Polylactide Matrix Research Articles

FTIR Spectroscopy Analysis of PLA Biocomposites Reinforced with Hemp Fibers

In this study, Fourier-transform infrared spectroscopy (FTIR) of polylactide (PLA) biocomposites reinforced with hemp fibers were analyzed. Three samples of biocomposites with different proportions of hemp fibers in the PLA matrix were compared. Hemp and PLA fibers in biocomposite were evenly blended using carding technology. Samples before and after water absorption were compared using scanning electron microscopy (SEM). Thermoset treated polylactide and hemp fiber biocomposites have high mechanical properties, that allow to reduce the number of materials in the product. The developed biocomposite can be used as a slab material and for molded parts of furniture, etc.

Significant enhancement of notched Izod impact strength of PLA-based blends through encapsulating PA11 particles of low amounts by EGMA elastomer

The binary blend of polylactide (PLA) and ethylene–acrylic ester-glycidyl methacrylate random terpolymer (EGMA) at the mass ratio of 80/20 possessed the notched Izod impact strength of 10 KJ/m2, much lower than an ideal value for a supertoughened PLA-based material. It was surprising to find in this study that supertoughened PLA-based blends could be easily obtained simply by adding a biomass polymer, polyamide-11 (PA11) of just very low amounts into the PLA/EGMA 80/20 blend during its late mixing stage. The PLA/EGMA/PA11 80/20/1 and 80/20/5 ternary blends showed the notched Izod impact strength of 31 and 61 KJ/m2, about 3 and 6 times of that of PLA/EGMA 80/20 blend, and about 16 and 48 times of that of neat PLA (1.9 KJ/m2), respectively. Various available measurements including differential scanning calorimetry, dynamic mechanical analysis, contact angle, transmission electron microscopy and scanning electron microscopy were taken to explore the possible toughening mechanisms. It was finally found that the formation of PA11-EGMA core–shell complex phase domains, dispersed in PLA matrix due to encapsulation of PA11 by EGMA component played a crucial role on significant enhancement of notched Izod impact strength for PLA/PA11/EGMA ternary blends.

Polyphosphoramide-intercalated MXene for simultaneously enhancing thermal stability, flame retardancy and mechanical properties of polylactide

The creation of thermostable, flame-retardant, mechanically robust bioplastics is highly desirable in the industry as one sustainable alternative to traditional petroleum-based plastics. Unfortunately, to date there lacks an effective strategy to endow commercial bioplastics, such as polylactide (PLA) with such desired integrated performances. Herein, we have demonstrated the fabrication of a novel MXene-phenyl phosphonic diaminohexane (MXene-PPDA) nanohybrid via the intercalation of PPDA into the MXene interlayer. The interlayer spacing of MXene nanosheets is enlarged and as-prepared MXene-PPDA is homogeneously dispersed in the PLA matrix. Incorporating 1.0 wt% MXene-PPDA enables PLA to achieve a UL-94 V-0 rating, with a ~22.2% reduction in peak heat release rate, indicating a significantly improved flame retardancy. Meanwhile, the 1.0 wt% MXene-PPDA also increases the initial decomposition temperature of PLA composite, giving rise to a ~25-fold enhancement in char yield relative to pure PLA. Additionally, the MXene-PPDA enhances the toughness while retains the mechanical strength for PLA. This work offers an innovative strategy for the design of multifunctional additives and the creation of high-performance polymers with high thermal stability, mechanical robustness and low flammability, expecting to find many practical applications in the industry.

Effects of molecular weight and crystallizability of polylactide on the cellulose nanocrystal dispersion quality in their nanocomposites

This study investigated how cellulose nanocrystals (CNC) dispersion quality and its percolation network formation could be influenced when using polylactide (PLA) with various molecular weights and crystallizability. In this context, systematic rheological experiments were conducted on PLA/CNC nanocomposites prepared through solution casting method using dimethylformamide (DMF) as the solvent. It was found that lower CNC percolation concentrations could be obtained when a PLA matrix possesses lower molecular weight as the shorter chains and CNCs interpenetration could be facilitated during their dissolution in the solvent. On the other hand, the CNC percolation concentration was further lowered when the PLA with higher crystallizability was used. During the solvent evaporation step that occurred at 85 °C, the isothermal heterogeneous crystallization of PLA around the dispersed CNCs could prevent the driving force of the CNCs towards their re-agglomeration. Therefore, the finest CNC dispersion was appeared in the highly crystallizable low molecular weight PLA through which the rheological properties were dramatically improved and the thermal stability was significantly extended to higher temperatures. The crystallization behavior of the prepared nanocomposites was also analyzed using differential scanning calorimeter and X-ray diffractometer. The thermal degradation behavior of the PLA/CNC nanocomposites were examined through thermogravimetric and rheological analysis.

Highly biodegradable, ductile all-polylactide blends

All-PLA blends have been fabricated by an easily scalable and green melt-blending of linear-PLLA and 3-armed star-shaped PDLLA at different proportions (100:0, 95:5, 90:10, 80:20, and 50:50, w:w). The fabrication process, carried out in a hot-press, consisted of three steps: an initial heating of the thoroughly blended polymer mixtures at 170 °C for 5 min, a second heating at 170 °C for 5 min with a pressure of 200 Pa, and a final cooling at room temperature during 20 min keeping the same pressure. This methodology resulted in very homogenous amorphous samples, as revealed by XRD and DSC. The incorporation of star-PDLLA toughened the polylactide matrix by a clear ductilization, opening opportunities for the expanded use of the developed blends in different applications, due to their increased processability. DSC analysis revealed indeed that by increasing star-PDLLA content it is possible to gradually reduce the Tg, as well as the capability of crystallization of the linear-PLLA component. Such properties determine a plasticizing effect on the final blends. The increased content of the star component turned the films from transparent to translucent and decreases the thermal decomposition temperatures, which remain in any case very well above room temperature. The water vapor transmission rates varied with the star-PDLLA content between values characteristic for isolating to breathable films, thus allowing the use of these blends in different applications such as food packaging and biomedical devices. Finally, no important changes of water contact angle and water uptake were observed between the different blends. Despite the negligible effect of seawater on the biodegradation of commercial PLA, star-PDLLA-containing blends showed high biodegradation rates at short-times in marine environments, reinforcing the environmentally friendly character of polylactide.

Investigation into hydroxypropyl-methylcellulose-reinforced polylactide composites for fused deposition modelling

Polylactide (PLA) is an aliphatic polyester biopolymer that can be derived from renewable agricultural products, such as corn, potatoes, rice, tapioca, and cane sugar. In this study, hydroxypropyl methylcellulose (HPMC)/PLA composite filaments with up to 7 % HPMC were prepared and used to produce parts via fused deposition modelling (FDM). The effect of the HPMC content on the microstructure, chemical structure, thermal properties, mechanical properties, and water contact angle (CA) was investigated. A uniform dispersion of HPMC within the PLA matrix was obtained. The incorporation of HPMC had no effect on the PLA chemical structure. Additionally, the cold crystallisation temperature decreased from 111 °C for the neat PLA filament to 104 °C for the composite filament with 7 % HPMC. The strengths of the composite filaments with 5 % and 7 % HPMC (51 MPa and 49 MPa, respectively) were maintained at a level comparable to that of their neat PLA counterpart (53 MPa). However, the tensile and impact strengths of the printed samples both decreased with the addition of HPMC, owing to the increased porosity. The hydrophilicity of the composites was significantly enhanced with the addition of HPMC, and the water contact angle of the sample with 7 % HPMC was reduced by approximately 30°.This work represents a step towards a simple but promising way to prepare biocompatible HPMC/PLA composites for FDM.

Recently Progress on Polylactide/Nanocellulose Nanocomposites

The development of renewable resources is a trend in the future. Polylactide (PLA), as one member of bio-polymers, has obtained a widely focus in industry and academy because of its renewability, biodegradability, biocompatibility and good thermomechanical properties. PLA is used in a wide variety of applications such as biomedical, food packaging, electrical and electronic equipment, and the automotive industry. However, PLA still has some shortcomings, such as lower heat distortion temperature, slower crystallization rate, lower thermal resistance, etc. These shortcomings also limit the further widespread use of PLA. One effective method to expand and improve these properties of PLA is adding nanofillers. This review summarizes and describes the role of nanocellulose as a filler in the modification of PLA matrix and some of the problems faced.

Study of polylactide matrices using x-ray microtomography

Three-dimensional matrices of biodegradable polymers are promising materials for regenerative medicine. They are widely used in restoring the integrity and functions of tissues and organs using bio-artificial tissue engineering structures. We present the results of studying the structure of porous bioresorbable polymer matrices for tissue engineering using X-ray microtomography. Samples were obtained by supercritical fluid plasticization of D,L-polylactide with subsequent foaming in cylindrical molds. The tomographic method makes it possible to construct a three-dimensional voxel model of the object under study and gain apart from the estimate on the integral matrix porosity (characteristic data obtained by traditional sorption procedures) additional information about the size and spatial distribution of pores thus providing a possibility of optimization of the process parameters for production of polylactide matrices required for specific biomedical applications of architectonics, as well as forecasting the processes of their bioresorption in enzymatic media. The experiments were carried out on a laboratory microtomograph (Mo anode, the scan time of the sample is 120 min, the detector pixel size is 9 μm). Tomographic reconstruction was performed by algebraic method. The binarization procedure required for calculation of the structural characteristics of studied matrices was implemented by the method with the choice of a global threshold. Calculations of the porosity and homogeneity of the porosity distribution in the bulk, as well as estimation of the specific surface area of pores revealed the isotropy of the spatial structure of polylactide matrices.

Valorization of Linen Processing By-Products for the Development of Injection-Molded Green Composite Pieces of Polylactide with Improved Performance

This work reports the development and characterization of green composites based on polylactide (PLA) containing fillers and additives obtained from by-products or waste-streams from the linen processing industry. Flaxseed flour (FSF) was first produced by the mechanical milling of golden flaxseeds. The resultant FSF particles were melt-compounded at 30 wt% with PLA in a twin-screw extruder. Two multi-functionalized oils derived from linseed, namely epoxidized linseed oil (ELO) and maleinized linseed oil (MLO), were also incorporated during melt mixing at 2.5 and 5 parts per hundred resin (phr) of composite. The melt-compounded pellets were thereafter shaped into pieces by injection molding and characterized. Results showed that the addition of both multi-functionalized linseed oils successfully increased ductility, toughness, and thermal stability of the green composite pieces whereas water diffusion was reduced. The improvement achieved was related to both a plasticizing effect and, more interestingly, an enhancement of the interfacial adhesion between the biopolymer and the lignocellulosic particles by the reactive vegetable oils. The most optimal performance was attained for the MLO-containing green composite pieces, even at the lowest content, which was ascribed to the higher solubility of MLO with the PLA matrix. Therefore, the present study demonstrates the potential use of by-products or waste from flax (Linum usitatissimum L.) to obtain renewable raw materials of suitable quality to develop green composites with high performance for market applications such as rigid food packaging and food-contact disposable articles in the frame of the Circular Economy and Bioeconomy.

Multifunctional biodegradable polymer/clay nanocomposites with antibacterial properties in drug delivery systems

The aim of this study was to investigate the possibility of intercalation of gentamicin and neomycin in montmorillonite (MMT) nanofillers, as well as to study the in vitro antimicrobial properties of nanocomposite films containing a small amount of thus obtained nanofillers. The polylactide matrix (PLA) nanocomposite films with drug-intercalated montmorillonite fillers were obtained by casting after intercalation of drugs in aqueous solutions. The efficiency of intercalation has been confirmed by X-ray diffraction (XRD) and Zeta potential measurements. The materials were studied for surface wettability, roughness and mechanical properties during 6 weeks of incubation in phosphate buffer saline, and their bactericidal activity was tested against Escherichia coli bacteria before and after 6 weeks of incubation in distilled water at 37 °C. The presence of antibiotics during the incubation was monitored by conductivity and pH measurements. The results indicate that nanocomposite polylactide films with montmorillonite filler intercalated with gentamicin and neomycin tend to degrade faster that their counterparts with non-intercalated fillers, which affects their mechanical properties. However, drug intercalation provided an antibacterial activity, which was confirmed by the presence of zones inhibiting the growth of Gram-negative bacteria for both antibiotics. It was also confirmed that the interaction of antibiotics with clay and polymer matrix did not adversely affect this bactericidal effect. Montmorillonite can be successfully intercalated with both gentamicin and neomycin, and then used as active filler for polylactide films having very good antibacterial properties, therefore their use in biomedical applications can be significantly expanded.

Study of the addition of the hybrid sisal fibers on the dynamic mechanical property of SFs reinforced polylactic acid (PLA) composites

When sisal fiber (SF) is added into polylactide (PLA) matrix, the storage modulus of PLA/SF composites increases greatly which indicate the rigidity of the composite material increases obviously. Comparing PLA composites with pure PLA, it can be found that the glass transition temperature (Tg) of PLA composites is significantly higher than that of PLA which showed the heat resistance of the PLA composites can be improved obviously because of the addition of SFs in PLA matrix. The energy storage modulus of PLA/HSFs is the highest of all PLA composites. HSFs could improve the dynamic mechanical properties of PLA composites more significantly than ASFs and USFs.

Ductility improvements of PLA-based binary and ternary blends with controlled morphology using PBAT, PBSA, and nanoclay

In this study, binary and ternary immiscible blends of polylactide (PLA) with poly[(butylene adipate)-co-terephthalate] (PBAT) and poly[(butylene succinate)-co-adipate] (PBSA) were prepared through an injection-molding (IM) process. Blend nanocomposites of PLA/PBAT/nanoclay were also prepared using a twin-screw extruder (TSE) followed by IM. An amorphous PLA (A-PLA), a semicrystalline PLA (SC-PLA), and their mixture were used as the matrix to investigate the matrix crystallization effect on blend morphology evolution and ductility enhancements. The results showed that in PLA/PBAT blends with 75/25 wt ratio, the increase in PLA crystallization capability caused finer and more homogenous blend morphology and hence the ductility increased significantly from around 5% to ~205%. In contrast, the ductility enhancements of co-continuous PLA/PBAT blends with 50/50 wt ratio became more profound when the PLA matrix was more amorphous. In PLA/PBSA blends, however, no ductility improvement was observed as the vitrification of PLA could hinder the PBSA crystallization which resulted in a non-uniform blend structure. In ternary blends, a matrix-core shell morphology was obtained and led to the improvements of the flexural strength and modulus. The use of nanoclay also significantly promoted the ductility of PLA/PBAT blends with 75/25 wt ratio, specifically in blends with A-PLA.

Thermal and mechanical properties of biodegradable composites with nanometric cellulose

These days, biodegradable polymers, due to their biocompatibility and biodegradability, gain much interest. They have significantly contributed to the development of new materials that can be used in packaging industry, medicine, and agriculture. Particularly, composites made of biodegradable polymers and renewable fillers are of great interest. In this work, two polymorphic forms of cellulose, differing also in terms of particle sizes, were used as fillers for polylactide (PLA). Composites were prepared by solvent casting method and then subjected to numerous tests. Wide-angle X-ray scattering, differential scanning calorimetry, and optical microscopy techniques were applied to define supermolecular structure of functional PLA/cellulose composites, crystallization parameters, as well as to observe phase transitions. Moreover, mechanical tests were carried out to assess the effect of polymorphic forms of cellulose on mechanical properties of composite materials. Polarization microscopy studies revealed that only cellulose I exhibits an ability to generate transcrystalline structures in the PLA matrix. Results of mechanical tests and thermogravimetric analysis showed a significant influence of particle size and polymorphic structure of cellulose on the tensile properties and thermostability of composites.

Composites based on polylactide and manganese (III) tetraphenylporphyrin. Influence of concentration on the structure and properties

The bactericidal action of porphyrin has a very promising potential for medical applications. Therefore, composite materials based on L-Polylactide and manganese (III) chloride tetraphenylporphyrin were prepared. The aim of this work was to study the effects of the concentration of tetraphenylporphyrin on the structural features and mechanical properties of these composites. The concentration of the filler in the composites was in the range of 0.1–2 wt%. The sizes of the tetraphenylporphyrin microinclusions (15–40 μm) were determined using optical microscopy. It was found that the phase transition temperatures of polylactide in the presence of tetraphenylporphyrin varied by 1–2 °C, and the crystallinity degree increased by 4–5% in the composites compared with the pure polylactide. Using the method of electron paramagnetic resonance at 70 °C, an increase in the segmental mobility of the polymer matrix was detected as the tetraphenylporphyrin concentration in the composites was increased. The addition of manganese (III) chloride tetraphenylporphyrin complex microinclusions in the composites slightly enhanced the tensile strength and elongation at break of the polylactide matrix. Thus, the effects of the porphyrin manganese complex on the polylactide matrix and the properties of the composites were shown.

The fabrication of polylactide/cellulose nanocomposites with enhanced crystallization and mechanical properties

Polylactide/cellulose nanocomposites were fabricated by blending of commercial polylactide (PLA) and modified cellulose nanocrystals (CNCs). Modified CNCs were prepared via the in situ polymerization of CNCs and L-lactic acid (CNCs-PLLA) or D-lactic acid (CNCs-PDLA). The actual occurrence of chemical bond between CNCs and PLA segment was confirmed by Fourier transform infrared, nuclear magnetic resonance, X-ray diffraction and solubility tests. Differential scanning calorimetry and X-ray diffraction characterization indicated that CNCs-PDLA better improved the crystallization ability of PLA matrix compared with CNCs-PLLA. Furthermore, compared with the neat PLA (60.0 MPa), the tensile strength of resulting nanocomposites showed an enhancement of up to 36% (81.65 MPa). And the nanocomposites with CNCs-PDLA exhibited both high crystallinity and improved mechanical properties.

Hydrogen bonding assisted toughness enhancement of poly(lactide) blended with a bio-based polyamide elastomer of extremely low amounts

A sustainable bio-based polyamide copolymer elastomer (PUDA-co-BUDA) was used to blend with polylactide (PLA) for the toughness enhancement purpose. Surprisingly, by adding only 1 wt% PUDA-co-BUDA, the PLA/PUDA-co-BUDA 99/1 blend exhibited a high elongation at break at 195%, which is about 23 times longer than that for neat PLA. By adding PUDA-co-BUDA of extremely low amounts (not exceeding 5 wt%), the elongation at break and tensile toughness values of PLA/PUDA-co-BUDA blends were significantly enhanced as compared with that of neat PLA, while certain transparency was kept. The nice aspect was that for these blends the Young's modulus and yield strength values remained above 1.0 GPa and 50 MPa, respectively. Torque analysis and FTIR spectra demonstrated the absence of reactive reactions during melt blending and the formation of hydrogen bonding between PLA and PUDA-co-BUDA components, respectively. Hydrogen bonding assisted homogeneous dispersion of plenty of PUDA-co-BUDA phase domains with micrometer sizes less than 2.0 μm in the PLA matrix. The sustainable bio-based polyamide copolymer elastomer showed a potential ability to toughen PLA due to hydrogen bonding interaction, which might provide an economical and effective prospect in the biomedical, packaging, and automotive applications for PLA materials.

Electrospun submicron NiO fibers combined with nanosized carbon black as reinforcement for multi-functional poly(lactic acid) composites

From the point of designing fiber reinforced multi-functional polymer composites, porous submicron nickel oxide (NiO) fibers were fabricated via electrospinning and subsequent pyrolysis process. Combined with nanosized carbon black (CB), the influences of NiO fibers on the mechanical properties and flame retardancy of polylactide (PLA) composites were investigated. The results showed the electrospun NiO fibers imparted higher tensile strength and modulus to PLA composites. With the increase of NiO fiber content in PLA composites, the Young’s modulus, storage modulus from dynamic mechanical analysis and elastic modulus derived from nanoindentation test showed similar increasing trends. In addition, compared with commercial NiO particles, NiO fibers exhibited a better flame retardant effect, which was attributed to the formation of continuous and intact char layer network. The proposed combination of electrospun NiO fibers and nanosized CB in PLA matrix is expected to inspire new strategies to prepare multi-functional fiber reinforced polymer matrix composites.

Nanofibrillar Green Composites of Polylactide/Polyhydroxyalkanoate Produced in Situ Due to Shear Induced Crystallization.

This study addresses the new concept of in situ inducing fibrillar morphology (micro or nanofibrils) of a minority component based on the simultaneous occurrence of orientation and shear induced crystallization of polymer fibers directly at the stage of extrusion in a single step. This possibility is demonstrated by using two entirely bio-sourced polymers: polylactide (PLA) and polyhydroxyalkanoate (PHA) as components. The shear induced crystallization allowed crystallization of PHA nanofibers immediately after applying high shear rate and elongation strain, avoiding subsequent cooling to initiate crystallization. Shearing of PHA increased non-isothermal crystallization temperature by 50 °C and decreased the temperature range in which the transition from a molten state to a crystallized one occurs by 17 °C. SEM observations demonstrate the successful transformation of the dispersed PHA phase into nanofibrils with diameters of nearly 200 nm. The transition from the droplets of PHA to fibers causes the brittle-to-ductile transition of the PLA matrix at a low concentration of PHA and contributes to the simultaneous increase of its rigidity and strength.

Morphology and mechanical properties of polylactide/montmorillonite composites

In this study, polylactide (PLA)/montmorillonite (MMT) composites were prepared by melt intercalation technique. Three types of MMT, Cloisite® 30B, Cloisite® Na+ and Cloisite® Ca++DEV were used as fillers. The morphology and mechanical properties of the composite materials were investigated and compared with unfilled PLA, keeping the same thermomechanical history. The morphology of the composite materials was evaluated by small-angle x-ray scattering (SAXS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the tensile properties of these composites were measured by an Instron universal testing machine. The morphology observations showed that the good affinity between the organo-modified clay (Cloisite® 30B) and the PLA was sufficient to form intercalated structure in the nanocomposite. Cloisite® Na+ and Cloisite® Ca++ DEV clays exhibited a modest improvement of the young’s modulus of about 18 % and 17 % respectively, due to poor dispersion in the PLA matrix as well as poor polymer-filler interactions compared to Cloisite® 30B. Compared to those of pure PLA, the PLA/Cloisite® 30B composites showed notable improvement of the Young’s modulus of about 54 %.

Novel platform for visualization monitoring of hydrolytic degradation of bio-degradable polymers based on aggregation-induced emission (AIE) technique

Although lots of works have been done on the hydrolysis of synthetic biodegradable polymers, the methods for monitoring the degradation process still suffer from some disadvantages, especially in terms of detection speed and non-invasive manners. In this work, a fast, non-invasive visualization monitoring platform was developed for hydrolytic degradation of bio-degradable polymers based on aggregation-induced emission (AIE) technique. We synthesized and introduced an amphiphilic AIE probe to the commercial polylactide (PLA) matrix through a simple co-precipitation process. Amphiphilic AIE probes gradually entered the aqueous media during the hydrolytic degradation process of PLA matrix, which exhibited fluorescence evolution. The variation of fluorescence emission corresponding to the evolution of PLA mass loss could be easily observed by naked eyes. Compared to traditional characterization techniques based on mass loss and molar mass measurements by sampling, this method is sensitive, fast and non-invasive, and has the potential to become a standard method for commercial bio-degradable product testing.