Effect of annealing on the thermal properties of poly (lactic acid)/starch blends

Poly (lactic acid)/ amine grafted mesoporous silica-based composite for food packaging application

The present study focuses on the development of environmentally friendly bio-composite films using poly(lactic acid) (PLA) as a biopolymer matrix. This is achieved by incorporating amine functionalized green mesoporous silica (GMS) and employing a solution casting method for film fabrication. The motivation behind the work is to improve the compatibility between PLA and green mesoporous silica sourced from rice husk by functionalizing GMS with APTES (3-Aminopropyltriethoxy silane). The primary objective is to explore how the inclusion of GMS influences both the physicochemical attributes and the efficacy of active food packaging in PLA. The introduction of GMS to the PLA matrix not only improves the flexibility of PLA/GMS composite films but also enhances their overall performance. The reinforcement of GMS in the PLA matrix has also significantly contributed towards the reduction in oxygen transmittance rate and provided an anti-bacterial effect towards pathogen i.e. S. aureus and E. coli. The PLA/GMS composite films exhibit antioxidant activity acting as potential scavengers with around 78 % efficacy against DPPH (2,2-diphenyl-1-picrylhydrazyl). Consequently, the PLA/GMS composite formulation proposed in this study shows promising outcomes in terms of strength, flexibility, antioxidant properties, and antibacterial characteristics. Also, the PLA/GMS films extended the shelf life of cut apple samples for seven days.

Accelerated hydrolytic degradation of poly(l-lactide) by blending with poly(ether-block-amide)

A continuing challenge in the most common biodegradable polyester of poly(l-lactide) (PLLA) is to improve the degradation rate in the environment, though it has been widely used in packaging and medical applications. In this study, PLLA/poly(ether-block-amide) (PEBA) blends are prepared by melt blending to investigate the effect of PEBA component on the phase morphology, thermal behavior, mechanical properties, and hydrolytic degradation of the blends. The incorporation of PEBA component is beneficial to the improved toughness and increased water absorption of the blends, and accelerated hydrolytic degradation of PLLA. The blend exhibits the optimal mechanical and hydrolytic degradation properties when the blend mass ratio of PLLA/PEBA is 80/20. The toughness of the blend is increased by 390 % compared to that of pure PLLA. After being hydrolyzed at 58 °C for 240 h, the water absorption, the mass loss and the decrease of molecular weight of the blend is increased by 138 %, 160 % and 40 %, respectively, indicating faster hydrolytic degradation rate of the blend than that of pure PLLA. Furthermore, the accelerated hydrolytic degradation mechanism of PLLA in the blend is revealed. The amorphous region of PLLA is hydrolyzed initially at the phase interface of the blend, and subsequently the crystalline structure of PLLA is degraded. The hydrolysis process causes a change in the relative content of crystalline regions in the system, resulting in an increase in crystallinity of PLLA first and then decrease. These findings provide a new strategy for the design of novel degradable PLLA materials for practical applications.

The Development of Sustainable Polyethylene Terephthalate Glycol-Based (PETG) Blends for Additive Manufacturing Processing-The Use of Multilayered Foil Waste as the Blend Component

The polymer foil industry is one of the leading producers of plastic waste. The development of new recycling methods for packaging products is one of the biggest demands in today's engineering. The subject of this research was the melt processing of multilayered PET-based foil waste with PETG copolymer. The resulting blends were intended for additive manufacturing processing using the fused deposition modeling (FDM) method. In order to improve the properties of the developed materials, the blends compounding procedure was conducted with the addition of a reactive chain extender (CE) and elastomeric copolymer used as an impact modifier (IM). The samples were manufactured using the 3D printing technique and, for comparison, using the traditional injection molding method. The obtained samples were subjected to a detailed characterization procedure, including mechanical performance evaluation, thermal analysis, and rheological measurements. This research confirms that PET-based film waste can be successfully used for the production of filament, and for most samples, the FDM printing process can be conducted without any difficulties. Unfortunately, the unmodified blends are characterized by brittleness, which makes it necessary to use an elastomer additive (IM). The presence of a semicrystalline PET phase improves the thermal resistance of the prepared blends; however, an annealing procedure is required for this purpose.

Tailoring PLA/ABS Blends Compatibilized with SEBS-g-MA through Annealing Heat Treatment

In this work, blends based on poly (lactic acid) (PLA)/acrylonitrile-butadiene-styrene (ABS) compatibilized with maleic anhydride-grafted (SEBS-g-MA) were prepared in a co-rotational twin-screw extruder by varying the concentrations of the compatibilizing agent. The influence of the compatibilizing agent on the morphology, mechanical, thermal, thermomechanical, and rheological properties of the prepared materials was analyzed. The effect of annealing on the properties of the blends was also investigated using injection-molded samples. The X-ray diffraction (XRD) results proved that the increments in crystallinity were an effect of annealing in the PLA/ABS/SEBS-g-MA blends, resonating at higher heat deflection temperatures (HDTs). The impact strength of the PLA/ABS blends compatibilized with 10 wt% SEBS-g-MA was significantly increased when compared to the PLA/ABS blends. However, the hardness and elastic modulus of the blends decreased when compared to neat PLA. The refined morphology shown in the scanning electron microscopy (SEM) analyses corroborated the improved impact strength promoted by SEBS-g-MA. The torque rheometer degradation study also supported the increased compatibility between SEBS-g-MA, PLA, and ABS. The TGA results show that the PLA/ABS and PLA/ABS/SEBS-g-MA blends are more thermally stable than the neat PLA polymer at higher temperatures. The results showed that the ideal composition is the heat-treated PLA/ABS/SEBS-g-MA (60/30/10 wt%), given the high impact strength and HDT results. The results of this work in terms of mechanical improvement with the use of compatibilizers and annealing suggest that the PLA/ABS/SEBS-g-MA system can be used in the production of 3D-printing filaments.

Poly(lactic acid)/cholecalciferol based composites for active food packaging application

Poly(lactic acid) (PLA) based sustainable composites incorporated with cholecalciferol (Vitamin D3) (CC) at different concentrations (1, 3, 5 and 10 wt%) were prepared using solvent casting method. Performance analysis of PLA/CC composite films in terms of food packaging properties like thermal, optical, oxygen barrier, mechanical, anti-bacterial as well as anti-oxidant effect is carried out. The PLA/CC-5 composite showed complete blockage of UV-B light at 320 nm, which is known to significantly induce the photo-chemical degradation of polymers. The incorporation of CC in the PLA matrix brought in improvement in mechanical and oxygen barrier properties. The PLA composite films showed effective antibacterial activity against food borne bacteria (S. aureus and E. coli), in addition to excellent antioxidant activity. All these important traits exhibited by PLA/CC composite films suggest its potential for food packaging application.

Preparation, Characterization, and Antimicrobial and Antiviral Properties of Silver-Containing Nanocomposites Based on Polylactic Acid-Chitosan

Antimicrobial and antiviral nanocomposites based on polylactic acid (PLA) and chitosan were synthesized by a thermochemical reduction method of Ag⁺ ions in the PLA-Ag⁺-chitosan polymer films. Features of the structural, morphological, thermophysical, antimicrobial, antiviral, and cytotoxic properties of PLA-Ag-chitosan nanocomposites were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and antiviral, antimicrobial, and cytotoxic studies. The effects of temperature and the duration of reduction of Ag⁺ ions on the structure of PLA-Ag-chitosan nanocomposites were established. During the thermochemical reduction (T = 160 °C, t = 5 min) of silver palmitate ions in PLA-Ag⁺-chitosan polymer films, Ag nanoparticles with an average size of 4.2 nm were formed. PLA-Ag-chitosan polymer nanocomposites have strong antimicrobial activity against S. aureus and E. coli strains. In particular, for PLA-chitosan samples containing 4% Ag, the diameters of the S. aureus and E. coli growth inhibition zones were 25.8 and 25.0 mm, respectively. The antiviral activity of the nanocomposites against influenza A virus, herpes simplex virus type 1, and adenovirus serotype 2 was also revealed. The PLA-4%Ag-chitosan nanocomposites completely inhibited the cytopathic effect (CPE) of herpes virus type 1 by 5.12 log₁₀TCID₅₀/mL (high antiviral activity) and the development of the CPE of influenza virus and adenovirus by 0.60 and 1.07 log₁₀TCID₅₀/mL (relative antiviral activity). The obtained nanocomposites were not cytotoxic; they did not inhibit the viability of MDCK, BHK-21, and Hep-2 cell cultures.

Pressure moisture treatment and hydro-thermal treatment of starch

Starch is often subjected to denaturation treatment to improve its useful properties and eliminate its shortcomings. Various methods have been developed to produce modified starches with different properties and for a variety of uses. Because physically modified starch can be produced without chemical substances or biological agents, the modification method is very simple and inexpensive, and the resulting material can be used as clean label starch. Among these physical modification technologies, heat moisture treatment (HMT) is a universally valid technology, but little is known about pressure moisture treatment (PMT)-related technology. Physical modification of starch using PMT results in new functions and value-added characteristics required by industry, and PMT has the potential to produce starch with new functions. In this paper, PMT-related technologies for physically modified starch, the difference between PMT and the hydro-thermal treatment, and clean label starch manufacturing using HMT and PMT were investigated.

Crystalline polysaccharides: A review

The biodegradability and mechanical properties of polysaccharides are dependent on their architecture (linear or branched) as well as their crystallinity (size of crystals and crystallinity percent). The amount of crystalline zones in the polysaccharide significantly governs their ultimate properties and applications (from packaging to biomedicine). Although synthesis, characterization, and properties of polysaccharides have been the subject of several review papers, the effects of crystallization kinetics and crystalline domains on the properties and application have not been comprehensively addressed. This review places focus on different aspects of crystallization of polysaccharides as well as applications of crystalline polysaccharides. Crystallization of cellulose, chitin, chitosan, and starch, as the main members of this family, were discussed. Then, application of the aforementioned crystalline polysaccharides and nano-polysaccharides as well as their physical and chemical interactions were overviewed. This review attempts to provide a complete picture of crystallization-property relationship in polysaccharides.

Physical modification of starch by heat-moisture treatment and annealing and their applications: A review

Heat-moisture treatment (HMT) and annealing are hydrothermal starch modifications. HMT is performed using high temperature and low moisture content range, whereas annealing uses excess of water, a long period of time, and temperature above the glass transition and below the gelatinization temperature. This review focuses on: research advances; the effect of HMT and annealing on starch structure and most important properties; combined modifications; and HMT-starch and annealed-starch applications. Annealing and HMT can be performed together or combined with other modifications. These combinations contribute to new applications in different areas. The annealed and HMT-starches can be used for pasta, candy, bakery products, films, nanocrystals, and nanoparticles. HMT has been studied on starch digestibility and promising data have been reported, due to increased content of slowly digestible and resistant starches. The starch industry is in constant expansion, and modification processes increase its versatility, adapting it for different purposes in food industries.

A green fabrication method of poly (lactic acid) perforated membrane via tuned crystallization and gas diffusion process

Poly (lactic acid) (PLA) perforated membrane is typically obtained through the solvent-volatilization-induced or non-solvent-induced phase separation (NIPS) method. However, the residual organic solvents would unavoidably limit the application of PLA perforated membrane in biomedical and high-end water purification fields. Herein, an innovative solution-free method was proposed for preparing the PLA perforated membrane via a simple and environmentally friendly way. We have successfully fabricated the PLA perforated membrane using a physical foaming technique with CO₂ as the blowing agent. By tuning the primary film thickness, saturation pressure, and foaming temperature, PLA perforated membrane's cell morphology could be accordingly adjusted. The PLA perforated membrane with a highly-ordered straight pore channel and high open cell content (OCC) approximately 72% was obtained under a mild condition. The formation mechanism of the PLA perforated membrane was discussed via the interaction of crystallization behavior and gas diffusion process. This green and solvent-free PLA perforated membrane possesses great potential for use in areas like the tissue engineering and high-end water purification.

Fabrication of waterproof gas separation membrane from plastic waste for CO2 separation

In this study, waste polystyrene (wPS) plastic was used to prepare gas-separation membranes with hot-pressing technology to reduce the accumulation of plastic waste. Polystyrene is a commonly used polymer for the production of plastic products, and it is also used in the synthesis of membranes for gas separation. Compared to the traditional synthesis process, hot-pressing is environmentally friendly because it does not require organic solvents. The mobility of the polymer chain and the integrity and free volume of the membrane are affected by the temperature, pressure, duration, and annealing environment of the hot-pressing process, thereby altering the performance of the membrane. Additionally, when the wPS contained polybutadiene, the gas separation membranes showed a selectivity of 17.14 for CO₂/N₂. The membranes also exhibited ideal waterproof performance when the membranes were operated under water pressures of 1-5 bar. Therefore, membranes derived from wPS through hot pressing are waterproof and can be used for gas separation. Furthermore, they are expected to maintain their separation performance in complex environments.

A Comprehensive Review on Corn Starch-Based Nanomaterials: Properties, Simulations, and Applications

Corn (Zea mays L.) is one of the major food crops, and it is considered to be a very distinctive plant, since it is able to produce a large amount of the natural polymer of starch through its capacity to utilize large amounts of sunlight. Corn starch is used in a wide range of products and applications. In recent years, the use of nanotechnology for applications in the food industry has become more apparent; it has been used for protecting against biological and chemical deterioration, increasing bioavailability, and enhancing physical properties, among other functions. However, the high cost of nanotechnology can make it difficult for its application on a commercial scale. As a biodegradable natural polymer, corn starch is a great alternative for the production of nanomaterials. Therefore, the search for alternative materials to be used in nanotechnology has been studied. This review has discussed in detail the properties, simulations, and wide range of applications of corn starch-based nanomaterials.

Synthesis and characterization of antibacterial polylactic acid film incorporated with cinnamaldehyde inclusions for fruit packaging

To maintain the quality of postharvest fruits continuously and meet the health requirements of consumers, a high barrier and long-lasting antibacterial polylactic acid film as packaging material was developed in this study. Polylactic acid-based antibacterial films incorporated with Cinnamaldehyde inclusions were used to achieve long-lasting antibacterial activity and improve the barrier properties. Cinnamaldehyde inclusions were prepared via the inclusion method and used as a sustained-release antibacterial agent and reinforcement to be incorporated into polylactic acid-based films within a concentration range of 0-30 wt%. The FT-IR spectrum demonstrated that the Cinnamaldehyde inclusions was physically interacting with PLA. The XRD results showed that the cinnamaldehyde inclusions at a concentration of 10 wt% enhanced the crystallinity of the antibacterial film. The oxygen and water vapor barrier properties of the film were respectively 14.29% and 12.38% higher than those of a pure PLA film. The tensile strength of the antibacterial film increased by 20%. And the antibacterial activity against Escherichia coli and Listeria monocytogenes was 100%. The release rate of cinnamaldehyde of the antibacterial film was slow and varied smoothly for 20 d.

Thermal Insulation and Mechanical Properties of Polylactic Acid (PLA) at Different Processing Conditions

This work aims to provide an extensive evaluation on the use of polylactic acid (PLA) as a green, biodegradable thermal insulation material. The PLA was processed by melt extrusion followed by compression molding and then subjected to different annealing conditions. Afterwards, the thermal insulation properties and structural capacity of the PLA were characterized. Increasing the annealing time of PLA in the range of 0-24 h led to a considerable increase in the degree of crystallization, which had a direct impact on the thermal conductivity, density, and glass transition temperature. The thermal conductivity of PLA increased from 0.0643 W/(m·K) for quickly-cooled samples to 0.0904 W/(m·K) for the samples annealed for 24 h, while the glass transition temperature increased by approximately 11.33% to reach 59.0 °C. Moreover, the annealing process substantially improved the compressive strength and rigidity of the PLA and reduced its ductility. The results revealed that annealing PLA for 1-3 h at 90 °C produces an optimum thermal insulation material. The low thermal conductivity (0.0798-0.0865 W/(m·K)), low density (~1233 kg/m3), very low water retention (<0.19%) and high compressive strength (97.2-98.7 MPa) in this annealing time range are very promising to introduce PLA as a green insulation material.

Improving the Toughness and Thermal Resistance of Polyoxymethylene/Poly(lactic acid) Blends: Evaluation of Structure-Properties Correlation for Reactive Processing

The study focuses on the development of polyoxymethylene (POM)/poly(lactic acid) (PLA) blends with increased impact and thermal resistance. The study was conducted in two phases; in the first part, a series of unmodified blends with PLA content of 25, 50, and 75 wt.% was prepared, while the second part focused on the modification of the PLA/POM (50/50) blends. An ethylene/butyl acrylate/glycidyl methacrylate terpolymer (E/BA/GMA) elastomer (EBA) was used to improve the impact strength of the prepared blends, while reactive blending was used to improve interfacial interactions. We used a multifunctional epoxy chain extender (CE) as the compatibilizer. Static tensile tests and notched Izod measurement were used to evaluate the mechanical performance of the prepared samples. The thermomechanical properties were investigated using dynamic mechanical thermal analysis (DMTA) analysis and heat deflection temperature (HDT)/Vicat softening temperature (VST) methods. The crystallinity was measured using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXS) measurements, while the rheology was evaluated using a rotational rheometer. The paper also includes a structure analysis performed using the SEM method. The structural tests show partial miscibility of the POM/PLA systems, resulting in the perfect compatibility of both phases. The impact properties of the final blends modified by the EBA/CE system were found to be similar to pure POM resin, while the E modulus was visibly improved. Favorable changes were also noticeable in the case of the thermomechanical properties. The results of most of the conducted measurements and microscopic observations confirm the high efficiency of the reaction for PLA as well as for the modified POM/PLA mixtures.

Effect of annealing on the functional properties of corn starch/corn oil/lysine blends

Annealing effects on the structure characteristics and the digestibility of corn starch (CS)/corn oil (oil)/lysine mixture were investigated. The objective of this study was to provide guidance for designing higher slowly digestible starch. Confocal laser confirmed that lysine adhered to granules surface. The interactions among starch, corn oil and lysine were further investigated by using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and rapid visco analyzer (RVA). After annealing treatment, in vitro digestion studies showed that the content of slowly digestible starch increased in the mixture blended with corn oil and lysine. The physical barrier of lysine, amylose-lipid complex and starch-oil-lysine three-dimensional network can provide resistance to digestive enzymes. Annealing with corn oil and lysine can be a good prospect for the efficient modification of in vitro digestibility of starch.

Thermal, morphological and structural characterization of a copolymer of starch and polyethylene

The objective of this paper was to perform a copolymerization between polyethylene and starch in order to obtain new environmentally friendly materials. The copolymer obtained was characterized thermally, morphologically and structurally, including its pasting profile. The starch-g-PE copolymer showed lower thermal stability compared to the control materials. FTIR analysis determined that the chemical bond signal between the starch and polyethylene in the copolymer overlaps with the native starch signals. The signal from this chemical bond was assigned by proton NMR spectroscopy at δ 4.45 ppm. X-ray studies of the copolymer showed a material with more amorphous characteristics compared to native starch. SEM analysis demonstrated the presence of cracks in the starch granules which favored the chemical interaction between the polymers. The pasting behavior of the copolymer was less pronounced compared to native starch. Therefore, the copolymerization of both polymers could be an alternative to recycle polyethylene and make biodegradable materials.

Thermal and thermo-oxidative degradation kinetics and characteristics of poly (lactic acid) and its composites

Thermal degradation behavior and kinetics of starch/PLA composites in an inert and oxygen atmosphere were investigated by TG and TG-FTIR techniques. It is shown that the thermal degradation process can be divided into three stages, and a significant difference between thermal and thermo-oxidative degradation is the third stage in which the residual chars are further cracked for the thermo-oxidative degradation. The activation energy was calculated using the iso-conversional Flynn-Wall-Ozawa (FWO) method. The lower activation energy for thermo-oxidative degradation indicated that oxygen had an accelerated effect on thermal degradation. The variation of activation energy indicated that the decomposition of all the samples was a complex process that included at least two different mechanisms. Evolution of the evolved gaseous products with temperature was studied to understand the thermal and thermo-oxidative decomposition comprehensively. According to the TG-FTIR analysis, the gaseous products mainly contained lactide, cyclic oligomers, aldehydes, CO₂, CO, and H₂O.

Strong and thermal-resistance glass fiber-reinforced polylactic acid (PLA) composites enabled by heat treatment

Polylactic acid (PLA) is a biodegradable polymer derived from renewable resources, showing potentials in replacing traditional petroleum-based polymers, yet its brittleness and low thermal-resistance limits its applications. Thus, glass fibers (GF) combined with heat treatment were used to prepare high-performance PLA. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) were employed to analyze crystallization behavior of PLA/GF composite. Tensile, flexural and impact tests were conducted to investigate mechanical properties, and heat deflection temperature was measured to evaluate thermal resistance. GF can coincidently enhance strength, rigidity, and toughness of PLA. Isothermal heat treatment can further improve the mechanical properties regardless of GF content. Compared with neat PLA, the tensile strength, flexural modulus, and impact strength can be increased by 162.5%, 266.4%, 232.5%, respectively, in the presence of 20 wt% GF after isothermal heat treatment, and meanwhile heat deflection temperature can be increased from 50.6 °C to 148.8 °C. Both DSC and XRD analysis results indicated that GF can significantly enhance crystallization of PLA. Thus, not only GF but also enhanced crystallization led to the outstanding mechanical performance of PLA/GF composites. While GF shows little effect on thermal resistance, heat treatment can remarkably improve thermal stability, in particular for PLA/GF composites.

Poly (lactic acid) blends: Processing, properties and applications

Poly (lactic acid) or polylactide (PLA) is a commercial biobased, biodegradable, biocompatible, compostable and non-toxic polymer that has competitive material and processing costs and desirable mechanical properties. Thereby, it can be considered favorably for biomedical applications and as the most promising substitute for petroleum-based polymers in a wide range of commodity and engineering applications. However, PLA has some significant shortcomings such as low melt strength, slow crystallization rate, poor processability, high brittleness, low toughness, and low service temperature, which limit its applications. To overcome these limitations, blending PLA with other polymers is an inexpensive approach that could also tailor the final properties of PLA-based products. During the last two decades, researchers investigated the synthesis, processing, properties, and development of various PLA-based blend systems including miscible blends of poly l-lactide (PLLA) and poly d-lactide (PDLA), which generate stereocomplex crystals, binary immiscible/miscible blends of PLA with other thermoplastics, multifunctional ternary blends using a third polymer or fillers such as nanoparticles, as well as PLA-based blend foam systems. This article reviews all these investigations and compares the syntheses/processing-morphology-properties interrelationships in PLA-based blends developed so far for various applications.

Poly(lactic acid) blends in biomedical applications

Poly(lactic acid) (PLA) has become a "material of choice" in biomedical applications for its ability to fulfill complex needs that typically include properties such as biocompatibility, biodegradability, mechanical strength, and processability. Despite the advantages of pure PLA in a wider spectrum of applications, it is limited by its hydrophobicity, low impact toughness, and slow degradation rate. Blending PLA with other polymers offers a convenient option to enhance its properties or generate novel properties for target applications without the need to develop new materials. PLA blends with different natural and synthetic polymers have been developed by solvent and melt blending techniques and further processed based on end-use applications. A variety of PLA blends has been explored for biomedical applications such as drug delivery, implants, sutures, and tissue engineering. This review discusses the opportunities for PLA blends in the biomedical arena, including the overview of blending and postblend processing techniques and the applications of PLA blends currently in use and under development.