The effect of plasticizer selection on properties of blends poly(butylene adipate-co-terephthalate) with thermoplastic starch

Development of starch-rich thermoplastic polymers based on mango kernel flour and different plasticizers

This work reports on the development of starch-rich thermoplastic based formulations produced by using mango kernel flour, avoiding the extraction process of starch from mango kernel to produce these materials. Glycerol, sorbitol and urea at 15 wt% are used as plasticizers to obtain thermoplastic starch (TPS) formulations by extrusion and injection-moulding processes. Mechanical results show that sorbitol and urea allowed to obtain samples with tensile strength and elongation at break higher than the glycerol-plasticized sample, achieving values of 2.9 MPa of tensile strength and 42 % of elongation at break at 53 % RH. These results are supported by field emission scanning electron microscopy (FESEM) micrographs, where a limited concentration of voids was observed in the samples with sorbitol and urea, indicating a better interaction between starch and the plasticizers. Thermogravimetric analysis (TGA) shows that urea and sorbitol increase the thermal stability of TPS in comparison to the glycerol-plasticized sample. Differential scanning calorimetry (DSC) and dynamic-mechanical-thermal analysis (DMTA) verify the increase in stiffness of the sorbitol and urea plasticized TPS and also illustrate an increase in the glass transition temperature of both samples in comparison to the glycerol-plasticized sample. Glass transition temperatures of 45 °C were achieved for the sample with sorbitol.

Effects of polyols with different hydroxyl numbers on the structure and properties of starch straws

To study the relationship between the number of hydroxyl groups of polyols and the plasticizing effect, the effects of different polyols including ethylene glycol, glycerol, erythritol, xylitol and sorbitol on the structure and properties of corn starch straws were analyzed and compared. The results showed that the addition of plasticizer significantly improved the performance of starch straws, which greatly improved the mechanical properties, water absorption rate (WAR) and thermal stability. However, there was no linear relationship between the plasticizing effect on starch straws and the number of hydroxyl groups in plasticizers. Fourier transform infrared (FTIR) results showed that erythritol formed the strongest intermolecular interaction with starch. Starch straws with erythritol (S-ERY) had the highest bending force (Fb = 25.78 N) and the lowest WAR. Starch straws with glycerol (S-GLY) showed the lowest relative crystallinity (RC = 12.87 %) and the highest temperature of the maximum degradation (Tdmax = 302.1 °C). In addition, after storing for 180 days, S-GLY showed higher modulus of elasticity in bending (Eb = 4.26 N/cm) and a uniform surface.

High-performance thermoplastic starch/poly(butylene adipate-co-terephthalate) blends through synergistic plasticization of epoxidized soybean oil and glycerol

Utilizing starch, an abundant polysaccharide, as the renewable filler to blend with poly(butylene adipate-co-terephthalate) (PBAT) is a feasible tactic to construct cost-effective and high-performance biodegradable materials. It's worth noting that the thermal processing properties of starch can be manipulated by its plasticized behavior. Herein, epoxidized soybean oil (ESO) and glycerol were used as the plasticizer for native corn starch and the plasticized starch was integrated with PBAT to manufacture starch-based biodegradable blend films. ESO breaks the hydrogen bonds between starch chains through the fatty chains grafting reaction and increases the distance between starch molecular chains due to the large molecular weight of ESO. Meanwhile, glycerol molecules are incorporated into the starch molecular chains, and fatty chains grafted starch chains, effectively reducing the intermolecular forces of molecular chains. On account of the synergistic plasticization of ESO and glycerol which possess good compatibility with PBAT, the PS_G20E10 blend film achieved a tensile strength, an elongation at break of 16.11 MPa and 612.09 %, and the balanced water and oxygen permeability properties.

Preparation and Properties of Poly(butylene adipate-co-terephthalate)/thermoplastic Hydroxypropyl Starch Composite Films Reinforced with Nano-Silica

The use of biodegradable plastics is gradually increasing, but its expensive cost limits promotion. In this study, poly(butylene adipate-co-terephthalate)/thermoplastic hydroxypropyl starch reinforced with nano-silica (PBAT/TPHS_g-SiO2) composite films with high hydroxypropyl starch content were prepared in a two-step process. The effect of reinforced thermoplastic hydroxypropyl starch on the mechanical, thermal, processing properties, and micromorphology of the composite films was investigated. The results showed that the tensile strength of the composite films was significantly improved by the addition of nano-silica, with 35% increase in horizontal tensile strength and 21% increase in vertical tensile strength after the addition of 4 phr of nano-silica. When the content of thermoplastic hydroxypropyl starch reinforced with nano-silica (TPHS_g-4SiO2) is 40%, the horizontal and vertical tensile strengths of the films are 9.82 and 12.09 MPa, respectively, and the elongation at break of the films is over 500%. Electron micrographs show that TPHS_g-4SiO2 is better homogeneously dispersed in the PBAT and exhibits a bi-continuous phase structure at a TPHS_g-4SiO2 content of 40%. In this study, the blowing PBAT/TPHS_g-4SiO2 composite films effectively reduce the cost and still show better mechanical properties, which are suitable for packaging applications.

Effect of polybutylene adipate terephthalate on the properties of starch/polybutylene adipate terephthalate shape memory composites

In this work, the starch/polybutylene adipate terephthalate (PBAT) composite films with high starch content were prepared by hot-pressing and ultraviolet cross-linking methods using cassava starch, benzophenone (BP), degradable PBAT and citric acid as film-forming substrate, photosensitizer, toughening material and solvent, respectively. The results showed that starch and PBAT had excellent performance, resulting in the composites films exhibit robust tensile strength (9.90 MPa), decent elongation at break (500.05 %) and excellent shape memory property. Under 30 % pre-tensile strain, the shape memory fixity and recovery ratios reached 96.58 % and 93.94 %, respectively. In addition, the starch-based films were successfully rendered hydrophobic by PBAT hydrophobic characteristics. PBAT not only secures the biodegradability of the starch/PBAT composites films, but also improves the mechanical properties of them, and meets the requirements of the thermal shrinkage films when subjected to large strain.

Effect of Chain Extending Cross-Linkers on the Disintegration Behavior of Composted PBAT/PLA Blown Films

A biodegradable blend of PBAT-poly(butylene adipate-co-terephthalate)-and PLA-poly(lactic acid)-for blown film extrusion was modified with four multi-functional chain extending cross-linkers (CECL). The anisotropic morphology introduced during film blowing affects the degradation processes. Given that two CECL increased the melt flow rate (MFR) of tris(2,4-di-tert-butylphenyl)phosphite (V1) and 1,3-phenylenebisoxazoline (V2) and the other two reduced it (aromatic polycarbodiimide (V3) and poly(4,4-dicyclohexylmethanecarbodiimide) (V4)), their compost (bio-)disintegration behavior was investigated. It was significantly altered with respect to the unmodified reference blend (REF). The disintegration behavior at 30 and 60 °C was investigated by determining changes in mass, Young's moduli, tensile strengths, elongations at break and thermal properties. In order to quantify the disintegration behavior, the hole areas of blown films were evaluated after compost storage at 60 °C to calculate the kinetics of the time dependent degrees of disintegration. The kinetic model of disintegration provides two parameters: initiation time and disintegration time. They quantify the effects of the CECL on the disintegration behavior of the PBAT/PLA compound. Differential scanning calorimetry (DSC) revealed a pronounced annealing effect during storage in compost at 30 °C, as well as the occurrence of an additional step-like increase in the heat flow at 75 °C after storage at 60 °C. The disintegration consists of processes which affect amorphous and crystalline phase of PBAT in different manner that cannot be understood by a hydrolytic chain degradation only. Furthermore, gel permeation chromatography (GPC) revealed molecular degradation only at 60 °C for the REF and V1 after 7 days of compost storage. The observed losses of mass and cross-sectional area seem to be attributed more to mechanical decay than to molecular degradation for the given compost storage times.

Electrospinning of Microstructures Incorporated with Vitamin B9 for Food Application: Characteristics and Bioactivities

The food industry has been expanding, and new vectors to entrap vitamins have been constantly investigated, aiming at versatile systems with good physico-chemical characteristics, low-cost production, high stability and the efficient release of active ingredients. The vitamin B9 (folic acid or folate) is essential for the healthy functioning of a variety of physiological processes in humans and is beneficial in preventing a range of disorders. In this study, two approaches were developed to encapsulate vitamin B9. Zein and the combination of modified starch with two plasticizers were the selected encapsulating agents to produce microstructures via the electrospinning technique. The objective was to improve the stability and the B9 antioxidant capacity in the final formulations. The work strategy was to avoid limitations such as low bioavailability, stability and thermosensitivity. The microstructures were fabricated and the morphology and shape were assessed by scanning electron microscopy. The B9 release profiles of modified starch and zein microstructures were analyzed in simulated gastric fluid at 37 °C, and in deionized water and ethanol at room temperature. The B9 encapsulation efficiency and the stability of the systems were also studied. The ABTS assay was assessed and the antioxidant activity of the produced microstructures was evaluated. The physico-chemical characterization of loaded B9 in the microstructures was achieved. High encapsulation efficiency values were achieved for the 1% B9 loaded in 12% w/w modified starch film; 5% B9 vitamin encapsulated by the 15% w/w modified starch with 4% w/w tween 80; and 4% w/w glycerol film with heterogeneous microstructures, 5% w/w zein compact film and 10% w/w zein film. In conclusion, the combinations of 7 wt.% of modified starch with 4 wt.% tween 80 and 4 wt.% glycerol; 15 wt.% of modified starch with 4 wt.% tween 80 and 4 wt.% glycerol; and 12 wt.% modified starch and 5 wt.% zein can be used as delivery structures in order to enhance the vitamin B9 antioxidant activity in the food and nutraceutical fields.

Effective Aging Inhibition of the Thermoplastic Corn Starch Films through the Use of Green Hybrid Filler

Recently, hybrid fillers have been widely used to improve the properties of biopolymers. The synergistic effects of the hybrid fillers can have a positive impact on biopolymers, including thermoplastic corn starch film (TPCS). In this communication, we highlight the effectiveness of hybrid fillers in inhibiting the aging process of TPCS. The TPCS, thermoplastic corn starch composite films (TPCS-C), and hybrid thermoplastic corn starch composite film (TPCS-HC) were stored for 3 months to study the effect of hybrid filler on the starch retrogradation. TPCS-C and TPCS-HC were prepared by casting method with 5 wt% of fillers: nanocellulose (NC) and bentonite (BT). The alteration of the mechanical properties, aging behavior, and crystalline structure of the films were analyzed through the tensile test, Fourier transform infrared (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and water absorption analysis. The obtained data were correlated to each other to analyze the retrogradation of the TPCS, which is the main factor that contributes to the aging process of the biopolymer. Results signify that incorporating the hybrid filler (NC + BT) in the TPCS/4BT1NC films has effectively prevented retrogradation of the starch molecules after being stored for 3 months. On the contrary, the virgin TPCS film showed the highest degree of retrogradation resulting in a significant decrement in the film’s flexibility. These findings proved the capability of the green hybrid filler in inhibiting the aging of the TPCS.

Process-Induced Morphology of Poly(Butylene Adipate Terephthalate)/Poly(Lactic Acid) Blown Extrusion Films Modified with Chain-Extending Cross-Linkers

Process-induced changes in the morphology of biodegradable polybutylene adipate terephthalate (PBAT) and polylactic acid (PLA) blends modified with various multifunctional chain-extending cross-linkers (CECLs) are presented. The morphology of unmodified and modified films produced with blown film extrusion is examined in an extrusion direction (ED) and a transverse direction (TD). While FTIR analysis showed only small peak shifts indicating that the CECLs modify the molecular weight of the PBAT/PLA blend, SEM investigations of the fracture surfaces of blown extrusion films revealed their significant effect on the morphology formed during the processing. Due to the combined shear and elongation deformation during blown film extrusion, rather spherical PLA islands were partly transformed into long fibrils, which tended to decay to chains of elliptical islands if cooled slowly. The CECL introduction into the blend changed the thickness of the PLA fibrils, modified the interface adhesion, and altered the deformation behavior of the PBAT matrix from brittle to ductile. The results proved that CECLs react selectively with PBAT, PLA, and their interface. Furthermore, the reactions of CECLs with PBAT/PLA induced by the processing depended on the deformation directions (ED and TD), thus resulting in further non-uniformities of blown extrusion films.

The Effects of Chain-Extending Cross-Linkers on the Mechanical and Thermal Properties of Poly(butylene adipate terephthalate)/Poly(lactic acid) Blown Films

This study investigates the effects of four multifunctional chain-extending cross-linkers (CECL) on the processability, mechanical performance, and structure of polybutylene adipate terephthalate (PBAT) and polylactic acid (PLA) blends produced using film blowing technology. The newly developed reference compound (M·VERA® B5029) and the CECL modified blends are characterized with respect to the initial properties and the corresponding properties after aging at 50 °C for 1 and 2 months. The tensile strength, seal strength, and melt volume rate (MVR) are markedly changed after thermal aging, whereas the storage modulus, elongation at the break, and tear resistance remain constant. The degradation of the polymer chains and crosslinking with increased and decreased MVR, respectively, is examined thoroughly with differential scanning calorimetry (DSC), with the results indicating that the CECL-modified blends do not generally endure thermo-oxidation over time. Further, DSC measurements of 25 µm and 100 µm films reveal that film blowing pronouncedly changes the structures of the compounds. These findings are also confirmed by dynamic mechanical analysis, with the conclusion that tris(2,4-di-tert-butylphenyl)phosphite barely affects the glass transition temperature, while with the other changes in CECL are seen. Cross-linking is found for aromatic polycarbodiimide and poly(4,4-dicyclohexylmethanecarbodiimide) CECL after melting of granules and films, although overall the most synergetic effect of the CECL is shown by 1,3-phenylenebisoxazoline.

Occurrence and Analysis of Thermophilic Poly(butylene adipate-co-terephthalate)-Degrading Microorganisms in Temperate Zone Soils

The ubiquity and character of thermophilic poly(butylene adipate-co-terephthalate) (PBAT)-degrading microorganisms in soils were investigated and compared to the process in an industrial composting plant. PBAT degraders were sought in 41 temperate zone soils. No mesophilic degraders were found by the employed method, but roughly 10² colony-forming units (CFUs) of thermophilic degraders per gram of soil were found in nine soils, and after an enrichment procedure, the PBAT-degrading consortia were isolated from 30 out of 41 soils. Thermophilic actinomycetes, Thermobispora bispora in particular, together with bacilli proved to be the key constituents of the isolated and characterized PBAT-degrading consortia, with bacilli comprising from about 30% to over 90% of the retrieved sequences. It was also shown that only consortia containing both constituents were able to decompose PBAT. For comparison, a PBAT film together with two types of PBAT/starch films were subjected to biodegradation in compost and the degrading microorganisms were analyzed. Bacilli and actinobacteria were again the most common species identified on pure PBAT film, especially at the beginning of biodegradation. Later, the composition of the consortia on all three tested materials became very similar and more diverse. Since waste containing PBAT-based materials is often intended to end up in composting plants, this study increases our confidence that thermophilic PBAT degraders are rather broadly present in the environment and the degradation of the material during the composting process should not be limited by the absence of specific microorganisms.

Improving the flexibility and compostability of starch/poly(butylene cyclohexanedicarboxylate)-based blends

Fully biobased blends of thermoplastic starch and a poly(butylene cyclohexanedicarboxylate)-based random copolyester containing 25 % of adipic acid co-units (PBCEA) are prepared by melt blending and direct extrusion film casting. The obtained films are characterized from the physicochemical and mechanical point of view and their fragmentation under composting conditions is evaluated. The results demonstrate that the introduction of adipic acid co-units in the PBCE macromolecular chains permits to decrease the blending temperature, thus avoiding unwanted starch degradation reactions. Moreover, the presence of small amounts of citric acid as compatibilizer further improves the interfacial adhesion between the two components and promotes the formation of micro-porosities within the films. The synergistic combination of these factors leads to the development of materials showing an elastomeric behavior, i.e. no evident yield and elongation at break higher than 450 %, good moisture resistance and fast fragmentation in compost.

The effect of plasticizers on thermoplastic starch films developed from the indigenous Ethiopian tuber crop Anchote (Coccinia abyssinica) starch

Anchote (Coccinia abyssinica) starch films were prepared by a solution casting method with glycerol, 1-ethyl-3-methylimidazolium acetate, sorbitol or triethylene glycol as plasticizers. The effect of these plasticizers and their concentration on film microstructure, thermal, and mechanical properties was investigated. Scanning electron microscopy revealed that regardless of plasticizer type, films possessing higher plasticizer content had more homogeneous morphologies than those with lower plasticizer content. The FTIR spectra of films plasticized with 1-ethyl-3-methylimidazolium acetate had higher intensity peaks at 3150, 1400 and 1000 cm-1 when compared to other film peaks. These data show that 1-ethyl-3-methylimidazolium acetate plasticized films have decreased molecular order which results in less hydrogen bonding. For this reason, films developed from 1-ethyl-3-methylimidazolium acetate were more flexible than the others. The effect of plasticizers on the thermal properties of the anchote starch films was investigated using thermogravimetric analysis (TGA). Films made from 30% (w/w) plasticizer concentration exhibited higher thermal stability for all types of plasticizer. Mechanical testing showed that sorbitol films had the highest tensile strength, approximately 2 times that of the triethylene glycol plasticized film and 3 times that of the film made from 1-ethyl-3-methylimidazolium acetate.