Miscibility, mechanical and thermal properties of poly(lactic acid)/polyester-diol blends

Embracing Sustainability: The World of Bio-Based Polymers in a Mini Review

The proliferation of polymer science and technology in recent decades has been remarkable, with synthetic polymers derived predominantly from petroleum-based sources dominating the market. However, concerns about their environmental impacts and the finite nature of fossil resources have sparked interest in sustainable alternatives. Bio-based polymers, derived from renewable sources such as plants and microbes, offer promise in addressing these challenges. This review provides an overview of bio-based polymers, discussing their production methods, properties, and potential applications. Specifically, it explores prominent examples including polylactic acid (PLA), polyhydroxyalkanoates (PHAs), and polyhydroxy polyamides (PHPAs). Despite their current limited market share, the growing awareness of environmental issues and advancements in technology are driving increased demand for bio-based polymers, positioning them as essential components in the transition towards a more sustainable future.

Potential Perspectives and Sustainability of Bioplastics Developed from Horticulture

In recent times, bioplastics have become an integrated sustainable alternative to plastic management to lessen the dependency on fossil fuels as well as better plastic disposal methods. Through this study, the focus is laid upon the dire need for developing bio-plastics for transforming to a sustainable future as bio-plastics are renewable, more feasible, and a sustainable option when compared to the high-energy consuming conventional oil-based plastics. Bioplastics might not be a one-stop solution for all environmental issues caused by plastics, but it will be a beneficial step for expanding biodegradable polymer as society's current concerns about the environment makes this an ideal time for further growth of biopolymers. Moreover, the potential market for agricultural materials in bioplastics is leading to an economic push toward the growth of the bioplastic industry, thus providing better alternatives for a future sustainable environment. The objective of the review is to provide detailed knowledge about plastics obtained from various renewable sources, their production, life cycle, market share, applications, and roles to act as a sustainable source of synthetic plastics, thereby featuring various possibilities and potentialities of bioplastics to perform as an alternative solution for waste reduction.

Role of Shear Flow on Structure Development during Post-Processing Annealing for Poly(lactic acid)

The effect of shear history on structure development during post-processing annealing was studied using poly(lactic acid) PLA. Since PLA shows a low crystallization rate, quenched films had no crystallinity. Moreover, molecular orientation was not detected in the films. During the annealing procedure beyond its glass transition temperature, however, molecular orientation to the flow direction occurred with the crystallization growth in the films having an appropriate shear history. This peculiar crystal growth during the annealing was most probably attributed to the crystallization from extended chain crystals generated during the applied shear history, although the amount of extended chain crystals was low. The results obtained in this study should be noted because the molecular orientation proceeded due to the annealing history applied. Furthermore, this phenomenon will be used to suppress dimensional change and increase product rigidity.

Biodegradation of Biodegradable Polymers in Mesophilic Aerobic Environments

Finding alternatives to diminish plastic pollution has become one of the main challenges of modern life. A few alternatives have gained potential for a shift toward a more circular and sustainable relationship with plastics. Biodegradable polymers derived from bio- and fossil-based sources have emerged as one feasible alternative to overcome inconveniences associated with the use and disposal of non-biodegradable polymers. The biodegradation process depends on the environment's factors, microorganisms and associated enzymes, and the polymer properties, resulting in a plethora of parameters that create a complex process whereby biodegradation times and rates can vary immensely. This review aims to provide a background and a comprehensive, systematic, and critical overview of this complex process with a special focus on the mesophilic range. Activity toward depolymerization by extracellular enzymes, biofilm effect on the dynamic of the degradation process, CO2 evolution evaluating the extent of biodegradation, and metabolic pathways are discussed. Remarks and perspectives for potential future research are provided with a focus on the current knowledge gaps if the goal is to minimize the persistence of plastics across environments. Innovative approaches such as the addition of specific compounds to trigger depolymerization under particular conditions, biostimulation, bioaugmentation, and the addition of natural and/or modified enzymes are state-of-the-art methods that need faster development. Furthermore, methods must be connected to standards and techniques that fully track the biodegradation process. More transdisciplinary research within areas of polymer chemistry/processing and microbiology/biochemistry is needed.

Tailoring Oligomeric Plasticizers for Polylactide through Structural Control

Structural variations (oligolactide segments, functionalized end groups, and different plasticizer cores) were utilized to tailor the performances of biobased plasticizers for polylactide (PLA). Six plasticizers were developed starting from 1,4-butanediol and isosorbide as cores: two monomeric (1,4-butanediol levulinate and isosorbide levulinate) and four oligomeric plasticizers with hydroxyl or levulinate ester end groups (1,4-butanediol-based oligolactide, isosorbide-based oligolactide, 1,4-butanediol-based oligomeric levulinate, and isosorbide-based oligomeric levulinate). Structural variations in plasticizer design were reflected in the thermal stability, plasticizing efficiency, and migration resistance. The monomeric plasticizer 1,4-butanediol levulinate decreased the glass-transition temperature of PLA from 59 to 16 °C and increased the strain at break substantially from 6 to 227% with 20 wt % addition. 1,4-Butanediol-based oligomeric levulinate exhibited better thermal stability and migration resistance, though the plasticizing efficiency was slightly lower (glass-transition temperature = 28 °C; strain at break = 202%). Compared to PLA films plasticized by plasticizers with flexible butanediol cores, those plasticized by plasticizers with rigid isosorbide cores exhibited higher Young's modulus and thermal stability and lower plasticizing efficiency. Furthermore, plasticizers with levulinate ester end groups had improved thermal stability, plasticizing efficiency, and migration resistance compared to the corresponding plasticizers with hydroxyl end groups. Hence, a set of controlled structural variations in plasticizer design were successfully demonstrated as a potent route to tailor the plasticizer performances.

Viscoelastic Properties of Fully Biomass-Based Transparent Plastic Comprising Cellulose Acetate and Citrate Ester

Viscoelastic properties including melt processability were evaluated for a fully biomass-based glassy plastic comprising cellulose acetate (CA) and triethyl citrate (TEC). The TEC exerted an excellent plasticizing effect without dissolving the CA crystals. Pure CA has poor melt processability. In contrast, the TEC-plasticized CA had good melt-processability at 205 °C, which is lower than the degradation temperature of CA. Extrusion was possible even at 1000 s−1 without any flow instabilities, similar to conventional plastics showing good processability at extrusion. Furthermore, there was marked strain-hardening behavior in the transient elongational viscosity, suggesting that various processing operations are possible, such as a long-chain branched polymer. This biomass-based plastic can be used as a substitute for conventional glassy plastics because it is highly transparent and its softening temperature is above 100 °C.

Investigations on Novel Ternary Green Polymer Composite

In this study, the novel ternary green polymer composites of poly(l-lactic acid) (PLLA)/poly(ethylene adipate)/hexagonal boron nitride (PLLA/PEA/h-BN) were synthesized and prepared. The crystallization rate of the biodegradable polymer PLLA in the composite was significantly increased with the addition of PEA and functional h-BN. In ternary PLLA/PEA/h-BN composites, PEA can be used as a plasticizer, while h-BN is a functional nucleation agent for PLLA. The analysis of the isothermal crystallization kinetics by the Avrami equation shows that the rate constant k of the ternary PLLA/PEA/h-BN composite represents the highest value, indicating the highest crystallization in the ternary composite. Adding h-BN in the composite can further increase the k value and increase the crystallization rate. Polarized optical microscopy (POM) images reveal that h-BN is an effective nucleation agent that increases the nucleation density of composites. Analysis of wide-angle X-ray diffraction (WAXD) further confirmed that the crystalline structures of PLLA were unchanged by the addition of PEA and h-BN. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show that the h-BN particles are uniformly distributed in the composite. The distribution of h-BN having a particle size of a few hundred nm causes an effective nucleation effect and promotes the crystallization of the ternary composites.

Sustainable biobased blends of poly(lactic acid) (PLA) and poly(glycerol succinate-co-maleate) (PGSMA) with balanced performance prepared by dynamic vulcanization

A sustainable and industrially viable method for toughening poly(lactic acid) by dynamic vulcanization using glycerol and succinic acid based polyesters.

Physical and mechanical properties of PLA, and their functions in widespread applications - A comprehensive review

Poly(lactic acid) (PLA), so far, is the most extensively researched and utilized biodegradable aliphatic polyester in human history. Due to its merits, PLA is a leading biomaterial for numerous applications in medicine as well as in industry replacing conventional petrochemical-based polymers. The main purpose of this review is to elaborate the mechanical and physical properties that affect its stability, processability, degradation, PLA-other polymers immiscibility, aging and recyclability, and therefore its potential suitability to fulfill specific application requirements. This review also summarizes variations in these properties during PLA processing (i.e. thermal degradation and recyclability), biodegradation, packaging and sterilization, and aging (i.e. weathering and hygrothermal). In addition, we discuss up-to-date strategies for PLA properties improvements including components and plasticizer blending, nucleation agent addition, and PLA modifications and nanoformulations. Incorporating better understanding of the role of these properties with available improvement strategies is the key for successful utilization of PLA and its copolymers/composites/blends to maximize their fit with worldwide application needs.

Effect of poly(vinyl alcohol) as an efficient crystallization-assisting agent on the enhanced crystallization rate of biodegradable poly(l-lactide)

PVA increases both the nucleation density and the growth rate of PLLA spherulites in blends.

Novel blends of polylactide with ethylene glycol derivatives of POSS

Polylactide (PLA), a main biodegradable and biobased candidate for the replacement of petrochemical polymers, is stiff and brittle at room conditions. It is therefore of high interest to formulate new PLA-based materials suitable for applications demanding flexibility and toughness. In this work, novel blends of PLA with polyhedral oligomeric silsesquioxanes (POSS) grafted with longer (P1) and shorter (P2) arms of ethylene glycol derivatives were prepared and studied. It was hypothesized that, owing to their architecture with the central POSS cage grafted with arms, miscibility and stability of the blends could be improved. Indeed, PLA/P1 blends were homogeneous despite P1 relatively high M_w of 9,500 g mol^-1. The blend with 20 wt% of P1, having T_g at 16 °C, was transparent and flexible, elastomer-like material with excellent drawability. The blend remained homogeneous and retained its good drawability as well as flexibility during 6 months of aging at room temperature: a 2 % secant modulus of elasticity well below 100 MPa, a low yield stress below 2 MPa, and and a large strain at break of 8 (800 %). Contary to that, PLA/P2 blends were only partially miscible. Nevertheless, owing to the liquid state of the dispersed phase, the blend with 15 wt% of P2 was transparent and ductile, with T_g at 49 °C, a relatively high yield strength of 29 MPa, and a large strain at break of 2.3 (230 %). The toughening mechanism involved the initiation of crazes and facilitation of their propagation by the liquid inclusions via the local plasticization effect.

The development of thermal nanoprobe methods as a means of characterizing and mapping plasticizer incorporation into ethylcellulose films

PURPOSE

The phase composition and distribution of ethylcellulose (EC) films containing varying amounts of the plasticizer fractionated coconut oil (FCO) were studied using a novel combination of thermal and mapping approaches.

METHODS

The thermal and thermomechanical properties of films containing up to 30% FCO were characterized using modulated temperature differential scanning calorimetry (MTDSC) and dynamic mechanical analysis (DMA). Film surfaces were mapped using atomic force microscopy (AFM; topographic and pulsed force modes) and the composition of specific regions identified using nanothermal probes.

RESULTS

Clear evidence of distinct conjugate phases was obtained for the 20-30% FCO/EC film systems. We suggest a model whereby the composition of the distinct phases may be estimated via consideration of the glass transition temperatures observed using DSC and DMA. By combining pulsed force AFM and nano-thermal analysis we demonstrate that it is possible to map the two separated phases. In particular, the use of thermal probes allowed identification of the distinct regions via localized thermomechanical analysis, whereby nanoscale probe penetration is measured as a function of temperature.

CONCLUSION

The study has indicated that by using thermal and imaging techniques in conjunction it is possible to both identify and map distinct regions in binary films.