Polylactide Composites Research Articles

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.

Preparation and characterization of poly(lactic acid) composites involving aromatic diboronic acid and organically modified montmorillonite

In this study, composites of polylactide, PLA, involving 1, 2 and 3 mass% 1,4-benzene diboronic acid, BDBA, in the absence and presence of 3 mass% organically modified montmorillonite, Cloisite 30B, C30B, were prepared and characterized. Homogenous dispersion for the composites involving only 1 mass% BDBA and agglomeration for the ones with higher BDBA content were observed. For the composites involving nanoclay, mainly intercalated dispersion was detected. Both TGA and DP-MS results indicated a decrease in thermal stability upon the addition of 1 mass% BDBA. However, as the amount of BDBA incorporated into PLA matrix was increased, thermal stability was also increased. Trans-esterification reactions between BDBA and PLA, although caused decomposition of PLA chains at low concentrations of BDBA to a certain extent, at high concentrations generated a cross-linked structure increasing thermal stability. In the presence of C30B, thermal stability of the composites was increased further. This behavior was associated with enhanced interactions of BDBA and PLA upon diffusion into clay layers.

Thermomechanical and viscoelastic properties of green composites of PLA using chitin micro-particles as fillers

Many thermoplastic biocomposites made with non-biodegradable polymers as a matrix polymer are not biodegradable. In this work, biodegradable polylactide (PLA)/chitin micro-particle composites were successfully prepared by melt blending without using any compatibilizer or processing aid. The effects of the addition of chitin micro-particles to PLA on its thermal stability, physicomechanical properties and microstructures were evaluated by thermo-gravimetric analysis, dynamic mechanical thermal analysis, differential scanning calorimetry, tensile strength measurement, and scanning electron microscopy. It was found that the addition of chitin micro-particle to PLA increased the stiffness, tensile strength, and hydrophobicity of PLA but negatively affected its thermal properties and elongation. The tensile strength exhibited by the pristine PLA was 41.5 MPa, which increased to 48.5 for the chitin loading of 3% but a further increase in the chitin loading resulted in a reduction in tensile strength. The increase in chitin loading resulted in an increase in stiffness of PLA as the storage modulus increased from 3.21 GPa for the neat PLA to 3.48 GPa for the PLA loaded with 3% chitin microparticles. The results show that chitin can be used for the reinforcement and also to enhance the moisture barrier properties of PLA.

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.

Pretreatment of Microfibrillated Cellulose on Polylactide Composites

Microfibrillated cellulose (MFC) in polymer has attracted increasing applications with the fully bioderived nanocomposites. Polymer composites from polylactide (PLA) and MFC were prepared using two different fiber preparations. Freezedried MFC was prepared and directly mixed with PLA in an internal mixer. The MFC premixed with PLA in an organic solvent was prepared, followed by an internal mixer for another composite. In addition, grafting cellulose on PLA using a compatibilizer was performed. In this research, composites containing 10 wt% MFC were used to investigate the influence of processing and compatibilizer on the mechanical and thermal properties. The processing procedure had a great influence on the mechanical and physical properties. The tensile strength was increased with filler loading and showed different values depending on the premixing step prior to processing. The storage modulus and loss tangent confirmed that the compatibilizer acted as the role of a bridge between filler and matrix, enhancing the mechanical properties. This experiment was conducted to compare the effect of pretreatment on the change of mechanical and thermal properties by using freeze-dried cellulose and cellulose suspension substituted with an organic solvent.

Simultaneous improvement of mechanical properties and electromagnetic interference shielding performance in eco-friendly polylactide composites via reactive blending and MWCNTs induced morphological optimization

Poly (l-lactide) (PLLA) based ternary nanocomposites were fabricated by introducing in situ crosslinked poly(ethylene glycol) diacrylate (CPEGDA) as the rubbery toughening modifier and multiwall carbon nanotubes (MWCNTs) as the conductive fillers. Due to the incorporation of MWCNTs, the domain size of CPEGDA became smaller and MWCNTs were selectively distributed in PLLA continuous phase, facilitating to balance the stiffness and toughness. Rheological investigation showed that the formation of a double network of CPEGDA and MWCNTs resulted in constrained molecular mobility, thus greatly increasing the modulus and viscosity at low frequencies and long-time relaxation strength. The low percolation threshold of MWCNTs in electrical conductivity was found to be 0.19 vol% and the electromagnetic interference shielding effectiveness (EMI SE) of 26.4 dB was achieved with incorporating 2.4 vol% of MWCNTs. This work could provide a novel way to fabricate PLLA based eco-friendly nanocomposites with simultaneous superior mechanical properties and excellent EMI shielding performance.

Accelerated Weathering of Polylactide-Based Composites Filled with Linseed Cake: The Influence of Time and Oil Content within the Filler.

This paper presents the effects of accelerated weathering on the properties of polylactide (PLA) composites filled with linseed cake. The particle-shaped waste filler with different linseed oil content (0.9–39.8 wt %) was incorporated with constant amount of 10 wt % to a polymeric matrix and subjected to accelerated weathering tests with different exposition times. The structure of the composites, their mechanical, thermal, and thermo-mechanical properties were evaluated by means of scanning electron microscopy, tensile test, dynamic mechanical thermal analysis, and differential scanning calorimetry prior to and after weathering. The results of the measurements were analyzed in reference to the amount of crude oil contained in the filler. The behavior of the multiphase composite during weathering was described. It was found that the oil-rich samples during the first stage of the process showed increased resistance to hydrolytic degradation due to their relatively high crystallinity. The presence of water and elevated temperatures caused swelling of the filler and cracking of the polymeric matrix. Those discontinuities enabled the plasticizing oil to be rinsed out of the composite and thus water penetrated into the samples. As a result, the PLA-based composites containing oil-rich linseed cake were found to be more vulnerable to hydrolytic degradation in a longer time.

Biodegradable Polymer Materials Based on Polylactide

Under conditions of shear deformations in a Brabender-type mixer by solid-phase mixing, polylactide compositions with different polysaccharides (starch, microcrystalline cellulose, ethylcellulose, and chitosan) are produced using. To improve the elasticity of the compositions, poly(ethylene glycol) is introduced as a plasticizer. It is shown that the mechanical characteristics, water absorption, and biodegradability of the compositions depend on the component ratio and nature of the polysaccharide used. A biodegradation mechanism has been proposed based on data from scanning electron microscopy and IR-spectroscopy.

Improved properties of corn fiber-reinforced polylactide composites by incorporating silica nanoparticles at interfaces

In this work, we report a novel strategy for improving the interfacial nature in corn fiber/polylactide (CRF/PLA) composites by directly applying a sizing containing silica nanoparticles on the surface of CRFs. This results in enhanced mechanical properties of the CRF/PLA composites. These improvements can be mainly attributed to the presence of silica nanoparticles on CRF-PLA interfaces, which act to resist the crack propagation. The increased surface roughness of CRFs from incorporated silica nanoparticles may also contribute to the enhanced mechanical properties. This simple methodology can be easily scaled up and thus shows great promise in industrial applications.

Effects of Fiber Dimension and Its Distribution on the Properties of Lyocell and Ramie Fibers Reinforced Polylactide Composites

The regenerated cellulose fiber (Lyocell) and natural cellulose fiber (ramie) with different initial lengths were used to reinforce polylactide (PLA) by melt compounding and injection molding. The fiber dimension and its distribution in composites after injection molding were analyzed by high-resolution Fiber Quality Analyzer (FQA). Moreover, the contents of small fibers with length < 0.2 mm were also provided by FQA. Then the influences of fiber dimension and its distribution on the mechanical properties of the composites were investigated. The results showed that fiber length was reduced during compounding and injection molding processes, and the longer the initial fiber length, the more severe the length declined. Compared with ramie fiber, Lyocell fiber showed a longer fiber length, smaller diameter and narrower width distribution in composite after injection molding. Additionally, the content of small fiber played an important role in the analysis of the relation between the fiber dimension and mechanical properties of composites owing to its smaller aspect ratio. The different mechanical characteristics of the PLA composites were attributed predominantly to the fiber aspect ratio and the small fiber content. By comparison, Lyocell fiber exhibited better reinforcement for PLA due to the higher aspect ratio and lower small fiber content. The tensile strength, tensile modulus and impact strength of Lyocell/PLA composite were increased by 8.61 %, 75.43 % and 26.9 %, respectively.

Regenerated cellulose nanofibers fabricated through electrospinning and saponification of cellulose acetate as reinforcement of polylactide composites

Cellulose-acetate nanofibers (CA-NF) and regenerated cellulose nanofibers (RC-NF) were separately compounded as reinforcement materials for enhancement of the mechanical property of polylactide (PLA). PLA has a great potential as an alternative to widely-used plastics such as polystyrene and poly(ethylene terephthalate), which are made from petroleum. PLA is well known for its biodegradability and renewability, but the mechanical property of PLA is not sufficient for industrial applications. In this study, CA-NF were successfully fabricated by electrospinning using 20 wt% cellulose-acetate solution with acetone/N,N-dimethylacetamide (6/4, wt/wt) mixture solvent, and RC-NF were synthesized by subsequent saponification, as reinforcement materials for PLA composites. The Young’s modulus of CA-NF/PLA composites increased linearly from 1670 to 1840 MPa with the increase in the nanofiber concentration to 15 wt%. In contrast, the Young’s modulus of RC-NF/PLA composites rapidly increased to ~ 1840 MPa at the relatively low nanofiber concentration of 5.0 wt%. Above 5.0 wt%, the Young’s modulus became stable and almost constant. RC-NF exhibited better reinforcing efficiency due to the excellent mechanical property of RC-NF, although the interfacial compatibility of RC-NF for PLA matrix was relatively poor as compared with that of CA-NF.

Polylactide Composite Pins Reinforced with Bioresorbable Continuous Glass Fibers Demonstrating Bone-like Apatite Formation and Spiral Delamination Degradation.

The emergence of polylactide composites reinforced with bioresorbable silicate glass fibers has allowed for the long-term success of biodegradable polymers in load-bearing orthopedic applications. However, few studies have reported on the degradation behavior and bioactivity of such biocomposites. The aim of this work was to investigate the degradation behavior and in vitro bioactivity of a novel biocomposite pin composed of bioresorbable continuous glass fibers and poly-L-D-lactide in simulated body fluid for 78 weeks. As the materials degraded, periodic spiral delamination formed microtubes and funnel-shaped structures in the biocomposite pins. It was speculated that the direction of degradation, from both ends towards the middle of the fibers and from the surface through to the bulk of the polymer matrix, could facilitate bone healing. Following immersion in simulated body fluid, a bone-like apatite layer formed on the biocomposite pins which had a similar composition and structure to natural bone. The sheet- and needle-like apatite nanostructure was doped with sodium, magnesium, and carbonate ions, which acted to lower the Ca/P atomic ratio to less than the stoichiometric apatite and presented a calcium-deficient apatite with low crystallinity. These findings demonstrated the bioactivity of the new biocomposite pins in vitro and their excellent potential for load-bearing applications.

Polylactide Composites Suitable for Medical Devices.

Biodegradable polymeric materials with antimicrobial surfaces could be a suitable alternative for production of medical devices, especially if they are prepared in form of composites containing functional matter. Their greatest advantage is that they do not need to be removed from patient's body and simultaneously they can prevent growth of biofilm. In this work, polymeric films of polylactide acid with biosynthetically prepared silver nanoparticles, commercial multiwall carbon nanotubes and organovermiculite with hexadecyltrimethylammonium bromide in various concentrations were prepared to get polylactide composite with antibacterial properties. The dispersibility of filler in matrix was one of the key issues to be controlled in nanocomposite. Using several analytical techniques and observing morphology of prepared composite it was found that best results provide organovermiculite filler. For the tests of functionality antimicrobial tests were performed.

Composites Based on Starch and Polylactide

The blends of polylactide with starch at different component ratio are obtained under shear deformation in a Brabender mixer. The thermal behavior of polylactide composites with starch is studied by DSC, and their crystallinity is determined using X-ray diffraction; according to GPC data, the biodegradation of these composites upon exposure in the soil is quantified. An analysis of the experimental results shows that polylactide is almost incompatible with starch. A decrease in the melting point of polylactide in the composites with an increase in the starch content indicates the formation of more defective small crystals due to the difficulty of the crystallization process. On the basis of the data of X-ray structural analysis, it is shown that the total degree of crystallinity of the composites increases after exposure in the soil. This is associated with the washing out of the amorphous polylactide region under the action of water and microorganisms in the soil. Using GPC, it is shown for the first time that the biodegradation of polylactide when exposed in the soil proceeds according to the depolymerization mechanism; in the composites, this process occurs more intensely.

Synthesis and characterization of polylactide/rice husk hydrochar composite

Polymer composites are fabricated by incorporating fillers into a polymer matrix. The intent for addition of fillers is to improve the physical, mechanical, chemical and rheological properties of the composite. This study reports on a unique polymer composite using hydrochar, synthesised by microwave-assisted hydrothermal carbonization of rice husk, as filler in polylactide matrix. The polylactide/hydrochar composites were fabricated by incorporating hydrochar in polylactide at 5%, 10%, 15% and 20 wt% by melt processing in a Haake rheomix at 170 °C. Both the neat polylactide and polylactide/hydrochar composite were characterized for mechanical, structural, thermal and rheological properties. The tensile modulus of polylactide/hydrochar composites was improved from 2.63 GPa (neat polylactide) to 3.16 GPa, 3.33 GPa, 3.54 GPa, and 4.24 GPa after blending with hydrochar at 5%, 10%, 15%, and 20%, respectively. Further, the incorporation of hydrochar had little effect on storage modulus (G′) and loss modulus (G″). The findings of this study reported that addition of hydrochar improves some characteristics of polylactide composites suggesting the potential of hydrochar as filler for polymer/hydrochar composites.

Preparation of Glass Fabric/Poly(l-lactide) Composites by Thermoplastic Resin Transfer Molding.

This study reports the first example of the production of polylactide composites prepared by Thermoplastic Resin Transfer Molding (T-RTM) via in situ bulk polymerization of l-lactide (l-LA) after injection in a closed mold containing glass fabrics. Tin octoate Sn(Oct)2 was used as the catalyst and first evaluated at the lab-scale in the experimental conditions required in the tank and in the mold of the RTM device. The reactions were then upscaled in the RTM in the absence of reinforcement to ensure the feasibility of the process (transfer and polymerization). Finally, poly-l-lactide (PLLA)-based composites with glass fabrics as the reinforcement were obtained. The resulting PLLA matrices exhibited conversions up to 99% along with high molar masses of up to 78,000 g·mol−1 when the polymerization was carried out under dynamic vacuum (vacuum-assisted RTM, VARTM). Moreover, a good impregnation of the glass fabrics by the matrix was observed by optical microscopy.

Production and investigation of structure and properties of polyethylene–polylactide composites

ABSTRACTUnder conditions of shear deformations, low‐density polyethylene (LDPE) and polylactide (PLA) composites are obtained in rotor disperser. The production of these composites allows one to use polymers derived from natural raw and to reduce the cost of the materials on their base. The addition of rigid PLA leads to increase in elastic modulus from 200 for LDPE to 1190 for LDPE–PLA (50:50 wt %) composites and in tensile strength from 13.3 for LDPE to 17.8 for LDPE–PLA. By differential scanning calorimetry method, it is shown that LDPE and PLA are incompatible. Using X‐ray diffraction analysis, it is found that degree of crystallinity of composites decreases from 46.1 at 50:50 wt % to 36.9 at 80:20 wt % component ratios with the rise in LDPE content. Tests on fungus resistance show that the composites containing 50 wt % PLA are more resistant than the composites containing 30 wt % PLA. First by gel‐permeation chromatography method, it is shown that composite degradation after exposure in soil is accompanied by the PLA chain scission and depolymerization with formation of monomers and dimers (M w of PLA decreases from 118,860 to 80,100). The obtained composites can be applied as packaging materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47598.

Development of short basalt fiber reinforced polylactide composites and their feasible evaluation for 3D printing applications

The objective of this work is to develop KH550-treated basalt fiber (KBF) reinforced polylactide (PLA) composite as a potential 3D-printed feedstock. Herein, physical (thermal, mechanical, and rheological) properties and the feasibility of PLA/KBF for 3D printing are investigated. KBF is found to be oriented-dispersed along the printing direction in printed specimen, in contrast with randomly-distributed KBF in casting counterparts. Mechanical tests, rheological behavior and microstructure observation of PLA/KBF filaments are performed to compare with carbon fiber (CF) reinforced counterparts with the same fiber weight fraction. The results suggest that PLA/KBF exhibit comparable tensile properties and superior flexural properties to those of PLA/CF control, which can be attributed to high complex viscosity of PLA/CF affecting the interlayer adhesion. Furthermore, the printing feasibility of PLA/KBF filaments are evaluated. With increasing fiber length and weight fraction of KBF, low infill and micro-defects are shown in CT scans, which explain the deterioration in mechanical performance. The present work proves PLA/KBF as a mechanical-improved and low-cost feedstock for 3D printing applications in complex design and variable sizes.

Toddy Palm (Borassus Flabellifer) Fruit Fibre Bundles as Reinforcement in Polylactide (PLA) Composites: An Overview About Fibre and Composite Characteristics

Toddy palm fruit fibre bundles have an apparent density below 0.8 g/cm³ and offer an interesting lightweight construction potential in polylactide (PLA) composites reinforced with 30 mass-% fibres. Single fibre bundles show similar mechanical properties compared with coir: a tensile strength of 240 MPa, a Young´s modulus of 3.8 GPa and an elongation at break of 31%. However, density and fibre bundle diameter (~ 50 µm) of toddy palm fruit fibre bundles are clearly lower. The compression moulded composites have a density of 0.9 g/cm³ and achieved an unnotched Charpy impact strength of 12 kJ/m², a tensile strength of 25 MPa, a Young´s modulus of 1.9 GPa and an elongation at break of 9%. Due to the high porosity of the composites and the different stress-strain behaviour of fibre and matrix the actual fibre-reinforcing potential could not be fully used. The maximum stress of the composite was reached at the elongation at break of the PLA-matrix (~2%) while the fibre achieved its maximum stress at an elongation of ~31%. After reaching the maximum stress of the composite, the fibres were pulled out from the matrix with low energy absorption, resulting in a decrease in stress and a limited reinforcing potential. Additionally, the study investigates whether an insect attack by the Asian fruit fly on the mesocarp has a significant influence on the mechanical fibre characteristics. The results have shown that only the rough surface of the fibre bundles is smoothed by insect infestation. The mechanical properties were not significantly affected. This means that insect-infested fruits of the Toddy palm, which are no longer suitable for food production, can be used for the production of sustainable composite materials.

Hybrid Composites of Polylactide with Basalt and Carbon Fibers and Their Thermal Treatment.

In this research, polylactide was hybrid-reinforced and heat-treated in order to obtain durable structural materials with the use of eco-friendly components. Differential scanning calorimetry (DSC) analysis, tensile tests at various temperatures, Vicat tests, impact tests, and microscopic observations were conducted on the annealed and non-heat-treated specimens. The theoretical and true density, as well as water absorption, were also determined. The simultaneous introduction of chopped carbon and basalt fibers in equal mass fractions of 7.5% and 12.5% resulted in satisfactory increases in stiffness and tensile strength. The reinforcing effect was more efficient for the heat-treated composites, especially at elevated temperatures. Heat treatment significantly increased the degree of crystallinity of the matrix, improving heat resistance and reducing water absorption. It also reduced the stress concentrations in the injection-molded specimens.