Lactic Acid Films Research Articles

Effect of biaxial stretching on the microstructure evolution, optical, mechanical and oxygen barrier properties of biodegradable poly(lactic acid) (PLA)/poly(butylene adipate-co-terephthalate) (PBAT) films

The poly(butylene adipate-co-terephthalate) (PBAT)/poly(lactic acid) (PLA) films have been widely used due to their biological degradability and excellent comprehensive properties. However, the reports regarding biodegradable PLA/PBAT films are rather scarce. In this work, systematical investigations of biaxially stretched PLA/PBAT films were performed. Compared with unstretched films, the PLA/PBAT 75/25 films with the stretching ratio of 5 × 1 exhibited an improvement on the crystallinity of PLA from 6 % to 58.6 %. According to 2D-WAXS results, the orientation of the α crystal in the MD increased with the increase of the stretching ratio. The stretched films showed favorable barrier properties. The oxygen permeability (OP) of 2 × 2 PLA/PBAT 75/25 films shows a decrement of 22 % compared with that of the unstretched films. Interestingly, the uniaxially stretched PLA/PBAT 75/25 films exhibits increased surface roughness (Ra) for 3 × 1 film whereas decreased Ra for the 5 × 1 film, which could be related to the phase separation under stretching. The tensile strength in the machine direction (MD) of the PLA/PBAT 75/25 films was improved up to 51.6 MPa for 5 × 1 film, which is 45 % higher than that of unstretched counterpart. The stretched films exhibit excellent mechanical and barrier properties, which could be utilized in packaging industry with high potential.

Fabrication and Characterization of Active Poly(Lactic Acid) Films Containing Thymus daenensis Essential Oil/Beta-cyclodextrin Inclusion Complex and Silver Nanoparticles to Extend the Shelf Life of Ground Beef

Fabrication and Characterization of Active Poly(Lactic Acid) Films Containing Thymus daenensis Essential Oil/Beta-cyclodextrin Inclusion Complex and Silver Nanoparticles to Extend the Shelf Life of Ground Beef

Effects of organic modified hectorite on performance, isothermal crystallization behavior and interface interaction of poly(lactic acid) film

In this work, in order to improve the properties of PLA, Hec-g@OA/PLA nanocomposite films were prepared by a single-screw extrusion film blown machine with PLA as a matrix and organically modified hectorite (Hec-g@OA) as a filler, and the optimum filler mass ratio of Hec-g@OA was preferred as an objective function of mechanical properties. The mechanical properties of PLA were found to increase from 24.31% to 61.75% when the mass percentage of Hec-g@OA was 0.3 wt%. Secondly, isothermal crystallization behavior of the nanocomposite films was analyzed by simultaneous rheology and FTIR technology for the purpose of further studied the effect of Hec-g@OA on the isothermal crystallization behavior of PLA, which showed that the half-crystallization time of Hec-g@OA/PLA decreased from 7.01 min, 28.99 min and 77.88 min to 3.87 min, 20.59 min and 65.78 min, respectively, at 130 °C, 135 °C and 140 °C. Finally, the form of the interaction between PLA and Hec-g@OA was analysis by electronic structure calculations and energy decomposition, it was analyzed that electrostatic interaction was found to be the main impact factor for induced crystallization of Hec-g@OA/PLA nanocomposite films, while induction and dispersion were found to be the minor impact factors.

Enhanced water vapor barrier and gas barrier properties of transparent poly(butylene adipate‑co‑terephthalate)/poly(lactic acid)/hexagonal boron nitride nanosheets composite films

The water vapor barrier and gas barrier properties are very important factors for biodegradable packaging films. Herein, nano-sized hexagonal boron nitride nanosheets (hBNNSs) were facilely exfoliated, and novel transparent poly(butylene adipate-co-butylene terephthalate) (PBAT)/poly(lactic acid) (PLA) films incorporated with hBNNS were developed. Compared to those properties of neat PBAT/PLA film, the water vapor barrier of PBAT/PLA/hBNNSs films was greatly enhanced by 67%. Meanwhile, the oxygen permeability (OP) and carbon dioxide permeability (CO2P) of CS/hBNNSs films are significantly lowered by 65% and 93%, respectively. In addition, their thermal stabilities and mechanical property are also enhanced.

One-step assembly of poly(vinyl alcohol)/tannic acid complexes as a high oxygen barrier coating for poly(lactic acid) packaging films

The low oxygen barrier property of poly(lactic acid) (PLA) film extremely impedes its widespread application for food package. Appling an oxygen barrier coating to the surface of PLA film represents an effective means of addressing this issue. However, existing coating strategies via layer-by-layer are often time-consuming. Herein, we report the design and fabrication of a one-step scalable assembled poly(vinyl alcohol) (PVA)/tannic acid (TA) complex coating on the surface of PLA film as an advancement of our previous layer-by-layer assembled PVA/TA multilayer coating. By tailoring the mass ratio of PVA and TA, the oxygen barrier property of PLA film can be improved from low grade to high grade, which is comparable to that of PVA/TA multilayer coating (20 bilayers), and even superior to those of many food packaging films. Meanwhile, the oxygen barrier mechanism is analyzed, which proposes a new guideline for the development of high oxygen barrier coatings via a convenient and efficient approach.

PLA Films Containing Montmorillonite Nanoclay–Citronella Essential Oil Hybrids for Potential Active Film Formulation

This work evaluated the synergistic effect of citronella essential oil (Ct) and montmorillonite (MMT) (called hybrid compound) incorporated in Poly(lactic acid) (PLA) films at different concentrations (3, 10, 15, and 20 wt%). PLA films were characterized using X-ray diffraction, SEM, TGA, and DSC considering their mechanical properties and essential oil migration. XRD analysis showed the effective interaction between MMT and oil. Thermal analysis, SEM, and mechanical tests were essential to understand the saturation point of the PLA composites. Samples with 15% and 20% of Ct showed a crystallinity reduction of 0.5% compared to samples with 3% and 10% of Ct. PLA/MMT–Ct showed a reduction in tensile strength of the order of 16 and 24, correlated to 15% and 20% of the Ct content, respectively, compared to PLA/MMT–Ct3%. Migration tests showed fast oil delivery correlated with high oil concentration, as evidenced using the PLA/MMT–Ct20% sample results, which showed an estimated release of 50% in the first 150 h due to system saturation, and the remaining being released in the last 350 h. Therefore, the migration tests provide an effective Ct concentration range promising for application with active packaging due to the intrinsic antimicrobial properties of Ct.

Active Poly (Lactic Acid) Films with Rice Straw Aqueous Extracts for Meat Preservation Purposes

Aqueous extracts from rice straw (RS), using ultrasound-assisted reflux heating extraction (USHT) and subcritical water extraction (SWE), under two process conditions (160 °C, 7 bars; and 180 °C, 11 bars), were obtained and characterised as to their phenolic content and antioxidant and antimicrobial capacities. These extracts were incorporated (6% wt.) into poly (lactic acid) (PLA) films by melt blending and compression moulding that were characterised as to their structural and functional properties and their capacity to preserve fresh pork meat, as vacuum thermo-sealed bags, throughout 16 days of cold storage. The extracts slightly reduced the extensibility, resistance to break, and water barrier capacity of the PLA films but enhanced their oxygen barrier capacity and the UV light-blocking effect. The films with RS extracts were effective at preserving meat quality parameters, inhibiting microbial growth, meat oxidation, discolouration, and weight loss. The SWE extract obtained at 180 °C was the most effective at obtaining active films for meat preservation, exhibiting the greatest antioxidant and antibacterial activity. Therefore, the green SWE technique is useful for obtaining active extracts from RS, allowing for its valorisation in the development of biodegradable active materials useful to preserve food quality.

Comparative analysis on poly lactic acid and chitin fortified poly lactic acid films

Comparative analysis on poly lactic acid and chitin fortified poly lactic acid films

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.

Blood compatible and noncytotoxic superhydrophobic graphene/titanium dioxide coating with antibacterial and antibiofilm properties

AbstractThe potential of superhydrophobic surfaces has gained vast attention in medical settings due to their self‐cleaning effect (including bacterial colonization reduction), minimized cell‐to‐surface interaction, and anti‐biofouling effect. These valuable features allow the vanquishment of some limitations accompanying the blood‐contacting medical devices that are widely used in clinical practice. The extracorporeal circulation used to perform hemodialysis, for instance, as well as the blood collection sets, these essential blood‐contacting medical devices are frequently associated with bacterial infection and hemolysis. Within this study, superhydrophobic surface was substantiated to enhance the biocompatibility. Herein, the graphene (Gr) and titanium dioxide (TiO2) nanoparticles were dip‐coated on poly(lactic acid) (PLA) film to produce a superhydrophobic surface. The uniform distribution of the Gr/TiO2 nanoparticles of the coating enhanced the surface roughness and therefore promoted superhydrophobic properties. Co‐occurrence of the Cassie‐Baxter regime and Wenzel regime was suggested to induce the low surface wettability. The superhydrophobic Gr/TiO2 demonstrated significant inhibition of biofilm formation and antibacterial activity against Staphylococcus aureus, Klebsiella pneumoniae and Pseudomonas aeruginosa. Besides, the in vitro blood compatibility assay showed a hemolysis rate lower than 2%, which was categorized as nonhemolytic. The exposure of human heart cells and kidney cells to the Gr/TiO2‐coated PLA film did not significantly affect the cell viability. The findings herein showed promising results for the superhydrophobic Gr/TiO2‐coated PLA film to act as a potential biomaterial for single‐use blood‐contacting medical devices. This study also provided insight for future medical applications that require superhydrophobic coatings.

A Novel Hydrophilic, Antibacterial Chitosan-Based Coating Prepared by Ultrasonic Atomization Assisted LbL Assembly Technique.

To explore the potential applicability of chitosan (CTS), we prepared aldehyde chitosan (CTS-CHO) with chitosan and sodium periodate via oxidation reaction and then a chitosan-based hydrophilic and antibacterial coating on the surface of poly (lactic acid) (PLA) film was developed and characterized. The oxidation degree was determined by Elemental analyser to be 12.53%, and a Fourier transform infrared spectroscopy was used to characterize the structure of CTS-CHO. It was evident that CTS-CHO is a biocompatible coating biomaterial with more than 80% cell viability obtained through the Live/Dead staining assay and the alamarBlue assay. The hydrophilic and antibacterial CTS-CHO coating on the PLA surface was prepared by ultrasonic atomization assisted LbL assembly technique due to Schiff's base reaction within and between layers. The CTS-CHO coating had better hydrophilicity and transparency, a more definite industrialization potential, and higher antibacterial activity at experimental concentrations than the CTS coating. All of the results demonstrated that the ultrasonic atomization-assisted LbL assembly CTS-CHO coating is a promising alternative for improving hydrophilicity and antibacterial activity on the PLA surface. The functional groups of CTS-CHO could react with active components with amino groups via dynamic Schiff's base reaction and provide the opportunity to create a drug releasing surface for biomedical applications.

Improving the active food packaging function of poly(lactic acid) film coated by poly(vinyl alcohol) based on proanthocyanidin functionalized layered clay

In this paper, natural plant polyphenol-proanthocyanidin (PAC) and layered clay-layered double hydroxides (LDHs) were firstly introduced into poly(vinyl alcohol) (PVA) based coatings to construct PAC/PVA and PAC functionalized LDHs (LDHs@PAC-Cu)/PVA dual active coatings, and further successively coated on the surface of PLA base films to develop PLA active films. The results showed that PAC and copper ions were successfully loading on the LDHs surface through adsorption and complexation. After a certain amount (≥3 wt%) of LDHs@PAC-Cu was added, active packaging functions and gas barrier properties of PLA active films were improved markedly. When 5 wt% LDHs@PAC-Cu was added, antioxidant and antibacterial properties of PLA active films reached 84.31% and 95.5%, oxygen and water vapor transmission rate decreased by 99.4% and 62.6% compared with PLA base film, and the shelf life of pasteurized milk was extended from 60 h to 96 h. Active substances release test indicated that LDHs@PAC-Cu could not only delay the release of active substances in the early stage, but also supplement the release of active substances in the later stage, thus extending the shelf life of food more effectively. Therefore, PLA active films have good application potential in the field of active food packaging.

Temporally programmed cyclic deformation to control structural hierarchy and shrinkage in poly lactic acid films

In this paper we explore the role of programmed deformation history on the strain induced crystallization-crystalline order and chain orientation developed in initially amorphous poly lactic acid films in rubbery state. For this purpose, we use highly instrumented programmable uniaxial stretcher that captures true strain, true stress, birefringence continuously during processing. Using this highly instrumented tool, we apply deformation up to strategically selected strain levels where initially amorphous PLA film potentially could strain-crystallize. This is followed by small strain cycling to affect the level of orientation and order in crystalline and amorphous phases through stretch-retract sequence.With application of strain cycling following deformation near strain hardening and beyond, the crystalline chain orientation increases dramatically as the oriented amorphous regions are allowed to relax to form oriented crystals as the number of sites forming crystals increases and unoriented amorphous regions are then oriented in subsequent cycles. Deformation followed by small strain cycling lead to near perfect crystalline chain orientation and high crystallinity but smaller crystallite sizes especially under moderate total strains.For the first time, stretching plus strain cycling the thermal shrinkage in oriented films has been shown to substantially decrease at the same overall strain levels as the fraction of taut oriented amorphous chains reduces while the number of crystalline sites increases substantially leading to a more thermally stable morphology. This opens new processing step that can be employed in large tenter frame biaxial stretching machines together with heat setting to produce thermally stable substrates.

Design and fabrication of anthocyanin functionalized layered clay/poly(vinyl alcohol) coatings on poly(lactic acid) film for active food packaging

Biodegradable polymers (poly(lactic acid) (PLA), etc.) have been severely limited in their practical applications due to their inherent limitations in performance. Surface coating technology can effectively improve the active packaging function for food packaging. In this study, anthocyanin (ACY) functionalized layered double hydroxides (LDHs@ACY-Cu) was synthesized for the first time by adsorption and complexation of ACY with Cu(II) on the LDHs. Further, ACY (5 wt%)/poly(vinyl alcohol) (PVA) coatings as the first layer and LDHs@ACY-Cu (1–7 wt%)/PVA coatings as the second layer were successively coated on the PLA base film to fabricate active multilayer films. The results showed that ACY-Cu(II) complexes were loaded on the LDHs successfully with a thickness of 4 nm. With the increase of LDHs@ACY-Cu content, UV barrier, antioxidant, antibacterial and gas barrier properties of active multilayer films were improved significantly. When the addition of LDHs@ACY-Cu increased to 7 wt%, UV barrier (at 280 nm) and oxygen barrier properties of active multilayer films were increased by 44.9% and 99.1% compared with PLA base film, and the antibacterial and antioxidant properties also reached 96.4% and 82.21%, respectively. Although the color of all films showed a tendency to brown, the light transmittance exceeded 89.0% in the visible light range (at 600 nm). The milk spoilage test indicated that active multilayer films can inhibit the rapid bacterial reproduction in the pasteurized milk and extend the shelf life of milk. Therefore, active multilayer films exhibit good potential for applications in the field of active food packaging.

The effect of alcoholic solutions on the thermomechanical properties of immersed poly(lactic acid) films

AbstractThe effects of aqueous and deuterium oxide (D2O) solutions of alcohols (methanol, ethanol, 1‐propanol, 2‐propanol, and 1‐butanol) on the thermomechanical properties of poly(lactic acid)—PLA—films were assessed by dynamic mechanical analysis. The glass transition temperature (Tg) of PLA films immersed in 25%, 50%, 75%, and 100% (v/v) alcoholic solutions were compared with the Tg of films immersed in 100% water and D2O. The Tg of PLA films immersed in methanol and ethanol aqueous solutions decreased as the concentration of the alcohol solutions increased. For methanol and ethanol, the Tg decreased by 8.6 and 7.6°C per 25% (v/v) increase in alcohol, respectively. When the PLA films were immersed in propanol aqueous solutions and butanol, the Tg reached the lowest value at 75% (v/v) and 100% (v/v), respectively. Tg of PLA films immersed in 1‐propanol and 2‐propanol decreased by 8.6 and 8.9°C for every 25% increase in propanol before reaching the minimum value, respectively. Aqueous and D2O solutions had similar effects on Tg. Selective studies of crystallinity evolution, ethanol sorption, degree of swelling, and Hansen solubility parameters of PLA were conducted. This work assists in developing PLA films intended for contact with aqueous‐alcoholic solutions.

Poly(lactic acid) films reinforced with hybrid zinc oxide‐polyhedral oligomeric silsesquioxane nanoparticles: Morphological, mechanical, and antibacterial properties

AbstractNanoparticles of zinc oxide (ZnO), polyhedral oligomeric silsesquioxane (POSS), and their hybrids were added to polylactic acid (PLA) using solution casting process at different weight percentages of the nanoparticles (1, 3, and 5 wt%) to form developed nanocomposites for food packaging applications. According to FTIR and XRD studies, both nanoparticles displayed fair chemical interactions with the PLA matrix. Furthermore, morphological investigations (SEM‐EDS) revealed that POSS, ZnO, and their hybrids were uniformly dispersed into the matrix despite some microaggregations at 5 wt% of nanoparticles, especially for those containing POSS. Moreover, adding 1 wt% of POSS to PLA increased its tensile strength and modulus by 20% and 149%, respectively, while decreasing the elongation‐at‐break by 54%. In addition, the tensile strength, tensile modulus, and elongation‐at‐break of PLA all increased by 7.5%, 28.7%, and 162%, respectively, with the addition of 1 wt% ZnO. Contact angle and surface free energy experiments demonstrated that after incorporating ZnO and POSS into the PLA matrix, the hydrophobicity of the samples increased, and POSS nanoparticles could minimize bacterial adherence effectively. In addition to the antibacterial properties of ZnO and POSS nanoparticles, increasing the concentration of hybrid nanoparticles up to 5 wt% expanded the bacteria's inhibitory zone, particularly in the case of Gram‐positive bacteria (Staphylococcus aureus). Finally, the hybrid nanocomposites exhibited both balanced mechanical characteristics and promising antibacterial activity compared with those with ZnO and POSS alone.

Highly efficiency flame-retardant and anti-dripping performance with dual effect of phosphaphenanthrene-benzimidazole for poly (lactic acid) film

To improve the flammability and severe melt-dripping behavior of poly (lactic acid) (PLA), we designed and successfully synthesized a flame retardant structure (D-AB) based on phosphaphenanthrene and benzimidazole groups with hydrogen bonds and π-π stacking effect. Then, D-AB was blended with PLA in solution to prepare PLA/D-ABs films. The results showed that the incorporation of D-AB significantly enhances the viscoelasticity and complex viscosity of PLA due to the synergistic effect of hydrogen bonds and π-π stacking of D-AB. Meanwhile, with the good char formation ability of benzimidazole group, PLA/D-ABs exhibit excellent flame retardancy. With only a 5 wt % addition of D-AB, the PLA film with 0.15 mm thickness easily achieve UL-94 VTM-0 rating and high LOI value of 30.5%, while its melt-dripping behavior is improved. In addition, the flame retardant mechanism of D-AB in PLA is studied in detail. It is found that the release of PO· radicals and non-combustible gas in the gas phase, as well as the formation of a dense and intact carbon layers in the condensed phase contribute to the good flame retardant performance of D-AB. This work provides a method for designing highly efficient flame retardants for PLA.

Antioxidant poly (lactic acid) films with rice straw extract for food packaging applications

Antioxidant PLA films incorporating 2%, 4% and 6% of phenol-rich extract from rice straw (RS) were obtained by melt blending and compression-moulding. Aqueous RS extract was obtained by a combined ultrasound-reflux heating method and characterised as to its total phenolic content (TPC) and antioxidant capacity. The effect of the extract ratio on the functional properties of the films was analysed, as well as the release kinetics of antioxidants in food simulants (ethanol 10% and 50%). Extract incorporation slightly reduced the strength of the polymer matrix, stretchability, resistance to break, barrier capacity and thermostability, while films became brownish and gained antioxidant capacity. Phenolic compounds from the extract were effectively released into food simulants, depending on the extract concentration, the food simulant and contact time. The radical scavenging capacity of the films reached asymptotic values from about 150 h contact time, and films with 6% of the extract exhibited similar values for both simulants. So, PLA films with approximately 6% of extract could be used as biodegradable active packaging material with antioxidant capacity in both aqueous foods (simulant A) and more fatty products (simulant D1). Further studies are required to verify the antioxidant efficiency of the films in real foods.

Carbon quantum dots-driven surface morphology transformation towards superhydrophobic poly(lactic acid) film

Focused on the design and implementation of superhydrophobic surface of poly(lactic acid) (PLA) film, the novel morphology regulating strategy (i.e., carbon quantum dots (CQDs)-nucleated interfacial-crystallization induced phase separation) is reported to fabricate CQDs-grafted-poly(D-lactic acid)/poly(L-lactic acid) (CQDs-g-PDLA/PLLA) films with tailorable hierarchical micro-nano structures. The hierarchical structures of CQDs-g-PDLA/PLLA films evolve from laminar protrusions to microspheres to petal-like structures and further to micro-nano sphere structures, only by adjusting the CQDs-g-PDLA content. 30 wt% CQDs-g-PDLA/PLLA film with lotus leaf-like microstructures exhibits a record-high contact angle of 168° and a rather small sliding angle of 7.8°, indicating the pretty superhydrophobicity. Constructing controllable hierarchical structures is key factor to attain the superhydrophobicity, instead of commonly introducing suitable nanoparticles or hydrophobization agents. In combination with the high porosity, 30 wt% CQDs-g-PDLA/PLLA film illustrates a maximal oil-absorption up to 9.7 g/g. This strategy provides a novel insight into designing and constructing superhydrophobic PLA materials for the enormous application potential in surface self-cleaning and oil-water separation.

Essential oil-loaded antimicrobial and antioxidant zein/poly(lactic acid) film as active food packaging

Food spoilage and poisoning can be caused by microbes in food. Active food packaging with the addition of antimicrobial compounds is a novel method to prolong the shelf life of food and improve product quality. PLA, a very popular synthetic biodegradable material, was mixed with zein, a widely studied food packaging material, and the plasticizer PEG to make a composite film ZLP. With the addition of PLA, the brittleness of zein film was reduced and the water barrier properties of zein and PEG composite film was enhanced. The mass ratio of zein, PLA, and PEG for the optimal mechanical and water barrier properties of the film was 5:5:2. High antioxidant effects were obtained in the eugenol- and carvacrol-loaded ZLP films, while good antibacterial effects against E. coli and S. aureus were found in the carvacrol- and cinnamaldehyde- loaded ZLP films.