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Miscibility study of thermoplastic starch/polylactic acid blends: Thermal and superficial properties

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In this work, the miscibility of blends of thermoplastic Achira Starch (AS) and polylactic acid (PLA) was evaluated, assisted by Pluronic® F127 an amphiphilic triblock copolymer that acts as a surfactant and promotes the reduction of surface tension among AS and PLA in solution by emulsion stabilization.

Carbohydrate Polymers 293 (2022) 119744 Contents lists available at ScienceDirect Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol Miscibility study of thermoplastic starch/polylactic acid blends: Thermal and superficial properties Abril Fonseca-García a, b, Brayan Hern´ andez Osorio c, Rocio Yaneli Aguirre-Loredo a, b, d Heidy Lorena Calambas , Carolina Caicedo e, * a Centro de Investigaci´ on en Química Aplicada (CIQA), Blvd Enrique Reyna Hermosillo 140, Saltillo, Coahuila 25294, Mexico CONACYT-CIQA, Blvd Enrique Reyna Hermosillo 140, Saltillo, Coahuila 25294, Mexico Semillero de Investigaci´ on en Química Aplicada (SEQUIA), Facultad de Ciencias B´ asicas, Universidad Santiago de Cali, Pampa linda, Santiago de Cali 760035, Colombia d Grupo de Investigaci´ on en Desarrollo de Materiales y Productos, Centro Nacional de Asistencia T´ecnica a la Industria (ASTIN), SENA, Cali 760003, Colombia e Grupo de Investigaci´ on en Química y Biotecnología (QUIBIO), Facultad de Ciencias B´ asicas, Universidad Santiago de Cali, Pampalinda, Santiago de Cali 760035, Colombia b c A R T I C L E I N F O A B S T R A C T Keywords: Achira starch PLA Pluronic® F127 Polymeric blend films Emulsion In this work, the miscibility of blends of thermoplastic Achira Starch (AS) and polylactic acid (PLA) was eval­ uated, assisted by Pluronic® F127 an amphiphilic triblock copolymer that acts as a surfactant and promotes the reduction of surface tension among AS and PLA in solution by emulsion stabilization Different formulations of AS/PLA blends were obtained at 75:25, 50:50, and 25:75 containing %, %, and % of Pluronic® F127, and glycerol was used as a plasticizer Solvent casting was the method used to obtain blended polymeric films, which were characterized by Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Xray diffraction (XRD), Thermogravimetric Analysis (TGA), differential scanning calorimetry (DSC) and wetta­ bility by contact angle measurements The results demonstrate that miscibility of PLA in AS or vice versa was achieved The stability of emulsion and posterior drying of the different formulations allows the production of films for packaging, pharmaceutical, or biomedical applications Introduction Synthetic polymers are produced from petroleum derivatives, and because of their characteristics, they have been used in many industrial areas In the food area, packaging materials play a fundamental role, not only for the protection of food and the maintenance of its quality, but it can also define the purchasing preference of consumers The world production of packaging has experienced exponential growth with 368 million tons remaining in 2020 due to the health crisis caused by Covid 19 (Manufacturers, 2021) Current synthetic packaging materials have favorable characteristics such as low cost, rapid transformation, good optical properties, and excellent mechanical and barrier performance (Ceron M, 2013), which is why they are used in more significant pro­ portions than other materials such as paper, cardboard, glass, and aluminum However, despite these advantages, they have become a severe environmental problem due to their slow degradation, which can take longer than 50 years (Mohanan et al., 2020) Due to the enormous amount of pollution that is generated by its widespread use, various solutions have been sought to reduce or replace its consumption Among the options are management strategies for recycling and generating new biodegradable and compostable materials that are sustainable (Villada Castillo, 2014) The use of biodegradable polymers such as chitosan, starch, collagen, zein, polyvinyl alcohol, polylactic acid, cellulose, and its derivatives have been extensively explored since they can be a viable option for the generation of novel, biodegradable, compostable, and sustainable packaging materials that can be used with food One of these biopolymers is starch, which is an excellent alternative due to its low cost and diverse sources of production The search for new sources of starch has become increasingly important, taking advantage of uncon­ ventional raw materials that can be a sustainable option and preferably that not compete with the human population's food Achira (Canna edulis sp.) is a root with high starch content, which it is native to South * Corresponding author E-mail addresses: abril.fonseca@ciqa.edu.mx (A Fonseca-García), brayan.hernandez00@usc.edu.co (B.H Osorio), yaneli.aguirre@ciqa.edu.mx (R.Y AguirreLoredo), hlcalambas@misena.edu.co (H.L Calambas), carolina.caicedo03@usc.edu.co (C Caicedo) https://doi.org/10.1016/j.carbpol.2022.119744 Received 28 March 2022; Received in revised form June 2022; Accepted 15 June 2022 Available online 20 June 2022 0144-8617/© 2022 The Authors Published by Elsevier Ltd This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/bync-nd/4.0/) A Fonseca-García et al Carbohydrate Polymers 293 (2022) 119744 America, widely known in countries such as Colombia, Bolivia and Peru as well as in the Asian continent in countries like China, Thailand, and Vietnam (Estrada Rivera, 2020) In the year 2000, the production of achira in Colombia was estimated at 14000 tons, with the departments of Huila and Cundinamarca being the main producers (Rodríguez Borray et al., 2003) In Peru, the consumption of achira root occurs mainly in isolated and marginalized rural areas Due to its low cost, it is a viable alternative for starch extraction It has been observed that starches with different physicochemical, thermal, structural, and viscosity properties can be obtained from achira's distinct varieties or ecotypes (Cisneros et al., 2009), even when the content of amylose and amylopectin is the same (Caceres et al., 2021) Its gel-forming ability can rival that of corn starch (Caceres et al., 2021) In recent years, achira starch has been evaluated as an additive in the restaurant industry (Caceres et al., 2021), ´mezas encapsulating material for active antimicrobial compounds (Go Aldapa et al., 2019), as a source to isolate nanofibers (Andrade-Mahecha et al., 2015), and in the generation of biodegradable materials (Andrade´mez-Aldapa et al., 2020) Mahecha et al., 2012; Caicedo et al., 2019; Go In the last two decades, blends of plasticized starch (starch/plasti­ cizer, TPS) and polylactic acid (PLA) have drawn attention because of their favorable cost and benefits, among which are chemical and phys­ ical properties such as chemical stability, mechanical and thermal resistance, water vapor and oxygen permeability, brightness, and biodegradability (Prieto, 2018; Tyuftin & Kerry, 2021) However, preparation of blends of this type is complicated because of their in­ compatibility, since starch is hydrophilic, while PLA is a hydrophobic polymer, and this limitation has been demonstrated experimentally and theoretical by phase separation of TPS and PLA (P Müller et al., 2016) Other approaches have been reported to promote compatibility between starch and PLA, including the use of plasticizers such as glycerol to render the starch more thermoplastic, which can promote better compatibility between TPS and PLA blends However, mechanical properties such elongation at break and impact resistance were not improved relative to the pure components (Cai et al., 2011; Martin & Av´erous, 2001) In addition, co-plasticizer such as glycerol-sorbitol and glycerol-formamide can promote migration from the TPS phase to PLA during melt blending (Esmaeili et al., 2019; Wang et al., 2008) Com­ patibilizing agents such as citric acid (Wang et al., 2007), maleic an­ hydride (Przybytek et al., 2018), polyethylene glycol (PEG), and oil polyols (VOP) (Hu et al., 2020) have been used to promote the depo­ lymerization of starch and disruption of the granules (Caicedo et al., 2019; Caicedo & Pulgarin, 2021; Wang et al., 2007) Blends of TPS/PLA can be prepared by extrusion or blow molding processes, and samples of TPS/PLA/citric acid processed in this manner produced highly deformable materials with improved toughness and reduced water vapor and oxygen permeability (Abdillahi et al., 2013; Chabrat et al., 2012) Naturals oils also have been employed as plasticizers, these include castor oil (Xiong et al., 2013), epoxidized castor oil (Przybytek et al., 2018), epoxidized thistle oil (Turco et al., 2019), epoxidized sesame oil (Ortega-Toro et al., 2021) and maleinized linseed oil (Ferri et al., 2018) Maleinized hemp oil (Lerma-Canto et al., 2021) has been employed as a plasticizer in TPS/PLA blends, and these combinations had a positive effect, since the blends could be processed by injection molding and blow molding In addition to plasticizing starch, plastici­ zation of PLA by citrate and adipate esters has also studied Adipate esters were incorporated at low concentrations due to their low molec­ ular weights and linear structures, and films produced with these ma­ terials by blown extrusion optimal characteristics (Shirai et al., 2013; Shirai et al., 2016) In addition to thermal and mechanical analyses, morphological results allow evaluation of immiscibility by observing relationships within the domain dimension (Müller et al., 2012) Sila­ nization of the starch used in blends where the concentration of PLA was dominant led to improved compatibility based on morphological ana­ lyses, and the Tg values decreased while the crystallinity increased The mechanical properties of these blends were comparable to those pre­ pared using PLA (Jariyasakoolroj & Chirachanchai, 2014) Chemical modifications to starch, such as etherification, provide an opportunity to alter its hydrophilicity and increase its compatibility with PLA, and are more effective than other treatments of starches, which contain a high content of amylose (Wokadala et al., 2014) Lactur grafting in starch, using PLA-g-starch as a compatibilizing agent in PLA/TPS blown films, resulted in improved droplet sizes, flowability, extensibility and a better distribution of TPS dispersed in the PLA matrix (Noivoil & Yoksan, 2020) Palai et al reported in situ chemical grafting using glycidyl methacrylate (GMA) react with the carboxyl or hydroxyl groups of PLA (Palai et al., 2019) Protection of hydroxyl groups with acetyl groups decreased the polarity and enhanced the intermolecular mobility of the starch (Jim´ enez-Regalado et al., 2021) In this regard, PLA-acetylated starch blends with varied acetylation grades have been developed and their mechanical properties were evaluated (Noivoil & Yoksan, 2021) Increasing the degree of acetylation did not produce favorable results Therefore, the challenge remains to find an effective, profitable and environmentally friendly procedure to expand the use of PLA by improving its toughness and ductile properties through an optimal formulation that achieves a homogeneous blend with TPS (Ferri et al., 2018) Chemical crosslinking, interfacial transition and the formation of amphiphilic bridges are some of the approaches being used to increase of the interfacial adhesion in a TPS/PLA phase (Koh et al., 2018; Mar­ tinez Villadiego et al., 2021) Therefore, to address these issues, amphoteric surfactants are proposed as an alternative for use as coupling agents among TPS and PLA However, the surfactants are active in aqueous environment, and the TPS/PLA blend only have studied by processes as molten state, injection or blow molding, and extrusion Therefore, the approaching toward to understand the miscibility of the blend TPS-PLA by a preparation of this blend by a method such as sol­ vent casting where in the beginning of the process polymers are in liquid phase and to promote the miscibility among them due to the presence of a surfactant as Pluronic® F127, it is an attractive work to develop, which it can gain more information about the miscibility of this biodegradable polymers Commercially available poloxamers, such as the Pluronics® are known for their properties as nonionic amphoteric surfactants that can generate thermoreversible aqueous gels The Pluronic® F127 is composed of polyethylene oxide (PEO) and polypropylene oxide (PPO) units, and its arrangement in the poloxamer provides it with amphi­ philicity, and a variation in the proportion of PEO and PPO in the composition allows it to be classified and characterized by its distinctive hydrophilic-hydrophobic balance (Zarrintaj et al., 2018) In aqueous solutions Pluronic® at concentrations above the critical micelle con­ centration (CMC), these copolymers self-assemble into micelles with a hydrophobic PPO core surrounded by hydrophilic PEO segments, which generates interesting self-assembly and thermogelling properties (Fon­ seca-García et al., 2021; Russo & Villa, 2019) They possess favorable solubilization properties and low toxicity; therefore, the Pluronics® have properties that are useful for applications in drug administration or controlled release systems (Feitosa et al., 2019; Shaker et al., 2020) The hypothesis proposed in this work is that the miscibility of biodegradable polymers such as TPS and PLA is low because of limited chemical affinity between the polymers; however, the incorporation of Pluronic® F127 to TPS/PLA aqueous blends promotes their miscibility to allow production of materials for a variety of applications in the pharmaceutical industry, biodegradable packaging, or material design The goal of this work was the preparation and stabilization of different formulations of TPS/PLA blends by solvent casting techniques, and to evaluate their structural, thermal, morphological, and surface proper­ ties We expect that the results will add to our knowledge regarding the structural interactions between TPS and PLA Material and methods 2.1 Materials Achira starch (AS) was supplied by Surtialmidones S.A.S (Huila, A Fonseca-García et al Carbohydrate Polymers 293 (2022) 119744 Colombia) with a density of 1.59 g/mL and 29.1 % of amylose content calculated by ISO 6647 The polylactic acid (PLA) Ingeo 2003-D was obtained from Nature Works Company (Lancaster, PA, EE UU.) with a density of 1.24 g/cm3 MFI (210 ◦ C/2.16 kg) of 6.0 g/10 Pluronic® F127 (P2443, 70 % ethylene oxide), glycerol (density of 1.28 g/mL and purity 99.5 %), and ethyl acetate (purity of 99.8 %) were purchased from Sigma-Aldrich electron microscope (SEM) was employed A voltage of 10 kV was applied The samples were covered with a gold layer The surface films were analyzed at 500× and 2000× magnification 2.3.2 Fourier Transformed Infrared Spectroscopy (FT-IR) FT-IR analysis of dry films at room temperature was carried out by ATR mode using a spectrophotometer Spectrum by PerkinElmer (Wal­ tham, MA, USA) 2.2 Methods 2.3.3 X-ray diffraction analysis The atomic arrangement of films was observed by X-ray diffraction (XDR) using a Malvern-Panalytical equipment (Empyrean model, Wor­ cestershire, United Kingdom) at 45 kV, 40 mA and Cu Kα = 1.541 Å The measurements were done by Bragg–Brentano configuration of powder diffraction 2.2.1 Film preparation Solvent casting was the method used in the preparation of polymeric blend films And, the preparation of the blends was done from Table 1, ´mez-Aldapa (Go ´mezwhich was elaborated according to reports by Go Aldapa et al., 2019) The precursor solutions of achira starch (AS) and PLA were prepared independently The PLA solutions at % w/v were prepared by solubilization of PLA in ethyl acetate by reflux at 100 ◦ C for h AS solutions at % w/v were prepared by solubilizing starch, glycerol and according to the case F127 in distilled water, the glycerol was added in relation of 25 % w/w respect to starch However, the incorporation of Pluronic® F127 was added according to glycerol re­ placements as shown in Table The starch dispersion reached the gelatinization at 85 ◦ C by min, later, were kept at 77 ◦ C and the PLA solution was incorporated slowly the bubbles were removed of the fil­ mogenic solutions by vacuum pump, and, the solutions were dumped circular molds with a diameter of 5.5 cm Finally, the film polymeric blends were dried in a Binder convection oven at 60 ◦ C by h 2.3.4 Thermal properties Thermal stability of films was determined by thermogravimetric analysis (TGA) using a TGA/DSC STAR System instrument (Mettler Toledo, Columbus, OH, USA) The sample was heated from 25 ◦ C to 600 ◦ C at a heating rate of 20 ◦ C/min under a nitrogen purge at a flow rate of 60 mL/min Weight loss was shown as a function of temperature Differential Scanning Calorimetry (DSC) was used with TA Q-2000 equipment (TA Instruments, New Castle, DE, USA), to identify the thermal transitions of films at a heating rate of 10 ◦ C/min in a tem­ perature range from 25 ◦ C to 200 ◦ C with a nitrogen purge The crystallinity grade was determined by calculations based on ΔH0m for 100 % crystalline PLA being equal to 93 J/g (Fischer et al., 1973) The degree of crystallinity (Xc) of the blends could be calculated from the melting enthalpy in the secondary heating curves (ΔHm) ac­ cording to the Eq (1): / ] [ (1) %Xc = ΔHm − ΔHc ωPLA ⋅ΔHm × 100 2.3 Physicochemical characterization of the films 2.3.1 Morphology by Scanning Electron Microscopy The surface morphology of polymeric blends was analyzed at low magnification using a canon EOS Rebel T5 camera at 1:1 scale, and, at higher magnification a JEOL, JCM 50,000 (Tokyo, Japan) scanning where ωPLA is the mass fraction of PLA in the blends and ΔHc is cold crystallization enthalpy Table Proportions of achira starch (AS), poly(lactic acid) (PLA), plasticizer, and poloxamer used for the preparation of the polymer blends 2.3.5 Wettability by contact angle The wettability of AS-PLA-pluronic® F127 polymeric blend films was evaluated by sessile drop contact angle method using distilled water drops of 20 μL The test was measured at room temperature using a goniometer Ram´ e-Hart Model 250 (New Jersey, USA) and performed by triplicate Film Achira starch (AS) (g) PLA (g) Pluronic® F127 (g) Glycerol (g) AS100-PLA00 AS100-PLA04 AS100-PLA08 AS75-PLA250 AS75-PLA254 AS75-PLA258 AS50-PLA500 AS50-PLA504 AS50-PLA508 AS25-PLA750 AS25-PLA754 AS25-PLA758 AS0-PLA1000 AS0-PLA1004 AS0-PLA1008 0 1.25 0.25 0.5 0.75 3.75 1.25 1.25 3.75 1.25 0.25 3.75 1.25 0.5 0.75 2.5 2.5 1.25 2.5 2.5 0.25 2.5 2.5 0.5 0.75 1.25 3.75 1.25 1.25 3.75 0.25 1.25 3.75 0.5 0.75 Results and discussion 1.25 3.1 Morphology 0.25 0.5 0.75 In Fig 1, images of AS-PLA-Pluronic® F127 blended films at a scale of 1:1 can be observed, as well as SEM micrographs of these blends for both sides, top and bottom, and transverse sections A visual inspection 2.3.6 Mechanical properties The mechanical properties of tensile stress and elongation at fracture were performed on an INSTRON EMIC 23–50 universal machine (S˜ ao Jos´e dos Pinhais, Paran´ a, Brazil) The films were cut into thin strips measuring 100 mm long and 25 mm wide Five replicates were evalu­ ated for each formulation, previously conditioned at 23 ◦ C, 50 % relative humidity for 48 h The determinations were carried out at a speed of 10 mm⋅min− until the sample ruptured 2.3.7 Statistical analysis Analysis of variance (ANOVA) was performed by Tukey's test (sig­ nificance level: 0.05) to compare mean differences of the film formu­ lations All statistical analyses were performed with IBM SPSS Statistics for Windows version 25 (New York, United States) A Fonseca-García et al Carbohydrate Polymers 293 (2022) 119744 Fig Images of AS-PLA blend films: (a) AS100-PLA0-0, (b) AS100-PLA0-8, (c) AS75-PLA25-0, (d) AS75-PLA25-8, (e) AS50-PLA50-0, (f) AS50-PLA50-8, (g) AS25PLA75-0, (h) AS25-PLA75-8, (i) AS0-PLA100-0 and (j) AS0-PLA100-8 Micrographs by SEM of AS/PLA blend films, the chemical composition correspond to the image of above, 1: is f1 correspond to contact with the environment or top side, opaque surface, 2: Transversal section of film, and, 3: is f2 side in touch with the mold or bottom side of the films by images at a scale of 1:1 shows that AS100-PLA-0 is a translucent film, and that AS100-PLA-8 is a translucent, slightly opaque film, compared to AS100-PLA-0 This result demonstrates the good miscibility between AS and Pluronic® F127 AS0-PLA100-0 is a white film, and no visible color changes are evident in AS0-PLA100-8 films with respect to AS0-PLA100-0 In the blended films AS75-PLA25-0, AS50-PLA50-0, and AS25-PLA75-0, the miscibility of AS and PLA is complicated, and segregation of PLA is visually observed However, the incorporation of poloxamer promotes miscibility, since the blended films AS25-PLA75-8, AS50-PLA50-8, and AS25-PLA75-8 exhibit conformation and homogeneity, suggesting that the incorporation of Pluronic® F127 at % w/w in these blends promoted miscibility in the A Fonseca-García et al Carbohydrate Polymers 293 (2022) 119744 films The SEM micrographs were obtained on three sections of the films: the top side of the films, which engages in contact with the environment (named f1), the transverse section of the film, and the bottom of the film, the side in contact with the mold (named f2) In general, the SEM images of the blended films showed that for both sides f1 and f2, the confor­ mation of the films are different on a micrometer scale, although for the AS100-PLA0-0, AS100-PLA0-8 And, AS25-PLA75-0 films, where both film sides f1 and f2 have the same conformational behavior, the topography is smooth, with no hills or valleys, and are without scratches The AS100-PLA0-0 and AS25-PLA75-0 films are transversely compact, and in the AS25-PLA75-0 film, it is possible to identify segregation of PLA particles The polymeric blends AS75-PLA25-8 and AS50-PLA50-8 contained spherical particles in the matrix, which may be due to PLA in solution with AS, and Pluronic® F127 is stabilized as an emulsion, where in these formulations a continuous phase emulsion corresponds to water (AS), and the disperse phase emulsion corresponds to ethyl acetate (PLA) Since poloxamer (a triblock polymer) acts as a surfactant and forms micelles that help to stabilize the emulsion by reducing the surface tension, even when the casting process with PLA is stable, as shown in Fig for AS75-PLA25-8 and AS50-PLA50-8 blends However, the AS50-PLA50-8 film contains a greater number of spherical particles due to the PLA content being higher than it is in the AS75PLA25-8 film, and both blends generate compact films with particles along the matrix However, with AS25-PLA75-0 and AS25-PLA75-8, the blends are stabilized in an inverse emulsion In these cases, the contin­ uous phase emulsion corresponds to ethyl acetate (PLA), and the dispersed phase emulsion corresponds to water (AS) The addition of poloxamer leads to a reduction in the surface tension, and interactions between ethyl acetate (PLA) and water (AS) are made possible, thereby promoting miscibility Micrographs of AS25-PLA75-0 and AS25-PLA758 blends are shown in Fig 1, and crushed spherical particles are observed with AS25-PLA75-8 These spherical particles may be associ­ ated with AS blends, as the AS is at a low concentration with respect to PLA; also, particles are observed in the transverse section of the AS25PLA75-0 film This result can be explained by the segregation of AS that is immiscible in PLA, while in the AS25-PLA75-8 film they are observed only in the f2 side Finally, differences in the AS0-PLA1000 and AS0-PLA100-8 blended films are a result of the use of Pluronic® F127 In the case of AS0-PLA100-0 films, a visible porosity at a micro­ meter scale is observed along the film on sides f1 and f2, and on the transverse sections of the film; while in the case of AS0-PLA100-8 blended films, the porosity is lower than that observed in the AS0PLA100-0 film PLA100-0) films, respectively, with different concentrations of Plur­ onic® F127 (0 %, % and % w/w, respectively) In the AS100-PLA00 film, the absorption band at 3280 cm− is attributed to -OH groups and is indicative of starch This band corresponds to stretching vibrations of the -OH groups of amylose, amylopectin, glycerol, and absorbed water (Collazo-Bigliardi, Ortega-Toro, & Chiralt, 2019) Another broadband with less intensity was observed at 1648 cm− 1, which is attributed to the vibrational bending mode of water molecules, which absorbs strongly along with the hydroxyl groups in the amorphous regions of the starch Other relevant bands are located at 2930 cm− and 1344 cm− 1, which are due to the C–H and –CH2 groups located at carbon of the starch glucose units (Caicedo et al., 2019; Caicedo & Pulgarin, 2021; FonsecaGarcía et al., 2021) Finally, the band at 1005 cm− corresponds to C–O–H bending, this band is very important due to changes in starch structure such as retrogradation (Warren et al., 2016) In the AS0PLA100-0 sample, characteristic bands for PLA were identified These include a band at 1750 cm− 1, which corresponds to stretching of the – O) an important band to describe PLA (Yang et al., carbonyl group (C– 2008), a band at 1453 cm− that is due to bending vibrations of the CH3 group, and bands at 1380 cm− and 1359 cm− which are attributed to symmetrical and asymmetrical strains of the –CH group A typical ab­ sorption for the asymmetric stretching of the C–O bond in the ester group (–COOR) appears at 1183 cm− (Yang et al., 2008) The bands at 867 and 754 cm− are related to the stretching vibration of the C–C bond and correspond to the amorphous phases and crystalline PLA, respectively, thus indicating a semi-crystalline PLA (Palai et al., 2019; Takkalkar et al., 2019; Turco et al., 2019) Other bands at 2998 cm− and 2948 cm− are related to asymmetric and symmetric stretching vi­ brations of the CH group, and the bands at 1127 cm− 1, 1084 cm− and 1033 cm− correspond to stretching vibrations of the asymmetric C–O–C bond The bands at 953 and 924 cm− are characteristic of vibrations of a helical structure with an oscillation of the CH3 group And finally, the -OH band centered at 3298 cm− is attributed to the acid groups of PLA Regarding the incorporated poloxamer Pluronic F127, characteristic bands are observed in the region from 1129 to 1082 cm− 1, which indicate stretching of the C–O bond of the C–OH group in TPS mixtures, and the bands at 1001 and 1041 cm− are attributed to stretching of the C–O bond of the C–O–C group (Fonseca-García et al., 2021; Shaker et al., 2020; Zarrintaj et al., 2018) After identifying the characteristic functional groups of each polymer, interactions within the polymer mixtures were evaluated in response to an increase in the content of starch and poloxamer in the PLA base matrix According to the spectra presented in Fig 2, the polymers predominate on one side of the film, leaving the PLA in the lower part of the mold (f2) and the starch on the surface (f1) When starch is added in low amounts (AS25-PLA75), with a poloxamer content of % or %, suitable material compatibility is observed, with a similar arrangement of the polymers on both sides of the film, which could indicate a homogeneous material in the matrix Fig presents a diagram of the possible interactions that originate during the formation of polymeric materials Regarding the increase in the concentration of the poloxamer, no significant change was observed in the spectrum of starch plasticized with glycerol; only a slight increase in the intensity of the bands was observed, especially those for OH and C–OH groups, which results in competition by interactions between glycerol and poloxamer However, the plasticizer may interact through hydrogen bonds with greater probability due to a greater chemical af­ finity with AS, and the fact that the molecule is smaller and therefore easier to mobilize (Müller et al., 2016) Thus, the poloxamer may be limited in its ability to generate new interactions by leaving available the functional groups that increase the intensity of the bands with an increase in surfactant In the PLA films without starch (AS0-PLA100) (Figs 2, 1-B), the incorporation of poloxamer caused a decrease in the band corresponding to –OH groups because the vibration of these groups is restricted when they interact with hydrogen bonds This same effect was observed at wavelengths of 1638 cm− and 1380 cm− These changes imply that the hydrogen groups present interact through dipole- 3.2 Fourier Transformed Infrared Spectroscopy (FT-IR) This technique provides a spectrum of bands that are related to various functional groups, making it possible to identify the materials According to the SEM, only one of the polymers could be present in a more significant proportion on each side of the film; therefore, FTIR analyses were performed on each side of the sample Fig shows the IR spectra obtained using ATR of PLA films that contain different pro­ portions of Achira Starch (AS) and poloxamer (0 %, % and % w/w, respectively) The spectra obtained are presented in two columns (A) and (B) and four numbered rows According to the signals reported in the different spectra, it was observed that the polymers were ordered during the drying process, so that a polymer was obtained from one side of the film and another from the opposite side Column A shows the spectra corresponding to the different compositions of the films that have a predominance of bands associated with AS (TPS) and that remained in the upper part of the material, that is, the f1 side In contrast, column B shows the spectra obtained from the side of the film that is in contact with the mold (f2) and has a more significant rela­ tionship with the characteristic bands of PLA Images A1 and B1 show the control spectra for Achira Starch (AS100-PLA0-0) and PLA (AS05 A Fonseca-García et al Carbohydrate Polymers 293 (2022) 119744 A) B) AS100-PLA0-0 AS100-PLA0-4 AS0-PLA100-0 Transmittance (%) 1) Transmittance (%) Pluronic AS0-PLA100-4 AS0-PLA100-8 AS100-PLA0-8 2) 1000 Transmittance (%) Wavenumber (cm-1) 3600 500 AS75-PLA25-0 f1 AS75-PLA25-4 f1 3000 2400 1800 Wavenumber (cm-1) 1200 Transmittance (%) 4000 3500 3000 2500 2000 1500 600 AS75-PLA25-0 f2 AS75-PLA25-4 f2 AS75-PLA25-8 f2 AS75-PLA25-8 f1 2400 1800 Wavenumber (cm-1) 1200 3600 600 AS50-PLA50-0 f1 AS50-PLA50-4 f1 3000 2400 1800 Wavenumber (cm-1) 1200 Transmittance (%) 3) 3000 Transmittance (%) 3600 AS50-PLA50-0 f2 AS50-PLA50-0 f2 AS50-PLA50-0 f2 AS50-PLA50-8 f1 2400 1800 Wavenumber (cm-1) 1200 600 3600 3000 2400 1800 Wavenumber (cm-1) 1200 AS25-PLA75-0 f1 AS25-PLA75-4 f1 AS25-PLA75-4 f2 AS25-PLA75-8 f2 AS25-PLA75-8 f1 3600 3000 2400 1800 Wavenumber (cm-1) 1200 600 600 A25-PLA75-0 f2 Transmittance (%) 4) 3000 Transmittance (%) 3600 600 3600 3000 2400 1800 Wavenumber (cm-1) 1200 600 Fig FTIR-ATR spectra of AS-PLA polymeric blend films in different proportions (25–75, 50–50, 75–25 w/w) with the addition of Pluronic® F127 (0 %, %, and % w/v), f1 and f2 are on each side of the material A Fonseca-García et al Carbohydrate Polymers 293 (2022) 119744 Starch – Glycerol Pluronic® F127 – PLA Pluronic® F127 – Starch Fig Proposed structure of the possible interactions between the components of the AS-PLA-Pluronic blend induced dipole interactions between the PLA and the poloxamer chains (Takkalkar et al., 2019) When the starch content in the polymer blend is equal to or higher than 50 % (w/w), the material maintains a structural matrix similar to that present in the AS25-PLA75 sample; however, a decrease in the size of the characteristic bands begins to be observed for PLA on the shiny side (f2) of the material At the same time, addition of the poloxamer had a significant effect on the accommodation of said polymers, since increasing their presence in the formulation with the same concentration of biopolymers led to a spectrum that identified the same functional groups with similar sizes on each side of the material The poloxamer promoted miscibility of these polymers, where the more starch in the mixture, the more poloxamer, up to % for equal pro­ portions of both Achira Starch and PLA (AS50-PLA50-8, Figs 2, 3-B) In Table is shown a summary of relevant bands in the FTIR spectra of AS, PLA and mixture of AS-PLA- Pluronic® F127 According to Table the characteristic band of AS is the band at 1005 cm− corresponds to C–O–H bending and this band is representative of AS in the mixture with PLA and Pluronic® F127 While to PLA the bands that represent it – O stretching are at 1750 cm− and 1183 cm− 1, which correspond to C– and C–O–C stretching, respectively Due to the important bands to AS and PLA are summarized in Table 2, it is possible to understand the interaction among AS with PLA along with the different formulations, and both sides of films pristine films and with Pluronic® F127 at % w/v, and AS75-PLA25 films with Pluronic® F127 concentrations at %, %, and % w/v In the diffraction patterns for Pluronic® F127 powder there are two characteristic peaks of this poloxamer at 19.4◦ and 23.35◦ (2θ), these peak previously were reported (Fonseca-García et al., 2021) Also, for both starch films, AS100-PLA0-0 and AS100-PLA0-8, no diffraction peaks were observed, thus, the poloxamer did not influence the atomic ordering in Achira Starch However, for PLA, the poloxamer prevented atomic ordering due to AS0-PLA100-0 as evidenced by three peaks at 17◦ , 19.5◦ , and 22.8◦ (2θ) These peaks are associated with the planes 200/110, 203, and 210, respectively These planes are characteristics of a pseudoorthorhombic α structure in PLA (Brizzolara et al., 1996; Hoogsteen et al., 1990; Sasaki & Asakura, 2003; Zhang et al., 2008) In the AS0PLA100-8 diffractogram, a small peak at 17◦ was identified, which is associated with plane 200/100 in the crystalline structure in phase α of PLA In both the AS0-PLA100-0 and AS0-PLA100-8 films, the α structure is formed due to PLA that was treated at 100 ◦ C, a temper­ ature that commonly produces an α structure for PLA Relative to the ASPLA-Pluronic® F127 blends, the AS75-PLA25-0 diffractogram showed a peak at 16.80◦ , and in the AS75-PLA25-4 diffraction pattern there are peaks at 16.80◦ and 19.30◦ Finally, the AS75-PLA25-8 diffraction pattern contains peaks at 17.42◦ , 19.80◦ and 23.95◦ The AS/PLA/ Pluronic® F127 blends showed an atomic ordering in the formulation AS75-PLA25-8 and AS25-PLA75-8, which can be associated with PLA in the phase α It is important to mention that the crystalline structure increases as the amount of Pluronic® F127 increases in the blends Also, in AS75-PLA25-8 and AS25-PLA75-8, the peaks are shifted slightly to higher angles, which suggest that the crystalline domain is compacted However, PLA in blends with AS/Pluronic® except to AS50-PLA50-8 behaves in opposite ways to PLA with Pluronic® F127, since in that 3.3 X-ray diffraction (XRD) analysis Table shows a summary of diffraction patterns of the AS and PLA pristine films and with Pluronic® as well as the AS75-PLA25 films with Pluronic® F127 concentrations at %, %, and % w/v Also, the Fig shows the diffraction patterns for Pluronic® F127 powder, AS and PLA A Fonseca-García et al Carbohydrate Polymers 293 (2022) 119744 Table Summary of relevant bands in the FTIR spectra and peaks identified from X-ray diffraction of AS, PLA, Pluronic® F127 and AS-PLA- Pluronic® F127 blends Film Important wavenumber (cm− 1) Assignment XRD peak (2θ) Crystalline phase AS100PLA0-0 AS100PLA0-4 AS100PLA0-8 AS75PLA25-0 AS75PLA25-4 AS75PLA25-8 AS50PLA50-0 AS50PLA50-4 AS50PLA50-8 AS25PLA75-0 AS25PLA75-4 AS25PLA75-8 AS0PLA1000 AS0PLA1004 AS0PLA1008 f1and f2:1005 C–O–H bending Amorphous f1and f2:1005 C–O–H bending One wide peak from 15◦ to 25◦ – f1and f2:1005 C–O–H bending f1: 1750s and 1005 f1: 1750s and 1005 f1: 1750s and 1005 f1: 1005 f2: 1750, 1183s and 1005s f2: 1750, 1183 and 1005s f2: 1750, 1183 and 1005s f2: 1750 and 1005 –O stretching and f1: C– C–O–H bending, resp –O stretching and f1: C– C–O–H bending, resp –O stretching and f1: C– C–O–H bending, resp f1: C–O–H bending f1: 1750s and f2:1750 and 1005 1005 f1: 1750s and f2: 1750 and 1005 1005 f1: 1750s and f2: 1750 and 1005 1005s f1: 1750 and f2: 1750 and 1005 1005 f1: 1750 and f2: 1750 and 1005 1005 f1and f2: 1750 and 1183, resp –O stretching, C–O–C stretching, f2:C– and C–O–H bending, resp –O stretching, C–O–C stretching, f2:C– and C–O–H bending, resp –O stretching, C–O–C stretching, f2:C– and C–O–H bending, resp –O stretching and C–O–H bending, f2: C– resp –O stretching and –O stretching and C–O–H bending, f1: C– f2: C– C–O–H bending, resp resp –O stretching and –O stretching and C–O–H bending, f1: C– f2: C– C–O–H bending, resp resp –O stretching and –O stretching and C–O–H bending, f1: C– f2: C– C–O–H bending, resp resp –O stretching and –O stretching and C–O–H bending, f1: C– f2: C– C–O–H bending, resp resp –O stretching and –O stretching and C–O–H bending, f1: C– f2: C– C–O–H bending, resp resp –O stretching and C–O–C stretching, resp C– f1and f2: 1750 and 1183, resp f1and f2: 1750 and 1183, resp No identified One wide peak from 15◦ to 25◦ 16.84◦ Amorphous 16.84 , 19.31 and 22.75 17.42◦ , 19.79◦ and 23.93◦ One wide peak from 15◦ to 25◦ – α compacted ◦ ◦ Amorphous α compacted Amorphous No identified One wide peak from 15◦ to 25◦ 17.44◦ Amorphous – No identified Amorphous 17.27, 19.71 and 23.36◦ 17.11◦ , 19.42◦ , and 22.79◦ α compacted –O stretching and C–O–C stretching, resp C– – No identified –O stretching and C–O–C stretching, resp C– 16.97◦ Amorphous ◦ α Abbreviations: f1: The film side that is in contact with environment, f2: the film side that is in contact with the mold, s: small or tiny; resp.: respectively and α: pseudoorthorhombic α structure Fig X-ray diffraction patterns of (a) Pluronic® F127, AS and PLA pristine films and, AS and PLA films with Pluronic® F127 % w/v and (b) F127, and AS/PLA blends at a relation of 75 % of starch and 25 % PLA with different Pluronic® F127 concentrations, %, % and % w/v this case the polymer did not show diffraction peaks, but in the pristine condition PLA exhibited typical diffraction peaks of α structure In ASPLA-Pluronic® F127 blends, the crystallization of PLA at concentration low or high can be promoted due to the chemical affinity with the Pluronic® F127 However, when the formulation contains a same con­ centration of AS and PLA the poloxamer promotes the microspheres formation of PLA but, with amorphous structure due to at this concentration the poloxamer interacts superficially and intrinsically with PLA causing disorganization in the PLA polymer network While at low and high concentration of PLA with respect to AS, the crystalline structure of the PLA in the blend is of α phase A Fonseca-García et al Carbohydrate Polymers 293 (2022) 119744 3.4 Thermal properties degradation temperature range of the same polymer, indicating a null absorption of moisture due to its low polarity In general, the first de­ rivative of the TGA curve for blends shown as DTG (see Fig 5A and B, Y2 axis) exhibits two bands for the maximum degradation temperature (Td): the first (Td1) which is related to starch appears at 299.9 ◦ C, and the second (Td2) is related to PLA at 367.7 ◦ C This behavior is typical of degradation when there is low miscibility due to the hydrophilic and hydrophobic nature of the polymers (Wang et al., 2008) The incorpo­ ration of surfactant produced an increase in the values of Td1 up to ◦ C, as did the increase in the concentration of PLA on AS, this increased the Td1 by ~2 ◦ C In the case of the PLA degradation band, no significant changes are observed for Td2 In contrast to other studies (Yokesahachart & Yoksan, 2011), the incorporation of poloxamer led to an improvement in the thermal stability of the mixtures in the process temperature range (>100 ◦ C and 100 ◦ C for bound water (or structural, strong in­ teractions) up to 180 ◦ C Table lists the differences in the values of the first loss at 10 % mass (T10) as very significant between the AS samples when increasing both the content of PLA and poloxamer The T10 for pure starch occurs at 93.4 ◦ C When comparing these data with those obtained for the AS control samples (AS100-PLA0-0) and AS100-PLA08, an increase in this temperature was observed that relates to the presence of glycerol and Pluronic® This effect is produced by a limi­ tation in the interactions of environmental water molecules (moisture) through hydrogen bonds with starch, and with glycerol and poloxamer, which function as plasticizers (Mikus et al., 2014) Likewise, an increase in the T10 (>40 ◦ C) was observed, which leads to an improvement in the thermal stability when incorporating PLA; this produces moderate in­ teractions between the components (it follows a mixing rule behavior) The presence of the poloxamer led to an improvement in the thermal stability with increases >60 ◦ C with respect to the homologue of the blend without surfactant In the case of pure PLA, the value for T10 is 342.9 ◦ C, and according to the TGA graphs, it is located within the 100 100 80 Pluronic Starch AS100-PLA0-0 AS100-PLA0-8 PLA AS0-PLA100-0 AS0-PLA100-8 60 40 TG (%) 0 -20 -5 -40 100 200 300 400 DTG (u.a) -20 -5 -40 500 Temperature (°C) a) 100 200 300 400 500 Temperature (°C) b) 1.4 2.0 Starch 1.2 Heat flow relative (Normalizaded) (W/g) Heat flow relative (Normalizaded) (W/g) 40 20 20 AS100-PLA0-0 1.0 0.8 AS100-PLA0-8 0.6 PLA 0.4 AS0-PLA100-0 0.2 AS0-PLA100-8 -0.2 Pluronic -0.4 -0.6 50 c) AS75-PLA25-0 AS75-PLA25-4 AS75-PLA25-8 AS50-PLA50-0 AS50-PLA50-4 AS50-PLA50-8 AS25-PLA75-0 AS25-PLA75-4 AS25-PLA75-8 60 DTG (u.a.) TG (%) 80 75 100 125 150 AS75-PLA25-0 AS75-PLA25-4 1.5 AS75-PLA25-8 1.0 AS50-PLA50-0 AS50-PLA50-4 0.5 AS50-PLA50-8 AS25-PLA75-0 AS25-PLA75-4 -0.5 AS25-PLA75-8 50 175 Temperature (°C) d) 75 100 125 150 175 Temperature (°C) Fig TG and DTG thermograms of a) neat biopolymers (Starch and PLA) and b) blends (AS/PLA) DSC thermograms of c) neat biopolymers (Starch and PLA) and d) blends (AS/PLA) A Fonseca-García et al Carbohydrate Polymers 293 (2022) 119744 Table Thermal analysis parameter summary for neat biopolymers (Starch and PLA) and blends with different content of Pluronic (0 %, % and %) Film sample T10 (◦ C) Td1 (◦ C) Td2 (◦ C) Tg (◦ C) Tc (◦ C) Tm (◦ C) ΔHc ΔHm %Xc Starch PLA Pluronic® F127 AS100-PLA0-0 AS100-PLA0-8 AS75-PLA25-0 AS75-PLA25-4 AS75-PLA25-8 AS50-PLA50-0 AS50-PLA50-4 AS50-PLA50-8 AS25-PLA75-0 AS25-PLA75-4 AS25-PLA75-8 AS0-PLA100-0 AS0-PLA100-8 93.4 342.9 367.0 232.7 216.0 135.2 183.9 195.8 175.8 287.4 231.2 221.7 285.2 283.3 340.0 314.7 299.9 – 390.5 300.4 303.9 304.5 306.6 307.1 307.1 307.8 309.5 315.1 313.5 337.7 – – – 367.7 – – – 362.7 366.8 369.9 368.1 366.4 368.2 365.2 368.9 366.7 367.1 366.5 59.5 61.0 – 90.9 101.1 88.6 82.9 56.5 94.6 68.5 71.8 71.1 67.3 64.5 66.2 50.1 – 112.9 – – – – – – – – – – – – – 85.5 – 148.8–156.5 55.9 – 161.6 153.8 153.9 157.3 148.2 154.5 151.9 153.5 151.9 151.9 154.0–158.3 145.9–149.8 – 23.01 – – – – – – – – – – – – – 18.21 – 30.71 – – – 5.27 7.05 6.97 7.40 15.29 27.16 37.39 14.77 15.66 32.84 24.41 – 7.16 – – – 19.62 26.24 25.93 13.76 28.44 50.52 46.37 18.32 19.42 30.54 5.76 completing the plasticization, which is seen with the fusion at 161.6 ◦ C In the AS-PLA blends, the Tg decreases (up to 32.1 ◦ C) with increasing poloxamer, this change is radical when the starch content increases This can be explained by interactions between starch and PLA chains that cause a nucleation effect This result is consistent with those obtained by others, who discuss a decrease in the ordering of the polymers in the mixture, and migration of the plasticizer toward the PLA phase that generates an increase in the free volume (Ortega-Toro et al., 2021; Park et al., 2000) In this case, the type of interactions that occur upon incorporation of an amphiphilic macromolecule allows the structure greater freedom of movement, on the other hand, to the functionalizing agents that induce chemical bonds (crosslinks) (Ortega-Toro et al., 2021) For each proportion of AS/PLA containing % surfactant, an excess is observed that appears in the characteristic Tm band of the poloxamer at 55 ◦ C The PLA exhibited a glass transition temperature (Tg) at approximately 61.0 ◦ C The other two transitions observed refer to the crystallization temperature located at 112 ◦ C and two bands that represent the melting temperature of the α and β conversion crystals at 148 and 156 ◦ C (Keridou et al., 2020) The melting temperatures remain close to the second transition band of PLA, ranging between 148 ◦ C and 156 ◦ C (see Table 3) (Takkalkar et al., 2019) This transition is modified as shown by a partial overlap after film formation with controlled release of the solvent A thermodynamic equilibrium for preparation of the samples with PLA favors an increase in crystallinity and was esti­ mated from the enthalpies of fusion and crystallization of PLA (%Xc = 30.54) It should be noted that a correspondence with the XRD pattern was observed for this same compound The crystallinity data identified the behavior in the degree of ordering of the polymers in the different emulsions In this case, the AS75PLA25 blend presents structures defined as-PLA spherulites dispersed in the starch matrix (see Fig 1, micrographs), these are more defined with the presence of poloxamer, which reduces the surface tension to produce a homogeneous dispersion This behavior was similar in the AS50PLA50 blend; however, a higher concentration of poloxamer allowed greater ordering, although in separate phases In contrast, the AS25-PLA75 mixture showed a decrease in the melting enthalpy values when poloxamer was incorporated, indicating greater miscibility between the amorphous region of the PLA with the surfactant, and in turn with the starch Furthermore, the formulations AS25-PLA75-8 and AS-AS100-8 were super hydrophilic in nature with 0◦ on both faces, f1 and f2, and AS50PLA50-0 exhibited super hydrophilicity only on the f1 side The blends AS100-PLA-0, AS100-PLA-4, AS100-PLA-8, AS25-PLA75-4 and AS0PLA100-0 produced a similar contact angle with no >8◦ of difference and were

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