Application of modified starch on glass bioplastic based on carrageenan from Eucheuma cottonii on mechanic and biodegradation properties

Polysaccharides from carrageenan have potential as bioplastic forming materials. Bioplastics have water resistance (hydrophobic) properties which can be improved by using modified starch. Modified Starch is a material that can reduce the hydrophilic properties of bioplastics. The objectives of this study were to determine the effect of modified starch application on carrageenan- based glass bioplastics on biodegradability and water resistance and to determine the best bioplastic formulation for biodegradability and water resistance. This research was conducted using experimental methods in the biodegradation test and the resistance or swelling test. The experimental method in this study used a completely randomized design (CRD) at a significance level of 5% (α = 0.05). The results of this study indicate that the addition of high modified starch can increase the water resistance of bioplastics but the addition of high modified starch will result in slower biodegradability.


Introduction
Plastic is a packaging material that is widely used in various products and includes single-use packaging. Plastics are produced worldwide in large quantities [1]. Plastics can be made from synthetic or semisynthetic organic materials [2]. Plastics as packaging are widely used because they are lightweight, costeffective, and durable [3]. Plastic is one of the main sources that can cause problems in environmental pollution [4]. One of the contributors to plastic waste that can cause waste is the use of plastic cups.
Plastic cups are glasses made of plastic material with lightweight and water-resistant properties. Plastic cups derived from polypropylene will be difficult to decompose by microorganisms, because the carbon element forms complex and long chemical chains [5]. The high use of plastic cups can be overcome by reducing the use of plastic cups. Reduction of plastic cup waste can be pursued with waste processing technology, recycling and incineration. The countermeasure that is often done is to burn plastic waste. The use of this method has not been effective in solving problems that arise due to plastic cup waste. Burning plastic waste can produce toxic gases such as dioxins, furans, mercury and polychlorinated biphenyls which can increase global warming [4]. Based on these problems and the many studies on bioplastics. So, it is necessary to solve problems that can reduce the use of plastic cups, namely by formulating materials that can decompose naturally as materials for glass bioplastics. Bioplastic is an alternative to plastic packaging that can be made from natural materials that can be widely used because it is environmentally friendly and easily degraded [6]. One of the characteristics of bioplastics or plastics is their resistance to water.
Materials from nature that are often used as materials to form bioplastics can be derived from polysaccharides derived from carrageenan and starch [7,8,9]. Carrageenan is a natural material that can be used as a gelling agent during the production of bioplastics [10]. Carrageenan is a group of galactose polysaccharides produced from the extraction of red seaweed. Carrageenan is a hydrocolloid compound that can be used in the manufacture of bioplastics [11]. Carrageenan has a free hydroxyl group (OH -) which is able to form hydrogen bonds with H2O so that carrageenan can be hydrophilic [12].
Bioplastics made from natural materials have properties that are rigid and easily brittle, so they require plasticizers (plasticizers). Plasticizer is an organic material that has a low molecular weight and can be added to a product to reduce the stiffness of the polymer, while increasing the flexibility and extensibility of the polymer [13]. Sorbitol is one of the plasticizers that is often used in the manufacture of bioplastics. Sorbitol ismonosaccharide compound polyhydric alcohol a hydrophilic [14].
One of the must-have properties of bioplastics is water resistance (hydrophobic). The filler that can be added to increase the hydrophobic properties of bioplastics is modified starch. Modified starch is starch that has been treated to produce better properties than before, besides that it will produce starch with the characteristics of a softer texture, high stability, and longer shelf life than unmodified starch [15].

Process of making modified starch by acetylation The production of modified
Starch was carried out by the method of [16]. The initial preparation for the material is to prepare 100 g of tapioca flour dispersed into 225 ml of distilled water, stirred with a magnetic stirrer for one hour at room temperature. pH was maintained to 8 by adding 3% NaOH. Furthermore, 16% acetic acid was added by weight of the material used and allowed to stand for 1 hour. The suspension was maintained at pH 8 for 50 minutes by adding 3% NaOH at room temperature. After that, 0.5 N HCl was added to pH 4.5-5. The next process was precipitation and washing with distilled water three times and ethanol once. Washing was carried out by pouring the suspension into a beaker glass and adding 50 mL of distilled water, stirring vigorously using a stirring rod and then filtering using whatman paper and vacuum pump, washing with distilled water was repeated three times. The washing steps with ethanol were carried out the same as washing with distilled water. Then drying in the oven at a temperature of 50 o C for 20 hours. The last stage is refining and filtering.

The process of making glass bioplastics
Making Bioplastic Packaging Making bioplastic packaging refers to the method used by [17] which is modified on the concentration of the basic ingredients, the concentration of plasticizers, and the drying method. Dissolve the modified starch according to the treatment concentration that has been applied (0, 1, 2, 3 grams) into 100 mL of distilled water, heated to a temperature of 85°C and while stirring using a hot plate and a magnetic stirrer. Then 3 grams of carrageenan was added and stirred until homogeneous [18], it took about 15 minutes. After being homogeneous, 5 mL of sorbitol was added and stirred for 2 minutes IOP Publishing doi:10.1088/1755-1315/1036/1/012012 3 while maintaining the suspension temperature at 60°C. The suspension was molded in a glass mold, allowed to stand at room temperature for 2 hours and then in an oven at 50°C for 24 hours [19].

Biodegradation on bioplastic
The biodegradation test refers to the method of [20] with slight modifications. The initial stage is cutting the sample with a size of 2 cm × 2 cm, then weighing (W1). Then the bioplastic samples were buried in the soil with a depth of 8 cm for a period of 7 days. After that, the samples were cleaned and the re-weighing process was carried out (W2). The percentage value of the average mass reduction of the buried bioplastic is obtained through the following equation: Note: Biodegradation Test (%) = percentage of decomposition of the bioplastic W1 = initial sample weight W2 = final sample weight

Water resistance test Water
Water resistance test is a test to determine whether the resulting bioplastic is water soluble or not within a certain time and temperature. This test is used to determine the occurrence of bonding in the polymer and the degree or regularity of the bond in the polymer which is determined from the percentage increase in polymer weight after experiencing swelling. The process of diffusion of solvent molecules into the polymer will produce a bulging gel. The test begins by cutting the sample with a size of 2 cm x 2 cm, then weighing the initial weight of the sample (W0). The sample was put in a beaker glass which had been filled with 30 mL of distilled water for 3 minutes. After 3 minutes the sample was removed and the water that was still attached to the surface of the bioplastic was removed with a dry tissue. Furthermore, the weighing of the end (W1). The value of the weighing is entered into the equation [21].   Table 3.

Time of biodegradation
The results of the biodegradation test of bioplastics with the addition of the highest concentration of modified starch (3 grams) has a biodegradation value of 42.75%. Meanwhile, without adding modified starch has a biodegradation value of 55.68%. Glass bioplastics can be completely degraded within 13-16 days. These results indicate that the biodegradability of glass bioplastics with the addition of modified starch can meet ASTM5336. According to the international plastic standard (ASTM5336) the biodegradability time for PLA plastic from Japan and PCL from the UK takes 60 days to completely decompose.
The results of the biodegradation test in this study indicate that the higher the addition of modified starch causes the bioplastic produced to experience a decreased biodegradability. The decrease in biodegradability can be influenced by the hydrophobic nature of the modified starch. This hydrophobic nature can affect the activity of microorganisms in their ability to degrade bioplastics. This is in accordance with [22], hydrophobic properties can affect the water absorption ability of bioplastics and will affect the rate of degradation of bioplastics. Hydrophobic properties affect the activity of microorganisms, because microorganisms need water for metabolism. The more addition of modified starch, the less water absorption. Such bioplastics will take a longer time to degrade due to the inhibition of degrading microorganisms.
Biodegradation in bioplastics can be influenced by temperature, humidity which determines soil pH, and microorganism activity [23]. Soil pH is very important because microorganisms can decompose bioplastics in soil. If the pH of the soil is in accordance with the activity of microorganisms, then its activity in degrading bioplastics will be optimal. According to [24], the optimum pH for soil microorganism activity produced by Bacillus sp. ranged from pH 6.5±7 or neutral pH. Bacillus sp. and Pseudomonas sp. can degrade bioplastics by breaking polymer chains into monomers [25].

Effect of modified starch to water resistance
Water resistance tests on bioplastics can be used to determine whether the properties of the bioplastics produced are close to those of conventional plastics or not, one of which is water resistance. To determine the water resistance of bioplastics can be done with a swelling test. The swelling test is the swelling ratio of the bioplastic in the presence of water [26]. The lower the percentage of water absorption means that the plastic properties are getting better, while the higher the percentage of water absorption means that the plastic properties will be easily damaged [7]. The following are the results of the water resistance test on glass bioplastics: a. Cold temperature Testing the water absorption capacity of glass bioplastic with the addition of modified starch obtained the least absorption at 48.86% at cold temperatures (4 o C) and the highest absorption at 135.80% at room temperature (25 o C). The test results on glass bioplastics using a hot temperature of 80 o C also resulted in a fairly high water absorption compared to cold temperatures and room temperature. The higher water absorption will produce bioplastics with lower water resistance. This statement is in accordance with [21], the lower water absorption will produce bioplastics with higher water resistance, while higher water absorption will result in lower water resistance in bioplastics and swelling of the sample will occur. Bioplastics derived from starch have a weakness, namely their resistance to water, so it is necessary to add hydrophobic materials.
The addition of modified starch in this study aims to improve the properties of glass bioplastics, one of which is water resistance. The starch modification process using acetylation method can be done by adding acetic acid which can weaken the hydrogen bonds in starch. Acetic acid containing an acetyl group can cause the abolition of the OH group so that the water absorption ability will be lower [27]. Thus the use of modified starch by acetylation can increase the hydrophobic properties of starch.
Damage to bioplastics is characterized by bioplastics that look soft and eventually break. Bioplastics that are in hot water will initially appear warped, then return to their original state after a while and will eventually break. Meanwhile, at hot temperatures, the bioplastic will melt. At first the heated bioplastic will harden and then at a certain temperature will melt [28].
The results obtained in this study indicate that the addition of modified starch will increase the water resistance of glass bioplastics. The increase in water resistance was due to the modified starch having hydrophobic properties. Modified starch is hydrophobic because the modification process in starch can produce smaller starch [29]. Amorphous area is an area that is less dense and tenuous so that in the end it can be easily penetrated by water and easily absorbs water.

Conclusion
The application of modified starch to glass bioplastic based on carrageenan from Eucheuma cottonii has a significant effect on the biodegradability and water resistance of the bioplastic. The best level of biodegradation is 55.68% while the lowest is 42.75%. The best results of water resistance are 48.86% with an initial temperature of 4 o C, 71.33% with a temperature of 25 o C, and 97.13% with an initial temperature of 80 o C. The best formulation for the biodegradability of glass bioplastic is the addition of 0% modified starch with a biodegradability value of 55.68%. Meanwhile, the best formulation for water resistance is 3 grams of carrageenan with the addition of 3 grams of modified starch with a water resistance value of 48.86% at cold temperature, 71.33% at room temperature, and 97.13% at hot temperature.