Anisotropy of poly(lactic acid)/carbon fiber composites prepared by fused deposition modeling

It is well known that 3D printed parts prepared by fused deposition modeling (FDM) exhibit large anisotropy of mechanical properties. In this article, poly(lactic acid; PLA)/carbon fiber (CF) composites with different built orientations (X, Y, Z) were prepared by FDM. The effects of printing temperature, speed, orientations, and layer thickness on the mechanical properties of the composites were systematically investigated. The mechanical properties of PLA/CF composites show more significant anisotropy. The orientation of the fibers along the printing direction is displayed by scanning electron microscopy. Printing parameters bring almost no effect on mechanical properties of the X-construct oriented specimen, and bring obvious effect on those of the Y-construct oriented specimen and Z-construct oriented specimen. According to the analysis, carbon fiber can amplify this anisotropy from layer fashion, and the key factors from printing parameters are porosity and bond strength between fuses. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48786.     

3D printing of copper particles and poly(methyl methacrylate) beads containing poly(lactic acid) composites for enhancing thermomechanical properties

Poly(lactic acid) (PLA) composite filaments with different copper (Cu) contents as high as 40 and 20 wt% of poly(methyl methacrylate) (PMMA) beads have been fabricated by twin-screw extruder for 3D printing. A fused-deposition modeling (FDM) 3D printing technology has been used to print the PLA composites containing hybrid fillers of Cu particles and PMMA beads. The morphology, mechanical, and thermal properties of the printed PLA composites were investigated. The tensile strength was slightly decreased, but storage modulus and thermal conductivity of PLA composites were significantly improved by adding Cu particles in the presence of PMMA beads. The PLA composites with hybrid fillers of 40 wt% of Cu particles and 20 wt% of PMMA beads resulted in thermal conductivity of 0.49 W m⁻¹ K⁻¹ which was three times higher than that of the bare PLA resin. The facilitation of the segregated network of high-thermally conductive Cu particles with the PMMA beads in PLA matrix provided thermally conductive pathways and resulted in a remarkable enhancement in thermal conductivity.     

Developing a novel technique for the fabrication of PLA-graphite composite filaments using FDM 3D printing process

Developing a uniform polymer-based composite filament is a critical factor for a successful 3D printing process. In this regard, a novel technique for the fabrication of PLA-graphite filament with the potential to be applied to other PLA-based composite filaments was proposed and compared to the solvent casting method. This modified mixing technique involves partial dissolution of the PLA pellets surface by dichloromethane (DCM), which creates a sticky surface for the strong adhesion of reinforcement powders. The manufactured composite filament by this method exhibited excellent structural features, while the solvent casting method yielded a heterogeneous filament with a non-uniform diameter and numerous voids. In addition, graphite, as a cost-effective carbon-based filler for polymer matrix composites, could effectively act as a reinforcement phase, leading to noticeable mechanical strength enhancement of PLA. Furthermore, significantly enhanced printability and mechanical properties of 3D-printed PLA-graphite composite specimens indicate the efficiency of the modified mixing method as a practical and time-saving technique for developing uniform PLA-based composite filaments for the extrusion-based additive manufacturing techniques such as FDM.     

Effects of the printing parameters on short-term creep behaviors of three-dimensional printed polymers

Polylactic acid (PLA), despite its widespread use in three-dimensional (3D) printing technique, is lacking in the literature on creep behavior due to the printing parameters. Also, the potential use of carbon fiber-reinforced composites as 3D printing materials is remarkable as it improves mechanical properties of the produced parts. Therefore, it is important to find out the positive/negative effects of composite filaments on creep strength. The main purpose of this research is to examine the creep behaviors of PLA and PLA composite produced with 3D printer and to reveal the effects of the printing parameters on the short-term creep. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47564.     

Fabrication and characterization of 3D printable nanocomposite filament based on cellulose nanocrystals and polylactic acid using ionic liquids

Nanocellulose, which is biodegradable and possesses excellent physicochemical properties, has high potential in many applications. However, its intrinsic hydrophilic nature makes it difficult to be used as fillers in most hydrophobic polymer composites. Here, cellulose nanocrystals (CNCs) were successfully prepared using 1-hexly-3-methylimidazolium hydrogen sulfate [Hmim][HSO₄] ionic liquid under optimized conditions at 71°C, ultra-sonication amplitude of 69%, and ultrasonication time of 23 min. The prepared CNCs were surface-modified using 1-butyl-3-methylimidazolium tetrafluoroborate [Bmim][BF₄]. A 3D printable nanocomposite filament containing CNCs embedded in polylactic acid was fabricated via extrusion process at 170°C. The prepared filaments were characterized using universal testing machine, field emission scanning electron microscopy, thermogravimetric analysis, and FTIR. It was shown that CNCs had a diameter and length of 10–24 and 60–400 nm, respectively. It was also found that incorporating 2 wt% of CNCs into the matrix phase increased filaments tensile strength by 2.5% (from 54.59 to 57.35 MPa) due to the plasticization effect of [Bmim][BF₄]. The prepared composites exhibited lower activation energies compared to neat PLA due to the small traces of sulfate group on F-CNC. The mechanical attributes of CNCs/PLA nanocomposites were retained at values comparable to that of fresh PLA and were demonstrated to be 3D printable.     

Effects of laser polishing on surface quality and mechanical properties of PLA parts built by fused deposition modeling

Fused deposition modeling (FDM) produces parts through layer by layer on the top of each other, making it almost impossible to obtain smooth printed parts. Hence, there is a huge demand for the postprocessing of the FDM-printed parts. Laser polishing is a novel technique that can be used to polish products to obtain a smoother surface. The aim of this work was to explore the feasibility of surface-finishing FDM-printed polylactic acid (PLA) parts by laser polishing. The surface roughness, surface morphology, dynamic mechanical analysis (DMA), and tensile properties were investigated. The results indicated that the lower laser power and the bigger laser beam diameter within a certain range could facilitate the formation of smoother surface. With optimized parameters, the surface roughness was reduced by 90.4%. DMA showed that the storage modulus (E’) and glass transition temperature of PLA specimens were significantly improved due to the decrease of molecular mobility of denser structures. Moreover, the tensile strength and Young's modulus of the PLA specimen were also significantly increased after laser polishing. The fracture morphologies were observed, and the possible strengthening mechanism was also discussed. These results indicated that laser polishing could be an efficient method for surface polishing of FDM parts. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48288.     

Reinforcement of polylactic acid with bioceramics (alumina and YSZ composites) and their thermomechanical and physical properties for biomedical application

Fused Deposition Modeling (FDM) is one of the most popular Additive Manufacturing (AM) techniques widely used in different fields, including the medical sector. FDM uses different thermoplastic polymers to fabricate the desired shapes. However, there is a need to enhance the mechanical properties of neat biopolymers with the help of reinforcements that can be used in medical applications. This work investigates the thermomechanical, physical, and biological properties of PLA-based composites fabricated using FDM. PLA-based bio-ceramics (Al₂O₃ and Yttria Stabilized Zirconia [YSZ]) filaments have been used to prepare tensile, compression, and flexural specimens. Scanning electron microscopy has been performed to reveal the fracture characteristics of the composite specimens. Besides this, the feasibility of the polymer composite for biomaterial applications has also been analyzed. The results show that PLA/Al₂O₃ has 30.44, 55.2, and 83.73 MPa tensile, compressive, and flexural strength, respectively. The present study also shows that the reinforcement of PLA with bioceramics also led to a reduction in wear and Coefficient Of Friction (COF) at varying loads.     

Surface organo-modification of hydroxyapatites to improve PLA/HA compatibility

Polylactide/hydroxyapatite (PLA/HA) composites are promising tissue engineering materials because of the PLA biodegradability and HA as a natural bone component. PLA/HA composites without HA modification lead to mechanical failure due to the interfacial immiscibility. In this study, an effective chemical surface methodology is used to modify HA to obtain PLA/HA composites with superior mechanical properties. The HA particles are modified with fatty acids (adipic, sebacic, lauric, and linoleic) and incorporated into a PLA matrix by polymer solution casting, using chloroform as the solvent. After the HA modification, the films exhibited an improvement in tensile strength, elongation at break, and elastic modulus. Yet, the best results observed are by sebacic and adipic acid modification. These increments are attributed to a higher affinity of the organo-modified HA particles within the PLA matrix. Therefore, the development of materials for osteo-regeneration engineering based on these systems is quite promising.     

Effect of reinforcement with carbon fabrics impregnated with nanoparticles on the tensile behavior of cement-based composites

The objective of this work was to modify the microstructure of carbon fabrics with mineral or organic fillers absorbed between the filaments of the fabric strands in order to optimize the composite tensile properties. The obtained mechanical properties of all composites with fillers were superior to those of the reference composite. In mineral fillers, the improvement in mechanical properties was attributed largely to an increased sleeve/core ratio, resulting mainly from a pozzolanic reaction between filler (silica) and calcium hydroxide of the cement paste products. In organic fillers, the improvement was attributed largely to good filling and the ability of the polymer to bind all the filaments within the bundle to form a single unit, such that the load is efficiently carried by all the filaments. However, these composites suffered from delamination. Silica-based fillers should be given special consideration since they provide good bonding with the cement matrix without suffering delamination.     

Enhancement of Mechanical Properties of FDM‐PLA Parts via Thermal Annealing

The objective of this study is to investigate the possibility of enhancing mechanical properties of poly(lactic acid) (PLA) samples processed by a rapid manufacturing (RM) technique by increasing PLA crystallinity degree via thermal annealing. The samples are manufactured by fused deposition modeling (FDM) at different temperatures and subsequently evaluated by three‐point bending flexural and tensile tests. The polymer processed at 215 °C is thermally annealed over its glass transition temperature in order to increase the degree of crystallinity to the maximum attainable level as measured by the differential scanning calorimetry and confirmed by X‐ray diffraction. The increase in the degree of crystallinity of FDM‐PLA enhances flexural stress of the samples by 11–17%. The study also demonstrates applicability of radiation sterilization for FDM‐PLA parts. Therefore, thermal annealing might be introduced into a standard RM technology of PLA, particularly for sterilizable customized implants, to efficiently improve their mechanical properties.     

FDM用PETG系列耗材的改性研究

对市售聚对苯二甲酸乙二醇酯-1,4-环己烷二甲醇酯（PETG）丝材及原材料进行研究,选用PETG 2012作为制备熔融堆积成型技术（FDM）用PETG丝材的基体树脂。选用聚碳酸酯（PC）对基体PETG进行增韧增强改性,并制成3D打印高分子丝材进行打印测试,探讨了PC含量对PETG耗材及制件性能的影响。结果表明,在低PC含量下,PETG与PC的相容性较好,PETG与PC制件未出现明显的分层,分布比较均匀;共混物的流动性随着PC含量的增加而降低,且打印件的维卡软化温度和热变形温度随着PC用量的增加而增加;此外,PC材料的加入使得PETG打印件的力学性能得到较大改善：打印件的拉伸强度随着PC用量的增加而增大,缺口冲击强度却随着PC用量的增加呈现先增加后减小的趋势; PETG/PC的配比为1∶1时,可制得力学性能优异的3D打印耗材。     

Improving the ductility of polylactic acid parts produced by fused deposition modeling through polyhydroxyalkanoate additions

Polylactic acid (PLA) is one of the most commonly used materials for fused deposition modeling (FDM) due to its low cost, biocompatibility, and desirable printing characteristics. However, its low ductility is a major disadvantage for engineering applications where high damage tolerance is needed. This study investigates the feasibility of polyhydroxyalkanoate (PHA) additions to PLA for improving the ductility of parts produced by FDM. Thermal and mechanical behavior of PLA/PHA specimens containing 12 wt % PHA is investigated for a range of printing nozzle temperatures. All PLA/PHA specimens exhibit amorphous PLA phase with semicrystalline PHA and possess outstanding ductility exceeding 160% for nozzle temperatures in the range of 200 °C–240 °C. Lower and higher nozzle temperatures result in low ductility, similar to that of pure PLA. Overall, PLA/PHA is a very promising polymer blend for FDM processes, providing a combination of sufficient strength with excellent damage tolerance. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48154.     

Raw and chemically treated bio-waste filled (Limonia acidissima shell powder) vinyl ester composites: Physical,mechanical, moisture absorption properties,and microstructure analysis

The rapid growth of environmentally sustainable and eco-friendly materials tends to the utilization of biowastes as filler in polymer matrix composites. The particulate composite with improved wettability of fillers and advanced approach can evolve polymer composites that exhibit promising applications in packaging, automobile, marine, construction, and aerospace. In the present work, one of the biowaste fillers were synthesized from Limonia acidissima shells via a top-down approach (pulverizing) and the surfaces were chemically modified using sodium hydroxide (NaOH) before they were used as fillers in vinyl ester polymer composites by different weight percentage (0, 5, 10, 15, and 20 wt%). The prepared particulate composites were characterized by mechanical properties, moisture absorption behavior, and morphology. At different filler loading the tensile strength, tensile modulus, flexural strength, flexural modulus, impact strength, hardness, density, and moisture intake tests were performed. The results reveal that the properties increased for composites filled with alkaline treated fillers for the same filler loading and found to be higher at filler loading of 15 wt%. The morphological analysis confirms the better interfacial bonding between alkali-treated particles and matrix due to the removal of non-cellulose materials from the surface of the particles.     

Highly loaded hydroxyapatite microsphere/ PLA porous scaffolds obtained by fused deposition modelling

The goal of the work was the manufacturing of hydroxyapatite microsphere/polylactic acid (PLA) scaffolds by means of fused deposition modelling (FDM). Micrometer-sized hydroxyapatite spheres synthesized by spray drying (sdHA), were dispersed in PLA by extrusion compounding. Composite filaments were obtained from extrusion which were used in FDM 3D printing for the production of macroporous scaffolds. The sdHA microspheres were used in the composite in order to improve the biomimicry and the bioactivity of the 3D printed scaffold to increase the bone regeneration capacity. Morphological, thermal, physical and mechanical characterizations were performed on the 3D printed composites. Pure PLA scaffolds were 3D printed and used as a reference.Thermal analyses, TGA and DSC evidenced that the glass transition temperature and the degree of crystallinity of PLA were not influenced by the presence of sdHA. Morphological analysis showed a smooth surface of the printed samples when pure PLA was used. A rough surface was found on the PLA/sdHA composites, confirming, the homogeneous dispersion of the ceramic phase in the polymeric matrix. The higher porosity of the composite samples compared to PLA ones, most likely caused a decrease of the mechanical performances of the PLA/sdHA scaffolds. Composite scaffolds displayed stiffness values compatible with that of bone tissue.     

Study on performance characteristics of fused deposition modeling 3D-printed composites by blending and lamination

Component contacting degree in a composite material is an important reference for evaluation the performance characteristics. In this article, two composite material systems involving polylactic acid (PLA) with acrylonitrile butadiene styrene (ABS) and PLA with thermoplastic polyurethane (TPU) were prepared by blending and laminating through fused deposition modeling (FDM) 3D printing technology. The mechanical and thermal properties of the as-prepared composite materials were examined. The results indicated that PLA and TPU played a dominant role in tensile strength and breaking elongation, respectively, in individual composite material. ABS and TPU changed the glass transition peek, crystallinity, and modulus of PLA. The results also suggested that although the processing design of the blending method was more suitable for the contact between two components, but the mechanical properties of laminated composites were closer to theoretical predictions. The structural design and processing technology provide a comparative method and reference basis for studying the performance characteristics of composite materials.     

Properties and Degradation of Novel Fully Biodegradable PLA/PHB Blends Filled with Keratin

The utilization of keratin waste in new materials formulations can prevent its environmental disposal problem. Here, novel composites based on biodegradable blends consisting of poly(lactic acid) (PLA) and poly(3-hydroxybutyrate) (PHB), and filled with hydrolyzed keratin with loading from 1 to 20 wt % were prepared and their properties were investigated. Mechanical and viscoelastic properties were characterized by tensile test, dynamic mechanical thermal analysis (DMTA) and rheology measurements. The addition of acetyltributyl citrate (ATBC) significantly affected the mechanical properties of the materials. It was found that the filled PLA/PHB/ATBC composite at the highest keratin loading exhibited similar shear moduli compared to the un-plasticized blend as a result of the much stronger interactions between the keratin and polymer matrix compared to composites with lower keratin content. The differences in dynamic moduli for PLA/PHB/ATBC blend filled with keratin depended extensively on the keratin content while loss the factor values progressively decreased with keratin loading. Softening interactions between the keratin and polymer matrix resulted in lower glass transitions temperature and reduced polymer chain mobility. The addition of keratin did not affect the extent of degradation of the PLA/PHB blend during melt blending. Fast hydrolysis at 60 °C was observed for composites with all keratin loadings. The developed keratin-based composites possess properties comparable to commonly used thermoplastics applicable for example as packaging materials.     

Enhancement of Mechanical Properties of PA6 Blending with Talcum for Fused Deposition Modeling

The objective of this work is to fabricate polyamide 6 (PA6) composite filament with enhanced mechanical properties and low cost for fused deposition modeling (FDM). The composite filaments are obtained by compounding PA6 and talcum fillers and then single screw extruding. Virgin PA6 and commercial e‐PA6 are set as controls. First, the rheological behaviors and thermal properties of PA6/talc, PA6, and e‐PA6 pellet materials are investigated, including viscosity, melting temperature, crystallinity, and decomposition temperature, which are important parameters for fabricating filament feedstocks. The results show that 10 wt% addition of talcum content accelerates the increase of the viscosity among the processing temperature. Accordingly, virgin PA6 and PA6/talc5 with good flowability are produced and subsequently evaluated by tensile and flexural tests. It is notable that the introduction of talcum increases the diameter constant and shape stability of PA6‐based filament. Also, it is found that both PA6 and Pa6/talc5 filaments exhibit superior tensile properties to the commercial e‐PA6 counterparts. Especially, PA6/talc5 filaments achieve the maximum tensile yield strength of 67.1 MPa and modulus of 3.10 GPa. Finally, auxetic lattice parts are successfully printed via FDM using lab‐made PA6, PA6/talc5, and commercial e‐PA6 filaments, and PA6/talc5 exhibits remarkable loading and energy absorption capability.     

Effect of different compatibilizers on environmentally friendly composites from poly(lactic acid) and diatomaceous earth

Environmentally friendly composites from poly(lactic acid) (PLA) and diatomaceous earth (DE) were successfully manufactured by extrusion, followed by injection moulding. DE was used as a filler; several compatibilizer/coupling agents, namely (3‐glycidyloxypropyl)trimethoxysilane, epoxy styrene acrylic oligomer and maleinized linseed oil, were used to improve polymer–filler interactions. Mechanical characterization was carried out by standard tensile, impact and hardness tests while morphological characterization of the fractured surfaces was conducted by field emission scanning electron microscopy. The effect of DE was evaluated by differential scanning calorimetry and dynamic mechanical thermal behaviour. The results show that the addition of DE provides an improved tensile modulus and induces more brittle composites due to stress concentration phenomena. The addition of compatibilizers in PLA‐DE positively contributes to improve ductile properties, thus leading to high environmental efficiency materials with balanced mechanical properties. Specifically, the compatibility improvement between the PLA and DE was good with maleinized linseed oil and contributed to improving the impact strength, which is a key factor in PLA‐based composites due to the intrinsic brittleness of neat PLA. © 2019 Society of Chemical Industry     

连续玻璃纤维增强PLA复合材料3D打印技术研究

以聚乳酸(PLA)为基体,连续玻璃纤维为增强体,采用熔融浸渍工艺制备连续玻璃纤维预浸丝,将制得的预浸丝作为3D打印耗材用于熔融沉积(FDM)的3D技术来制备连续玻璃纤维增强PLA复合材料试样,并研究了打印温度、层厚和打印速度对复合材料力学性能的影响。结果表明,当打印层厚为0. 5 mm,打印温度为230℃,打印速度为2 mm/s时,连续玻璃纤维增强PLA复合材料的弯曲性能最佳,弯曲强度和弯曲模量分别为327. 84 MPa和20. 293 GPa。综合考虑复合材料的力学性能、表面质量和尺寸稳定性,连续玻璃纤维增强PLA复合材料的最佳打印层厚为0. 5 mm,适宜的打印温度范围为200~220℃,打印速度范围为2~4 mm/s。     

Mechanical and thermal properties of bamboo fiber reinforced polypropylene/polylactic acid composites for 3D printing

In this article, a kind of degradable composite was prepared from bamboo fiber (BF), poly lactic acid (PLA), and polypropylene (PP). The mechanical and thermal properties were characterized by the universal testing machine, thermogravimetric analysis, differential scanning calorimetry. In order to improve the compability between BF and polymer matrix several modification on the surface of BF were explored and compared. Moreover, a compatibilizer (maleated PP) was applied to further increase compatibility between the fiber and matrix. It is found that the thermal stability of BF/PP/PLA composites decreased with the increase of maleated polypropylene (MAPP) content. When 5% MAPP was used the tensile strength, flexural strength, and impact strength of composites reached 33.73, 47.18 MPa, and 3.15 KJ/m², with an increase by 13, 11.7, and 23.5%, respectively, compared with the composites without MAPP. The improvement of mechanical properties is attributed to the fact that irregular grooves and cracks induced by the modification of BF facilitate the infiltration of polymer into fiber due to the strong capillary effect. Furthermore, BF/PP/PLA composites are potential to be used in 3D printing. POLYM. ENG. SCI., 59:E247–E260, 2019. © 2018 Society of Plastics Engineers