Maleated thermoplastic starch by reactive extrusion

Effect of Starch Plasticization on Morphological, Mechanical, Crystalline, Thermal, and Optical Behavior of Poly(butylene adipate-co-terephthalate)/Thermoplastic Starch Composite Films

Starches plasticized with glycerol/citric acid/stearic acid and tributyl 2-acetylcitrate (ATBC), respectively, were processed with poly (butylene adipate-Co-terephthalate (PBAT) via extrusion and a film-blown process. All the composite films were determined for morphology, mechanical, thermal stability, crystalline, and optical properties. Results show that the most improved morphology was in the 30% glycerol plasticized PBAT/thermoplastic starch (TPS) composite films, characterized by the smallest and narrowest distribution of TPS particle sizes and a more uniform dispersion of TPS particles. However, the water absorption of PBAT/TPS composite films plasticized with glycerol surpassed that observed with ATBC as a plasticizer. Mechanical properties indicated insufficient plasticization of the starch crystal structure when using 10% ATBC, 20% ATBC, and 20% glycerol as plasticizers, leading to poor compatibility between PBAT and TPS. This resulted in stress concentration points under external forces, adversely affecting the mechanical properties of the composites. All PBAT/TPS composite films exhibited a negative impact on the initial thermal decomposition temperature compared to PBAT. Additionally, the haze value of PBAT/TPS composite films exceeded 96%, while pure PBAT had a haze value of 47.42%. Films plasticized with 10% ATBC, 20% ATBC, and 20% glycerol displayed lower transmittance values in the visible light region. The increased transmittance of films plasticized with 30% glycerol further demonstrated their superior plasticizing effect compared to other PBAT/TPS composite films. This study provides a simple and feasible method for preparing low-cost PBAT composites, and their extensions are expected to further replace general-purpose plastics in daily applications.

Molecular insight into toughening induced by core-shell structure formation in starch-blended bioplastic composites

Binary and ternary blends with poly(lactic acid) (PLA), poly(butylene succinate) (PBS), and thermoplastic starch (TPS) were prepared by a melt process to produce biodegradable biomass plastics with both economical and good mechanical properties. The mechanical and structural properties of each blend were evaluated. Molecular dynamics (MD) simulations were also conducted to examine the mechanisms underlying the mechanical and structural properties. PLA/PBS/TPS blends showed improved mechanical properties compared with PLA/TPS blends. The PLA/PBS/TPS blends with a TPS ratio of 25-40 wt% showed higher impact strength than PLA/PBS blends. Morphology observations showed that in the PLA/PBS/TPS blends, a structure similar to that of core-shell particles with TPS as the embedding phase and PBS as the coating phase was formed, and that the trends in morphology and impact strength changes were consistent. The MD simulations suggested that PBS and TPS tightly adhered to each other in a stable structure at a specific intermolecular distance. From these results, it is clear that PLA/PBS/TPS blends are toughened by the formation of a core-shell structure in which the TPS core and the PBS shell adhered well together and stress concentration and energy absorption occurred in the vicinity of the core-shell structure.

Bio-nanocomposites films based on unmodified and modified thermoplastic starch reinforced with chemically modified nanoclays

The use of polymers capable of being degraded by the action of microorganisms and/or enzymes without causing harmful effects is a strategy in waste management and environmental care. In this work, bio-nanocomposites based on thermoplastic starch (TPS) were synthesized by reactive extrusion using a twin-screw extruder. Two strategies were evaluated to reduce the disadvantages of TPS for packaging applications. First, starch was chemically modified producing the reaction of native starch with chemical reagents that introduce new functional groups to reduce the water adsorption. And two, nano-fillers were incorporated into TPS in order to enhance the mechanical and barrier properties, driving to materials with improved performance/cost ratio. The synergistic strategies of chemical modification and incorporation of modified nanoclays were also effective to reduce the dependence of properties of TPS with the environment humidity and the evolution thereof over time, which influences the performance during the service life of the product.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10853-023-08354-1.

Isosorbide plasticized corn starch filled with poly(3-hydroxybutyrate-co-3-hydroxyvalerate) microparticles: Properties and behavior under environmental factors

In this work, new green and fully biodegradable composites, based on corn starch, plasticized with two different amounts of isosorbide and filled by poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) microparticles, were obtained by melt processing. The analysis of their morphologies, crystallinity, structural interactions and dynamomechanical properties as well as the evaluation of their moisture resistance and biodegradability in soil, were performed in function of the plasticizer and/or microparticle amount. The analysis of morphology, crystallinity and structural interactions showed that the plasticization process was completed under the melting processing conditions used. The microparticles were homogeneously dispersed in the thermoplastic starch matrix without suffering any deformation or breaking during the processing. Biocomposites with adequate storage modulus values were obtained, especially the TPS plasticized with 35% of isosorbide and filled with 5 wt% of PHBV microparticles. The incorporation of PHBV microparticles leads to biocomposites with higher moisture resistance. All the biocomposites were completely biodegraded in soil in a short period of time. The performed study demonstrated that these biocomposites could be used for applications in the packaging industry.

Multi-scale reactive extrusion modelling approaches to design polymer synthesis, modification and mechanical recycling

Reactive extrusion (REX) is an important processing and production technique with applications in the field of polymer synthesis, modification and recycling.

Effects of Modified Thermoplastic Starch on Crystallization Kinetics and Barrier Properties of PLA

This study reports on using reactive extrusion (REX) modified thermoplastic starch particles as a bio-based and biodegradable nucleating agent to increase the rate of crystallization, percent crystallinity and improve oxygen barrier properties while maintaining the biodegradability of PLA. Reactive blends of maleated thermoplastic starch (MTPS) and PLA were prepared using a ZSK-30 twin-screw extruder; 80% glycerol was grafted on the starch during the preparation of MTPS as determined by soxhlet extraction with acetone. The crystallinity of PLA was found to increase from 7.7% to 28.6% with 5% MTPS. The crystallization temperature of PLA reduced from 113 °C to 103 °C. Avrami analysis of the blends showed that the crystallization rate increased 98-fold and t_1/2 was reduced drastically from 20 min to <1 min with the addition of 5% MTPS compared to neat PLA. Observation from POM confirmed that the presence of MTPS in the PLA matrix significantly increased the rate of formation and density of spherulites. Oxygen and water vapor permeabilities of the solvent-casted PLA/MTPS films were reduced by 33 and 19% respectively over neat PLA without causing any detrimental impacts on the mechanical properties (α = 0.05). The addition of MTPS to PLA did not impact the biodegradation of PLA in an aqueous environment.

Production of Cyclic Anhydride-Modified Starches

Modified starches offer a biodegradable, readily available, and cost-effective alternative to petroleum-based products. The reaction of alkenylsuccinic anhydrides (ASAs), in particular, is an efficient method to produce amphiphilic starches with numerous applications in different areas. While ASAs are typically derived from petroleum sources, maleated soybean oil can also be used in an effort to produce materials from renewable sources. The reaction of gelatinized waxy maize starch with octenylsuccinic anhydride (OSA), dodecenylsuccinic anhydride (DDSA), a maleated fatty acid (TENAX 2010), phthalic anhydride (PA), 1,2,4-benzenetricarboxylic acid anhydride (trimellitic anhydride, TMA), and three maleated soybean oil samples, was investigated under different conditions. To minimize the reaction time and the amount of water required, the outcome of the esterification reaction was compared for starch dispersions in benchtop dispersed reactions, for starch melts in a heated torque rheometer, and for reactive extrusion in a pilot plant scale twin-screw extruder. The extent of reaction was quantified by ¹H NMR analysis, and changes in molecular weight and diameter were monitored by gel permeation chromatography (GPC) analysis. The outcome of the reactions varied markedly in terms of reaction efficiency (RE), molecular weight distribution, and average hydrodynamic diameter, for the products derived from the different maleated reagents used, as well as for the different reaction protocols.

Cellulose nanofibrils reinforced PBAT/TPS blends: Mechanical and rheological properties

Poly(butylene adipate-Co-terephthalate)/thermoplasticized starch PBAT/TPS blends are among the most produced biodegradable plastic for wide application packaging, sharing more than 20% of the global production capacity of bioplastics. However, this class of material suffers from poor mechanical strength in comparison of neat PBAT, especially when the TPS content exceeds 30 wt%. Aiming at enhancing the mechanical performance of PBAT/TPS blends while maintaining relatively high TPS content, cellulose nanofibrils (CNFs) was incorporated into the TPS phase using twin screw extrusion. The effects of CNFs content on the microstructure, mechanical properties, melt-rheology and humidity absorption were investigated. An enhancement in the tensile strength and modulus was noted with the inclusion of CNFs, with optimal performance attained at 8 wt% of CNFs. A narrowing in the distribution of the TPS nodules within the PBAT matrix was also observed with the addition of CNFs, which is expected to be on the origin of the main evolution in the mechanical, rheological and humidity observed. Because of the availability of CNFs, biodegradability and facile processability, the ternary PBAT-TPS-CNFs blends might contribute to improve the performance of this class of biodegradable bioplastic.

Production of starch-polyester bio-support for lipases immobilization: synergistic action of itaconic acid and nanoclay

The objective of the present work was to develop biodegradable polymeric films (starch-PBAT) as support for the immobilization of lipases using sodium montmorillonite (MMT) as a reinforcing agent (2% w/w) and itaconic acid (IA - 0.5-1.5% w/w) as a compatibilizing agent. The films were produced through a two steps blow-extrusion. The addition of MMT increased the tensile strength and Tg of the films, while the presence of IA made the films more flexible, reducing their Tg. Lipases from Burkholderia cepacia LTEB11 were immobilized in the films by the adsorption method. The ester yield (% of ethyl oleate synthesis) has shown best results (96%, 6 h) for immobilized enzyme in the MMT film and six cycles of reuse were carried out until a reduction of 50% in the catalytic activity of the enzyme.

Starch-Based Fishing Composite Fiber and Its Degradation Behavior

The starch-based fishing composite fibers were prepared by one-step reactive extrusion and melt spinning. The effects of starch contents on the microstructural, thermal, dynamic mechanical, and mechanical properties of starch-based composite fibers were studied. And the degradation behaviors in soil of the fibers were also investigated. The compatibility between starch and HDPE is improved significantly by grafting maleic anhydride (MA) using one-step reactive blending extrusion. As the starch content increased, the melting temperature and the crystallinity of the fibers gradually decreased due to fluffy internal structures. Dynamic mechanical analysis showed that the transition peak α in the high-temperature region was gradually weakened and narrowed with increasing starch content; moreover, a shoulder appeared on the low-temperature side of the α peak was assigned to the β-relaxation related to starch phase. In addition, the mechanical results showed the significant decrease in the breaking strength and increase in the elongation at break of the starch-based composite fibers as the starch content increased. After degradation in soil for 5 months, the surface of the composite fibers had been deteriorated, while flocculent layers were observed and a large number of microfibers appeared. And the weight loss rate of the starch-based composite fibers (5.2~34.8%) significantly increased with increasing starch content (50~90 wt%).

Use of Starch Granules Enriched with Carvacrol for the Lesser Mealworm, Alphitobius diaperinus Control in Chicken House: Effects on Insects and Poultry

The aim of this study was to investigate the effect of starch granules enriched with carvacrol and mixed with straw pellets (as poultry litter) on the mortality of larvae and adults of the lesser mealworm, Alphitobius diaperinus Panzer, a cosmopolitan pest inhabiting chicken houses in vast numbers worldwide. Additionally, the effect of starch granules on the growth parameters and survival of broiler chickens exposed to treated litter was examined. In this study, granules containing 3, 5, and 10% carvacrol was used. In a simulated chicken house bioassay, this material was mixed with pellets in three different proportions: 30/70%, 40/60%, and 50/50% (granules/pellets, respectively). On this medium, young larvae (approximately 10 days old), older larvae (last stage before pupa), and unsexed 7–10 days old adults of the lesser mealworm, with access to food, were colonized. Experiments were performed at 29°C in the dark. The study shows that poultry litter with the addition of starch granules enriched with 10% of carvacrol in the proportion of 40:60% (granules:pellets) appears to be the optimal medium applicable to broiler houses for A. diaperinus control. In this environment, all larvae and adults died within 3–4 days and the overall development of the experimental chickens was similar to that of the control. However, the feed conversion rate was slightly higher in the treated group (1.72) than in the control group (1.56). The average final body weight in the treated group was 100 g lower than that in the control group (the differences were not statistically significant).

Catalyst-free esterification of high amylose starch with maleic anhydride in 1-butyl-3-methylimidazolium chloride: The effect of amylose content on the degree of MA substitution

The limited reactivity of starch towards maleic anhydride (MA) affords maleate with a low degree of MA substitutions (CC and COOH groups). In this study, we investigated the relationship between the starch structure, controlled by its amylose (AM)/amylopectin (AP) ratio, and the DS of starch maleates using C₄[mim]Cl as the recyclable media, and catalyst. The results indicated that starches with varying AM/AP ratio produced maleates with comparable CC groups (DS_NMR = 0.06-0.07). Following dissolution, the high amylose (DS_titration = 1.17, yield = 69.2 %) and regular starches (DS_titration = 1.17; yield = 59.3 %) produced high DS_titration maleates (COOH groups) at MA/AGU ratio of 12:1 (80 °C, 10 min). Comparatively, DS_titration value of waxy starch maleates (DS_titration = 0.88, yield = 59.3 %) was lower than AM-based starches, possibly due to the crosslinking tendency of AP branches consisting of carboxylic end-groups. Interestingly, DS_titration value for EHCS (1.17) ranged between its bulk (DS_NMR: 0.06) and surface distribution of MA (DSS_XPS 1.7); therefore, we considered it reliable for future reference.

Cornstarch-based wound dressing incorporated with hyaluronic acid and propolis: In vitro and in vivo studies

The unique physicochemical and functional characteristics of starch-based biomaterials and wound dressings have been proposed for several biomedical applications. Film dressings of cornstarch/hyaluronic acid/ ethanolic extract of propolis (CS/HA/EEP) were prepared by solvent-casting and characterized by attenuated total reflectance/Fourier transform infrared spectroscopy, scanning electron microscopy, gas chromatography/mass spectrometry, light transmission, opacity measurements, EEP release, equilibrium swelling, and in vitro and in vivo evaluations. The CS/HA/0.5%EEP film dressing exhibited higher antibacterial activity against Staphylococcus aureus (2.08 ± 0.14 mm), Escherichia coli (2.64 ± 0.18 mm), and Staphylococcus epidermidis (1.02 ± 0.15 mm) in comparison with the CS, CS/HA, and CS/HA/0.25%EEP films. Also, it showed no cytotoxicity for the L929 fibroblast cells. This wound dressing could effectively accelerate the wound healing process at Wistar rats' skin excisions. These results indicate that enrichment of cornstarch wound dressings with HA and EEP can significantly enhance their potential efficacy as wound dressing material.

Physical assessment, spectroscopic and chemometric analysis of starch-based foils with selected functional additives

The paper presents the results of studies related to the impact of functional additives in the form of polylactide (PLA), polyvinyl alcohol (PVA), and keratin hydrolysate (K) on the physical characteristics of biopolymer foils. TPS granulate was obtained using a TS-45 single-screw extruder with L/D = 16. Foil was produced with the use of an L/D = 36 extruder with film-blowing section. The impact of the quantity and type of the functional additives on the processing efficiency and energy consumption of granulate extrusion, as well as the physical characteristics of the foil produced: thickness, basis weight, and colour were determined. By measuring the FTIR spectra it was determined the type and origin of the respective functional groups. It was observed that foils produced from granulates with the addition of 3% PVA were characterised by the lowest thickness and basis weight. Addition of 2 and 3% of PLA increased thickness and basis weight of starch-based foils significantly. Increasing the content of keratin in SG/K samples resulted in a decrease of brightness and intensify the yellow tint of foils, especially when 2 and 3% of keratin was used. In terms of the other samples, it was observed that the colour remained almost unchanged irrespective of the percentage content of the additive used. Infrared analyses conducted on foil containing PVA, PLA, and K revealed a change in spectra intensity in the frequency range associated with-OH groups originating from the forming free, intra- and intermolecular hydrogen bonds. Based on an analysis of the respective bands within the IR range it was also concluded that considerable structural changes took place with respect to the glycosidic bonds of starch itself. The application of the mentioned additives had a significant structural impact on the produced starch-based foils. Furthermore, the conducted UV-Vis analyses revealed a substantial increase in absorbance and a related reduction of the permeability (colour change) of the obtained materials in the range of ultraviolet and visible light.

Preparation and Characterization of Hydrophobically Grafted Starches by In Situ Solid Phase Polymerization

Three kinds of hydrophobic groups grafted starches of maleic anhydride grafted starch (MAH-g-starch), lactic acid grafted starch (LA-g-starch), and methyl acrylate grafted starch (MA-g-starch) were prepared by in situ solid phase polymerization. The results of Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) confirmed successful grafting. The grafting ratios of MAH-g-starch, LA-g-starch, and MA-g-starch were 6.50%, 12.45%, and 0.57%, respectively. Influenced by the grafting ratio, LA-g-starch had the best relative hydrophobicity and the largest molecular weight, and those for MA-g-starch were the worst. The surfaces of grafted starches were covered with graft polymer, with obvious surface roughness and bond degree of MAH-g-starch and LA-g-starch. The crystalline structure of grafted starches showed some damage, with LA-g-starch exhibiting the greatest decrease in crystallinity, and less of a change for MA-g-starch. Overall, the grafting reaction improved thermoplasticity, with LA-g-starch the most improved, followed by MAH-g-starch, and then MA-g-starch.

Reactive compatibilization of plant polysaccharides and biobased polymers: Review on current strategies, expectations and reality

Our society is amidst a technological revolution towards a sustainable economy, focused on the development of biobased products in virtually all sectors. In this context, plant polysaccharides, as the most abundant macromolecules present in biomass represent a fundamental renewable resource for the replacement of fossil-based polymeric materials in commodity and engineering applications. However, native polysaccharides have several disadvantages compared to their synthetic counterparts, including reduced thermal stability, moisture absorption and limited mechanical performance, which hinder their direct application in native form in advanced material systems. Thus, polysaccharides are generally used in a derivatized form and/or in combination with other biobased polymers, requiring the compatibilization of such blends and composites. In this review we critically explore the current status and the future outlook of reactive compatibilization strategies of the most common plant polysaccharides in blends with biobased polymers. The chemical processes for the modification and compatibilization of starch and lignocellulosic based materials are discussed, together with the practical implementation of these reactive compatibilization strategies with special emphasis on reactive extrusion. The efficiency of these strategies is critically discussed in the context on the definition of blending and compatibilization from a polymer physics standpoint; this relies on the detailed evaluation of the chemical structure of the constituent plant polysaccharides and biobased polymers, the morphology of the heterogeneous polymeric blends, and their macroscopic behavior, in terms of rheological and mechanical properties.

Ductility and Toughness Improvement of Injection-Molded Compostable Pieces of Polylactide by Melt Blending with Poly(ε-caprolactone) and Thermoplastic Starch

The present study describes the preparation and characterization of binary and ternary blends based on polylactide (PLA) with poly(ε-caprolactone) (PCL) and thermoplastic starch (TPS) to develop fully compostable plastics with improved ductility and toughness. To this end, PLA was first melt-mixed in a co-rotating twin-screw extruder with up to 40 wt % of different PCL and TPS combinations and then shaped into pieces by injection molding. The mechanical, thermal, and thermomechanical properties of the resultant binary and ternary blend pieces were analyzed and related to their composition. Although the biopolymer blends were immiscible, the addition of both PCL and TPS remarkably increased the flexibility and impact strength of PLA while it slightly reduced its mechanical strength. The most balanced mechanical performance was achieved for the ternary blend pieces that combined high PCL contents with low amounts of TPS, suggesting a main phase change from PLA/TPS (comparatively rigid) to PLA/PCL (comparatively flexible). The PLA-based blends presented an "island-and-sea" morphology in which the TPS phase contributed to the fine dispersion of PCL as micro-sized spherical domains that acted as a rubber-like phase with the capacity to improve toughness. In addition, the here-prepared ternary blend pieces presented slightly higher thermal stability and lower thermomechanical stiffness than the neat PLA pieces. Finally, all biopolymer pieces fully disintegrated in a controlled compost soil after 28 days. Therefore, the inherently low ductility and toughness of PLA can be successfully improved by melt blending with PCL and TPS, resulting in compostable plastic materials with a great potential in, for instance, rigid packaging applications.

Starch carboxymethylation by reactive extrusion: Reaction kinetics and structure analysis

An efficient reaction of carboxymethylation using reactive extrusion (REX) on plasticized starch was studied. The reaction products were characterized by Nuclear Magnetic Resonance (NMR) spectroscopy and high-performance liquid chromatography (HPLC). Several parameters affecting the reaction were investigated including the amount of plasticizer, reagent stoichiometry and reaction time. Reaction efficiency (RE) up to 65% was achieved in one step after 5 min of reaction, showing that the reaction kinetics is hundred times faster than the same reaction described in solution. The degree of substitution (DS) of 2.1 was obtained in 3 steps. The regioselectivity of the reaction on the anhydroglucose monomers units (AGU) was respectively C-2 > C-6 > C-3. A significant deviation from the Spurlin statistical model was observed. Multisubstituted AGU were analyzed by chromatography. Different multi-substitution patterns were obtained by using different starch sources. Tetra-carboxymethyl glucose corresponding to the complete modification of the terminal non-reducing glucoses from branched amylopectin chains was analysed.

Effect of replacement of corn starch by whey protein isolate in biodegradable film blends obtained by extrusion

The aim of this study was to evaluate the effect of replacing corn starch by whey protein isolated (WPI) in biodegradable polymer blends developed by extrusion. X-ray diffraction showed the presence of a Vh-type crystalline arrangement. The films were homogeneous, indicating strong interfacial adhesion between the protein and the thermoplastic starch matrix (TPS) as observed in scanning electron microscopy. The addition of WPI on TPS matrix promoted an increase in the thermal stability of the materials. It was observed 58.5% decrease in the water vapor permeability. The effect of corn starch substitution by WPI on mechanical properties resulted in a more resistant and less flexible film when compared the TPS film. The addition of WPI caused greenish yellow color and less transparent films. The substitution of corn starch by WPI made it possible to obtain polymer blends with improved properties and represents an innovation for application as a packaging material.

Starch Modification by Organic Acids and Their Derivatives: A Review

Starch has been an inexhaustible subject of research for many decades. It is an inexpensive, readily-available material with extensive application in the food and processing industry. Researchers are continually trying to improve its properties by different modification procedures and expand its application. What is mostly applied in this view are their chemical modifications, among which organic acids have recently drawn the greatest attention, particularly with respect to the application of starch in the food industry. Namely, organic acids naturally occur in many edible plants and many of them are generally recognized as safe (GRAS), which make them ideal modification agents for starch intended for the food industry. The aim of this review is to give a short literature overview of the progress made in the research of starch esterification, etherification, cross-linking, and dual modification with organic acids and their derivatives.