Improvements in the crystallinity and mechanical properties of PLA by nucleation and annealing

Accelerated hydrolytic degradation of poly(l-lactide) by blending with poly(ether-block-amide)

A continuing challenge in the most common biodegradable polyester of poly(l-lactide) (PLLA) is to improve the degradation rate in the environment, though it has been widely used in packaging and medical applications. In this study, PLLA/poly(ether-block-amide) (PEBA) blends are prepared by melt blending to investigate the effect of PEBA component on the phase morphology, thermal behavior, mechanical properties, and hydrolytic degradation of the blends. The incorporation of PEBA component is beneficial to the improved toughness and increased water absorption of the blends, and accelerated hydrolytic degradation of PLLA. The blend exhibits the optimal mechanical and hydrolytic degradation properties when the blend mass ratio of PLLA/PEBA is 80/20. The toughness of the blend is increased by 390 % compared to that of pure PLLA. After being hydrolyzed at 58 °C for 240 h, the water absorption, the mass loss and the decrease of molecular weight of the blend is increased by 138 %, 160 % and 40 %, respectively, indicating faster hydrolytic degradation rate of the blend than that of pure PLLA. Furthermore, the accelerated hydrolytic degradation mechanism of PLLA in the blend is revealed. The amorphous region of PLLA is hydrolyzed initially at the phase interface of the blend, and subsequently the crystalline structure of PLLA is degraded. The hydrolysis process causes a change in the relative content of crystalline regions in the system, resulting in an increase in crystallinity of PLLA first and then decrease. These findings provide a new strategy for the design of novel degradable PLLA materials for practical applications.

Preparation and properties of polydimethylsiloxane-regulated oriented microporous poly (L-lactic acid) biomimetic bone repair materials

Despite the exceptional biocompatibility and degradability of Poly (L-lactic acid) (PLLA), its brittleness, low melting strength, and poor bone induction makes it challenging to utilize for bone repair. This study used a simple, efficient solid hot drawing (SHD) method to produce high-strength PLLA, using supercritical CO2 (SC-CO2) foaming technology to give PLLA a bionic microporous structure to enhance its toughness, while precisely controlling micropore homogeneity and improving the melt strength by using Polydimethylsiloxane (PDMS). This PDMS-regulated oriented microporous structure resembled that of natural bone, displaying a maximum tensile strength of 165.9 MPa and a maximum elongation at break of 164.2 %. Furthermore, this bionic structure promoted the polarization of mouse bone marrow macrophages (iBMDM), exhibiting a simultaneous pro- and anti-inflammatory effect. This structure also contributed to the adhesion and growth of mouse embryonic fibroblasts (NIH-3 T3), promoting osteogenic differentiation, which paved the way for developing degradable PLLA bone-repair load-bearing materials.

Melt Compounding of Poly(lactic acid)-Based Composites: Blending Strategies, Process Conditions, and Mechanical Properties

Polylactic acid (PLA), derived from renewable resources, has the advantages of rigidity, thermoplasticity, biocompatibility, and biodegradability, and is widely used in many fields such as packaging, agriculture, and biomedicine. The excellent processability properties allow for melt processing treatments such as extrusion, injection molding, blow molding, and thermoforming in the preparation of PLA-based materials. However, the low toughness and poor thermal stability of PLA limit its practical applications. Compared with pure PLA, conditions such as processing technology, filler, and crystallinity affect the mechanical properties of PLA-based materials, including tensile strength, Young's modulus, and elongation at break. This review systematically summarizes various technical parameters for melt processing of PLA-based materials and further discusses the mechanical properties of PLA homopolymers, filler-reinforced PLA-based composites, PLA-based multiphase composites, and reactive composite strategies for PLA-based composites.

Enhancing Polylactic Acid Properties with Graphene Nanoplatelets and Carbon Black Nanoparticles: A Study of the Electrical and Mechanical Characterization of 3D-Printed and Injection-Molded Samples

This study investigates the enhancement of polylactic acid (PLA) properties through the incorporation of graphene nanoplatelets (GNPs) and carbon black (CB) for applications in 3D printing and injection molding. The research reveals that GNPs and CB improve the electrical conductivity of PLA, although conductivity remains within the insulating range, even with up to 10% wt of nanoadditives. Mechanical characterization shows that nanoparticle addition decreases tensile strength due to stress concentration effects, while dispersants like polyethylene glycol enhance ductility and flexibility. This study compares the properties of materials processed by injection molding and 3D printing, noting that injection molding yields isotropic properties, resulting in better mechanical properties. Thermal analysis indicates that GNPs and CB influence the crystallization behavior of PLA with small changes in the melting behavior. Dynamic Mechanical Thermal Analysis (DMTA) results show how the glass transition temperature and crystallization behavior fluctuate. Overall, the incorporation of nanoadditives into PLA holds potential for enhanced performance in specific applications, though achieving optimal conductivity, mechanical strength, and thermal properties requires careful optimization of nanoparticle type, concentration, and dispersion methods.

The Effects of Nucleating Agents and Processing on the Crystallization and Mechanical Properties of Polylactic Acid: A Review

Polylactic acid (PLA) is a biobased, biodegradable, non-toxic polymer widely considered for replacing traditional petroleum-based polymer materials. Being a semi-crystalline material, PLA has great potential in many fields, such as medical implants, drug delivery systems, etc. However, the slow crystallization rate of PLA limited the application and efficient fabrication of highly crystallized PLA products. This review paper investigated and summarized the influence of formulation, compounding, and processing on PLA's crystallization behaviors and mechanical performances. The paper reviewed the literature from different studies regarding the impact of these factors on critical crystallization parameters, such as the degree of crystallinity, crystallization rate, crystalline morphology, and mechanical properties, such as tensile strength, modulus, elongation, and impact resistance. Understanding the impact of the factors on crystallization and mechanical properties is critical for PLA processing technology innovations to meet the requirements of various applications of PLA.

OH End-Capped Silicone as an Effective Nucleating Agent for Polylactide-A Robotizing Method for Evaluating the Mechanical Characteristics of PLA/Silicone Blends

Current research on materials engineering focuses mainly on bio-based materials. One of the most frequently studied materials in this group is polylactide (PLA), which is a polymer derived from starch. PLA does not have a negative impact on the natural environment and additionally, it possesses properties comparable to those of industrial polymers. The aim of the work was to investigate the potential of organosilicon compounds as modifiers of the mechanical and rheological properties of PLA, as well as to develop a new method for conducting mechanical property tests through innovative high-throughput technologies. Precise dosing methods were utilized to create PLA/silicone polymer blends with varying mass contents, allowing for continuous characterization of the produced blends. To automate bending tests and achieve comprehensive characterization of the blends, a self-created workstation setup has been used. The tensile properties of selected blend compositions were tested, and their ability to withstand dynamic loads was studied. The blends were characterized through various methods, including rheological (MFI), X-ray (XRD), spectroscopic (FTIR), and thermal properties analysis (TG, DSC, HDT), and they were evaluated using microscopic methods (MO, SEM) to examine their structures.

Enhancing Sustainability and Antifungal Properties of Biodegradable Composites: Caffeine-Treated Wood as a Filler for Polylactide

This study investigates the suitability of using caffeine-treated and untreated black cherry (Prunus serotina Ehrh.) wood as a polylactide filler. Composites containing 10%, 20%, and 30% filler were investigated in terms of increasing the nucleating ability of polylactide, as well as enhancing its resistance to microorganisms. Differential scanning calorimetry studies showed that the addition of caffeine-treated wood significantly altered the crystallization behavior of the polymer matrix, increasing its crystallization temperature and degree of crystallinity. Polarized light microscopic observations revealed that only the caffeine-treated wood induced the formation of transcrystalline structures in the polylactide. Incorporation of the modified filler into the matrix was also responsible for changes in the thermal stability and decreased hydrophilicity of the material. Most importantly, the use of black cherry wood treated with caffeine imparted antifungal properties to the polylactide-based composite, effectively reducing growth of Fusarium oxysporum, Fusarium culmorum, Alternaria alternata, and Trichoderma viride. For the first time, it was reported that treatment of wood with a caffeine compound of natural origin alters the supermolecular structure, nucleating abilities, and imparts antifungal properties of polylactide/wood composites, providing promising insights into the structure-properties relationship of such composites.

Crystallization of Polylactic Acid with Organic Nucleating Agents under Quiescent Conditions

Polylactic acid (PLA) is a versatile and sustainable polymer used in various applications. This research explores the use of orotic acid (OA) and ethylene bis-stearamide (EBS) as nucleating agents to enhance the quiescent crystallization of PLA within the temperature range of 80 °C to 140 °C. Different blends were produced via melt processing before analyzing via DSC, XRD, and SEM. Our results show that both nucleating agents significantly accelerated the crystallization process and reduced the incubation time and the crystallization half-time. The most promising results were obtained with 1% EBS at 110 °C, achieving the fastest crystallization. The XRD analysis showed that at 80 °C, the disordered α'phase predominated, while more stable α phases formed at 110 °C and 140 °C. Combining the 1% nucleating agent and 110 °C promotes densely packed crystalline lamellae. The nucleated PLA exhibited a well-organized spherulitic morphology in agreement with the Avrami modeling of DSC data. Higher nucleating agent concentrations yielded smaller, more evenly distributed crystalline domains. Utilizing OA or EBS in PLA processing could offer enhanced properties, improved processability, and cost-efficiency, making PLA more competitive in various applications.

Enhancing the Mechanical Properties of Poly(vinyl alcohol) Fibers by Lithium Iodide Addition

The effect of lithium iodide (LiI) on the mechanical strength, properties, and molecular orientation of poly(vinyl alcohol) (PVA) fibers spun by wet spinning and then heat-stretched was studied. The stretchability of LiI-PVA fibers was improved, and the rupture during stretching was suppressed compared to PVA fibers. In addition, the tensile strength and elastic modulus of the thermally stretched fibers have been significantly improved. It was also found that the addition of LiI improves the molecular orientation of PVA. This was achieved because LiI reduced the hydrogen bonds between the molecular chains of PVA, resulting in reduced crystallinity. Most of the LiI in the fiber could be removed by a coagulation bath and washing during the spinning process. This means that LiI is eventually removed, and the heat-treatment strengthens the hydrogen bonds, resulting in excellent mechanical strength.

Effects of modified elastin-collagen matrix on the thermal and mechanical properties of Poly (lactic acid)

Poly (lactic acid) (PLA) has distinctive characteristics, including biodegradability, biocompatibility, thermal process ability, high transparency and good film-forming ability. However, PLA has some poor properties that limit its wide applicability. These properties include a low crystallization rate, poor thermal stability, and high brittleness. The main objective of this research was to investigate the effect of a modified elastin-collagen (m-ELA-COLL) matrix on the properties of PLA. The ELA-COLL matrix was extracted from broiler skin waste and modified by grafting using lactic acid monomer to facilitate compatibility with PLA. The extracted and modified ELA-COLL matrix was investigated using FTIR, and α-helix and β-sheet structures were confirmed in both cases (pre- and post-modifications). Modified elastin-collagen dispersed Poly (lactic acid) (PLA-m-ELA-COLL) blend films were prepared using the solution casting method and characterized using DSC and UTM. The effect of m-ELA-COLL as a nucleating agent resulted in the degree of crystallinity improvement of 58.8% with 10 wt% m-ELA/COLL loading, and the elongation at break was improved by 161.3% for PLA-40%-m-ELA-COLL with a tensile strength of 33.75 MPa. The results obtained revealed that the biofilms can be considered as a good candidate to be studied further in the packaging industry.

Investigating the Mechanical Properties of Annealed 3D-Printed PLA-Date Pits Composite

Biomedical applications are crucial in rehabilitation medicine, assisting individuals with disabilities. Nevertheless, materials failure can sometimes result in inconvenience for users. Polylactic Acid (PLA) is a popular 3D-printed material that offers design flexibility. However, it is limited in use because its mechanical properties are inadequate. Thus, this study introduces an artificial intelligence model that utilizes ANFIS to estimate the mechanical properties of PLA composites. The model was developed based on an actual data set collected from experiments. The experimental results were obtained by preparing samples of PLA green composites with different weight fractions of date pits, which were then annealed for varying durations to remove residual stresses resulting from 3D printing. The mechanical characteristics of the produced PLA composite specimens were measured experimentally, while the ANSYS model was established to identify the composites' load-carrying capacity. The results showed that ANFIS models are exceptionally robust and compatible and possess good predictive capabilities for estimating the hardness, strength, and Young's modulus of the 3D-printed PLA composites. The model results and experimental outcomes were nearly identical.

Additive Manufacturing Post-Processing Treatments, a Review with Emphasis on Mechanical Characteristics

Additive manufacturing (AM) comes in various types of technologies and comparing it with traditional fabrication methods provides the possibility of producing complex geometric parts directly from Computer-Aided Designs (CAD). Despite answering challenges such as poor workability and the need for tooling, the anisotropy of AM constructions is the most serious issue encountered by their application in industry. In order to enhance the microstructure and functional behavior of additively fabricated samples, post-processing treatments have gained extensive attention. The aim of this research is to provide critical, comprehensive, and objective methods, parameters and results' synthesis for post-processing treatments applied to AM builds obtained by 3D printing technologies. Different conditions for post-processing treatments adapted to AM processes were explored in this review, and demonstrated efficiency and quality enhancement of parts. Therefore, the collected results show that mechanical characteristics (stress state, bending stress, impact strength, hardness, fatigue) have undergone significant improvements for 3D composite polymers, copper-enhanced and aluminum-enhanced polymers, shape memory alloys, high-entropy alloys, and stainless steels. However, for obtaining a better mechanical performance, the research papers analyzed revealed the crucial role of related physical characteristics: crystallinity, viscosity, processability, dynamic stability, reactivity, heat deflection temperature, and microstructural structure.

Strengthening-toughening pure poly(lactic acid) with ultra-transparency through increasing mesophase promoted by elongational flow field

Poly(lactic acid) (PLA), as a biodegradable material, finds wide applications in packaging, automotive, and biological industries. However, achieving high strength, toughness, ultra-transparency, and heat resistance simultaneously in pure PLA through continuous one-step manufacturing remains a significant challenge. In this study, we addressed this challenge by utilizing the eccentric rotor extruder (ERE) in combination with cooling rolls to manufacture PLA sheets with outstanding mechanical performance. The ERE's elongational flow field combined with the cooling roller's weak stretching action induced orientation in the PLA molecular chains and promoted the formation of more mesophase, significantly improving mechanical properties. When the extrusion-stretch ratio (λ) value was 3.5, the tensile yield strength, Young's modulus, and elongation at break of ERE-fabricated samples ER-3.5 reached 86.2 MPa, 1777 MPa, and 57.9 %, respectively. Compared to the SE-3.5 samples manufactured with traditional methods, the increases were 38.8 %, 25.8 %, and 9.4 times, respectively. Additionally, the ERE manufactured samples maintained ultra-transparency and high heat resistance, making them suitable for food packaging, biomedicine, and other related fields. This methodology provides an efficient industrial-scale approach for manufacturing neat, biodegradable PLA with outstanding mechanical performance and ultra-transparency.

Experimental Study of In-Process Heat Treatment on the Mechanical Properties of 3D Printed Thermoplastic Polymer PLA

The scientific literature regarding additive manufacturing, mainly the material extrusion method, suggests that the mechanical characteristics of the parts obtained by this technology depend on a number of the input factors specific to the printing process, such as printing temperature, printing trajectory, layer height, etc., and also on the post-process operations for parts, which, unfortunately, requires supplementary setups, equipment, and multiple steps that raise the overall costs. Therefore, this paper aims to investigate the influence of the printing direction, the thickness of the deposited material layer, and the temperature of the previously deposited material layer on the part tensile strength, hardness by means of Shore D and Martens hardness, and surface finish by using an in-process annealing method. A Taguchi L9 DOE plan was developed for this purpose, where the test specimens, with dimensions according to ISO 527-2 type B, were analysed. The results showed that the presented in-process treatment method is possible and could lead to sustainable and cost-effective manufacturing processes. The varied input factors influenced all the studied parameters. Tensile strength tended to increase, up to 12.5%, when the in-process heat treatment was applied, showed a positive linear variation with nozzle diameter, and presented considerable variations with the printing direction. Shore D and Martens hardness had similar variations, and it could be observed that by applying the mentioned in-process heat treatment, the overall values tended to decrease. Printing direction had a negligible impact on the additively manufactured parts' hardness. At the same time, the nozzle diameter presented considerable variations, up to 36% for Martens hardness and 4% for Shore D, when higher diameter nozzles were used. The ANOVA analysis highlighted that the statistically significant factors were the nozzle diameter for the part's hardness and the printing direction for the tensile strength.

Poly(1,3-Propylene Glycol Citrate) as a Plasticizer for Toughness Enhancement of Poly-L-Lactic Acid

Despite the unique features of poly-L-lactic acid (PLLA), its mechanical properties, such as the elongation at break, need improvement to broaden its application scope. Herein, poly(1,3-propylene glycol citrate) (PO3GCA) was synthesized via a one-step reaction and evaluated as a plasticizer for PLLA films. Thin-film characterization of PLLA/PO3GCA films prepared via solution casting revealed that PO3GCA shows good compatibility with PLLA. The addition of PO3GCA slightly improves the thermal stability and enhances the toughness of PLLA films. In particular, the elongation at break of the PLLA/PO3GCA films with PO3GCA mass contents of 5%, 10%, 15%, and 20% increases to 172%, 209%, 230%, and 218%, respectively. Therefore, PO3GCA is promising as a plasticizer for PLLA.

Establishing a Framework for Fused Filament Fabrication Process Optimization: A Case Study with PLA Filaments

Developments in polymer 3D printing (3DP) technologies have expanded their scope beyond the rapid prototyping space into other high-value markets, including the consumer sector. Processes such as fused filament fabrication (FFF) are capable of quickly producing complex, low-cost components using a wide variety of material types, such as polylactic acid (PLA). However, FFF has seen limited scalability in functional part production partly due to the difficulty of process optimization with its complex parameter space, including material type, filament characteristics, printer conditions, and "slicer" software settings. Therefore, the aim of this study is to establish a multi-step process optimization methodology-from printer calibration to "slicer" setting adjustments to post-processing-to make FFF more accessible across material types, using PLA as a case study. The results showed filament-specific deviations in optimal print conditions, where part dimensions and tensile properties varied depending on the combination of nozzle temperature, print bed conditions, infill settings, and annealing condition. By implementing the filament-specific optimization framework established in this study beyond the scope of PLA, more efficient processing of new materials will be possible for enhanced applicability of FFF in the 3DP field.

The Effect of Heat Treatment on a 3D-Printed PLA Polymer's Mechanical Properties

Three-dimensional printing is a useful and common process in additive manufacturing nowadays. The advantage of additive polymer technology is its rapidity and design freedom. Polymer materials' mechanical properties depend on the process parameters and the chemical composition of the polymer used. Mechanical properties are very important in product applicability. The mechanical properties of polymers can be enhanced by heat treatment. Additive-manufactured PLA's mechanical properties and structure can be modified via heat treatment after the 3D printing process. The goal of this research was to test the effect of heat treatment on the mechanical and structural parameters of additive-manufactured PLA. This was achieved via the FDM processing of standard PLA tensile test specimens with longitudinal and vertical printing orientations. After printing, the test specimens were heat-treated at 55 °C, 65 °C and 80 °C for 5 h and after being held at 20 °C for 15 h. The printed and heat-treated specimens were tested using tensile tests and microscopy. Based on the test results, we can conclude that the optimal heat treatment process temperature was 65 °C for 5 h. Under the heat treatment, the test specimens did not show any deformation, the tensile strength increased by 35% and the porosity of the PLA structure decreased.

A Practical Tool for the Assessment of Polymer Biodegradability in Marine Environments Guides the Development of Truly Biodegradable Plastics

Environmental persistence is one of the few shortcomings of plastic materials. As a consequence, alternative plastics labeled as compostable are replacing polyolefins in some commercial applications, such as food bags and trash bags. A rapid, high-throughput, and environmentally relevant method to assess the potential biodegradability in marine conditions is used to assess these materials already on the market, as well as novel bio-based polymers still in development. By fitting experimental data to a non-linear logistic model, ultimate biodegradability can be calculated without regard for incubation time. Whereas the commercial products show negligible or very low marine biodegradability, one of the novel materials exceeds the 20% biodegradation threshold relative to fully marine biodegradable PHB after 28 days. In addition, the sensitivity of the method can be enhanced and its duration reduced, at the expense of labor-demanding preconditioning of the microbial inoculum, by increasing the bacterial density in the incubation vessels. In contrast, pre-exposure of the inoculum to plastic, either in laboratory or field conditions, does not enhance the performance of the test.

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.

Effect of Nucleating Agents Addition on Thermal and Mechanical Properties of Natural Fiber-Reinforced Polylactic Acid Composites

In this study, natural fiber-reinforced polylactic acid (NFRP) composite materials were prepared by adding nucleating agents (NAs) and natural fiber (NF) to compensate for the low thermal stability and brittleness of polylactic acid (PLA). The thermal stability of the fabricated composite material was investigated by differential scanning calorimetry and thermogravimetric analysis. In addition, the tensile modulus of elasticity according to the crystallinity of the composite was measured. The crystallinity of the PLA composite increased to ~700% upon the addition of the NA; thus, the thermal stability also increased. However, the changes in crystallinity and tensile modulus were insignificant when the concentration of the NA added was 4 wt.% or higher. The study demonstrates that the addition of NA and NF is effective in improving the thermal stability and mechanical properties of NFRP.

Varied Bulk Powder Properties of Micro-Sized API within Size Specifications as a Result of Particle Engineering Methods

Micronized particles are commonly used to improve the content uniformity (CU), dissolution performance, and bioavailability of active pharmaceutical ingredients (API). Different particle engineering routes have been developed to prepare micron-sized API in a specific size range to deliver desirable biopharmaceutical performance. However, such API particles still risk varying bulk powder properties critical to successful manufacturing of quality drug products due to different particle shapes, size distribution, and surface energetics, arising from the anisotropy of API crystals. In this work, we systematically investigated key bulk properties of 10 different batches of Odanacatib prepared through either jet milling or fast precipitation, all of which meet the particle size specification established to ensure equivalent biopharmaceutical performance. However, they exhibited significantly different powder properties, solid-state properties, dissolution, and tablet CU. Among the 10 batches, a directly precipitated sample exhibited overall best performance, considering tabletability, dissolution, and CU. This work highlights the measurable impact of processing route on API properties and the importance of selecting a suitable processing route for preparing fine particles with optimal properties and performance.

The Use of Nanoscale Montmorillonite (MMT) as Reinforcement for Polylactide Acid (PLA) Prepared by Fused Deposition Modeling (FDM)—Comparative Study with Biocarbon and Talc Fillers

The subject of the presented research focuses on a comparative assessment of three types of polymer fillers used to modify highly crystalline poly(lactic acid) PLA intended for the FDM technique. The aim of the presented work was to determine the performance of the developed materials. The key aspect of the work was the use of polymer fillers of three different types. Nano-sized montmorillonite (MMT), biobased biocarbon (BC) and mineral talc. The several types of composites were prepared using extrusion technique. The maximum content for BC and talc filler was limited to 20 wt%, while for MMT it was 5 wt%. Prepared samples were subjected to detailed material analysis including mechanical tests (tensile, flexural, Charpy), thermal analysis (DSC, DMTA), HDT/Vicat tests and structure analysis. The results of the test confirmed that even relatively small amount of nano-type filler can be more efficient than micrometric particles. The used type of matrix was highly crystalline PLA, which resulted in a significant nucleation effect of the crystalline structure. However, thermomechanical tests revealed no improvement in thermal resistance. Microscopic survey confirmed that for MMT and talc filler the structure anisotropy was leading to more favorable properties, especially when compared to structures based on spherical BC particles.

Controlling stereocomplex crystal morphology in poly(lactide) through chain alignment

The incorporation of poly(d-lactide) (PDLA) to form stereocomplex crystallites (SCs) within a poly(l-lactide) (PLLA) matrix is among the most effective strategies in overcoming PLLA's numerous drawbacks. However, high concentrations of PDLA (>3 wt%) are required to improve PLLA's crystallization kinetics and melt strength, which is undesirable owing to PDLA's high cost. In this study, we use chain alignment as a levier to tune stereocomplex superstructure morphology to overcome these limitations. Herein, PLLA/PDLA blends were manufactured using an environmentally friendly and low-cost single step spunbond fibrillation process, yielding microfibers stretched to diameters of 5-20 μm. During this stretching process, PLLA and PDLA chains are aligned along the flow direction. SCs subsequently formed in situ upon heating, dramatically improving crystallization kinetics, melt elasticity, and tensile performance compared with neat PLLA and non-stretched blend analogues, even with low PDLA content (<3 wt%). These improvements were attributed to topological variations in SC superstructures caused by alignment of PLLA and PDLA chains. The application of chain alignment in tuning SC superstructure morphology is ubiquitous in fibrillation processes.

Active PLA Packaging Films: Effect of Processing and the Addition of Natural Antimicrobials and Antioxidants on Physical Properties, Release Kinetics, and Compostability

The performance characteristics of polylactic acid (PLA) as an active food packaging film can be highly influenced by the incorporation of active agents (AAs) into PLA, and the type of processing technique. In this review, the effect of processing techniques and the addition of natural AAs on the properties related to PLA performance as a packaging material are summarized and described through a systematic analysis, giving new insights about the relation between processing techniques, types of AA, physical–mechanical properties, barriers, optical properties, compostability, controlled release, and functionalities in order to contribute to the progress made in designing antioxidant and antimicrobial PLA packaging films. The addition of AAs into PLA films affected their optical properties and influenced polymer chain reordering, modifying their thermal properties, functionality, and compostability in terms of the chemical nature of AAs. The mechanical and barrier performance of PLA was affected by the AA’s dispersion degree and crystallinity changes resulting from specific processing techniques. In addition, hydrophobicity and AA concentration also modified the barrier properties of PLA. The release kinetics of AAs from PLA were tuned, modifying diffusion coefficient of the AAs in terms of the different physical properties of the films that resulted from specific processing techniques. Several developments based on the incorporation of antimicrobial and antioxidant substances into PLA have displayed outstanding activities for food protection against microbial growth and oxidation.

Assessment of Petroleum-Based Plastic and Bioplastics Degradation Using Anaerobic Digestion

Bioplastics have emerged as a viable alternative to traditional petroleum-based plastic (PET). Three of the most common bioplastic polymers are polyhydroxybutyrate-valerate (PHBV), polylactide (PLA), and cellulose-based bioplastic (CBB). This study assessed biodegradation through anaerobic digestion (AD) of these three bioplastics and PET digested with food waste (FW) at mesophilic (35 °C) and thermophilic (55 °C) temperatures. The four plastic types were digested with FW in triplicate batch reactors. Additionally, two blank treatments (inoculum-only) and two PHBV treatments (with FW + inoculum and inoculum-only) were digested at 35 and 55 °C. The PHBV treatment without FW at 35 °C (PHBV-35) produced the most methane (CH4) normalized by the volatile solids (VS) of the bioplastics over the 104-day experimental period (271 mL CH4/g VS). Most bioplastics had more CH4 production than PET when normalized by digester volume or gram substrate added, with the PLA-FW-55 (5.80 m3 CH4/m3), PHBV-FW-55 (2.29 m3 CH4/m3), and PHBV-55 (4.05 m3 CH4/m3) having 848,275 and 561%, respectively, more CH4 production than the PET treatment. The scanning electron microscopy (SEM) showed full degradation of PHBV pellets after AD. The results show that when PHBV is used as bioplastic, it can be degraded with energy production through AD.

Extrusion and Injection Molding of Poly(3-Hydroxybutyrate-co-3-Hydroxyhexanoate) (PHBHHx): Influence of Processing Conditions on Mechanical Properties and Microstructure

Biobased and biodegradable polyhydroxyalkanoates (PHAs) have great potential as sustainable packaging materials. However, improvements in their processing and mechanical properties are necessary. In this work, the influence of melt processing conditions on the mechanical properties and microstructure of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) is examined using a full factorial design of experiments (DoE) approach. We have found that strict control over processing temperature, mold temperature, screw speed, and cooling time leads to highly increased elongation at break values, mainly under influence of higher mold temperatures at 80 °C. Increased elongation of the moldings is attributed to relaxation and decreased orientation of the polymer chains together with a homogeneous microstructure at slower cooling rates. Based on the statistically substantiated models to determine the optimal processing conditions and their effects on microstructure variation and mechanical properties of PHBHHx samples, we conclude that optimizing the processing of this biopolymer can improve the applicability of the material and extend its scope in the realm of flexible packaging applications.

Characterisation and Modelling of PLA Filaments and Evolution with Time

The properties of polylactic acid (PLA) filaments have not yet been analysed in detail, and they are strongly affected by the extrusion process used in some additive manufacturing systems. Here we present the mechanical, thermal, physical, and fractographical properties of an extruded filament (not the bulk material or scaffolds), the basic building block of any PLA structure printed via material extrusion. This research aims to create a reference point for the modelisation of additively manufactured structures via extrusion processes, as the main building block is characterised in detail for a deep understanding. Furthermore, we investigated the natural ageing (up to one year), the effect of the printing (extruding) temperature (180 and 190 °C), and the effect of the crosshead speed during the tensile tests (10⁻¹ to 10² mm/min) to provide a deeper analysis of the material. The results showed that the material extruded at 190 °C performed better than the material extruded at 180 °C. However, after one hundred days of natural ageing, both materials behaved similarly. This was related to the flow-induced molecular orientation during the extrusion. The crosshead rate produced a logarithmic increase of the mechanical properties, consistent with the Eyring model. Additionally, the ageing produced significant changes in both the elastic modulus and the yield strength: from 2.4 GPa and 40 MPa, in one-day-aged samples, up to 4 GPa and 62 MPa once entirely aged. Finally, it was observed that the glass transition and the enthalpic relaxation increased with ageing, agreeing with the Kohlraushch–William–Watts model.

The Blending of Poly(glycolic acid) with Polycaprolactone and Poly(l-lactide): Promising Combinations

Poly(glycolic acid) (PGA) holds unique properties, including high gas barrier properties, high tensile strength, high resistance to common organic solvents, high heat distortion temperature, high stiffness, as well as fast biodegradability and compostability. Nevertheless, this polymer has not been exploited at a large scale due to its relatively high production cost. As such, the combination of PGA with other bioplastics on one hand could reduce the material final cost and on the other disclose new properties while maintaining its “green” features. With this in mind, in this work, PGA was combined with two of the most widely applied bioplastics, namely poly(l-lactide) (PLLA) and poycaprolactone (PCL), using the melt blending technique, which is an easily scalable method. FE-SEM measurements demonstrated the formation of PGA domains whose dimensions depended on the polymer matrix and which turned out to decrease by diminishing the PGA content in the mixture. Although there was scarce compatibility between the blend components, interestingly, PGA was found to affect both the thermal properties and the degradation behavior of the polymer matrices. In particular, concerning the latter property, the presence of PGA in the blends turned out to accelerate the hydrolysis process, particularly in the case of the PLLA-based systems.

Effect of heat treatment on mechanical properties of 3D printed PLA

Polylactic acid (PLA) is one of the predominant filaments used in the process of 3D printing which is a type of Additive Manufacturing (AM) technology in which a printer prints the semi-molten filament on the bed, layer by layer forming a part of the desired dimension. The final 3D printed parts generally have lower mechanical properties than conventional manufacturing techniques such as injection moulding. The primary reasons for the comparatively poor mechanical property are the poor formation of bonds between inter-filaments and the residual thermal stresses induced due to the temperature difference while 3D printing the filament. Heat treatment of the 3D printed part can significantly reduce the internal stresses developed during the process of printing and also improve the formation of bonds between inter-filaments. The mechanical properties of the PLA, particularly tensile properties can be enhanced to about 80% by heat treating to about 100 °C for 4 h. Heat distortion temperature (HDT) test is used to analyze the heat resistance of the specimens. HDT test also showed an improvement of the heat resistance of heat-treated parts compared to the non-heat treated of about 73%. There is a significant improvement in the mechanical properties just by heat-treating the 3D printing parts compared to the parts that were not heat treated.

Effect of Basalt Powder Surface Treatments on Mechanical and Processing Properties of Polylactide-Based Composites

Legislative restrictions and the needs of consumers have created a demand for sustainable materials. Polylactide (PLA) is a biodegradable polyester with advantageous mechanical properties, however, due to its low crystallization rate, it also has low thermomechanical stability. Its range of application temperatures can be widened using nucleating agents and fillers including basalt powder (BP), a waste product from the mining industry. This study analyzed the possibility of enhancing the properties of a PLA-BP composite by chemically treating the filler. Basalt powder was subjected to silanization with 3-aminopropyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane and mixed with PLA at 5-20 wt%. The nucleating effect of a potassium salt of 3,5-bis(methoxycarbonyl) (LAK-301) in the silanized composite was also evaluated. The properties of the materials with silanized BP were compared with the unmodified basalt powder. The miscibility of the filler and the polymer was assessed by oscillatory rheometry. The structure of the composites was studied using scanning electron microscopy and their thermomechanical properties were analyzed using dynamic mechanical thermal analysis. Mechanical properties such as tensile strength, hardness and impact strength, and heat deflection temperature of the materials were also determined. It was concluded that BP-filled nucleated PLA composites presented satisfactory thermomechanical stability without silanization, but chemical treatment could improve the matrix-filler interactions.

Synergistic Effect of Cellulose Nanofiber and Nanoclay as Distributed Phase in a Polypropylene Based Nanocomposite System

Since the plastic-based multilayer films applied to food packaging are not recyclable, it is necessary to develop easily recyclable single materials. Herein, polypropylene (PP)-based cellulose nanofiber (CNF)/nanoclay nanocomposites were prepared by melt-mixing using a fixed CNF content of 1 wt %, while the nanoclay content varied from 1 to 5 wt %. The optimum nanoclay content in the PP matrix was found to be 3 wt % (PCN3), while they exhibited synergistic effects as a nucleating agent. PCN3 exhibited the best mechanical properties, and the tensile and flexural moduli were improved by 51% and 26%, respectively, compared to PP. In addition, the oxygen permeability was reduced by 28%, while maintaining the excellent water vapor permeability of PP. The improvement in the mechanical and barrier properties of PP through the production of PP/CNF/nanoclay hybrid nanocomposites suggested their possible application in the field of food packaging.

Gas Transport Phenomena and Polymer Dynamics in PHB/PLA Blend Films as Potential Packaging Materials

Actually, in order to replace traditional fossil-based polymers, many efforts are devoted to the design and development of new and high-performance bioplastics materials. Poly(hydroxy alkanoates) (PHA_S) as well as polylactides are the main candidates as naturally derived polymers. The intention of the present study is to manufacture fully bio-based blends based on two polyesters: poly (3-hydroxybutyrate) (PHB) and polylactic acid (PLA) as real competitors that could be used to replace petrol polymers in packaging industry. Blends in the shape of films have been prepared by chloroform solvent cast solution methodology, at different PHB/PLA ratios: 1/0, 1/9, 3/7, 5/5, 0/1. A series of dynamic explorations have been performed in order to characterize them from a different point of view. Gas permeability to N₂, O₂, and CO₂ gases and probe (TEMPO) electron spin resonance (ESR) analyses were performed. Blend surface morphology has been evaluated by Scanning Electron Microscopy (SEM) while their thermal behavior was analyzed by Differential Scanning Calorimetry (DSC) technique. Special attention was devoted to color and transparency estimation. Both probe rotation mobility and N₂, O₂, and CO₂ permeation have monotonically decreased during the transition from PLA to PHB, for all contents of bio-blends, namely because of transferring from PLA with lower crystallinity to PHB with a higher one. Consequently, the role of the crystallinity was elucidated. The temperature dependences for CO₂ permeability and diffusivity as well as for probe correlation time allowed the authors to evaluate the activation energy of both processes. The values of gas transport energy activation and TEMPO rotation mobility are substantially close to each other, which should testify that polymer segmental mobility determines the gas permeability modality.