PLLA Films Research Articles

Development of high barrier poly(l-actic acid)/chitosan/graphene oxide flexible films for meat packaging by layer-by-layer

An new high-barrier packaging films for meat preservation were obtained by depositing graphene oxide (GO) layer-by-layer (LbL) on poly(l-lactic acid)(PLLA)-poly (butylene itaconate) (PBI) copolymers (PLBI) with chitosan (CS) as bonding layer in this study. The 1H NMR results revealed that PLBI copolymer was successful synthesized. The introduction of PBI reduced the Tg and crystallization capacity of PLLA film, which made the copolymer films exhibit extremely high flexibility (up to 186.1% elongation at break). The film also exhibited high hydrophilicity, which was favorable for the effective attachment of CS. With CS as an intermediate layer, the FTIR and SEM results showed that the GO was evenly distributed onto the PLBI film surface due to the electrostatic interaction. The oxygen, water vapor and UV light barrier properties of PLBI/CS/(GO-CS)x films were improved and increased with the GO-CS layers. The PLBI/CS/(GO-CS)10 films, with extremely low oxygen permeability coefficients about 0.4 × 10−8 cm3 m/m2·h·Pa, delayed the increase in weight loss, hardness, pH, TVB-N, TBARS, and total viable counts of chilled meat during storage. It also decreased the discoloration, and loss of springness and cohesiveness of chilled meat caused by long-term refrigeration. The LbL films even showed better freshness-keeping effect than commercial PA/PE films due to its superior barrier and certain antibacterial properties, suggesting great potential application in fresh meat preservation.

Robust Superhydrophobic Films Based on an Eco-Friendly Poly(l-lactic acid)/Cellulose Composite with Controllable Water Adhesion.

Poly(l-lactic acid) (PLLA) featuring desirable biodegradability and biocompatibility has been recognized as one of the promising eco-friendly biomaterials. However, low crystallization and poor mechanical and chemical performances dramatically hamper its practical application. In this work, we report that functionalized cellulose/PLLA composite superhydrophobic stereocomplex films with controllable water adhesion and protein adsorption can be fabricated by a facile approach for the first time. First, cellulose is surface-modified by means of two silanization modification methods. Then, superhydrophobic cellulose/PLLA composite films are prepared through a solvent-evaporation-induced phase separation method. The two cellulose/PLLA composite films exhibit extreme water repellency but tunable water adhesion from sticky to slippery. The protein adsorption capacity of the cellulose/PLLA composite films can also be regulated. In addition, the stereocomplexation of the composite film provides excellent mechanical properties with an elongation at break of 22.36%, which is 237.8% higher than that of a pure PLLA film, which is more suitable for biomaterials. Furthermore, good biodegradability of the PLLA composite films in nature enables the bio-based composites as alternative materials to replace conventional petroleum-based polymers. The superhydrophobic films have also been demonstrated for many applications, including slippery surfaces, liquid transportation without loss, and antifouling.

Argon nonthermal plasma etching of poly(L-lactic acid) films: Tunning the local surface degradation and hydrolytic degradation rate

Plasma technology is widely used in the industry for the surface modification of polymeric materials, improving the adhesion of paints in polymeric packaging and cellular adhesion on polymers' surfaces without using hazardous chemicals. Plasma etching is a fast way to modify polymers, creating new nanostructure surfaces and adding chemical groups for new applications like antimicrobial surfaces. Poly(L-lactic acid) (PLLA) is a biodegradable polymer with exciting properties for biomedical, tissue engineering, food packaging, and other applications. In many cases, these products must undergo plasma surface treatments to meet the technical requirements of their function. Herein, we evaluated the effects of surface modification of PLLA using Argon nonthermal plasma etching. The results from Gel Permeation Chromatography (GPC), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), X-ray Excited Photoelectron Spectroscopy (XPS), and Matrix-assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry (MALDI-ToF-MS) show that increasing the plasma exposure time causes an enhancement in bulk and local surface degradation, crystallization kinetics and susceptibility to hydrolytic degradation for PLLA. Atomic Force Microscopy (AFM) show that the PLLA films present the highest surface roughness after 60 s of plasma etching times. Our findings suggest that plasma etching can be a suitable tool to adjust the polymer degradation rate to design intracorporeal devices with controlled degradation kinetics.

Synthesis and Performance Evaluation of Bio-Sourced PO3G Ester Plasticizer in L-Polylactic Acid Thin Films

This study aims to synthesize and evaluate the properties of bio-sourced poly(1,3-propanediol) laurate (PO3G-LA) as a plasticizer in the fabrication of poly(1,3-propanediol) laurate/L-polylactic acid (PO3G-LA/PLLA) thin films. Utilizing an esterification reaction between poly(1,3-propanediol) (PO3G) and lauric acid (LA), PO3G-LA is synthesized and incorporated into PLLA films via solution casting. Results demonstrate that PO3G-LA exhibits excellent compatibility with PLLA, markedly enhancing the toughness and slightly improving the thermal stability of the resulting films. Specifically, the addition of 20% PO3G-LA increases the elongation at the break of the films to 190%, indicating enhanced flexibility. Accelerated degradation experiments conducted at 60 °C revealed that the presence of PO3G-LA under neutral conditions had minimal impact on the degradation rate of the film samples. Conversely, variations in the PO3G-LA content of the films when exposed to acidic and alkaline conditions were found to influence their degradation rates.

Supercritical CO2-impregnation of clove extract in PLLA films: assessing process parameter effects on extract loading and composition

The supercritical carbon dioxide (scCO2) impregnation of clove extract (CE) into poly(L-lactic acid) (PLLA) films was explored with varying pressure (10–30MPa) and temperature (35–60 °C), achieving high clove extract loadings (CL) (12.3 - 44.4%). In all conditions, impregnated extracts exhibited elevated eugenol content and reduced content of eugenyl acetate, β-caryophyllene, and α-humulene, compared to crude extract, showing the selective character of the process. Strong eugenol/PLLA affinity demonstrated by solubility parameters and hydrogen bonds permitted its effective impregnation. Eugenol significantly plasticized PLLA film, resulting in alterations in its microstructure, including increased crystallinity and smaller crystals. A CL of 23.8% maintained a dense and uniform structure of PLLA, while 44.4% induced a thick microporous layer on the surfaces. CE-impregnated PLLA, rich in eugenol, is promising for developing active food packaging and extract-releasing medical.

Replicated biopolymer pattern on PLLA-Ag basis with an excellent antibacterial response

The design of functional micro or nanostructured surfaces is undergoing extensive research for their intriguing multifunctional properties and for large variety of potential applications in biomedical field (tissue engineering or cell adhesion), electronics, optics or microfluidics. Such nanosized topographies can be easily fabricated by various lithography techniques and can be also further reinforced by synergic effect by combining aforementioned structures along materials with already outstanding antibacterial properties. In this work we fabricated novel micro/nanostructured substrates using soft lithography replication method and subsequent thermal nanoimprint lithography method, creating nanostructured films based on poly (l-lactic acid) (PLLA) fortified by thin silver films deposited by PVD. Main nanoscale patterns were fabricated by replicating surface patterns of optical discs (CDs and DVDs), which proved to be easy, fast and inexpensive method for creating relatively large area patterned surfaces. Their antimicrobial activity was examined in vitro against the bacteria Escherichia coli and Staphylococcus epidermidis strains. The results demonstrated that nanopatterned films actually improved the conditions for bacterial growth compared to pristine PLLA films, the novelty is based on formation of Ag nanoparticles on the surface/and in bulk, while silver nanoparticle enhanced and nanopatterned films exhibited excellent antibacterial activity against both bacterial strains, with circa 80 % efficacy in 4 h and complete bactericidal effect in span of 24 h.

Tracking of Protein Adsorption on Poly(l-lactic acid) Film Surfaces: The Role of Molar Mass.

Poly(l-lactic acid) (PLLA) has been extensively utilized as a biomaterial for various biomedical applications. The first and one of the most critical steps upon contact with biological fluids is the adsorption of proteins on the material's surface. Understanding the behavior of protein adsorption is vital for guiding the synthesis and preparation of PLLA for biomedical purposes. In this study, total internal reflection fluorescence microscopy was employed to investigate the adsorption of human serum albumin (HSA) on PLLA films with different molar masses. We found that molar mass affects HSA adsorption in such a way that it affects only the adsorption rate constants, but not the desorption rate constants. Additionally, we observed that HSA adsorption is spatially heterogeneous and exhibits many strong binding sites regardless of the molar mass of the PLLA films. We found that the free volume of PLLA plays a crucial role in determining its water uptake capacity and surface hydration, consequently impacting the adsorption of HSA.

Fabrication of polymer-based stents: Impact of test specimen manufacturing protocol

Abstract Various manufacturing techniques are available for polymer stent fabrication. Polymer semi-finished products can be prepared using solvent based methods, e.g. dip coating, as well as thermal processes, e.g. extrusion. These different methods may lead to an altered polymer crystal structure, resulting in a different deformation mechanism during mechanical stress. For the material property characterization needed for implant development, the test specimens usually are prepared using laser-cut or die-cut methods. Due to these different preparation protocols, a change in polymer microstructure, causing a material property variation, may also result. For this purpose, comparison of laser-cut versus die-cut of PLLA films has been performed. PLLA films have been prepared by dip-coating and were evaluated with respect to structural, thermal, and mechanical properties. In this study, a combination of uniaxial tensile tests, SEM and DSC studies was used. The results of the mechanical tests showed drastic differences in the elongations at break of die-cut specimens compared to laser-cut ones. The results point out formation of complex crystal structures during the manufacturing process. By the use of SEM imaging and DSC measurements, we were able to attribute these changes to the different plastic deformation mechanisms.

Manufacture and extraction of PLLA films with incorporated metal ions

Abstract For the in vitro examination of the effects on cells and tissues of metal ions derived from implants by wear and corrosion, a system is needed to release metal ions in a controlled and sustained manner. As small concentrations may have an impact on biological systems, a corresponding slow release over a defined period of time is necessary. Here, a manufacturing method of polymeric Poly(L-lactic acid) (PLLA) films with incorporated cobalt ions via dip coating is reported. The establishment of two analytical methods for the detection and quantification of cobalt ions is shown. High performance liquid chromatography enables cobalt quantification over a concentration range of 0.33 μg/mL up to 33 μg/mL in sample solutions. Extraction and detection of cobalt ions from solvent cast PLLA-cobalt-films shows the feasibility of the manufacturing method. Initial biocompatibility tests with manufactured PLLA-cobaltfilms showed no effects on adipose derived primary mesenchymal stem cells (adMSCs).

Towards ductile and high barrier poly(L-lactic acid) ultra-thin packaging film by regulating chain structures for efficient preservation of cherry tomatoes

The irreconcilable paradox between barrier performance and ductility is a “stumbling block” restricting the development of poly(L-lactic acid) (PLLA) films in the packaging industry. In this work, we reported the fabrication of an ultra-thin PLLA-based film with barrier properties and ductility by adjusting the polarity and conformational behavior of the polymer chains. Firstly, a novel unsaturated poly(L-lactic acid-co-butyrate itaconate) P(LA-BI) copolymer containing CC double bonds was synthesized using melt polycondensation. The results reveal that the addition of 60 % of P(LA-BI) enables PLLA film to achieve an elongation at a break of 83.6 % due to P(LA-BI) containing partially branched structures, which resulted in the polymer chains being arranged more in a high-energy gg conformer. Meanwhile, because of the large number of CO polar groups in P(LA-BI), PLLA/P(LA-BI)60 film show CO2 and O2 permeability coefficients (CDP and OP) of 1.8 and 0.45 × 10−8 g·m·m−2·h−1·Pa−1 respectively, which means that it has excellent gas barrier properties. Moreover, PLLA/P(LA-BI)60 film shows a 33.3 % increase in CO2/O2 ratio and an excellent ultraviolet (UV) barrier performance compared to neat PLLA. Preservation results suggested that the CO2 and O2 levels within the package could be regulated by varying the amount of P(LA-BI) added. Among them, PLLA/P(LA-BI)40 film generated a more desirable CO2 and O2 atmosphere for cherry tomatoes preservation, which was reflected by the delaying of senescence, discoloration, and decay, inhibition of oxidative cell damage through reduced malondialdehyde production, and maintenance of nutritional and flavor substances in cherry tomatoes. This PLLA-based film offers the advantages of operational simplicity, environmental friendliness, and inexpensive cost, making it great promising for food preservation and other applications requiring barrier properties and ductility.

Studies on the effect of polylactide in-situ grafting during melt processing on poly(ʟ-lactide)/graphene oxide composite films

The present work tried to solve the compatibility and dispersion problems of industrial grade graphene oxide (GO) mixing with polylactide (PLA) by melt processing for practical application. PLA was grafted on the GO using the silane coupling agent (KH560) as “bridge” by in-situ melting reaction to improve the compatibility. For better compatibility and dispersion, poly(ᴅ-lactide) (PDLA) was grafted on GO (D-G) to form stereocomplex crystallites with poly(ʟ-lactide) (PLLA) to enhance the interaction between GO and PLLA matrix. By biaxial stretching, the PLLA and GO composite films were prepared. Results show that GO was seriously aggregated in the film containing GO without PLA grafting (PLLA/L/G0.05) and the average size of aggregated GO was about 19.5 μm. PLA grafting decreased the aggregated GO size, so that the films containing L-G or D-G presented better dispersion. The film containing 5 % D-G (PLLA/D-G0.05) exhibited the smallest average size of aggregated GO, about 12.7 μm. Compared with neat PLLA film, PLLA/L/G0.05 film presented worse tensile properties due to serious aggregation of GO. While, PLLA/D-G0.05 film presented the best tensile performance that tensile strength and elongation at break reached 120 MPa and 107 %, respectively.

Extensional Stress-Induced Ductility of Poly(l-lactide) Films: Role of the Entangled Network in Amorphous Regions.

The relationship between the density of the entangled amorphous network and the ductility of oriented poly(l-lactide) (PLLA) films is explored based on the preferential hydrolysis of the amorphous regions in phosphate buffer solution (PBS). PLLA films with a balance of ductility and stiffness have been prepared by the "casting-annealing stretching" based on mechanical rejuvenation, and the structural evolution and mechanical properties at different hydrolysis durations have been identified. Various stages are found during the transition of ductility to brittleness for hydrolyzed PLLA films. First, the elongation at break for hydrolyzed PLLA films remains unchanged in the first stage of hydrolysis and then gradually decreases. Eventually, the films turn to be brittle in the third stage. The strain-hardening modulus (GR) of the hydrolyzed films is utilized to reflect the density of the entangled amorphous network, and a gradual decrease of GR with hydrolysis time indicates the decisive role of the amorphous entanglement network in the mechanical rejuvenation-induced ductility of PLLA. The quantitative relationship between the entangled amorphous network and the stress-induced ductility of PLLA films is revealed. The dependence of deformation behavior on entangled amorphous network density is closely correlated to activated primary structure during deformation. The intact chain network plays a crucial role in sufficiently activating the primary structure to yield and disentanglement during the subsequent necking. These findings could advance the understanding of the PLLA's ductility induced by mechanical rejuvenation and offer guidance for awakening the intrinsic toughness of PLLA.

Poly(L-lactic acid)/graphene composite films with asymmetric sandwich structure for thermal management and electromagnetic interference shielding

The blowout growth of the power density and transmission efficiency of microelectronic devices makes the problems of “overheating” and electromagnetic pollution of electronic devices increasingly prominent, and it is raising an urgent demand to improve the thermal conductivity and electromagnetic interference (EMI) shielding performance of packaging materials. Additionally, the environmental damage caused by fossil-based electronic waste should not be ignored. Hence, a scalable production strategy was proposed to prepare sandwich structure poly(L-lactic acid) (PLLA) composite films with high thermal conductivity and excellent EMI shielding efficiency (SE), which was achieved via solution pouring method and stacking hot-pressing process, in which PLLA/graphene nanoplatelets (PLLA/GNPs) with different GNPs contents was the top and substrate layers, and PLLA/poly(D-lactic acid)/Fe3O4 (PLLA/PDLA/Fe3O4) with a small amount of PDLA and Fe3O4 was the middle layer. Owing to the asymmetric distribution of filler and the successful introduction of magnetic particles, when the GNPs and Fe3O4 contents of the whole film are respectively only 5.61 wt% and 4.39 wt%, and the asymmetric ratio is 1:9, the in-plane thermal conductivity (K‖) and EMI SE of the composite film reaches 7.49 W m−1 K−1 and 41.7 dB, respectively, higher than those of PLLA film with symmetric structure (3.31 W m−1 K−1 and 33.0 dB) at the same contents of fillers. Furthermore, a small amount of PDLA (4.39 wt%) promotes the formation of stereocomplex (SC) crystallites in the middle layer and further induces the interlayer SC microcrystals during the stacking hot-pressing process, enhancing the interlayer interaction to maintain the mechanical robustness of the PLLA film. This work provides a new direction for the manufacture of polymer based composite films with high thermal conductivity and directional EMI shielding, and has broad application potential in the field of large-scale production of green electronic products.

Preparation and Performance Study of Poly(1,3-propanediol) Ester/PLLA Blended Membrane

Poly(1,3-propanediol palmitate)/L-polylactic acid (PO3G-PA/PLLA) composite films were prepared by solution casting. The two raw materials used to prepare the film are 100% renewable. The experimental results of the composite films show that the addition of PO3G–PA can significantly improve the toughness and crystallinity of PLLA while keeping the thermal stability of the film unchanged. When PO3G–PA was added to the film at concentrations of 0%, 5%, 10%, 15%, 20%, and 25%, the elongation at break of the film reached 37.5%, 68.8%, 118.9%, 226.8%, and 95.9%, respectively. The crystallinity of PLLA could reach 4.5%, 6.19%, 10.59%, 23.00%, 25.28%, and 16.62%, separately. The accelerated degradation experiments at 60 °C showed that adding different quantities of PO3G-PA under neutral conditions had a minimal effect on the rate of PLLA film degradation. The degradation rate of the PLLA membrane can be successfully modified by varying the concentration of PO3G–PA under acidic and alkaline conditions.

Biocompatible Piezoelectric Polymer Poly(Lactic Acid)-Based Stethoscope for Wearable Health Monitoring Devices

With the development of wearable devices and the Internet of Things (IoT), there is a growing demand for portable and comfortable human health monitoring devices. Because of the advantages of biocompatibility, relatively large piezoelectric coefficients, and nonpyroelectricity, poly(L-lactic acid) (PLLA) polymers have been greatly utilized in the applications of tissue engineering, sensors, and energy harvesting devices. In this investigation, the PLLA film was fabricated for the first time for real-time wearable stethoscope and pulse wave sensor applications. First, the stretched PLLA film was glued onto a Mylar film as the active layer of the PLLA film-based stethoscope (PFS) and pulse sensor device. After the PFS device was measured in a semianechoic chamber, the device showed a sensitivity of –53.4 dB at 1 kHz and it also exhibited a stable frequency response in the range of 100 Hz–4 kHz. In addition, the PFS device showed an output voltage of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim $ </tex-math></inline-formula> 90 mV when measuring the heart rate and pulse signal of an adult volunteer. Furthermore, the PFS device was integrated a portable stethoscope system, which can detect a clear pulse signal and send it to a data collection application designed in a cellphone. The biodegradability, stable frequency response, and temperature stability indicate the great potential of PFS device for wearable human health monitoring devices.

Fabrication and design of poly(l‐lactic acid) membrane for passive MAP packaging of Brassica chinensis L

PLDx L copolymers were synthesized from physically stable rigid poly(l-lactic acid) (PLLA) and a few different molecular weights of polydimethylsiloxane (PDMS) to increase the O2 and CO2 permeabilities of PLLA films and make them acceptable for packaging highly respirable products. The effect of PDMS on the morphology, mechanical properties, and gas permeability of PLDx L was investigated. Copolymers showed approximately 10 times the fracture strain and 1.7 times the CO2 and O2 permeabilities of neat PLLA. Additionally, PLDx L maintained an increased CO2 /O2 perm-selectivity consistent between 5 and 40°C. Passive modified atmosphere packaging of Brassica chinensis L was developed to assess the membrane's impact on headspace gas inside the package. The results showed that poly(amide)/poly(ethylene) packaging with 48cm2 PLD1.8 L membrane as a breathing window can provide 50g B. chinensis L. with a healthy atmosphere of 3%-8% O2 and 5%-8% CO2 between 6 and 22 days. Vegetables packaged in PLD1.8 L had the lower respiration rate, lower nitrite contents, and less proliferation of microorganisms. Moreover, a suitable atmosphere kept vegetables with higher ascorbic acid and a good appearance after more than 2 weeks of storage at 5°C. PRACTICAL APPLICATION: The permeability of the PLLA-based membrane can be adjusted for the breathable window membrane of sealed fresh products. In the future, several types of film could be developed to match the respiratory and metabolic characteristics of different kinds of products. Such PLLA-based specialized membranes can refine the fresh-keeping function and be more attractive to the customer.

Construction of fully biodegradable poly(L-lactic acid)/poly(D-lactic acid)-poly(lactide-co-caprolactone) block polymer films: Viscoelasticity, processability and flexibility

Development of biodegradable polymer films is essential for sustainable energy conservation and ecological protection. In this work, to improve the processability and toughness of poly(lactic acid) (PLA) films, poly(lactide-co-caprolactone) (PLCL) segments were introduced into poly(L-lactic acid) (PLLA)/poly(D-lactic acid) (PDLA) chains via chain branching reactions during reactive processing, and fully biodegradable/flexible PLLA/D-PLCL block polymer with long-chain branches and stereocomplex (SC) crystalline structure was prepared. Compared with neat PLLA, PLLA/D-PLCL exhibited much higher complex viscosity/storage modulus, lower tanδ values in terminal region and obvious strain-hardening behavior. Through biaxial drawing, PLLA/D-PLCL films were prepared, which showed improved uniformity and non-preferred orientation. With increasing draw ratio, the total crystallinity (Xc) and Xc for SC crystal both increased. By introduction of PDLA, the two phases of PLLA and PLCL penetrated and entangled with each other, and the phase structure transformed from “sea-island” structure to “co-continuous network” structure, which was beneficial for exerting the toughening effect of flexible PLCL molecules on PLA matrix. The tensile strength and elongation at break of PLLA/D-PLCL films increased from 51.87 MPa and 28.22 % of neat PLLA film to 70.82 MPa and 148.28 %. This work provided a new strategy for developing fully biodegradable polymer films with high performance.

Facile preparation of highly crystalline poly(L‐lactide) films with inversed wettability and their potential application in oil–water separation

AbstractHighly crystallized poly(L‐lactide) (PLLA) films with enhanced hydrophobicity are easily prepared by casting PLLA solution into a poor solvent like isopropyl alcohol (IPA). The crystallinity of the PLLA film can be controlled by PLLA's concentration, the kind of poor solvent, and the volume ratio of poor solvent dichloromethane (DCM). Results show the addition of poor solvents obviously accelerate the crystallization of PLLA film and enhance the crystallinity up to 48.7%. A lower volume ratio of IPA/DCM at higher PLLA concentration as well as a higher volume ratio of IPA/DCM at lower PLLA concentration is conducive to raising the crystallinity of the PLLA film. In the meanwhile, microscopy observation and wettability tests confirm the PLLA films present multidimensional microstructure including fibrils, lamellas, and flower‐like stacks or spherulite‐like superstructure, and display high porosity as well as enhanced hydrophobicity. Despite the volume ratio of IPA/DCM, the PLLA films prepared at lower concentrations display higher crystallinity, porosity as well as hydrophobicity than those prepared at higher concentrations. The highly crystalline PLLA films with enhanced porosity and hydrophobicity are supposed to be applied in oil–water separation, and so forth.

One-Step Synthesis of Poly(L-Lactic Acid)-Based Soft Films with Gas Permselectivity for White Mushrooms (Agaricus bisporus) Preservation.

Proper packaging can extend the shelf life and maintain the quality of mushrooms during storage. The purpose of this study is to investigate the preservation of Agaricus bisporus using copolymer-modified poly (L-lactide-co-butylene fumarate) and poly (L-lactide-co-glycolic acid) (PLBF and PLGA) packaging. Shelf life and quality were evaluated over 15 days of storage of Agaricus bisporus at 4 ± 1 °C and 90% relative humidity, including weight loss, browning index (BI), total phenolics (TP), ascorbic acid (AA), malondialdehyde content (MDA), electrolyte leakage rate (EC), and superoxide dismutase (SOD) and catalase (CAT). The results showed that mushrooms packaged in PLBF films exhibited better retention in BI, TP, and AA than those with PLLA, PLGA, or polyethylene (PE) films. They can reduce the rate of weight loss, EC, and MDA, which in turn increases the activity of SOD and CAT. PLBF and PLGA have substantially improved flexibility in comparison with PLLA. They also significantly reduced oxygen (O2) and carbon dioxide (CO2) permeability and changed the gas permeability ratio. These positive effects resulted in the effective restriction of O2 and CO2 in these packages, extending the post-harvest storage period of white mushrooms.

Controlling orientation, polymorphism, and crystallinity in thin films of poly(lactic‐acid) homopolymer and stereocomplex aligned by high temperature rubbing

AbstractHigh temperature rubbing is a fast and low‐cost method that can align semi‐crystalline polymers such as poly(lactic acid) (PLA) by application of a shear‐force via a rotating cylinder covered with a microfiber cloth on a thin film maintained at high temperature. A multi technique approach uncovers the role of rubbing temperature and film thickness on the PLA thin film structure. Both poly(l‐lactic acid) (PLLA) and the stereo‐complex (SC‐PLA) can be readily aligned by high temperature rubbing. The rubbing temperature TR and the film thickness are the key parameters that control polymorphism, in‐plane orientation, crystallinity and contact plane of the polymer crystals. Rubbing PLLA films in the range 80–140°C affords different aligned polymorphs (mesophase, α′, α′ + α mixtures and pure α phase) depending on the rubbing temperature. Pure α form of PLLA with 53% crystallinity is obtained at TR = 140°C whereas pure oriented crystalline SC‐PLA films are obtained by rubbing at 200°C.