Rationale
Biodegradable packaging is gaining significant attention due to the shift towards environmentally friendly materials and the need for sustainable waste management solutions in countries with limited landfill space Unlike petroleum-based synthetic polymers, biodegradable options are derived from renewable and abundant resources Since the 1970s, there has been a resurgence of interest in biodegradable plastics, particularly those made from natural polymers like starch Starch is a promising candidate for future materials due to its cost-effectiveness, availability, thermoplastic properties, and inherent biodegradability in soil and water, making it suitable for large-scale production.
Cassava starch is a significant and commercially valuable source of starch, known for its high starch content and low levels of proteins, ash, and lipids in cassava roots.
[39] Cassava starch contains about 20-26% starch that depends on soil, cultivation and time of harvest [57] They were used in many different fields such as starch foam [39]
Starch-based foam can be manufactured using various methods, such as extrusion and hot mold baking The production process involves two key stages: first, the gelatinization of starch, followed by the evaporation of water from the batter However, these materials tend to be fragile and have a strong affinity for water, which limits their practical applications.
[20] Water molecules attack the hydrogen bonds of starch leading to weak and decrease the functional properties of the materials [8]
Research indicates that incorporating natural polymers can enhance the properties of starch foam Gáspár et al (2005) demonstrated that the addition of polysaccharides and proteins, including cellulose, hemicellulose, and corn zeins, positively affects starch foam characteristics Their findings concluded that hemicellulose and zeins significantly improve the foam's properties.
Research indicates that incorporating lignin-containing cellulose nanofibrils into starch bio foams significantly reduces water absorption and enhances mechanical properties, making them comparable to polystyrene foams (Ago et al., 2016) Additionally, the addition of aspen fiber to baked cornstarch foams improves their strength, with optimal results observed at a fiber content of around 15% Beyond this threshold, specifically between 15-30% fiber, there is no significant change in foam strength However, exceeding 30% fiber content leads to a decrease in strength, likely due to uneven fiber distribution (Lawton et al., 2004; Kaisangsri et al., 2012).
Research by [26] demonstrated that foam derived from cassava starch, combined with 30% Kraft fiber and 4% chitosan, exhibits properties comparable to polystyrene foam Additionally, the study by Soykeabkaew et al (2004) indicated that incorporating jute and flax as additives enhances the flexural strength of the foam.
[55] The results showed foams markedly improved with the addition of 5–10% by weight of the fibers
Research has explored biodegradable synthetic polymers blended with starch, including polycaprolactone (PCL), polylactic acid (PLA), polybutylene succinate adipate (PBSA), and polyhydroxybutyrate (PHB) (Averouse et al., 2000; Shin et al., 2004; Bergeret et al., 2011; Ratto et al., 1999).
Research by Kotnit et al (1995) and Averouse et al (2000) indicates that incorporating polycaprolactone (PCL) into thermoplastic starch significantly enhances its properties, effectively addressing its inherent weaknesses Notably, even a low concentration of PCL at 10 wt% can yield substantial improvements in the material's performance Further studies by Tudorachi et al (2000) and Ke et al support these findings, highlighting the benefits of PCL in thermoplastic applications.
Research indicates that increasing the concentration of PVA enhances the tensile strength of starch/PVA blends, while PLA can improve the compatibility of these blends The incorporation of PVA significantly boosts the mechanical properties of starch/PVA composites Additionally, studies show that adding PBSA at 5%-30% by weight to starch significantly accelerates biodegradation rates in soil, eventually reaching a plateau Furthermore, findings by Yu et al (2007) reveal that the mechanical properties and moisture content of PBSA/starch blends improve incrementally, with both yield strength and impact strength increasing as the PBSA content rises.
Recent advancements in biodegradable foam trays have emerged, yet limited research exists on cassava starch-based foams combined with rice bran and cassava pulp These materials are both biodegradable and cost-effective, derived from agricultural byproducts This study focuses on exploring food packaging solutions utilizing composite cassava starch that offers enhanced resistance to oil and water.
Objectives
The objective of this study was carried out to:
- Improve water and oil resistance of biodegradable food packaging made from cassava starch with additives are rice bran and cassava pulp
- Apply biodegradable packaging as food packaging
Hypothesis
Biodegradable packaging from cassava starch blended with naturally particular additives could improve water and oil resistance.
Expected benefits
Providing information on cassava starch foam and its applications for the alternative of the biodegradable food packaging
The limited properties of cassava starch foam, water resistance, and oil resistance were overcome
The cassava starch foam trays could be an alternative biodegradable packaging for food products
Food Packaging
Effective packaging is crucial for preserving food products, offering protection against breakage and creating barriers to moisture, gases, and external flavors It also blocks light to safeguard nutrients and colors from deterioration Modern packaging not only provides passive protection but actively helps maintain an optimal atmosphere around the product The primary functions of packaging materials include protection, utility, and information, tailored to three environments: physical, atmospheric, and human The ultimate goal is to optimize packaging to efficiently fulfill all three functions across these environments.
Throughout history, various materials such as grasses, wood, and bamboo were traditionally used to weave baskets, while pottery, paper, and glass emerged as primary food container options around 7000 B.C The Egyptians industrialized pottery and glass production by 1500 B.C., but the invention of plastics by Leo Hendrik Baekeland in 1907 marked a significant turning point in packaging Plastics quickly replaced traditional materials due to their durability, low cost, lightweight nature, and versatility in design According to Statista, global plastic production surged from 1.5 million tonnes in 1950 to 311 million tonnes by 2014, raising environmental concerns due to their slow degradation and widespread use in countless products The rise of plastics has irrevocably altered consumer habits, contributing to overconsumption, littering, and pollution, creating a detrimental impact on the environment.
Plastics can leach toxic chemicals into the soil, contaminating groundwater and nearby water sources This poses significant risks to wildlife that rely on this water for survival Additionally, landfills are overflowing with plastic waste, exacerbating environmental damage.
Plastics are composed of various chemicals, which contribute to their versatility but also pose significant risks to human health and the environment One of the most alarming issues is the impact of plastic on marine life, with over 260 species, including invertebrates, reported to ingest or become entangled in plastic debris This entanglement severely restricts their movement, making it challenging for them to find food and survive.
Plastic poses significant environmental challenges, highlighting the need for biodegradable alternatives Biodegradable polymers, sourced from renewable agricultural feedstocks, animal byproducts, marine waste, or microbial sources, offer a sustainable solution These materials decompose into eco-friendly products like carbon dioxide, water, and compost, thereby reducing environmental impact Starch, a naturally abundant and renewable biopolymer, stands out for its thermo-processability and potential for large-scale production While natural polysaccharides like starch lack plasticity, they can be chemically modified or blended with biodegradable synthetic polymers to enhance their properties Utilizing starch-based materials can significantly decrease reliance on nonrenewable resources and mitigate the environmental effects of rising CO2 emissions.
Cassava starch
Cassava starch offers a significant advantage over corn starch, which dominates over 75% of the global starch market, due to its lack of undesirable "cereal flavor." This characteristic makes cassava starch highly sought after for use in various processed foods, especially in bland-flavored products Additionally, its unique physicochemical properties when cooked further establish cassava starch as an essential ingredient in the food industry and other applications.
Cassava starch offers high clarity and viscosity in aqueous dispersion, with a lower gelatinization temperature and higher apparent viscosity compared to cornstarch at the same concentration, making it advantageous for various applications Additionally, cassava starch paste exhibits a reduced tendency to retrograde after cooking, which is often desirable in industrial processes However, despite these benefits, cassava starch has limitations, including instability when exposed to cooking and acidity, similar to other native starches.
Starch foam
Starch is utilized to create starch-based films that share physical characteristics with plastic films, such as being odorless, tasteless, colorless, non-toxic, biologically absorbable, semi-permeable to carbon dioxide, and resistant to oxygen passage High amylose starch films are noted for their flexibility, oxygen impermeability, oil resistance, heat sealability, and water solubility, making them effective in protecting meat products during frozen storage while dissolving during thawing and cooking Additionally, starch serves as a cost-effective, low-density, non-toxic, and biodegradable material for producing foam through methods like extrusion or hot mold baking The process of creating starch-based foam involves starch gelatinization and the evaporation of water from the batter Research indicates that shaped starch foams can be formed by baking starch/water batters in heated closed molds, although foams made solely from starch tend to be brittle and exhibit poor water resistance.
Starch-based foam often suffers from limitations such as weak mechanical properties and water sensitivity To address these issues, incorporating agricultural material composites can lead to the creation of cost-effective products with enhanced performance Notably, affordable additives from plant proteins, fibers, chitosan, oils, and natural rubber could significantly improve the quality of cassava starch foam trays.
Improvement of starch foam
The association of starch foam with other natural polymers is a new strategy to obtain low cost and compostable material In this context, rice bran and cassava pulp
The use of inexpensive additives derived from waste products of rice bran oil extraction and cassava pulp starch may enhance the quality of cassava starch foams As indicated in Table 2.1, the chemical composition of these additives, which includes fiber, protein, and lipids, has the potential to improve the properties of starch foams.
Table 2.1 Chemical composition of rice bran and cassava pulp*
(* These results are results of another research work in Phytobio-active and Flavor Laboratory, at School of Bioresources and Technology, King Mongkut’s University of Technology Thonburi (KMUTT) )
Cellulose, an organic polysaccharide with the formula (C6H10O5)n, comprises a linear chain of β(1→4) linked D-glucose units, differing from the α(1→4) glycosidic bonds found in starch and glycogen This straight-chain polymer does not coil or branch, resulting in a stiff rod-like conformation due to the equatorial arrangement of glucose residues The numerous hydroxyl groups on the glucose molecules allow for strong inter-chain bonding, forming microfibrils that provide high tensile strength This structural integrity is crucial for plant cell walls, where microfibrils are integrated into a carbohydrate matrix, enhancing the rigidity of plant cells.
Cellulose, a non-digestible element found in plant cell walls, is utilized in the production of edible films that are water-soluble, fat-resistant, durable, and flexible Research indicates that cellulose-based films can effectively reduce oil absorption during frying, minimize cooking runoff, and decrease moisture loss when used as glazes for poultry and seafood.
Lipids are a diverse group of naturally occurring molecules that encompass fats, waxes, sterols, monoglycerides, diglycerides, and phospholipids They play essential roles in biological systems, serving as energy storage, structural components of cell membranes, and crucial signaling molecules.
Waxes and fat-based oils are incorporated into protein or polysaccharide films to enhance flexibility, improve coating properties, and prevent sticking during cooking Edible lipid or resin coatings derived from waxes offer several benefits for food applications These lipids enhance hydrophobicity, cohesiveness, and flexibility while serving as effective moisture barriers due to their tightly packed crystalline structure, which restricts water vapor movement.
Proteins can be categorized into plant-based sources, such as gluten, soy, pea, and potato, and animal-based sources like casein, whey, collagen, and keratin These proteins are essentially random copolymers of amino acids, with side chains that are amenable to chemical modification This characteristic is advantageous for material engineers seeking to adjust properties like relative humidity, thanks to the hydrophilic nature of these proteins Chemical modification is one effective method to enhance protein properties, offering a broad spectrum of possibilities for various applications.
18 variety of chemical moieties which may help to tailor protein properties towards specific applications
The protein-polysaccharide complex demonstrates enhanced functional properties compared to polysaccharides alone, significantly improving the mechanical characteristics of bio-foam The inclusion of protein contributes to a denser outer skin, effectively preventing oil penetration into cassava starch foam, which in turn enhances the oil absorption capacity of the starch foam.
Materials
Materials were used for this study, as bellows:
1 Cassava starch was bought from the local market in Thailand
2 Rice bran was obtained from Thai Dynamics Master Co Ltd
3 Cassava pulp was obtained from Premier Bio Energy Co., Ltd
4 Water bath (Memmert, WNB 45, Germany)
5 Centrifuge (PLC - 05, Germany Industrial crop, Taiwan)
7 Hot air oven (Memmert, UFE600, Germany)
8 Vortex mixture (vortex genie, Scientific Industries, USA)
9 Texture analyzer (LLOYD Instruments, TA plus)
10 Baking machine (180 mm in length, 105 mm in width, and 10 mm in depth)
13 Hotplate and stirrer (Well model WSAHS1, We source Co., Ltd Thailand)
14 Vernier Caliper (Mitutoyo Corporation, Japan)
16 Laboratory instruments such as a micropipette, falcon tube, crucible, beaker, dispensing bottle, Erlenmeyer flask, desiccator
All other reagents were of analytical reagent grade and were used without further purification
Methods
Effect of increased water and oil resistance of cassava starch for biodegradable food packaging was divided into two experiments:
Experiment 1: Improve water and oil resistance of biodegradable starch foam using rice bran
Experiment 2: Improve water and oil resistance of biodegradable starch foam using cassava pulp
3.2.1 Experiment 1: Improve water and oil resistance of biodegradable starch foam using rice bran
Cassava starch was combined with rice bran at varying concentrations of 40%, 60%, and 80% starch, mixed with 0%, 10%, and 20% rice bran by weight An 80-gram starch batter with these additives was poured into a heated baking mold measuring 180 mm in length, 105 mm in width, and 10 mm in depth The mold was maintained at a temperature of 250 ± 5°C for 5 minutes Key measurement parameters for the biodegradable foam included thickness, density, compressive strength, flexural strength, water absorption index, water solubility index, and oil resistance.
Measurement parameters of cassava starch foam: thickness (Kaisangsri et al.,
2015 [26]), density (Cinelli et al., 2006 [13]), compressive strength (ATM D1621-10,
2010), flexural strength (ASTM D790-10, 2010), water absorption index (WAI) and water solubility index (WSI) (AACC method 56-20) and oil absorption (Karnnet et al., 2005 [28])
Foam thickness was assessed using a Mitutoyo Corporation Venier Caliper, with measurements taken at ten distinct points along the length of each sample The results are presented as mean ± standard deviation (SD).
Foam density was determined using a sand volumetric displacement method, analyzing three different foam samples Each foam piece was weighed on a Mettler AE260 analytic balance before being placed in a 25 ml graduated cylinder After tapping the cylinder for one minute, the displaced sand volume was recorded Foam density was then calculated by dividing the mass of the foam by the volume of sand displaced.
Flexural tests were conducted to assess the mechanical properties of starch foam using a TA Plus textural analyzer from LLOYD Instruments, equipped with a 500-N load cell Samples, measuring 25 mm × 100 mm, were prepared for testing, and flexural strength was evaluated through three-point bending tests in accordance with ASTM D790-10, utilizing a span of 50 mm and a crosshead speed of 2.5 mm/min The foam specimens were subjected to deformation until failure occurred, allowing for the calculation of flexural strength.
Where F is load (force) at the fracture point (N), L is the length of the support span, b is the width, and d is thickness (mm)
The density of foam = mass of foam volume of foam
Figure 3.2 Three-point flexural test [3]
Compressive strength was assessed using a texture analyzer (TA plus, LLYOD Instruments, UK) equipped with a 500-N load cell, following ASTM D1621-10 standards A starch foam tray was positioned on a flat plate and subjected to compression at a rate of 2.5 mm/min until it reached 10% of its original diameter, utilizing a metal probe The test concluded by halting the crosshead, allowing for the calculation of compressive strength, which was determined by dividing the maximum load by the probe's cross-sectional area.
Each sample, measuring 50 mm × 50 mm, was positioned on white paper, and a 25 mm diameter tube, exceeding 25 mm in height, was placed over it Subsequently, 5 g of sand was added into the tube, followed by the application of 1.1 ml of palm oil, which was then sealed with a glass lid The experiment was conducted at a temperature range of 20-25°C and 75% relative humidity over a period of 5 days, with oil absorption calculated accordingly.
Where, W 1 and W 2 (g) were the weight of the foam before and after oil absorption, and A was the surface area of the foam (cm 2 )
3.2.1.6 Water absorption index (WAI) and water solubility index (WSI) (AACC method 56-20, 1993 [1])
A one-gram sample was mixed with 30 ml of distilled water and incubated in a water bath at 30°C for 30 minutes Following this, the mixture was centrifuged at 6000 rpm for 30 minutes, and the supernatant was collected and placed in an aluminum can The sample was then dried at 105°C for 24 hours The Water Absorption Index (WAI) and Water Solubility Index (WSI) were subsequently calculated.
WAI = weight of tube with sample−weight of tube weight of sample
WSI = weight of aluminum can with solid−weight of aluminum can weight of sample × 100
3.2.2 Experiment 2: Improve water and oil resistance of biodegradable starch foam using cassava pulp
In this study, cassava starch was combined with cassava pulp at varying concentrations of 40%, 60%, and 80%, along with 0%, 10%, and 20% by weight of starch, respectively A total of 80 grams of the starch batter mixture was then poured into a hot baking mold with dimensions of 180 mm in length, 105 mm in width, and 10 mm in depth The mold was heated to a temperature of 250 ± 5°C for 5 minutes The resulting biodegradable foam was evaluated based on several parameters, including thickness, density, compressive strength, flexural strength, water absorption index, water solubility index, and oil resistance.
Foam thickness was assessed using a Mitutoyo Corporation Venier Caliper, with measurements taken at ten distinct points along the length of each sample The results are presented as mean ± standard deviation (SD).
Foam density was determined using a sand volumetric displacement method, analyzing three different foam samples Each foam piece was weighed on a Mettler AE260 analytic balance and placed in a 25 ml graduated cylinder After tapping the cylinder for one minute, the displaced sand volume was recorded The foam density was then calculated by dividing the mass of the foam by the displaced volume.
Measurement parameters of cassava starch foam: thickness (Kaisangsri et al.,
2015 [26]), density (Cinelli et al., 2006 [13]), compressive strength (ATM D1621-10,
2010), flexural strength (ASTM D790-10, 2010), water absorption index (WAI) and water solubility index (WSI) (AACC method 56-20) and oil absorption (Karnnet et al., 2005 [28])
Flexural tests were conducted to evaluate the mechanical properties of starch foam using a TA Plus textural analyzer from LLOYD Instruments, equipped with a 500-N load cell Samples measuring 25mm × 100mm were prepared for testing, and three-point bending tests were performed in accordance with ASTM D790-10, utilizing a span of 50 mm and a crosshead speed of 2.5 mm/min The foam specimens were subjected to deformation until failure occurred, allowing for the calculation of flexural strength.
2𝑏𝑑 2 Where F is load (force) at the fracture point (N), L is the length of the support span, b is the width, and d is thickness (mm)
Compressive strength was evaluated using a texture analyzer (TA plus, LLYOD Instruments, UK) equipped with a 500-N load cell, following ASTM D1621-10 standards The starch foam tray was positioned on a flat plate and subjected to compression at a rate of 2.5 mm/min until it reached 10% of its original diameter Once this compression point was achieved, the crosshead was halted, and the compressive strength was calculated by dividing the maximum load by the probe's cross-sectional area.
Each sample, measuring 50 mm × 50 mm, was positioned on a white paper A tube with a diameter of 25 mm and a height exceeding 25 mm was placed over each sample, followed by the addition of 5 g of sand into the tube Subsequently, 1.1 ml of liquid was introduced.
The density of foam = mass of foam volume of foam
A test was conducted by placing 26 palm oil droplets onto sand, which were then covered with a glass lid This method requires a controlled environment of 25-29°C and 75% relative humidity, maintained over a period of 5 days The absorption of the oil was subsequently calculated based on these conditions.
Where, W 1 and W 2 (g) were the weight of the foam before and after oil absorption and A was the surface area of the foam (cm 2 )
3.2.1.6 Water absorption index (WAI) and water solubility index (WSI) (AACC method 56-20, 1993 [1])
A one-gram sample was mixed with 30 ml of distilled water and incubated in a water bath at 30°C for 30 minutes Afterward, the mixture was centrifuged at 6000 rpm for 30 minutes, and the supernatant was collected This supernatant was then transferred to an aluminum can and dried at 105°C for 24 hours The Water Absorption Index (WAI) and Water Solubility Index (WSI) were subsequently calculated.
WAI = weight of tube with sample−weight of tube weight of sample
WSI = weight of aluminum can with solid−weight of aluminum can weight of sample × 100
Statistical analysis
The analysis of variance (ANOVA) and least significant difference (LSD) for all analyzed data were conducted using SAS software (version 9, SAS Institute Inc., Cary, NC, USA), with the LSD determined at a confidence interval of α = 0.05 The data are presented as mean ± standard deviation (SD).
Appearance of cassava starch foam, cassava starch foam mixed with rice bran and
Figure 4.1 Appearance of cassava starch foam, cassava starch foam mixed with rice bran and cassava pulp
Thickness of cassava starch foam, cassava starch foam mixed with rice bran and
The thickness of cassava starch foam was assessed at three starch concentrations: 40%, 60%, and 80%, combined with rice bran and cassava pulp at varying levels of 0%, 10%, and 20% by weight The results indicated that the thickness of the cassava starch foam increased with higher starch content, reaching a maximum thickness of 5.53 mm at 80% cassava starch This increase in thickness can be attributed to the formation of a starch network during water evaporation from the batter, where the proximity of starch chains at elevated concentrations promotes a denser matrix Additionally, the incorporation of rice bran as an additive further enhanced the foam's thickness, as higher rice bran content contributed protein, which is essential for the structural integrity of foam trays This trend aligns with findings by Salgado et al (2008), which noted that foam thickness increases with rising protein content.
Figure 4.2 Thickness of cassava starch foam, cassava starch foam mixed with rice bran and cassava pulp.
Density of cassava starch foam, cassava starch foam mixed with rice bran and
Figure 4.3 Density of cassava starch foam, cassava starch foam mixed with rice bran and cassava pulp
Foam trays with higher additive content exhibit greater density compared to those made from cassava starch This increased density and thickness are attributed to the higher protein and fiber content, which enhances resistance to swelling during the foam formation process Additionally, the presence of fibers in the foam formulation leads to increased viscosity, resulting in less expandable material, smaller average cell sizes, and thicker cell walls.
CS CS+10%RB CS+20%RB CS+10%CP CS+20%CP
CS CS+10%RB CS+20%RB CS+10%CP CS+20%CP
The density of starch-based foam varies, with values ranging from 0.21 to 0.53 g/cm³ The highest density, measured at 0.53 g/cm³, was found in foam produced from a composition of 60% cassava starch and 20% rice bran, while the lowest density of 0.21 g/cm³ was observed in foam made solely from 80% cassava starch.
Flexural strength of cassava starch foam, cassava starch foam mixed with rice
The flexural strength of cassava starch foam, both alone and when combined with rice bran and cassava pulp, is illustrated in Figure 4.4 As the starch content increases, the flexural strength of cassava starch rises to between 1.09 and 2.92 MPa, aligning with findings from Shogren et al (1998) on starch-based trays Incorporating cassava pulp at 10-20% of the starch weight enhances flexural strength further, reaching values of 1.63-4.61 MPa and 1.97-5.16 MPa, respectively However, at 80% cassava starch content, the flexural strength diminishes to 3.63 MPa and 4.63 MPa This decline may be attributed to the high starch and fiber content of cassava pulp, which could lead to fiber discontinuities in the trays, creating weak points that compromise overall strength.
The accumulation of fiber leads to a non-homogeneous structure in materials Research indicates that the flexural strength of cassava starch foam improves with higher rice bran content, suggesting that increased protein levels can also enhance this strength.
Figure 4.4 Flexural of cassava starch foam, cassava starch foam mixed with rice bran and cassava pulp
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Compressive strength of cassava starch foam, cassava starch foam mixed with rice
The compressive strength of cassava starch foam increases with higher cassava starch content, ranging from 0.49 to 2.09 MPa, as shown in Figure 4.5 This trend aligns with findings by Glenn et al (2001), which highlighted the impact of starch concentrations Notably, a mixture of 80% cassava starch and 20% rice bran yielded the highest compressive strength of 4.1 MPa The incorporation of protein into cassava starch foam enhances its functional properties, as protein-polysaccharide complexes outperform polysaccharides alone Additionally, the inclusion of cassava pulp contributes to increased compressive strength by forming a fibrous network, corroborating Mali et al (2010), who noted that foam compression strength rises with higher fiber proportions, and supporting earlier research by Kaisangsri et al (2014) and Soykeabkaew et al (2004).
Figure 4.5 Compressive strength of cassava starch foam, cassava starch foam mixed with rice bran and cassava pulp
Oil absorption of cassava starch foam, cassava starch foam mixed with rice bran
The oil absorption of cassava starch foam decreased with the addition of the rice bran and cassava pulp (Figure 4.6) Rice bran and cassava pulp provide protein
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The incorporation of protein and fiber into cassava starch foam enhances oil resistance by creating denser outer skins that prevent oil penetration However, increasing the rice bran content alongside cassava starch leads to higher oil absorption rates Specifically, when cassava starch content reaches 40%, oil absorption increases to 0.056-0.073 g/cm², and at 60%, it rises to 0.0067-0.009 g/cm², further increasing to 0.009-0.01 g/cm² with 80% cassava starch Rice bran, containing 12-22% oil and 11-17% protein, contributes to this effect by increasing the hydrophobicity of the starch foam, allowing more oil to penetrate Similar findings were reported by Kaisangsri et al (2014) with palm oil additives.
Figure 4.6 Oil absorption of cassava starch foam, cassava starch foam mixed with rice bran and cassava pulp
Water absorption index (WAI) and water solubility index (WSI) of cassava starch foam, cassava starch foam mixed with rice bran and cassava pulp
Starch foams are vulnerable to moisture in high humidity conditions, as water molecules disrupt the hydrogen bonds within the starch, leading to a decline in the material's functional properties Therefore, enhancing water resistance in foam trays relies on optimizing water absorption and water solubility.
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O il Abs o rpt io n(g /cm 2 )
Figure 4.7 Water absorption of cassava starch foam, cassava starch foam mixed with rice bran and cassava pulp
Table 4.1 WAI of cassava starch foam mixed with 10 and 20% rice bran Cassava starch concentration
Different data in the same column mean significant difference (p ≤ 0.05)
The water absorption index (WAI) of cassava starch foam, cassava starch mixed with rice bran, and cassava starch combined with cassava pulp is illustrated in Figure 4.7 The cassava starch foam exhibits high WAI values, with measurements of 11.31, 9.79, and 11.51 for starch concentrations of 40%, 60%, and 80%, respectively, indicating that water molecules can easily interact with the hydroxyl groups of glucose units along the polymer chains As the proportion of rice bran increases, the water absorption of cassava starch mixed with rice bran decreases, likely due to the oil content in rice bran which reorganizes the starch structure and reduces the exposure of hydroxyl groups Although the WAI of cassava starch foam mixed with rice bran shows a non-significant decrease with higher rice bran content (p ≤ 0.05), this may be attributed to the hydrophilic nature of proteins in rice bran, which enhances its water-holding capacity Additionally, incorporating cassava pulp into cassava starch foam results in a slight reduction in water absorption.
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33 absorption index of the foam The fibers in cassava pulp, which may be absorbed less water, are responsible for this water sensitivity reduction for composites [8]
Figure 4.8 Water solubility of cassava starch foam, cassava starch foam mixed with rice bran and cassava pulp
The water solubility index (WSI) of cassava starch foam is influenced by the incorporation of cassava pulp and rice bran Increasing the cassava pulp content in the foam results in a decreased WSI, with a mixture of 80% cassava starch and 20% cassava pulp exhibiting the lowest WSI at 4.31% Research by Guan et al (2004) suggests that cellulosic fibers, such as those from cassava pulp, can enhance the moisture resistance of starch foams by creating a hydrophobic barrier Additionally, the WSI for foams containing 80% cassava starch mixed with 10% and 20% rice bran were measured at 12.32% and 7.41%, respectively An increase in protein concentration in rice bran correlates with a further reduction in WSI, likely due to the formation of covalent intermolecular bonds and interactions within the foam, which contribute to its reduced water solubility.
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Rice bran
The incorporation of rice bran into starch foam trays significantly enhanced their functional properties Specifically, trays made with a composition of 80% cassava starch and 20% rice bran exhibited compressive and flexural strengths of 4.1 MPa and 5.05 MPa, respectively Additionally, the proteins and oils present in rice bran contributed to a marked decrease in both water absorption and water solubility of the trays, while also improving their oil resistance.
The study demonstrated that rice bran significantly contributes to the development of starch foam; however, an excessive amount of rice bran can lead to brittleness and cracking in the foam The optimal formulation identified was 60% starch and 10% rice bran, which showcased superior properties, including enhanced shape retention, maximum resistance, and reduced water absorption.
Cassava pulp
The incorporation of cassava pulp as an additive significantly enhanced the mechanical properties and water resistance of cassava starch foam without compromising other characteristics At a constant concentration of 60% cassava starch, the addition of 20% cassava pulp resulted in a notable increase in compressive strength from 1.27 MPa to 2.18 MPa, and flexural strength rose from 1.99 MPa to 4.61 MPa Furthermore, the water absorption and solubility of the foam decreased, indicating improved performance.
35 produced from 80% cassava starch + 20% cassava pulp has the lowest water solubility was 4.31 Furthermore, shape, structure, and color of starch foam were stable
To reduce costs, the content of cassava starch and cassava pulp is 60% and 20%, respectively Increasing the content of cassava starch improves the properties of foam trays but non-significantly