Influence of linear and branched amine functionalization in mesoporous silica on the thermal, mechanical and barrier properties of sustainable poly(lactic acid) biocomposite films

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.

Poly (lactic acid)-based pH responsive membrane combined with chitosan and alizarin for food packaging

A poly (lactic acid) (PLA) -based functional partition composite membrane (PLA/CA) containing chitosan (CS) and alizarin (AL) was designed by solution casting method. The PLA/CA membrane contains the antibacterial zone of the edge part (PLA/CS) and the pH response detection zone of the central part (PLA/AL). At the same time, the environmentally friendly plasticizer tributyl citrate (TBC) was added to make the prepared PLA/CA composite membrane have good flexibility and high transparency. The results of FE-SEM and FTIR showed that CS and AL were uniformly dispersed in PLA matrix and had good compatibility with PLA. The antioxidant activities of PLA/CS and PLA/AL composite films were 43.3 % and 72.8 %, respectively. At the same time, the inhibitory rates of PLA/CS membrane against Escherichia coli and Staphylococcus aureus were as high as 87.91 % and 75.17 %, respectively. PLA/AL films exhibit excellent UV barrier properties. When the environmental pH (ammonia and acetic acid vapor) changed repeatedly, the PLA/AL membrane showed reversible color change of yellow under acidic condition and purple under alkaline condition. During the packaging and storage of chicken breast meat, the freshness of chicken breast meat can be detected by the color change of functional PLA/CA composite membrane.

Composites Based on Poly(Lactic Acid) (PLA) and SBA-15: Effect of Mesoporous Silica on Thermal Stability and on Isothermal Crystallization from Either Glass or Molten State

Several composites based on an L-rich poly(lactic acid) (PLA) with different contents of mesoporous Santa Barbara Amorphous (SBA-15) silica were prepared in order to evaluate the effect of the mesoporous silica on the resultant PLA materials by examining morphological aspects, changes in PLA phases and their transitions, and, primarily, the influence on some final properties. Melt extrusion was chosen for the obtainment of the composites, followed by quenching from the melt to prepare films. Completely amorphous samples were then attained, as deduced from X-ray diffraction and differential scanning calorimetry (DSC) analyses. Thermogravimetric analysis (TGA) results demonstrated that the presence of SBA-15 particles in the PLA matrix did not exert any significant influence on the thermal decomposition of these composites. An important nucleation effect of the silica was found in PLA, especially under isothermal crystallization either from the melt or from its glassy state. As expected, isothermal crystallization from the glass was considerably faster than from the molten state, and these high differences were also responsible for a more considerable nucleating role of SBA-15 when crystallizing from the melt. It is remarkable that the PLA under analysis showed very close temperatures for cold crystallization and its subsequent melting. Moreover, the type of developed polymorphs did not accomplish the common rules previously described in the literature. Thus, all the isothermal experiments led to exclusive formation of the α modification, and the observation of the α’ crystals required the annealing for long times at temperatures below 80 °C, as ascertained by both DSC and X-ray diffraction experiments. Finally, microhardness (MH) measurements indicated a competition between the PLA physical aging and the silica reinforcement effect in the as-processed amorphous films. Physical aging in the neat PLA was much more important than in the PLA matrix that constituted the composites. Accordingly, the MH trend with SBA-15 content was strongly dependent on aging times.

Synthesis of flexible poly(l-lactide)-b-polyethylene glycol-b-poly(l-lactide) bioplastics by ring-opening polymerization in the presence of chain extender

Poly(l-lactide)-b-polyethylene glycol-b-poly(l-lactide) (PLLA-PEG-PLLA) is found to be more flexible than PLLA due to the flexibility of PEG middle blocks. Melt flow and mechanical properties of PLLA-PEG-PLLA were improved through post melt blending with a chain extender (CE). In this work, in situ chain-extended PLLA-PEG-PLLAs were synthesized by ring-opening polymerization in the presence of Joncryl® CE. The influence of CE content (1.0, 2.0, and 4.0 phr) on the gel content, melt flow index (MFI), thermal properties, and mechanical properties of the obtained in situ chain-extended PLLA-PEG-PLLAs was investigated. The gel content of in situ chain-extended PLLA-PEG-PLLA increased while the MFI and degree of crystallinity significantly decreased with increasing CE content. The in situ chain-extended PLLA-PEG-PLLA with 1.0 phr CE showed the best tensile properties. The extensibility of in situ chain-extended PLLA-PEG-PLLA films decreased when the CE contents were higher than 1.0 phr. These in situ chain-extended PLLA-PEG-PLLA films can be used as highly flexible bioplastics.

Improvement in Mechanical Properties and Heat Resistance of PLLA-b-PEG-b-PLLA by Melt Blending with PDLA-b-PEG-b-PDLA for Potential Use as High-Performance Bioplastics

Ecofriendly poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) (PLLA-b-PEG-b-PLLA) are flexible bioplastics. In this work, the blending of poly(D-lactide)-b-poly(ethylene glycol)-b-poly(D-lactide) (PDLA-b-PEG-b-PDLA) with various blend ratios for stereocomplex formation has been proved to be an effective method for improving the mechanical properties and heat resistance of PLLA-b-PEG-b-PLLA films. The PLLA-b-PEG-b-PLLA/PDLA-b-PEG-b-PLDA blend films were prepared by melt blending followed with compression molding. The stereocomplexation of PLLA and PDLA end-blocks were characterized by differential scanning calorimetry and X-ray diffraction (XRD). The content of stereocomplex crystallites of blend films increased with the PDLA-b-PEG-b-PDLA ratio. From XRD, the blend films exhibited only stereocomplex crystallites. The stress and strain at break of blend films obtained from tensile tests were enhanced by melt blending with the PDLA-b-PEG-b-PDLA. The heat resistance of blend films determined from testing of dimensional stability to heat and dynamic mechanical analysis were improved with the PDLA-b-PEG-b-PDLA ratio. The sterecomplex PLLA-b-PEG-b-PLLA/PDL-b-PEG-b-PDLA films prepared by melt processing could be used as flexible and good heat-resistance packaging bioplastics.

Electrospun Antimicrobial Films of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Containing Eugenol Essential Oil Encapsulated in Mesoporous Silica Nanoparticles

The main goal of this study was to develop poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) films with long-term antimicrobial capacity of interest in food packaging applications. To this end, eugenol was first highly efficiently encapsulated at 50 wt.-% in the pores of mesoporous silica nanoparticles by vapor adsorption. The eugenol-containing nanoparticles were then loaded in the 2.5⁻20 wt.-% range into PHBV by electrospinning and the resultant electrospun composite fibers were annealed at 155 °C to produce continuous films. The characterization showed that the PHBV films filled with mesoporous silica nanoparticles containing eugenol present sufficient thermal resistance and enhanced mechanical strength and barrier performance to water vapor and limonene. The antimicrobial activity of the films was also evaluated against foodborne bacteria for 15 days in open vs. closed conditions in order to simulate real packaging conditions. The electrospun PHBV films with loadings above 10 wt.-% of mesoporous silica nanoparticles containing eugenol successfully inhibited the bacterial growth, whereas the active films stored in hermetically closed systems increased their antimicrobial activity after 15 days due to the volatile portion accumulated in the system's headspace and the sustained release capacity of the films. The resultant biopolymer films are, therefore, potential candidates to be applied in active food packaging applications to provide shelf life extension and food safety.