plastics. This research provides an update, namely examining the effect of the storage time of biodegradable plastic from porang starch with glycerol plasticizer on mechanical and thermal properties.

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Biodegradable plastic is made from the starch of the Porang plant (Amorphophallus oncophyllus) which is a perennial plant. This plant originates from the southeastern region of Asia and is consumed in several countries such as India, Sri Lanka, China, Malaysia including Indonesia and contains a lot of starch, namely as resistant starch [5].

Porang starch is easily degraded but has weak hydrogen bonds because the distance between molecules is tenuous and causes biodegradable plastics to become less dense, so it is necessary to add starch adhesive, one of which is chitosan.

Chitosan is the most abundant natural polysaccharide after cellulose and most of the biopolymers of animal origin [6].

Chitosan can interact with starch polymer chains in the form of hydrogen bonds so that it can fill the voids between starches and make biodegradable plastics stronger but not elastic. Glycerol is needed as a plasticizer because it can increase the flexibility of biodegradable plastics by reducing hydrogen bonds between molecules and increasing the distance between molecules into the starch polymer network [7].

This study aims to analyze the effect of the storage time of biodegradable plastic porang starch on the mechanical properties of tensile strength and elongation, and on the thermal properties which is carried out once a week to four weeks to determine the strength and heat-resisting ability of biodegradable plastic. Degradability analysis and microstructural analysis of SEM and FTIR were also carried out in this study.

METHOD

The method used is the Melt Intercalation method. The process of making biodegradable plastic begins with making porang starch which is mashed, then filtered with gauze and deposited for 24 hours then stored in the form of starch and dried in an oven for 24 hours at a temperature of 60^oC. The starch obtained was weighed by the ratio of starch mass, chitosan, and glycerol volume. Starch was dissolved in distilled water, while chitosan was dissolved in 1% acetic acid with stirring for ±25 minutes. The stages of making biodegradable plastic are made in the research flow chart as follows.

FIGURE 1. Research Flow Chart

.

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Test method with storage time for once a week on mechanical analysis and thermal analysis. Mechanical test of tensile strength and elongation with ASTM D882-91:1996 using Tensilon UTM RTF 1350, analysis of thermal properties with TGA DTG-60 SHIMADZU, degradation ability test with ASTM D-5488-84d:1994, and SEM and FTIR tests with SEM ZEISS EVO MA 10 and FTIR Agilent Cary 630. The sampling technique used was Completely Randomized Design (CRD). Data analysis was carried out using the ANOVA method using the ORIGIN LAB 2021b software.

RESULTS AND DISCUSSION Characterization of Porang Starch

The results of the characterization of porang starch can be seen in the following table.

TABLE 1. Characterization Results of Porang Starch.

Starch Content (%) Water content (%) Fat level (%) Protein Content (%)

12 4.3 1.6 3.02

The amount of starch content of plant tubers is influenced by the level of maturity, the extraction process and also the growing environment [8]. According to SNI 7939:2013, the water content standard of porang flour is in quality III with a moisture content of 15%-16%, quality II with a water content of 13% to 15%, and quality I less than 13%. So that the water content of porang starch in this study has met the standard and reached quality I. The lower the water content, the better the quality of the starch product, because it can reduce the medium for microbial growth. Starch moisture content of less than 12% can prevent the growth of mold or fungus [9]. The fat content of starch according to SNI 2997:1996 is 0.568%, high fat content will affect the starch storage process because it can cause rancidity [10].

Protein content according to SNI 3727:1995 is 1.250%. Protein plays a role in the water binding process, the higher the protein content, the stronger the protein-water bond [11].

Effect of Biodegradable Plastic Storage Time on Mechanical Properties

The effect of the storage time of biodegradable plastic on the mechanical properties of tensile strength results in the data in the following graphic image.

FIGURE 2. Graph of the Result of the Effect of Storage Time on the Mechanical Properties of Tensile Strength.

Figure 1 shows the effect of storage time on the tensile strength of biodegradable plastic porang starch, where the tensile strength value decreases every week. The percent decrease in tensile strength value for 4 weeks of storage time for biodegradable plastics for each variation of glycerol is at a concentration of 60% glycerol plasticizer experiencing a decrease in tensile strength value of 12.59%, at a concentration of 80% glycerol plasticizer 20.99%, and at a concentration of plasticizer 100% glycerol by 24.10%. This shows the effect of increasing the concentration of

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glycerol plasticizer on the percent decrease in the tensile strength of biodegradable plastic every week. The increasing percent decrease in tensile strength value with the addition of glycerol is due to the glycerol plasticizer reducing internal hydrogen bonds in intermolecular bonds. As a result, the resulting biodegradable plastic has weak physical properties which will reduce the tensile strength of the resulting biodegradable plastic [12]. The standard value for tensile strength of ecogreen plastic according to SNI 7188:2016 is 24.7-302 MPa. If using the JIS Z-1707:2019 standard regarding food packaging standards, the tensile strength of biodegradable plastic is at least 4 KgF/cm2 or 0.392 MPa. In this study, the tensile strength value until the fourth week of storage time still met the standard JIS Z- 1707:2019.

Effect of shelf life of biodegradable plastic on elongation mechanical properties generate data in the following graphic image.

FIGURE 3. Graph of the Result of the Effect of Storage Time on the Mechanical Properties of Elongation at Break

.

Figure 2 shows that there is an effect of storage time on the percent elongation of biodegradable plastic Porang starch, namely the percent elongation value is decreasing every week. In this study, biodegradable plastic with 100%

glycerol variation had the highest percent elongation value, namely at the initial elongation value of 97.324% and until the fourth week the elongation value of 74,699% was still the highest when compared to the glycerol variation of 60%

and 80% in the fourth week. The decrease in glycerol as a plasticize results in a decrease in the elongation of biodegredable plastics, which then causes biodegredable plastics to break easily [13]. The standard value of elongation for ecogreen plastic according to SNI 7188:2016 is 21-220%.

Effect of Biodegradable Plastic Storage Time on Thermal Properties

The characterization of thermal properties can be measured using a tool called a Thermogravimetric Analyzer (TGA) and Differential Thermal Analysis (DTA). The specifications of the equipment used are the DTG-60 series of the SHIMADZU brand. The results of the thermal analysis in the form of a thermogram that can show changes in endothermic and exothermic enthalpy. TGA-DTA analysis was carried out with the aim of knowing the thermal stability of biodegradable plastics made from porang starch and chitosan. Thermal properties analysis provides information about the physical changes of biodegradable plastics which can be seen as Figure 4.

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(a) (b)

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FIGURE 4. Thermogram Image of TGA-DTA Analysis of Biodegradable Plastic Storage Time (a) 1 Week, (b) 2 Weeks, (c) 3 Weeks, and (c) 4 Weeks.

The information shown in the TGA-DTA analysis results with storage times of 1 week, 2 weeks, 3 weeks and 4 weeks is processed and made in the following table.

TABLE 2. Effect of Storage Time on Thermal Properties of TGA-DTA.

Storage Time (Week)

Peak 1 2 3 4

Temperature (^oC)

A 39-168.5 27.2 -178.2 24.6-165.2 28.5-174.1

B 168.5-366.7 178.2-343.4 165.2-341.7 174.1-328.4 C 366.7-522.9 343.4-564.9 341.7-582.4 328.4-561.4

Weight Loss (mg)

A 2154 3153 2862 2568

B 6741 6018 6346 6545

C 1019 743 726 841

Total 9914 9914 9934 9954

Process

A Endothermic Endothermic Endothermic Endothermic B Endothermic Endothermic Endothermic Endothermic

C Exothermic Exothermic Exothermic Exothermic

Table 2 shows the effect of storage time on the thermal properties of the biodegradable plastic of starch porang, where the longer the storage time, the more the reduction in mass of biodegradable plastic when tested thermally. In the first and second weeks they had the same total mass reduction of 9914 mg, then in the third week there was an increase in the total mass reduction of 9934 mg, the total mass reduction continued to increase in the fourth week of 9954 mg. This shows that biodegradable plastics are more thermally stable in the first week and second week than the third and fourth weeks and the thermal stability continues to decrease with increasing storage time. When compared with previous studies Maneking et al., 2020 namely biodegradable plastic using cassava starch and glycerol plasticizer

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a mass loss of 1243 g [14], while in this study the temperature range was close to that of 174.1ºC has experienced a mass loss of 2568 mg. This mass reduction shows the occurrence of an endothermic process in the reduction of the mass of point A and point B with the occurrence of a downward peak on the DTA thermogram. In the endothermic process, the composition of the biodegradable plastic material begins to absorb heat and change shape (deformation).

The endothermic process is a process of removing water that occurs during heating, this decrease in mass occurs due to evaporation and decomposition of biodegradable plastics [15]. At point C mass reduction with the occurrence of an upward peak on the DTA thermogram indicates an exothermic process, in which the material begins to give off heat.

The exothermic process informs the temperature limit of the biodegradable plastic to withstand the given heat. In this process, biodegradable plastic begins to break down and burn to ashes.

Degradability Test

Biodegradation is carried out by planting a number of biodegradable plastics in the soil at a certain depth at intervals of four weeks. The results of bioplastic biodegradation can be seen in the following table.

TABLE 3. Results of Porang Starch Biodegradable Plastic Mass Reduction. Glycerol

(%)

Starch : Chitosan (%)

Mass Loss (g) Sunday

0

week 1 week 2 week 3 week 4

60 50 : 50 579 578 544.6 256.24 74.11

80 50 : 50 657 653 599.5 261.22 Visual

100 30 : 70 707 700 589.49 150.23 Visual

TABLE 4. Biodegradation Results of Porang Starch Biodegradable Plastics.

Glycerol (%)

Starch : Chitosan (%)

Degradation (%)

week 1 week 2 week 3 week 4

60 50 : 50 0.17 5.94 54.19 87.2

80 50 : 50 0.60 8.74 60.24 Visual

100 30 : 70 0.99 16.62 78.75 Visual

Based on table 3 and table 4 shows the effect of planting time on mass reduction and percent degraded every week.

At the concentration of glycerol plasticizer 60% starch: chitosan 50%:50% with an initial mass of 579 g, in the first week the mass became 578 g, then in the second week it decreased to 544.6 g, and the decrease in mass continued to occur to 265.24 g in the second week. third, until the fourth week the mass of biodegradable plastic was only 74.11 g.

Weekly mass reduction also occurred at concentrations of glycerol plasticizer 80%, and 100%, but at these two concentrations in the fourth week the biodegradable plastic could not be weighed and the final mass could not be known because it had become a gel and almost mixed with the soil. This is because there are photosynthetic bacteria, archebacterial bacteria, aerobic bacteria, anaerobic bacteria, and eukaryotic bacteria that affect the biodegradation of biodegradable plastics. In the soil these microorganisms can be found widely up to 90 types and cause a decrease in the mass of biodegradable plastic every week [16].

The effect of the addition of glycerol plasticizer and length of planting time on the biodegradable ability of porang starch biodegradable plastics carried out in this study was the greater the glycerol plasticizer, the higher the porang starch biodegradable plastics degraded ability. In the variation of plasticizer glycerol 60% in the first week is degraded 0.17%, then in the variation of plasticizer glycerol 80% is increasing, namely in the first week it has a higher percent degraded which is 0.60%, and the percent degraded in the first week at a concentration of 100% glycerol plasticizer also get bigger, that is 0.99%. This is because the addition of glycerol increases the ability to absorb water from biodegradable plastics, and the more water that is absorbed, the faster the degradation occurs. Glycerol is amorphous, which in turn will affect the degradation process, namely the ability of biodegradable plastic to decompose microbes, moisture and chemical factors in the soil so that the addition of glycerol will affect whether or not biodegradable plastic is degraded [17].

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Microstructural Characteristics

(a) (b)

FIGURE 5. (a) SEM Results of Biodegredable Plastics Magnification of 1000 times (b) SEM Results of Biodegredable Plastics Magnification of 2000 times

.

SEM analysis aims to image the surface of biodegradable plastic [18]. The SEM results revealed a non-uniform compact structure, some parts have an even appearance, which is almost completely black, this indicates that starch, chitosan and glycerol have been mixed well, in certain parts of the crack surface is visible which causes high and low values of tensile strength. However, there are white parts and indentations on the surface of the biodegradable plastic indicating the presence of insoluble starch, this causes an uneven surface of the biodegredable plastic. This is due to the weak cohesion between starch and chitosan [19]. The presence of insoluble starch in biodegradable plastic is due to the stirring factor in porang starch and stirring affects the solubility of porang starch. In a previous study by Amin et., al in 2019 it was explained that the SEM results described contained the remnants of insoluble starch granules remnants [20]. The surface appearance of biodegradable plastic explains the reason for its low reflectance and explains that the manufacture of biodegradable plastics can be further processed for better application of biodegradable plastics [21].

FIGURE 6. Spectrum of Glycerol, Porang Starch, Biodegredable Plastics, and Chitosan.

TABLE 5. FT-IR Analysis Interpretation of Porang Starch Biodegradable Plastic Function Groups.

Chemical Functional Group

Absorption Area (Cm^-1)

Glycerol Starch Biodegredable Plastic Citosan

C-H 2929 2929 2937 2877

O-H 3280 3280 3265 3205

N-H - 1640 1595 1587

FTIR analysis on glycerol absorption appears at a wave number of 2929 cm^-1 showing a C-H group and a wave

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cm^-1 indicates an O-H group, 2929 cm^-1 indicates a C-H group, 1640 cm^-1 indicates an N-H group. FTIR spectra analysis on chitosan showed absorption at wave number 3205 cm-1 indicating an O-H group, 2877 cm^-1 indicating a C-H group, 1587 cm^-1 indicating an N-H group. FTIR analysis on biodegradable plastic Porang starch concentration:

50% chitosan: 50% with 60% glycerol plasticizer showed an absorption wave of 3265 cm^-1 indicating an O-H group, 2937 cm^-1 indicating a C-H group, 1595 cm^-1 indicating an N-H functional group. The absorption wave number of the biodegradable plastic porang starch in this study is similar to the previous study by Amin, M.R et al in 2019 [20], which has an absorption value of 3277.76 cm-1 in the O-H functional group, while in this study it shows an absorption value of 3265 cm-1 also in the O-H functional group. From the results of the FTIR test, it was found that there were groups that were the same as their constituent components, namely O-H, C-H and N-H. If the results of the FT-IR test show that the wave numbers of some of the functional groups of the constituent materials with the functional groups of biodegradable plastics do not change significantly. This shows that the biodegredable plastic produced is a physical mixing process because no new functional groups have been found so that the biodegredable plastic has similar properties to its constituent components [22].

CONCLUSION

The effect of the storage time of biodegradable plastic porang starch on the mechanical properties of tensile strength and elongation decrease every week. Biodegradable plastics still meet the standard of tensile strength and elongation at all concentrations of glycerol plasticizer up to four weeks of storage with tensile strength values of 7.137 MPa, 4.541 MPa and 2.657 MPa and elongation values of 58.574%, 47.324%, 74.699%. The effect of storage time on the thermal properties of TGA-DTA analysis in the first and second weeks, the thermal properties were still stable, then in the third and fourth weeks the thermal stability decreased with a total mass reduction of 9,934 mg and 9,954 mg. The degradation ability test showed a decrease in mass every week, in the third week or 21 days the percent degradation reached 54.19%, 60.24% and 78.75%.

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