Effects of high starch content on the physicochemical properties of starch/PBAT nanocomposite films prepared by extrusion blowing

Blown film extrusion of PBAT/TPS/ZnO nanocomposites for shelf-life extension of meat packaging

Biodegradable polymers typically have inferior barrier properties compared to petroleum-based nonbiodegradable plastic. The addition of zinc oxide nanoparticles may enhance the functional properties of biodegradable packaging and extends the shelf life of packaged foods. Polybutylene adipate-co-terephthalate (PBAT) and thermoplastic starch (TPS) blended ZnO (1-5%) nanocomposite films were developed via blown extrusion for functional active meat packaging. The nanocomposite film morphology showed agglomeration of the nanoparticles, causing poor mechanical properties. Nanovoids formed at the interface between the polymer and nanoparticles, increasing permeability. Dispersion of ZnO nanofillers modified CO and C-O ester bonding in PBAT and increased hydrogen bonding with TPS. The interaction between ZnO and polymers increased the dispersion and reduced the agglomeration of nanoparticles. The highest ZnO content at 5% resulted in a stronger interaction between ZnO and TPS due to increased amorphous starch content, which improved homogeneous dispersion within the matrices, reducing nanoparticle size. The ZnO nanocomposite films reduced lipid oxidation and delayed microbial growth, resulting in a lower total viable count, lactic acid bacteria and yeast and mold in packaged pork meat. Higher ZnO concentrations from 3% showed microbial inhibitory effects. The growth of microorganisms was controlled by residual oxygen, morphology of the films and nanoparticle characteristics. The nanocomposite films effectively extended the shelf life by more than 3 days under refrigerated conditions.

Biomimetic Robust Starch Composite Films with Super-Hydrophobicity and Vivid Structural Colors

The starch composite films (SCFs) will be one of the best alternative packaging materials to petroleum based plastic films, which mitigates white pollution and energy consumption. However, weak mechanical stability, water resistance, and dyeability has hindered the application of SCFs. Herein, a bioinspired robust SCFs with super-hydrophobicity and excellent structural colors were prepared by fiber-reinforcement and assembling SiO₂/Polydimethylsiloxane (PDMS) amorphous arrays on the surface of SCFs. The properties of the designed SCFs were investigated by various methods including scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), a tensile test, contact angle (CA) test, and an optical test. The results showed that the obtained SCFs possessed a higher tensile strength (55.17 MPa) attributed to the formed abundant hydrogen bonds between the molecular chains of the starch, cellulose fiber, and polyvinyl alcohol. Benefiting from the nanostructure with rough surface which were modified by materials with low surface free energy, the contact angle and sliding angle of the film reached up to 154° and 2°, respectively. The colors which were produced by the constructive interference of the coherent scattered light could cover all of the visible regions by tuning the diameters of the SiO₂ nanoparticles. The strategy in the present study not only reinforces the mechanical strength and water resistance of SCFs but also provides an environmentally friendly way to color the them, which shows unprecedented application potential in packaging materials of the starch composite films.

Progress in the Degradability of Biodegradable Film Materials for Packaging

In today’s world, the problem of “white pollution” is becoming more and more serious, and many countries have paid special attention to this problem, and it has become one of the most important tasks to reduce polymer waste and to protect the environment. Due to the degradability, safety, economy and practicality of biodegradable packaging film materials, biodegradable packaging film materials have become a major trend in the packaging industry to replace traditional packaging film materials, provided that the packaging performance requirements are met. This paper reviews the degradation mechanisms and performance characteristics of biodegradable packaging film materials, such as photodegradation, hydrodegradation, thermo-oxidative degradation and biodegradation, focuses on the research progress of the modification of biodegradable packaging film materials, and summarizes some challenges and bottlenecks of current biodegradable packaging film materials.

The Use of Branching Agents in the Synthesis of PBAT

Biodegradable polyesters represent an advanced alternative to polyolefin plastics in various applications. Polybutylene adipate terephthalate (PBAT) can compete with polyolefins in terms of their mechanical characteristics and melt processing conditions. The properties of PBAT depend on the molecular weight, dispersity, and architecture of the copolymer. Long-chain branching (LCB) of the PBAT backbone is an efficient method for the improvement of the copolymer characteristics. In the present work, we studied branching agents (BAs) 1–7 of different structures in the two-stage polycondensation of 1,4-butanediol, dimethyl terephthalate, and adipic acid and investigated the composition and melt rheology of the copolymers. According to the results of the research, 1,1,1-tris(hydroxymethyl)ethane 2 and 3-hydroxy-2-(hydroxymethyl)-2-methylpropanoic acid 5 outperformed glycerol 1 as BAs in terms of shear thinning behavior and viscoelasticity.

Antimicrobial starch/poly(butylene adipate-co-terephthalate) nanocomposite films loaded with a combination of silver and zinc oxide nanoparticles for food packaging

Antimicrobial starch/PBAT films with the combination of silver nanoparticles (AgNPs) and zinc oxide nanoparticles (ZnONPs) were prepared by extrusion blowing. SEM demonstrated the relatively homogeneous distribution of nanoparticles on the fracture surfaces of the nanocomposite films. The incorporation of nanoparticles improved mechanical and barrier properties of the film. The UV-vis spectroscopy revealed that the SP-ZnO(1) film had the highest UV-absorbance. The inhibition effects of the nanocomposite films against both Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria were observed. The antimicrobial efficiency of SP-Ag(0.8)-ZnO(0.2) and SP-Ag(0.6)-ZnO(0.4) films reached more than 95% within 3 h of contact. The combination of AgNPs and ZnONPs into starch/PBAT blends showed synergistic effects on improving material properties and antimicrobial efficiency of the films. Furthermore, preliminary packaging studies on peaches and nectarines revealed that the antimicrobial films inhibited spoilage of fresh produce and extended their shelf life compared with commercial LDPE packaging films.

Properties and Degradability of Poly(Butylene Adipate-Co-Terephthalate)/Calcium Carbonate Films Modified by Polyethylene Glycol

Poly(butylene adipate-co-terephthalate) (PBAT) is a biodegradable polymer synthesized from petrochemical resources. PBAT has an exceptionally high elongation at break values which makes it one of the most promising substitutes for LDPE packaging films. However, the applicability of PBAT films is still limited by low strength and high production costs. In this work, we used polyethylene glycol 600 (PEG-600) as a coating agent to modify the surface of calcium carbonate and improve compatibility with the polymer matrix. A series of PBAT/CaCO₃ composite films having different CaCO₃ particle size and content of coating agent was prepared using extrusion blow molding. The effect of particle size of CaCO₃ filler and the content of a coating agent on the mechanical and rheological properties of composite films have been studied. The biodegradation properties have been tested by burying the samples in soil or keeping them in artificial seawater for 90 days. It was shown that the addition of PEG-600 improves compatibility between the matrix and CaCO₃ filler as polar –OH groups of PEG have a high affinity toward the polar surface of CaCO₃. Moreover, the hydrophilicity of PEG-600 increased the diffusivity of water molecules and facilitated PBAT degradation. This work provides experimental data and theoretical guidance that support the development of high-performance PBAT/calcium carbonate films for the single use packaging industry.

Cationized high amylose maize starch films reinforced with borax cross-linked nanocellulose

In this study, a novel strategy for modifying nanocellulose (NC) by borax cross-linking was developed, and the obtained borax modified nanocellulose (BNC) was incorporated into cationized high amylose maize starch (CS) films to evaluate the applicability. Cellulose molecules were successfully cross-linked by boron ester bonds, and the original crystal type and basic chemical structure were not changed. Compared with NC, the relative crystallinity of BNC was slightly increased, and the thermal stability was obviously enhanced. Addition of NC and BNC to CS films significantly improved their tensile strength and water resistance. The dispersion of nanocellulose in CS films was effectively improved by borax cross-linking modification. CS/BNC films showed higher mechanical and water resistance properties compared with CS/NC films. Compared with pure CS film, tensile strength of the composite film with 6 wt% BNC increased about 4.0 times, and its water-vapor permeability decreased about 37%. The novel strategy for preparing BNC by using boron ester bonds will provide a potential approach for the development of starch films with desirable properties.

Degradable photo-crosslinked starch-based films with excellent shape memory property

With the increasingly serious plastic pollution, people's demand for the multi-functional biodegradable plastics is becoming more and more urgent. Inspired by the crosslinked shape memory polymers, the crosslinked starch films were synthesized by inducing the decomposition of benzophenone into free radical and depriving hydrogen on starch macromolecules under UV irradiation, in order to gain a high shape memory performance. The results showed that a three-dimensional crosslinking network between starch macromolecule chains was formed. Compared with the uncrosslinked starch films, the photo-crosslinked films not only had higher mechanical property (tensile strength increased by 154%), but also had better water resistance (water contact angle from 60° to 87°) due to the reduction of free hydroxyl groups. In addition, the stable covalent bonds serving as netpoints endow photo-crosslinked films with great improvement in shape memory property, with nearly 180° bending recovery. More importantly, the maximum shape memory fixity ratio (R_f) and shape memory recovery ratio (R_r) under stretch deformation were 96.5% and 99.8%, respectively. And the R_f and R_r could reach 94.6% and 79.8% even at higher strain. In all, the excellent shape memory performance and good degradability crosslinked starch films, which have great potential application in disposable heat-shrinkable packaging materials.

Compatibilization of Starch/Synthetic Biodegradable Polymer Blends for Packaging Applications: A Review

The health and environmental concerns of the usage of non-biodegradable plastics have driven efforts to explore replacing them with renewable polymers. Although starch is a vital renewable polymer, poor water resistivity and thermo-mechanical properties have limited its applications. Recently, starch/synthetic biodegradable polymer blends have captured greater attention to replace inert plastic materials; the question of ‘immiscibility’ arises during the blend preparation due to the mixing of hydrophilic starch with hydrophobic polymers. The immiscibility issue between starch and synthetic polymers impacts the water absorption, thermo-mechanical properties, and chemical stability demanded by various engineering applications. Numerous studies have been carried out to eliminate the immiscibility issues of the different components in the polymer blends while enhancing the thermo-mechanical properties. Incorporating compatibilizers into the blend mixtures has significantly reduced the particle sizes of the dispersed phase while improving the interfacial adhesion between the starch and synthetic biodegradable polymer, leading to fine and homogeneous structures. Thus, Significant improvements in thermo-mechanical and barrier properties and water resistance can be observed in the compatibilized blends. This review provides an extensive discussion on the compatibilization processes of starch and petroleum-based polymer blends.

Anchor and bridge functions of APTES layer on interface between hydrophilic starch films and hydrophobic soyabean oil coating

One of the well-recognized weaknesses of starch-based materials is their sensitivity to moisture, which limits their expanding applications. Natural materials, soyabean oils have been used as a coating for starch film, but the poor interface between hydrophilic starch and hydrophobic soyabean oil needs to be improved. In this work, (3-Aminopropyl) triethoxysilane (APTES) was used to reinforce the bonding between starch matrix and the coating of bio-based acrylated epoxidized soyabean oil (AESO). Study results show that APTES interacted effectively with both starch films via hydrogen bonding, and chemical bonds with AESO through the Michael addition reaction. Pull adhesion and cross-cutting tests demonstrated that the interfacial adhesion was significantly improved after treating their surface with APTES. The interfacial adhesion strength increased over 4 times after treating with 1.6 wt% APTES. The starch films treated with APTES and AESO coating were intact after soaking in water for more than 2 h.

High-Throughput Fabrication of Antibacterial Starch/PBAT/AgNPs@SiO2 Films for Food Packaging

In this current work, antimicrobial films based on starch, poly(butylene adipate-co-terephthalate) (PBAT), and a commercially available AgNPs@SiO₂ antibacterial composite particle product were produced by using a melt blending and blowing technique. The effects of AgNPs@SiO₂ at various loadings (0, 1, 2, 3, and 4 wt%) on the physicochemical properties and antibacterial activities of starch/PBAT composite films were investigated. AgNPs@SiO₂ particles were more compatible with starch than PBAT, resulting in preferential distribution of AgNPs@SiO₂ in the starch phase. Infusion of starch/PBAT composite films with AgNPs@SiO₂ marginally improved mechanical and water vapor barrier properties, while surface hydrophobicity increased as compared with films without AgNPs@SiO₂. The composite films displayed superior antibacterial activities against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. The sample loaded with 1 wt% AgNPs@SiO₂ (SPA-1) showed nearly 90% inhibition efficiency on the tested microorganisms. Furthermore, a preliminary study on peach and nectarine at 53% RH and 24 °C revealed that SPA-1 film inhibited microbial spoilage and extended the product shelf life as compared with SPA-0 and commercial LDPE packaging materials. The high-throughput production method and strong antibacterial activities of the starch/PBAT/AgNPs@SiO₂ composite films make them promising as antimicrobial packaging materials for commercial application.

Continuous Blown Film Preparation of High Starch Content Composite Films with High Ultraviolet Aging Resistance and Excellent Mechanical Properties

Starch/PBAT blown films with high ultraviolet aging resistance and excellent mechanical properties were prepared by introducing lignin with polyurethane prepolymer (PUP) as a starch modifier and physical compatibilizer and 4,4'-methylene diphenyl diisocyanate (MDI) as a crosslinker. Starch was modified by reacting the NCO groups of the PUP with the OH groups of the starch to form a carbamate bond. The mechanical properties, hydrophobic properties, ultraviolet barrier, ultraviolet aging properties and microscopic morphology of starch/PBAT films with different contents of lignin were investigated. The results showed that the starch/PBAT films were blown continuously. The addition of lignin did not decrease the mechanical properties. On the contrary, the film with 1% lignin possessed the excellent mechanical properties with longitudinal tensile strength of 15.87 MPa and the elongation at a break of 602.21%. In addition, the higher the lignin content, the better the UV blocking effect. The introduction of lignin did not affect the crystalline properties but improved the hydrophilic properties and sealing strength of the high starch content composite films.

Controlled moisture permeability of thermoplastic starch/polylactic acid/poly butylene adipate-co-terephthalate film for the autolysis of straw mushroom Volvariella volvacea

Straw mushrooms are prone to autolyze, leading to a high requirement of environmental humidity. In this work, thermoplastic starch/polylactic acid/poly (butylene adipate-co-terephthalate) (TPS/PLA/PBAT) film was produced by extrusion. The moisture permeability of the film was controlled by adjusting the content of TPS, which could be expected to further control humidity of the microenvironment in the package. Results revealed that the water vapor transmission rate of the film linearly increased from 612.31 g/m²·24 h to 1082.50 g/m²·24 h with the increase in the TPS concentration. The TPS/PLA/PBAT film with 30 wt% TPS showed the strongest inhibition on the autolysis of straw mushrooms compared with other groups, effectively delaying the increase in the free water, soluble solid content, rate of weight loss, and polyphenol oxidase of straw mushrooms and extending the shelf life of straw mushrooms from 24 h to 72 h.

Cinnamon Essential Oil Nanocellulose-Based Pickering Emulsions: Processing Parameters Effect on Their Formation, Stabilization, and Antimicrobial Activity

This work aimed to prepare nanocellulose-based Pickering emulsions using cinnamon essential oil. Different formulations were investigated by varying the preparation time, homogenization speed, oil and nanocellulose concentration, and morphology. The emulsions were first characterized by droplet size, morphologies, and storage stability. The Design of Experiments (DoE) was used to evaluate the parameter’s effects on the emulsions’ stability, and the emulsions with optimum particle size and stability were evaluated by antimicrobial activity. The more stable emulsions required higher energy in the system to obtain efficient emulsification. The cellulose nanocrystal (CNC) emulsions showed a 30% oil volume as a constant to obtain a low creaming index (34.4% and 42.8%) and zeta potential values around −29 mV, indicating an electrostatic stabilization. The cellulose nanofiber (CNF) emulsions showed 100% stability after a month using a 20% oil volume as a constant and Zeta potential values around −15 mV, indicating a steric stabilization. CNF-emulsions’ inhibition halos for Bacilus subtilis were 30.1 ± 3.7% smaller than those found in CNC-emulsions (65 ± 2.9 mm), while Pseudomonasaeruginosas almost do not present differences in the inhibition halos. These results suggest that the nanocellulose morphology may promote a regulation on the EO migration to the medium, as well that this migration ratio does not affect the bacteria.

Effect of lipids with different physical state on the physicochemical properties of starch/gelatin edible films prepared by extrusion blowing

The effects of various physical state lipids (rapeseed oil (RO), shortening (ST), beeswax (BW)), on the physicochemical properties of starch (S) (hydroxypropyl distarch phosphate (HP), oxidized hydroxypropyl starch (OS))/gelatin (G) blown films were studied. S/G-lipid blends showed decreased storage modulus and complex viscosity. The formation of hydrogen bonds was inhibited by the ST and BW, but facilitated by the RO. Compared with BW and ST, RO was more effective to promote the melted and fractured of starch. Lipids addition promoted the compatibility of starch and gelatin. The presence of the lipids significantly improved the surface hydrophobicity, mechanical, water vapor barrier and water resistance properties of S/G films. S/G-RO films exhibited the strongest surface hydrophobicity and tensile strength, while HP/G-BW film showed the strongest water resistance and water vapor barrier properties. These results revealed that the appropriate lipids could be used to produce S/G-lipid films with desirable physicochemical properties.

Essential oils as additives in active starch-based food packaging films: A review

The production of sustainable food packaging from renewable sources represents a prominent alternative to the use of petrochemical-based plastics. For example, starch remains one of the more closely studied replacement options due to its broad availability, low cost and significant advances in improving properties. In this context, essential oils as additives fulfil a key role in the manufacture of renewable active packaging with superior performances. In this review, a comprehensive summary of the impact of adding essential oils to the starch-based films is provided. After a brief introduction to the fundamental concepts related to starch and essential oils, details on the most recent advances in obtaining active starch-based films are presented. Subsequently, the effects of essential oils addition on the structure-property relationships (from physicochemical to antimicrobial ones) are thoroughly addressed. Finally, applications and challenges to the widespread use of essential oils are critically discussed.

Preparation and evaluation of starch-based extrusion-blown nanocomposite films incorporated with nano-ZnO and nano-SiO2

The effects of nano-ZnO and nano-SiO₂ nanoparticles on the properties of starch-based films prepared by extrusion blowing were investigated in this study. New hydrogen bonds between hydroxypropyl starch (HS) and nanoparticles during the extrusion process were formed as shown by Fourier transform infrared spectroscopy (FTIR). The diffraction patterns of nanocomposite films reinforced with nano-ZnO were similar to those of nano-ZnO, except that the peak intensity decreased, whereas, the addition of SiO₂ nanoparticles decreased the intensity of the main characteristic peaks, regardless of the HS and nano-ZnO reinforced films. The thermal stability, tensile strength, moisture barrier property, and surface hydrophobicity of nanocomposite films were improved with the incorporation of nano-ZnO and nano-SiO₂, the finding that could be attributed to a strong interplay between nano-ZnO, nano-SiO₂, and the starch matrix during the extrusion film blowing process. Similarly, the nano-ZnO/nano-SiO₂ composite-reinforced films showed smooth, flat, and uniform appearances by scanning electron microscopy (SEM) and atomic force microscope (AFM) tests. In sum, Nano-ZnO and nano-SiO₂ nanoparticles can be used as composite reinforcing agents for preparation of starch-based films through extrusion blowing.

Preparation and characterization of biodegradable trilayer films based on starch and polyester

The trilayer films of polyester/starch/polyester with different starch/polyester layer thickness ratios were prepared by co-extrusion blowing. FTIR and SEM results showed the successful fabrication of trilayer films. The crystallinity of trilayer films gradually increased as the thickness of polyester layer increased. Dynamic mechanical analysis was used to investigate the compatibility between starch and polyester. The presence of polyester layer significantly increased the tensile strength and water contact angle of starch film. All trilayer films had lower water vapor permeability than the starch film, and lower oxygen permeability than the polyester film. The trilayer films were degraded to a much greater extent compared with the polyester film. The weight loss of P10 trilayer film in 120 days is about 80% through degradation test. These results suggested that the polyester/starch/polyester films with excellent mechanical and hydrophobic properties could serve as packaging material for wider applications.

Comprehensive insight into surfactant modified-PBAT physico-chemical and biodegradability properties

This work aimed to prepare surfactant modified-PBAT (poly(butylene adipate-co-terephthalate)) sheets with superior properties to increase the PBAT applicability and be a possible solution for plastic disposal environmental problems. Three different surfactant contents (0, 1, 5, and 10 wt%) were investigated, and their effects on PBAT chemical structure, mechanical and morphological properties, wettability, and water absorption were investigated. Modified-PBAT samples showed high hydrogen bond coefficients (0.57) than the pristine PBAT (0.54), indicating an excellent electrostatic interaction between both components and the formation of a rigid hydrogen-bonded network, as confirmed by mechanical tests, where the elastic modulus values for PBAT and PBAT+10% surfactant were 44 and 60 MPa. SEM images and roughness measurements showed changes in PBAT morphology after surfactant addition, improving the roughness and wettability by the voids and polar groups presence, altering the water absorption (WA) behavior. The higher water affinity resulted in high water absorption for PBAT-10%S (17%) compared to the pristine PBAT (2%), which improves hydrolysis tendency, which is the initial step to biodegradation. Biodegradation results indicated that the roughness and WA behavior influenced the biodegradation rate, facilitating hydrolysis and microbial attack, and accelerating modified samples weight loss. Our results suggested developing a material with superior mechanical properties, mainly for PBAT-10%S, that can be applied in several applications, such as packaging and furniture. After discharge, it is not an environmental problem, being a biodegradable material with a green character.

Robust multiphase and multilayer starch/polymer (TPS/PBAT) film with simultaneous oxygen/moisture barrier properties

The demands for bioplastics that provide good barrier properties against moisture and oxygen while simultaneously displaying good physical properties without compromising their biodegradability is ever-increasing. In this work, a multiphase and multilayer film assembly composed of thermoplastic starch (TPS) and its maleated counterpart (MTPS) with poly(butylene adipate-co-terephthalate) (PBAT) was constructed as a suitable barrier film with excellent mechanical properties. The bioplastic film assemblies were fabricated through reactive extrusion, compression molding, and dip-coating process. The incorporation of PBAT co-blend with TPS in the core layer enhanced the multilayer film's interfacial bond. The MTPS/PBAT film assembly provided 86.8% and 74.3% improvement in moisture barrier and oxygen barrier as compared to the baseline TPS and PBAT films, respectively. Overall, the multiphase and multilayer film assembly displayed good mechanical properties in conjuncture with excellent barrier properties indicating their potential as a biodegradable and cost effective alternative to conventional plastics used in the packaging industry.

Sustainable composites from biodegradable poly(butylene succinate) modified with thermoplastic starch and poly(butylene adipate-co-terephthalate): preparation and performance

A ternary blend of biodegradable polymers, namely PBS-g-GMA, thermoplastic starch (TPS) and poly(butylene adipate-co-terephthalate) (PBAT), was successfully fabricated attempt to achieve novel biodegradable composites with comprehensive properties.