Filmes derivados de amidoalginatoborra de café termoplastico para aplicações em embalagens de alimentos

Prévia do material em texto

<p>Vol.:(0123456789)1 3</p><p>Journal of Polymer Research (2023) 30:191</p><p>https://doi.org/10.1007/s10965-023-03565-1</p><p>ORIGINAL PAPER</p><p>Films derived from thermoplastic starch/alginate/spent coffee</p><p>grounds for food packaging applications</p><p>Vy H.T. Nguyen1,5 · Prabhakar M.N.2  · Dong‑Woo Lee2 · In Chul Lee 3 · Jung‑il Song4</p><p>Received: 16 September 2022 / Accepted: 18 April 2023 / Published online: 9 May 2023</p><p>© The Polymer Society, Taipei 2023</p><p>Abstract</p><p>In this study, spent coffee grounds (SCG) were utilized as a reinforcing biowaste filler in thermoplastic starch/alginate (TPS-</p><p>Alg) films. Wet ball milling was used to reduce the SCG particle size. The UV transmission barrier of the TPS-Alg films</p><p>comprising dark brown SCG particles was 1.5–3.4 times higher than that of binary matrices. The incorporation of SCG</p><p>induced several voids within the polymeric chains, decreasing the moisture content by 2.10% and reducing the water vapor</p><p>permeability from (10.50 ± 1.07) × 10− 13 to (9.03 ±1.69) × 10− 13 ng·s− 1  m− 2  Pa− 1. A slight improvement in the thermal</p><p>stability of the TPS-Alg/SCG blends was observed in comparison to that of the pure TPS-Alg, owing to the partial substitution</p><p>of TPS with SCG. The notable tensile strength and tensile modulus of TPS-Alg/SCG-10 were respectively 67.6 ± 6.1 MPa</p><p>and 4.7 ± 0.3 GPa in spite of the stress concentration and plasticizing effects from SCG fillers. The overall results indicate</p><p>a significant potential of the as-developed material for application in food packaging.</p><p>Keywords Thermoplastic starch · Alginate · Spent coffee grounds · Food packaging film</p><p>Introduction</p><p>Global warming, which is predominantly caused by green-</p><p>house gases (GHGs), has triggered severe economic and</p><p>environmental crises. Significantly, the amount of CO2</p><p>released into the atmosphere from the processing (including</p><p>the extraction of fossil fuels, polymer manufacture, and</p><p>product end-of-life) of conventional plastics—“a fundamen-</p><p>tal human need” [1]— constitutes ~2% of the global CO2</p><p>yield [2]. In addition to the adverse effects of plastic pol-</p><p>lution on ecosystem health, tourism, fishing, and shipping</p><p>fields [1, 3], it has also been reported that the CO2 capturing</p><p>capacity of oceanic creatures is compromised by stubborn</p><p>microplastic debris. Among the industrial plastic applica-</p><p>tions, packaging (particularly, packaging films) has the most</p><p>transient working life of a few minutes and inevitably con-</p><p>tributes to the global production of over 140 million tons of</p><p>plastic waste per year [3, 4]. Therefore, the use of bio-based</p><p>and biodegradable polymeric materials for packaging appli-</p><p>cations is attractive because of their significant potential in</p><p>the bioplastic market [3, 5].</p><p>Starch-based thermoplastic or thermoplastic starch</p><p>(TPS) has gained increasing attention on account of its</p><p>affordability, renewability, comestible film-forming abil-</p><p>ity, and biodegradability [6]. However, moisture sensitivity,</p><p>low long-term stability due to the retrogradation process</p><p>(i.e., rebuilding hydrogen bonds), and insufficient mechani-</p><p>cal properties are regarded as major limitations of TPS [5,</p><p>7]. Additionally, as a consequence of policy backing and</p><p>the competitiveness in food feedstock resources, the cost of</p><p>starch-derived plastics is estimated to be approximately 1.6</p><p>* Prabhakar M.N.</p><p>dr_prabhakar@changwon.ac.kr</p><p>* Jung-il Song</p><p>jisong@changwon.ac.kr</p><p>1 Department of Smart Manufacturing Engineering,</p><p>Changwon National University, 20 Changwondaehak-ro,</p><p>Uichang-gu, Changwon 51140, Gyeongsangnam-do,</p><p>Republic of Korea</p><p>2 Research Institute of Mechatronics, Department</p><p>of Mechanical Engineering, Changwon National University,</p><p>20 Changwondaehak-ro, Uichang-gu, Changwon,</p><p>Gyeongsangnam-do 51140, Republic of Korea</p><p>3 Center for Remote Education Assistance, Inha Technical</p><p>College, Inha-ro, Nam-gu, Incheon 22212, Republic of Korea</p><p>4 Department of Mechanical Engineering, Changwon</p><p>National University, 20 Changwondaehak-ro, Uichang-gu,</p><p>Changwon 51140, Gyeongsangnam-do, Republic of Korea</p><p>5 School of Chemical, Biological, and Materials Engineering,</p><p>The University of Oklahoma, Norman, Oklahoma, USA</p><p>http://crossmark.crossref.org/dialog/?doi=10.1007/s10965-023-03565-1&domain=pdf</p><p>http://orcid.org/0000-0002-5274-5632</p><p>Journal of Polymer Research (2023) 30:191</p><p>1 3</p><p>191 Page 2 of 9</p><p>times higher than that of LDPE [8]. To improve TPS prop-</p><p>erties, various experiments have been conducted, including</p><p>combining TPS with other polymers (fossil-based or bio-</p><p>based) and/or reinforcements with fibrous or non-fibrous</p><p>additives. Innovative preparation techniques, such as elec-</p><p>trospinning, reactive extrusion, and three-dimensional</p><p>printing, have also been investigated [6].</p><p>Commonly, the mechanical properties and water uptake</p><p>of the packaging films can be improved using TPS/syn-</p><p>thetic polymer blends, which modify interfacial adhesion</p><p>and processing of the film. Examples of synthetic poly-</p><p>mers used in conjunction with TPS include polypropyl-</p><p>ene (PP), polyethylene (PE), polyvinyl acetate (PVA),</p><p>and polylactic acid (PLA) [7]. Owing to their comparable</p><p>performance that of synthetic films, film-forming natural</p><p>polymers, such as pectin, chitosan, carboxymethyl cellu-</p><p>lose, and alginate (Alg), have also been melded with TPS,</p><p>yielding “green” alternatives [9–12]. Despite excellent</p><p>compatibility between members of the carbohydrate fam-</p><p>ily, their hygroscopicity and barrier efficacy limit their</p><p>practical application. To overcome these shortcomings,</p><p>significant efforts have been devoted to introduce micro</p><p>or nano-sized particles into biopolymer blends [9, 13–15].</p><p>Alg, which is an anionic polysaccharide of alginic acid</p><p>salts, is commercially obtained in the form of sodium alginate</p><p>and extracted from the cell walls of brown marine algae. It is</p><p>a linear, binary copolymer of 1β-d-mannuronic acid (M) and</p><p>α-l-guluronic acid (G) residues with M/G ratio and sequence,</p><p>G-block length, and molecular weight varying with the algi-</p><p>nate origins [16, 17]. Alg is a versatile biopolymer utilized in</p><p>agriculture, food technologies, chemical and environmental</p><p>engineering, and pharmaceuticals and cosmetics because of</p><p>its characteristics, such as non-toxicity, biocompatibility, high</p><p>stability in the environment, strong film-forming ability, and</p><p>the capacity to form water-insoluble gel when cross-linked</p><p>with divalent or trivalent cations [18]. Moreover, the water</p><p>sensitivity of TPS could be significantly reduced in the pres-</p><p>ence of calcium-crosslinked Alg [19].</p><p>Recently, the use of particulate biowastes as fillers in</p><p>polymer blends has increased. Biowaste filler is anticipated</p><p>to replace conventional reinforcements, such as alumina,</p><p>carbon, glass, and aramid, owing to its abundance, eco-</p><p>friendliness, cost-effectiveness, and light weight in addi-</p><p>tion to high toughness, hardness, thermal performance, and</p><p>wear and abrasive resistance [20, 21]. Spent coffee grounds</p><p>(SCG), which constitute the residual matter of the coffee</p><p>brewing process, possess a beneficial array of organic com-</p><p>pounds, such as polysaccharides, polyphenols, and fatty</p><p>acids, with noteworthy properties, including water and oil</p><p>holding capacity, thermostability, and antioxidant potential.</p><p>Therefore, it has been widely utilized in many technolo-</p><p>gies, such as remediation, adsorption, fermentation, and</p><p>pyrolysis [22]. SCG is also used as a baking additive [23].</p><p>In general, synthesized particulate materials (inorganic</p><p>nanoparticles, nanocellulose, bioactive substances, etc.)</p><p>are incorporated into TPS-based or Alg-based films [14,</p><p>24–27], and the potential of using biowaste as alternative</p><p>materials is yet to be explored. To address this knowl-</p><p>edge gap, this study investigates the use of SCG as a bio-</p><p>reinforcing agent to prepare edible starch/Alg (TPS-Alg)</p><p>films, to be applied in food packaging. The related pros-</p><p>pects and challenges associated with these combinations</p><p>are also discussed.</p><p>Experimental methods</p><p>Materials</p><p>Corn starch</p><p>(CJ Cheiljedang Corporation, Korea) and</p><p>sodium alginate (Junsei Chemical Co., Ltd., Japan,</p><p>code:001S2245) were the basic precursors used for film</p><p>preparation. Glycerol (99.0%, code:000G0274) and anhy-</p><p>drous calcium chloride (CaCl2, 96%, code:000C0104) were</p><p>provided by Samchun Chemical Co. Ltd. (Korea). SCGs</p><p>obtained from a café at Changwon National University</p><p>(Korea) were washed, dried, and sieved through a 200μm</p><p>-mesh for impurity removal prior to ball milling.</p><p>Preparation method</p><p>For size reduction, the SCG was subjected to a wet ball-</p><p>milling process for 9 h with an SCG:ball:water ratio of</p><p>1:80:30 (w/w/w). The resulting paste was subsequently</p><p>sieved through a 45 μm-mesh, rinsed with distilled water</p><p>several times, and dried at 70 °C for 24 h.</p><p>For the preparation of TPS-Alg/SCG films, a specific</p><p>amount (Table 1) of ball-milled SCG was dispersed in 100</p><p>ml distilled water using a high-speed lab disperser (ESYN</p><p>DMT Co., Korea) for 20 min. Corn starch (1 wt%) and</p><p>sodium alginate (1 wt%) were added to the above suspen-</p><p>sion. The mixture was stirred at 45 °C for 1 h and sub-</p><p>sequently at 80 °C for 30 min. This was followed by the</p><p>addition of glycerol (30 wt% of total weight of the powder</p><p>compounds). The mixture was stirred for 20 min and cooled</p><p>to room temperature. The polymeric solution (20 g) was cast</p><p>on a polystyrene petri dish (Ø = 150 mm) and dried at room</p><p>temperature for 24 h. Thereafter, calcium chloride (50 ml,</p><p>2% w/w) was added to each TPS-Alg-based film for 10 min.</p><p>The cross-linked samples were then rinsed with distilled</p><p>water to remove excess CaCl2, transferred to Teflon-coated</p><p>petri dishes, and dried at room temperature. Pure TPS-Alg</p><p>films were prepared using a similar procedure, without the</p><p>inclusion of SCG.</p><p>Journal of Polymer Research (2023) 30:191</p><p>1 3</p><p>Page 3 of 9 191</p><p>Characterization and testing</p><p>Chemical structural analysis</p><p>Fourier-transform infrared (FTIR) spectra were recorded</p><p>using an FT/IR-6300 system (JASCO Inc., Japan) operat-</p><p>ing in the attenuated total reflection (ATR) method. The</p><p>samples were dried in a high-temperature forced-convec-</p><p>tion oven (Model: LO-US100, KLABKOREA Co., Ltd.,</p><p>Korea) at 70 °C for 5 h before testing. The spectra were</p><p>recorded in the range of 4000–400  cm− 1 with 32 scans in</p><p>each case at a resolution of 4  cm− 1.</p><p>Crystallinity analysis</p><p>X-ray diffraction (XRD) patterns were obtained using an</p><p>X’ pert PRO MPD diffractometer (PANalytical, Nether-</p><p>lands) with Cu-Kα radiation ( � = 1.5406 Å) at 40 kV and</p><p>30 mA. Scattered radiation was obtained at a scanning</p><p>speed of 2°/min over a 2θ range of 10° to 50°.</p><p>Morphology</p><p>The surface microstructure of each fabricated sample was</p><p>inspected using an Olympus BX53M upright microscope</p><p>(Techsan Co. Ltd., Japan).</p><p>Optical properties</p><p>Ultraviolet-visible (UV-vis) light absorbance was scanned</p><p>at a rate of 10 nm/min using an Evolution 201 UV-Visible</p><p>spectrophotometer (Thermo Fisher Scientific Inc., USA)</p><p>at 280, 320, 400, 600, and 800 nm.</p><p>Moisture content (MC)</p><p>The MC of the samples was investigated using the follow-</p><p>ing procedure. A piece of film (2 × 2 cm) was weighed</p><p>(M1) and dried at 105 °C until a constant mass (M2) was</p><p>achieved. The percentage of water eliminated from the</p><p>dry film (weight loss) represents the MC, which was cal-</p><p>culated using the following equation:</p><p>Water vapor permeability (WVP)</p><p>The WVP of the prepared composite films was evaluated fol-</p><p>lowing the method of Mousavi et al. [9]. A glass vial contain-</p><p>ing anhydrous CaCl2 (0% Relative Humidty (RH)) was covered</p><p>(1)MC (%)</p><p>M</p><p>1</p><p>−M</p><p>2</p><p>M</p><p>1</p><p>× 100</p><p>with the film samples and fully sealed with glue. Each cell was</p><p>subsequently placed in a desiccator containing saturated NaCl</p><p>solution (75% RH). The mass of the cells was recorded every</p><p>12 h for 120 h using an analytical balance (± 0.0001 g). The</p><p>water vapor transmission rate (WVTR) and WVP of the films</p><p>were calculated using the following equations:</p><p>where A is the area of the exposed film surface (m2); S is</p><p>the saturation vapor pressure at the test temperature (kPa);</p><p>RH1 is the relative humidity inside the desiccator; RH2 is</p><p>the relative humidity inside the vials, and x is the mean film</p><p>thickness (mm).</p><p>Thermogravimetric analysis (TGA)</p><p>The thermal stability was assessed by interpreting TGA and</p><p>derivative thermogravimetric (DTG) data obtained using a</p><p>thermogravimetric analyzer (Model: TGA Q600/SDT, TA</p><p>instruments, USA) at a heating rate of 10 °C/min under</p><p>inert (N2) atmosphere. The examined temperature range was</p><p>30–800 °C, and the sample weight was 6–9 mg.</p><p>Mechanical testing</p><p>The film samples were cut into 80 mm × 10 mm strips and</p><p>attached to a paper frame. In accordance with ASTM D882,</p><p>the crosshead speed was set to 10 mm/min with a gauge</p><p>length of 60 mm, according to the paper frame size.</p><p>Results and discussion</p><p>Physicochemical properties</p><p>Chemical structural analysis</p><p>The Infrared (IR) spectra shown in Fig. 1 shows the chemi-</p><p>cal bonding within the SCG, TPS-Alg, and TPS-Alg/SCG</p><p>films. The individual spectra of SCG and TPS-Alg (Fig. 1A)</p><p>exhibit characteristic peaks with distinct intensities. The</p><p>peaks at 3500–3300 (O‒H stretching of cellulose), 2924</p><p>(asymmetric C‒H vibration), 2871 (symmetric C‒H vibra-</p><p>tion), and 1719  cm− 1 (‒C = O groups of hemicellulose,</p><p>lignin, chlorogenic acids, and caffeine), indicated the pres-</p><p>ence of SCG [28, 29]. Regarding the polymeric matrices,</p><p>a broad band centered at 3243  cm− 1 was assigned to the</p><p>(2)WVTR =</p><p>�W</p><p>�t × A</p><p>(3)WVP =</p><p>WVTR × x</p><p>S × (RH</p><p>1</p><p>− RH</p><p>2</p><p>)</p><p>Journal of Polymer Research (2023) 30:191</p><p>1 3</p><p>191 Page 4 of 9</p><p>intermolecular hydrogen bonding between glycerol, starch,</p><p>and alginate chains with the O–H stretching vibration, while</p><p>the asymmetrical aliphatic C–H stretch was observed at</p><p>2923  cm− 1 [30]. The peaks at 1594 and 1413  cm− 1 were</p><p>assigned to the asymmetric and symmetric stretching vibra-</p><p>tions of the carboxylate (–COO−) groups of alginate salts,</p><p>respectively [9], and the heteroconstituent blocks of alginate</p><p>were observed at 814  cm− 1 [31]. The C–O stretching vibra-</p><p>tions in the C–O–H groups of the glucose rings and α-1,4-</p><p>glycosidic linkages were detected at 1144 and 1075  cm− 1,</p><p>indicating TPS characteristics. In addition, the C–O stretch-</p><p>ing at 1003  cm− 1 and C–H deformation at 932  cm− 1 were</p><p>attributed to carbohydrate features.</p><p>Considering composite films, in a pattern similar to that</p><p>of the combination of TPS and SCG in our previous study</p><p>[32], the alcoholic hydroxyl groups from alginate, starch,</p><p>and glycerol in binary TPS-Alg matrices were esterified by</p><p>the insertion of SCG containing diverse carboxylic acids.</p><p>The appearance of a new peak was observed, at ~1740  cm− 1,</p><p>which is indicative of a –C = O stretching vibration [30].</p><p>Furthermore, intensified peaks with moderate blue shifts</p><p>were observed in the O–H region, which could be the result</p><p>of the introduction of a large number of hydroxyl groups</p><p>from SCG.</p><p>Crystalline structure</p><p>The differences in the crystalline structures of the TPS-Alg</p><p>films with the inclusion of SCG were analyzed via XRD.</p><p>Figure 2 shows the diffraction patterns of the SCG, TPS-</p><p>Alg, and TPS-Alg/SCG films. The diffractograms of SCG</p><p>were dominated by the amorphous portion of lignocellulose</p><p>and other components. The peaks at 2θ = 19.9°, 21.4°, and</p><p>34.7° were attributed to crystalline cellulose [33]. Pristine</p><p>alginate-based polymers display a semi-crystalline nature</p><p>with two predominant peaks at 2θ values of approximately</p><p>13.5° and 22.0° [34, 35], with variations according to the</p><p>plasticizing and cross-linking conditions [36, 37]. These</p><p>Fig. 1 FTIR spectra of SCG, TPS-Alg, and TPS-Alg/SCG films</p><p>Fig. 2 XRD patterns of SCG, TPS-Alg, and TPS-Alg/SCG films</p><p>Journal of Polymer Research (2023) 30:191</p><p>1 3</p><p>Page 5 of 9 191</p><p>peaks are assigned to the crystal planes of the guluronate</p><p>(G-block) and mannuronate (M-block) units. In particular,</p><p>only G blocks react intermolecularly with divalent cations</p><p>(e.g., Ca2+) to form</p><p>Ca-alginate junctions [16]. This could</p><p>explain the absence of the former diffraction peak in the</p><p>XRD patterns of TPS-Alg and TPS-Alg/SCG films. Another</p><p>possibility is the presence of strong interactions (i.e., inter-</p><p>molecular hydrogen bonds and ionic bonds) between algi-</p><p>nate and starch, disrupting the close packing within alginate</p><p>molecules [38]. In addition, the peak at 2θ = 19.7° charac-</p><p>terized the VH crystalline form of TPS in the binary TPS-</p><p>Alg film [39]. For the SCG-reinforced samples, this peak</p><p>marginally shifted to 20.0°, overlapping with the distinctive</p><p>region of the SCG [28].</p><p>Moisture content</p><p>MC measurements indirectly reveals the void volume of</p><p>a material by determining the number of occupied water</p><p>molecules during the drying process [9]. The MC results</p><p>for the TPS-Alg and TPS-Alg/SCG films are presented in</p><p>Table 1. The value of the former was 14.58%, which is</p><p>comparable to that reported in previous studies on alginate/</p><p>starch blends with corresponding ratios [9, 40]. For the</p><p>composite films, the larger the mass of ball-milled SCG,</p><p>the lower the MC of the TPS-Alg-based films. This could</p><p>be a positive outcome of the SCG particles partially filling</p><p>the porous polymer chains.</p><p>Morphology</p><p>The surfaces of the TPS-Alg and TPS-Alg/SCG films were</p><p>investigated using light micrographs (Fig. 3) obtained via</p><p>optical microscopy. Pure TPS-Alg films displayed a smooth</p><p>and continuous surface without any starch granules, which</p><p>indicated the excellent compatibility between alginate and</p><p>TPS, as opposed to the complete plasticization of starch. The</p><p>observed smoothness was maintained with the inclusion of</p><p>5% ball-milled SCG in the TPS-Alg films, while rougher</p><p>surfaces and more agglomeration spots of ball-milled SCG</p><p>were noted in the remaining samples.</p><p>WVP</p><p>The water vapor transmission through the TPS-Alg films,</p><p>with varying amounts of inserted SCG, was inferred</p><p>via the WVP test. From Table 1, TPS-Alg/SCG-5 film</p><p>Fig. 3 Digital photos and light micrographs of TPS-Alg and TPS-Alg/SCG films</p><p>Journal of Polymer Research (2023) 30:191</p><p>1 3</p><p>191 Page 6 of 9</p><p>exhibited the highest water vapor barrier performance</p><p>with a WVP of (9.03 ±1.69) × 10− 13 g/Pa·m·s, while fur-</p><p>ther addition of ball-milled SCG resulted in a gradual</p><p>upward trend in the WVP. Compared to binary matri-</p><p>ces, the inclusion of ball-milled SCG resulted in a denser</p><p>structure with fewer cavities within the polymer chains.</p><p>Furthermore, the formation of chemical linkages moder-</p><p>ately reduced the WVP of TPS-Alg films. Meanwhile, the</p><p>latter tendency could be explained by the abundant hydro-</p><p>philic SCGs on the film surface attracting more water</p><p>molecules, which led to the acceleration of water vapor</p><p>penetration through the film [13].</p><p>Optical properties</p><p>UV absorption capacity is regarded as one of the most</p><p>vital parameters for food quality preservation against pho-</p><p>tooxidation, especially for photosensitive and lipid-rich</p><p>products, such as nuts, meat, fish, and dairy [41]. Table 2</p><p>lists the UV-visible light transmission (T%) efficiencies</p><p>of the TPS-Alg and TPS-Alg/SCG composite films at the</p><p>selected wavelengths. A more compact polymer struc-</p><p>ture was observed with the incorporation of ball-milled</p><p>SCG particles, thereby resulting in higher opacity with</p><p>increasing ball-milled SCG content [42]. SCG has an</p><p>intrinsic dark brown color that diminishes the transpar-</p><p>ency (Fig. 3) and the transmission of UV and visible light</p><p>through the films. Even with a film thickness of approxi-</p><p>mately 0.002 mm (Table 1), the T% value in the UV spec-</p><p>tral region of TPS-Alg combined with ball-milled SCG</p><p>was practically 1.52–3.43 times lower than that of pure</p><p>TPS-Alg, indicating a significant improvement in the UV</p><p>absorption capacity.</p><p>Thermal properties</p><p>TGA was used to understand the influence of SCG on the ther-</p><p>mal stability of the TPS-Alg matrices. Figure 4A, B present</p><p>the thermogravimetric (TG) and derivative thermogravimetry</p><p>(DTG) thermograms of the SCG, TPS-Alg, and TPS-Alg/SCG</p><p>films. SCG exhibited three primary weight loss steps. In the first</p><p>stage, a marginal mass loss of approximately 2.8% from 30 to</p><p>200 °C was observed, owing to dehydration and the evaporation</p><p>of light volatile matter. The decomposition of lignocellulosic and</p><p>coffee oil constituents (200–500 ℃) caused the highest mass</p><p>loss of over 76%, marked by two dominant peaks at 303 and</p><p>314 ℃, along with a shoulder at ~382 ℃ [28, 43]. The last phase</p><p>could be attributed to the consolidation of carbon structures,</p><p>leading to a weight loss of 16.3% of residual matter at 800 °C.</p><p>Three stages of weight loss were also observed in the TPS-Alg</p><p>thermogram. The first step (30–150 °C) involved the evapora-</p><p>tion of absorbed and bound water. The subsequent phase in the</p><p>temperature range of 210–600 °C indicated the destruction of</p><p>polysaccharide compounds and the formation of sodium carbon-</p><p>ate [44]. The two thermal degradation peaks observed at 242 and</p><p>312 °C (Fig. 4D) represent the decomposition of alginate and</p><p>starch, respectively [45, 46]. The final stage corresponded to the</p><p>degradation of Na2CO3 and carbonized materials that gradually</p><p>decomposed from 600 to 800 °C in N2 [44, 46], resulting in a</p><p>char residue of 21.8%.</p><p>The decomposition stages of the TPS-Alg/SCG films are</p><p>analogous to those of the binary matrices. Considering the</p><p>thermal stability of each precursor component of the composite</p><p>films (Fig. 4A and C), the values of the char residue followed</p><p>the order: starch granules < SCG < Alg. Therefore, the intro-</p><p>duction of SCG into TPS-Alg affected the minor refinement</p><p>of the thermal stability of the TPS-Alg films, which could be</p><p>explained by the partial TPS replacement of SCG.</p><p>Mechanical properties</p><p>Table 3 presents the data obtained from the tensile testing</p><p>of the TPS-Alg/SCG samples with varying SCG amounts</p><p>(0–20 wt%). The mechanical properties of alginate-based</p><p>Table 2 UV-Vis transmittance</p><p>data of TPS-Alg and TPS-Alg/</p><p>SCG films</p><p>Sample Transmittance (%)</p><p>280 nm 320 nm 400 nm 600 nm 800 nm</p><p>TPS-Alg 58.72 ± 3.2% 63.89 ± 3.14% 69.58 ± 2.92% 75.49 ± 2.40% 78.35 ± 2.12%</p><p>TPS-Alg /SCG-5 38.65 ± 3.58% 43.52 ± 3.41% 50.90 ± 2.88% 60.04 ± 2.02% 64.44 ± 1.55%</p><p>TPS-Alg /SCG-10 26.09 ± 2.30% 30.57 ± 2.22% 38.54 ± 1.79% 49.77 ± 0.89% 55.08 ± 0.50%</p><p>TPS-Alg /SCG-15 17.14 ± 2.63% 21.20 ± 2.68% 30.40 ± 2.18% 45.37 ± 1.83% 52.42 ± 2.44%</p><p>TPS-Alg /SCG-20 15.61 ± 1.88% 18.65 ± 1.97% 25.47 ± 2.04% 36.11 ± 1.78% 41.25 ± 1.58%</p><p>Table 1 Thickness, MC, and WVP of TPS-Alg based films</p><p>Sample Thickness</p><p>(mm)</p><p>MC</p><p>(%)</p><p>WVP</p><p>(x10− 13 g/Pa.m.s)</p><p>TPS-Alg 0.023 ±0.004 14.58 ±0.61 10.50 ±1.07</p><p>TPS-Alg/SCG-5 0.023 ±0.003 14.67 ± 1.51 9.03 ±1.69</p><p>TPS-Alg/SCG-10 0.023 ±0.003 14.00 ± 1.03 9.58 ±1.20</p><p>TPS-Alg/SCG-15 0.025 ±0.002 13.19 ± 1.66 9.85 ±0.77</p><p>TPS-Alg/SCG-20 0.023 ±0.004 12.48 ± 1.28 10.52 ±0.44</p><p>Journal of Polymer Research (2023) 30:191</p><p>1 3</p><p>Page 7 of 9 191</p><p>films are influenced by the cross-linking conditions (i.e.,</p><p>concentration of CaCl2 and contact time) [47]. The alginate/</p><p>starch matrices prepared in this study exhibited a high tensile</p><p>strength of approximately 80 MPa and tensile modulus of</p><p>4.91 GPa. The presence of particulate fillers could influ-</p><p>ence the composite strength in two ways: the weakening</p><p>effect owing to the filler-induced stress concentration and</p><p>the reinforcing effect caused by their functioning as barri-</p><p>ers against crack propagation [48]. In this study, the former</p><p>was more prominent because the tensile strengths of the</p><p>composite films were lower than those of the pure TPS-</p><p>Alg. The tensile strength of TPS-Alg decreased by 15%</p><p>and 28%, with the addition of SCG up to 10% and higher,</p><p>respectively. As an illustration of the predominant lubricat-</p><p>ing effect of SCG, the tensile modulus of TPS-Alg/SCG-</p><p>10 exhibited the least deterioration, while that of TPS-Alg/</p><p>SCG-20 deteriorated the most. Increasing the SCG content</p><p>decreased the elongation at break of TPS-Alg-based films</p><p>because the incorporation of particulate filler could</p><p>confine</p><p>the mobility of polymer chains [9]. Meanwhile, an increase</p><p>in the elongation at break with a further increase in the SCG</p><p>content was probably caused by plasticization due to the cof-</p><p>fee oil, along with the non-homogenous distribution of the</p><p>Fig. 4 A TGA and B DTG curves of TPS-Alg and TPS-Alg/SCG films; C TGA and D DTG curves of starch granules, Alg, and TPS-Alg</p><p>Table 3 Tensile properties of TPS-Alg and TPS-Alg/SCG films</p><p>Sample Tensile</p><p>strength</p><p>(MPa)</p><p>Tensile</p><p>modulus</p><p>(GPa)</p><p>Elongation</p><p>at break</p><p>(%)</p><p>TPS-Alg 79.5 ± 7.1 4.9 ± 0.3 6.5 ± 1.1</p><p>TPS-Alg/SCG-5 67.8 ± 8.3 4.4 ± 0.3 6.0 ± 1.1</p><p>TPS-Alg/SCG-10 67.6 ± 6.1 4.7 ± 0.3 5.2 ± 1.2</p><p>TPS-Alg/SCG-15 57.8 ± 4.7 4.2 ± 0.3 5.0 ± 0.7</p><p>TPS-Alg/SCG-20 57.8 ± 6.3 4.0 ± 0.2 5.3 ± 1.4</p><p>Journal of Polymer Research (2023) 30:191</p><p>1 3</p><p>191 Page 8 of 9</p><p>agglomerated SCG particles that was previously examined</p><p>via light micrographs.</p><p>However, the acquired results are promising for packaging</p><p>applications. It is noteworthy that the incorporation of SCG into</p><p>TPS-Alg films reduces the environmental burdens as well as the</p><p>product cost, thereby offering an opportunity for commercializa-</p><p>tion of starch-based plastics. Table 4 presents a comparison of</p><p>the tensile properties exhibited by the composites in the present</p><p>study and that of previous studies on Alg-based films and con-</p><p>ventional packaging materials (i.e., HDPE, PP, and PET films).</p><p>Conclusions</p><p>For the first time, SCG was employed as a biowaste filler in</p><p>binary matrices of TPS-Alg using a solution-casting technique.</p><p>The insertion of dark brown SCG considerably enhanced the</p><p>UV protection of TPS-Alg films with less than 20% UV light</p><p>transmitted through the films. A more compact polymeric</p><p>structure, which was confirmed through the MC analysis,</p><p>could explain the enhancement in moisture barrier properties</p><p>observed in the film blended with a low SCG content. How-</p><p>ever, the addition of a high amount of SCG resulted in surplus</p><p>hydrophilic residues on the film surface, thereby increasing the</p><p>WVP. Without disturbing the onset and maximum degradation</p><p>temperatures, the introduction of SCG marginally improved</p><p>the thermal stability of the TPS-Alg-based films. Meanwhile,</p><p>because a large amount of SCG induced stress concentration</p><p>in addition to the plasticizing effect in the composite films, the</p><p>tensile strength and modulus were reduced to approximately</p><p>58 MPa and 4 GPa, respectively. However, compared to simi-</p><p>lar materials developed in previous studies and conventional</p><p>packaging materials, the as-developed materials are promising</p><p>alternatives for packaging applications.</p><p>Acknowledgements This study was supported by the Basic Science</p><p>Research Program through the National Research Foundation of Korea</p><p>(NRF), funded by the Ministry of Science Education (grant numbers</p><p>2018R1A6A1A03024509 and 2023R1A2C1006234).</p><p>Declarations</p><p>Conflict of interest All authors declare that they have no conflicts of interest.</p><p>References</p><p>1. Millican JM, Agarwal S (2021) Plastic pollution: a material prob-</p><p>lem? Macromolecules 54(10):4455–4469</p><p>2. CfIEL (CIEL) Plastic & Climate. The hidden costs of a plastic planet</p><p>3. Rosenboom J-G, Langer R, Traverso G (2022) Bioplastics for a</p><p>circular economy. Nat Rev Mater 7(2):117–137</p><p>4. Ritchie H, Roser M (2018) Plastic pollution, Our World in Data</p><p>5. Nanda S, Patra BR, Patel R, Bakos J, Dalai AK (2021) Innovations</p><p>in applications and prospects of bioplastics and biopolymers: A</p><p>review. Environ Chem Lett 1–17</p><p>6. Cheng H, Chen L, McClements DJ, Yang T, Zhang Z, Ren F, Miao M,</p><p>Tian Y, Jin Z (2021) Starch-based biodegradable packaging materials:</p><p>a review of their preparation, characterization and diverse applications</p><p>in the food industry. Trends Food Sci Technol 114:70–82</p><p>7. Prabhakar MN, Rehman shah AU, Jungil S (2017) Improved</p><p>flame-retardant and tensile properties of thermoplastic starch/</p><p>flax fabric green composites. Carbohydr Polym 168:201–211</p><p>8. Brizga J, Hubacek K, Feng K (2020) The unintended side effects of</p><p>bioplastics: carbon, land, and water footprints. One Earth 3(1):45–53</p><p>9. Mousavi SN, Daneshvar H, Dorraji MSS, Ghasempour Z, Panahi-</p><p>Azar V, Ehsani A (2021) Starch/alginate/Cu-g-C3N4 nanocompos-</p><p>ite film for food packaging. Mater Chem Phys 267:124583</p><p>10. Ghanbarzadeh B, Almasi H, Entezami AA (2010) Physical prop-</p><p>erties of edible modified starch/carboxymethyl cellulose films.</p><p>Innov Food Sci Emerg Technol 11(4):697–702</p><p>11. Ren L, Yan X, Zhou J, Tong J, Su X (2017) Influence of chitosan</p><p>concentration on mechanical and barrier properties of corn starch/</p><p>chitosan films. Int J Biol Macromol 105:1636–1643</p><p>12. Dash KK, Ali NA, Das D, Mohanta D (2019) Thorough evaluation</p><p>of sweet potato starch and lemon-waste pectin based-edible films</p><p>with nano-titania inclusions for food packaging applications. Int</p><p>J Biol Macromol 139:449–458</p><p>13. Hou X, Xue Z, Xia Y, Qin Y, Zhang G, Liu H, Li K (2019) Effect</p><p>of SiO2 nanoparticle on the physical and chemical properties of</p><p>eco-friendly agar/sodium alginate nanocomposite film. Int J Biol</p><p>Macromol 125:1289–1298</p><p>14. Noorbakhsh-Soltani S, Zerafat M, Sabbaghi S (2018) A compara-</p><p>tive study of gelatin and starch-based nano-composite films modi-</p><p>fied by nano-cellulose and chitosan for food packaging applica-</p><p>tions. Carbohydr Polym 189:48–55</p><p>15. Prabhakar MN, Naga Kumar CN, Woo LD, Jung-il S (2022)</p><p>Hybrid approach to improve the flame retardant and thermal prop-</p><p>erties of sustainable biocomposites used in outdoor engineering</p><p>applications. Compos Part A Appl Sci Manuf 152:106674</p><p>16. Lee KY, Mooney DJ (2012) Alginate: properties and biomedical</p><p>applications. Prog Polym Sci 37(1):106–126</p><p>17. Angra V, Sehgal R, Kaur M, Gupta R (2021) Commercialization</p><p>of bionanocomposites. Bionanocomposites in tissue engineering</p><p>and regenerative medicine. Elsevier, pp 587–610</p><p>18. Wang B, Wan Y, Zheng Y, Lee X, Liu T, Yu Z, Huang J, Ok YS,</p><p>Chen J, Gao B (2019) Alginate-based composites for environmental</p><p>Table 4 Comparison of tensile properties of the present study and</p><p>previous literature on packaging materials</p><p>Material Tensile</p><p>strength</p><p>(MPa)</p><p>Tensile</p><p>modulus</p><p>(GPa)</p><p>Reference</p><p>HDPE film 28 2.0 [49]</p><p>PP film 36 3.5 [50]</p><p>PET film 40.2 1.76 [51]</p><p>TPS-Alg/SCG-10% 67.6 4.7 Present study</p><p>TPS-Alg/Cu-doped</p><p>g-C3N4 nanoparticles</p><p>0.5%</p><p>36.6 - [9]</p><p>Alg/ZnO nanoparticles 42.3 2.3 [52]</p><p>Alg/Castor oil 1% 48.2 0.08 [53]</p><p>Alg/Sulfur nanoparticles</p><p>2%</p><p>65.5 1.99 [26]</p><p>Alg/Cellulose</p><p>nanocrystals 8%</p><p>97.0 2.85 [27]</p><p>Alg/PMMA 30% 98.1 - [54]</p><p>Journal of Polymer Research (2023) 30:191</p><p>1 3</p><p>Page 9 of 9 191</p><p>applications: a critical review. Crit Rev Environ Sci Technol</p><p>49(4):318–356</p><p>19. Mohamed SA, El-Sakhawy M, El-Sakhawy MA-M (2020) Poly-</p><p>saccharides, protein and lipid-based natural edible films in food</p><p>packaging: a review. Carbohydr Polym 238:116178</p><p>20. Prabhakar MN, Rehman shah AU, Jungil S (2016) Fabrication and</p><p>characterization of eggshell powder particles fused wheat protein</p><p>isolate green composite for packaging applications. Polym Com-</p><p>pos 37:3280–3287</p><p>21. Prabhakar MN, Jung-il S (2020) Influence of chitosan-centered</p><p>additives on flammable properties of vinyl ester matrix compos-</p><p>ites. Cellulose 27:8087–8103</p><p>22. Stylianou M, Agapiou A, Omirou M, Vyrides I, Ioannides IM,</p><p>Maratheftis G, Fasoula D (2018) Converting environmental risks</p><p>to benefits by using spent coffee grounds (SCG) as a valuable</p><p>resource. Environ Sci Pollut Res 25(36):35776–35790</p><p>23. Martinez-Saez N, García AT, Pérez ID, Rebollo-Hernanz M,</p><p>Mesías M, Morales FJ, Martín-Cabrejas MA (2017) Del Castillo,</p><p>Use of spent coffee grounds as food ingredient in bakery products.</p><p>Food Chem 216:114–122</p><p>24. Peighambardoust SJ, Peighambardoust SH, Pournasir N, Pakdel</p><p>PM (2019) Properties of active starch-based films incorporating a</p><p>combination of Ag, ZnO and CuO nanoparticles for potential use</p><p>in food packaging applications. Food Packaging and Shelf Life</p><p>22:100420</p><p>25. Nieto-Suaza L, Acevedo-Guevara L, Sánchez LT, Pinzón MI</p><p>(2019) J.</p><p>F. S. Villa, characterization of Aloe vera-banana starch</p><p>composite films reinforced with curcumin-loaded starch nanopar-</p><p>ticles. Food Struct 22:100131</p><p>26. Priyadarshi R, Kim H-J, Rhim J-W (2021) Effect of sulfur nan-</p><p>oparticles on properties of alginate-based films for active food</p><p>packaging applications. Food Hydrocolloids 110:106155</p><p>27. Achaby ME, Kassab Z, Barakat A, Aboulkas A (2018) Alfa fibers</p><p>as viable sustainable source for cellulose nanocrystals extraction:</p><p>application for improving the tensile properties of biopolymer</p><p>nanocomposite films. Ind Crops Prod 112:499–510</p><p>28. Ballesteros LF, Teixeira JA, Mussatto S (2014) Chemical, func-</p><p>tional, and structural properties of spent coffee grounds and coffee</p><p>silverskin. Food Bioprocess Technol 7(12):3493–3503</p><p>29. Zhuang J, Li M, Pu Y, Ragauskas AJ, Yoo CG (2020) Observa-</p><p>tion of potential contaminants in processed biomass using fourier</p><p>transform infrared spectroscopy. Appl Sci 10(12):4345</p><p>30. Donald GML, Pavia L, Geroge S, Kriz JR, Vyvyan (2013) Infrared</p><p>spectroscopy, in: introduction to spectroscopy. Cengage Learning,</p><p>USA, pp 14–106</p><p>31. Leal D, Matsuhiro B, Rossi M, Caruso F (2008) FT-IR spectra of</p><p>alginic acid block fractions in three species of brown seaweeds.</p><p>Carbohydr Res 343(2):308–316</p><p>32. HT Nguyen V, MN Prabhakar, Lee DW, Song JI (2022) Spent</p><p>coffee grounds: An intriguing biowaste reinforcement of thermo-</p><p>plastic starch with potential application in green packaging. Polym</p><p>Compos. https:// doi. org/ 10. 1002/ pc. 26856</p><p>33. French AD (2014) Idealized powder diffraction patterns for cel-</p><p>lulose polymorphs. Cellulose 21(2):885–896</p><p>34. Kavitha N, Karunya TP, Kanchana S, Mohan K, Sivaramakrishnan</p><p>R, Uthra S, Kapilan K, Yuvaraj D, Arumugam M (2019) Formula-</p><p>tion of alginate based hydrogel from brown seaweed, Turbinaria</p><p>conoides for biomedical applications. Heliyon 5(12):e02916</p><p>35. Sundarrajan P, Eswaran P, Marimuthu A, Subhadra LB, Kannaiyan</p><p>P (2012) One pot synthesis and characterization of alginate sta-</p><p>bilized semiconductor nanoparticles. Bull Korean Chem Soc</p><p>33(10):3218–3224</p><p>36. Laia AG, Costa Junior ED, Costa HD (2014) A study of sodium</p><p>alginate and calcium chloride interaction through films for</p><p>intervertebral disc regeneration uses. In: 21 CBECIMAT: Brazil-</p><p>ian congress of engineering and materials science, Brazil</p><p>37. Gao C, Pollet E, Avérous LJFH (2017) Properties of glycerol-</p><p>plasticized alginate films obtained by thermo-mechanical mixing.</p><p>Food Hydrocolloids 63:414–420</p><p>38. Wang Q, Hu X, Du Y, Kennedy JF (2010) Alginate/starch blend</p><p>fibers and their properties for drug controlled release. Carbohydr</p><p>Polym 82(3):842–847</p><p>39. Van Soest JJ, Hulleman S, De Wit D, Vliegenthart J (1996) Crys-</p><p>tallinity in starch bioplastics. Ind Crops Prod 5(1):11–22</p><p>40. Lopes IA, Paixao LC, da Silva LJS, Rocha AA, Barros Filho</p><p>AKD, Santana AA (2020) Elaboration and characterization of</p><p>biopolymer films with alginate and babassu coconut mesocarp.</p><p>Carbohydr Polym 234:115747</p><p>41. Tao L (2015) Oxidation of polyunsaturated fatty acids and its impact</p><p>on food quality and human health. Adv Food Technol Nutritional</p><p>Sci 1:135–142</p><p>42. de Oliveira Begali D, Ferreira LF, de Oliveira ACS, Borges SV,</p><p>de Sena Neto AR, de Oliveira CR, Yoshida MI, Sarantopoulos CI</p><p>(2021) Effect of the incorporation of lignin microparticles on the</p><p>properties of the thermoplastic starch/pectin blend obtained by</p><p>extrusion. Int J Biol Macromol 180:262–271</p><p>43. Jagdale P, Ziegler D, Rovere M, Tulliani JM, Tagliaferro A (2019)</p><p>Waste coffee ground biochar: a material for humidity sensors.</p><p>Sensors 19(4):801</p><p>44. Soares J, Santos J, Chierice G, Cavalheiro E (2004) Thermal behavior</p><p>of alginic acid and its sodium salt. Eclética Química 29(2):57–64</p><p>45. Tarique J, Sapuan S, Khalina A (2021) Effect of glycerol plasti-</p><p>cizer loading on the physical, mechanical, thermal, and barrier</p><p>properties of arrowroot (Maranta arundinacea) starch biopoly-</p><p>mers. Sci Rep 11(1):1–17</p><p>46. da Silva Fernandes R, de Moura MR, Glenn GM, Aouada FA (2018)</p><p>Thermal, microstructural, and spectroscopic analysis of Ca2+ algi-</p><p>nate/clay nanocomposite hydrogel beads. J Mol Liq 265:327–336</p><p>47. Abdullah NAS, Mohamad Z, Khan ZI, Jusoh M, Zakaria ZY,</p><p>Ngadi N (2021) Alginate Based sustainable films and composites</p><p>for packaging: a review. Chem Eng Trans 83:271–276</p><p>48. Fu S-Y, Feng X-Q, Lauke B, Mai Y-W (2008) Effects of particle</p><p>size, particle/matrix interface adhesion and particle loading on</p><p>mechanical properties of particulate–polymer composites. Com-</p><p>pos Part B Eng 39(6):933–961</p><p>49. Majewski K, Mantell S, Bhattacharya M (2020) Relationship between</p><p>morphological changes and mechanical properties in HDPE films</p><p>exposed to a chlorinated environment. Polym Degrad Stab 171:109027</p><p>50. Ren Y, Zou H, Wang S, Liu J, Gao D, Wu C, Zhang S (2018)</p><p>Effect of annealing on microstructure and tensile properties of</p><p>polypropylene cast film. Colloid Polym Sci 296(1):41–51</p><p>51. Thongsong W, Kulsetthanchalee C, Threepopnatkul P (2017) Effect</p><p>of polybutylene adipate-co-terephthalate on properties of polyethyl-</p><p>ene terephthalate thin films. Mater Today: Proc 4(5):6597–6604</p><p>52. Satriaji KP, Garcia CV, Kim GH, Shin GH, Kim JT (2020) Antibac-</p><p>terial bionanocomposite films based on CaSO4-crosslinked alginate</p><p>and zinc oxide nanoparticles. Food Packag Shelf Life 24:100510</p><p>53. Aziz MSA, Salama HE, Sabaa MW (2018) Biobased alginate/</p><p>castor oil edible films for active food packaging. Lwt 96:455–460</p><p>54. Yang M, Wang L, Xia Y (2019) Ammonium persulphate induced</p><p>synthesis of polymethyl methacrylate grafted sodium alginate</p><p>composite films with high strength for food packaging. Int J Biol</p><p>Macromol 124:1238–1245</p><p>Publisher’s Note Springer Nature remains neutral with regard to</p><p>jurisdictional claims in published maps and institutional affiliations.</p><p>Springer Nature or its licensor (e.g. a society or other partner) holds</p><p>exclusive rights to this article under a publishing agreement with the</p><p>author(s) or other rightsholder(s); author self-archiving of the accepted</p><p>manuscript version of this article is solely governed by the terms of</p><p>such publishing agreement and applicable law.</p><p>https://doi.org/10.1002/pc.26856</p><p>Films derived from thermoplastic starchalginatespent coffee grounds for food packaging applications</p><p>Abstract</p><p>Introduction</p><p>Experimental methods</p><p>Materials</p><p>Preparation method</p><p>Characterization and testing</p><p>Chemical structural analysis</p><p>Crystallinity analysis</p><p>Morphology</p><p>Optical properties</p><p>Moisture content (MC)</p><p>Water vapor permeability (WVP)</p><p>Thermogravimetric analysis (TGA)</p><p>Mechanical testing</p><p>Results and discussion</p><p>Physicochemical properties</p><p>Chemical structural analysis</p><p>Crystalline structure</p><p>Moisture content</p><p>Morphology</p><p>WVP</p><p>Optical properties</p><p>Thermal properties</p><p>Mechanical properties</p><p>Conclusions</p><p>Acknowledgements</p><p>References</p>