Kinetic thermal behavior of nanocellulose filled polylactic acid filament for fused filament fabrication 3D printing

Fused filament fabrication (FFF) with thermoplastic filaments is the most popular 3D printing technology. The continuous polymer filaments undergo a series of thermal processes, including heating, melting, cooling, and solidification. Therefore, it is necessary to investigate the thermal behavior of polymer filaments. The present study aims to provide a fundamental study of the thermal decomposition behavior and the isothermal melting crystallization behavior of nanocellulose filled polylactic acid (PLA) filaments. The influences of nanocellulose contents on the thermal decomposition properties such as onset temperature (137_onset), the temperature at 20-wt % conversion (T_α20), and the temperature at the peak decomposition rate (T_p) were examined by thermogravimetric analysis (TGA). The effects of nanocellulose contents on the glass transition temperature (T_g) and the melting temperature (T_m) were studied by differential scanning calorimetry (DSC). Effects of nanocellulose and polyethylene glycol (PEG) incorporation on the thermal decomposition activation energy, isothermal melting crystallization rate, and semi-crystallization time are also investigated. The addition of nanocellulose improves the thermal stability of PLA filament, whereas the addition of plasticizer PEG decreases the thermal stability. TGA and DSC kinetic analyses indicate that nanocellulose alone or together with PEG could drastically increase the crystallization rate and shorten the semi-crystallization time. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48374.     

Inkjet printing of polylactic acid on substrates prepared by fused deposition modeling and its potential for selective surface finishing

Fused deposition modeling (FDM) is an additive manufacturing technology commonly used for prototyping. One limiting aspect for the use in functional prototyping and small‐lot production is the achievable surface roughness. The aim of this work was to investigate a potential method of processing polylactic acid (PLA), as it is commonly used for FDM printing, via inkjet technology. PLA solvent inks with different concentrations were prepared by dissolving PLA in 1,4‐dioxane. The tested PLA substrates were prepared by FDM with different layer thicknesses and the change in surface roughness after multilayer inkjet printing was measured by a stylus profilometer. The surface roughness was reduced by up to 50% and further increasing the number of inkjet layers caused voids and PLA accumulations. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43527.     

熔融沉积3D打印设备研究进展

阐述了3D打印技术的种类,介绍了熔融沉积成型(FDM)技术的原理、特点及其目前存在的问题;从控制方法(温度控制、运动控制、路径控制)和运动机构(送料机构、喷嘴、运动机构)两个方面系统综述了国内外FDM 3D打印设备的最新研究进展;最后,指出了目前FDM 3D打印设备所面临的挑战及需要解决的问题,展望了FDM 3D打印设...     

催化超临界水氧化处理焦化废水

采用催化超临界水氧化技术处理武汉某焦化厂废水。Ir-Ta/堇青石催化剂在反应温度380～460℃,反应时间20～100 s,反应压力为22～30 MPa,过氧比0～4下,探究处理焦化废水的影响因素;用COD的去除率表示超临界水氧化降解有机物的进程对其进行动力学分析。结果表明,在超临界水中添加催化剂后的有机物去除效果明显高于无催化剂;反应温度、压力、时间和过氧比等影响因素与COD和氨氮去除率呈正相关;加入催化剂后,在反应压力24 MPa,过氧比为200%(2倍)时,反应活化能为46.26 kJ/mol,频率因子为73.20 s^(-1)。     

聚乳酸材料在3D打印中的研究与应用进展

综述了最近PLA材料在3D打印中的研究和应用进展。介绍了PLA的结构性质和合成方法,以及熔融沉积成型3D打印PLA材料的特性。重点介绍了最近3D打印PLA材料的改性和成型工艺研究。最后详细描述了3D打印PLA材料在生物医学领域中的应用进展,并对未来的发展方向和应用前景进行了展望。     

The feasibility of printing polylactic acid–nanohydroxyapatite composites using a low‐cost fused deposition modeling 3D printer

The current “gold standard” to treat bone lesions is allografts and autografts, both presenting important disadvantages such as risk of infection and morbidity. Synthetic grafts and scaffolds for bone regeneration represent a promising solution. Fused deposition modeling is a valid tool for developing synthetic bone grafts of complex shapes, which is a key issue. The possibility of building polylactic acid–nanohydroxyapatite (PLA/nanoHA) composites by 3D printing was systematically evaluated. PLA/nanoHA filaments for low‐cost 3D printers were produced by a multistep solvent‐free procedure and characterized by scanning electron microscopy, energy dispersive X‐ray spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry, and rheometry. TGA analysis confirmed the presence of the nanoHA amounts used in the composites, equal to 5 and 15 wt %. The glass‐transition temperature and degree of crystallinity of PLA are not influenced by presence of nanoHA, which remains substantially amorphous. The morphological analysis and compression testing on printed samples showed that nanoHA was uniformly dispersed within the PLA matrix and improved the PLA mechanical properties without changing the rheological performance. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44656.     

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.     

3D printing of porcelain by layerwise slurry deposition

The Layerwise Slurry Deposition is a technology for the deposition of highly packed powder layers. A powder bed is achieved by depositing and drying layers of a ceramic suspension by means of a doctor blade. This deposition technique was combined with the binder jetting technology to develop a novel Additive Manufacturing technology, named LSD-print. The LSD-print was applied to a porcelain ceramic. It is shown that it was possible to produce parts with high definition, good surface finish and at the same time having physical and mechanical properties close to those of traditionally processed porcelain, e.g. by slip casting.This technology shows high future potential for being integrated alongside traditional production of porcelain, as it is easily scalable to large areas while maintaining a good definition. Both the Layerwise Slurry Deposition method and the binder jetting technologies are readily scalable to areas as large as >1?m².     

熔融沉积3D打印机机械结构的设计

3D打印技术作为一种快速成型技术,其采用数字式模型文件作为基础,采取逐层打印的办法将可粘合性的塑料或者粉末金属用以构筑所预想的实体技术.由于3D打印技术可采用的耗材种类不同,故其存在着不同的3D打印技术用于构造不同类型的部件.3D打印耗材常有尼龙玻纤、铝合金、钛合金、石膏、镀金银以及橡胶等材料.为了拓宽3D打印机所使用...     

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     

Thermal decomposition behavior of 3D printing filaments made of wood-filled polylactic acid/starch blend

Dynamic thermogravimetric analysis under nitrogen environment was used to understand the thermal decomposition process of 3D printing filaments made of wood-filled polylactic acid (PLA)/starch blend. The characteristic temperatures and apparent activation energy (AAE) of the filaments with various starch contents were calculated with well-known kinetic models by Friedman, Flynn–Wall–Ozawa, Coats–Redfern, and Kissinger. With the increased starch content in the filament, the onset thermal decomposition temperatures of the filaments decreased gradually from 272.4 to 155.1°C. The thermal degradation degree became smaller, and the transitional temperature interval became larger with increased starch proportion. The AAE values of the three types of filaments with different starch ratios varied between 97 and 114 kJ/mol, depending on material composition and method of calculation. The four kinetics methods provide complementary techniques for analyzing thermal stability behavior of composite materials. The improved understanding of thermal decomposition behavior of PLA-starch-wood composites can help develop PLA/starch-based filaments for 3D printing.     

Phosphor powders-incorporated polylactic acid polymeric composite used as 3D printing filaments with green luminescence properties

A new class of multifunctional nanocomposites holds strong potential in three-dimensional (3D) printing. In this study, SrAl₂O₄:Eu²⁺,Dy³⁺ powders with fluorescence property were modified with SiO₂ to improve its dispersibility and compatibility in the polylactic acid (PLA) matrix. The composite filaments with a diameter of 1.75 ± 0.05 mm containing 2 wt % of modified particles were prepared by a melt blending method. The fluorescent analysis reveals that the composite filaments can be excited by light with a broad band of wavelength from 345 to 455 nm with the highest excitation intensity at 426 nm and have a major emission peak at 487 nm. The morphological analysis and mechanical performance testing on the printed samples showed that modified particles were uniformly dispersed within the PLA matrix and improved the mechanical properties of the composite filaments. Moreover, the modified particles improved hydrophobic behavior and antibacterial properties in comparison with unmodified composite. Therefore, the composite material will have potential applications such as making prototypes for customized furniture and accessories by 3D printing technology. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48644.     

Morphological and electrical characterization of conductive polylactic acid based nanocomposite before and after FDM 3D printing

Three dimensional (3D) printing holds strong potential for the formation of a new class of multifunctional nanocomposites. Therefore, both the nanocomposites and 3D printing communities need to make more collaborations and innovations for developing and processing of new polymers and composites to get benefit of functionalities of 3D printed nanocomposites. The contribution of this paper is the creation of 3D printable filaments from conductive polymer nanocomposites using a melt mixing process. Multi-walled carbon nanotubes (MWNTs) and high-structured carbon black (Ketjenblack) (KB) were incorporated into polylactic acid. The percolation threshold of MWNT composites is 0.54 wt % and of KB composites is 1.7 wt % by four-point resistance measurement method. In the similar melt mixing process, there was no dependence of diameter of produced 3D printer filaments on the MWNT loading, instead the diameter was dependent on the KB loading and increased with increasing the filler amount. The conductivity of extruded filaments from 3D printer in low filler contents decreases with increasing extruder temperature, yet in higher filler contents there is no effect of extruder temperature on conductivity. Finally, the resistance decreases exponentially with the increase of cross-sectional area of 3D printed tracks. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47040.     

High-toughening modification of polylactic acid by long-chain hyperbranched polymers

The hyperbranched polyester synthesized by “one-step method” was grafted with stearic acid to obtain long-chain hyperbranched polymers (LCHBPs) with a large number of long stearic acid chains at the end. By means of FTIR and ¹³C-NMR characterization, it was proved that stearic acids were grafted onto hyperbranched polyesters (HBPE) to yield LCHBPs successfully. It was determined by GPC and hydroxyl value titration that the number average molecular weight of HBPE was 4.86 × 10³ and the grafting rate of stearic acid was 47%. Polylactic acid (PLA)/LCHBPs blends were prepared by melt processing method. The results showed that comparing with neat PLA, the tensile strength of PLA/LCHBPs blends decreased slightly with the increase of LCHBPs, but still maintained a high level, while the elongation at break and the impact strength of the PLA with 3.0 phr LCHBPs were greatly improved by 1360.0% and 119.8%, respectively. In addition, the impacted fracture characteristics of PLA changed significantly from brittle fracture to ductile fracture after LCHBPs incorporation, with the formation of a large number of filamentous structures. Thus, LCHBPs was an excellent toughening modifier for PLA and the resulting blends with improved performance possess wider applications.     

Synthesis and properties of macroporous SiC ceramics synthesized by 3D printing and chemical vapor infiltration/deposition

Open porosity cellular SiC-based ceramics have a great potential for energy conversion, e.g. as solar receivers. In spite of their tolerance to damage, structural applications at high temperature remain limited due to high production costs or inappropriate properties. The objective of this work was to investigate an original route for the manufacturing of porous SiC ceramics based on 3D printing and chemical vapor infiltration/deposition (CVI/CVD). After binder jetting 3D-printing, the green α-SiC porous structures were reinforced by CVI/CVD of SiC using CH₃SiCl₃/H₂. The multiscale structure of the SiC porous specimens was carefully examined as well as the elemental and phase content at the microscale. The oxidation and thermal shock resistance of the porous SiC structures and model specimens were also studied, as well as the thermal and mechanical properties. The pure and dense CVI/CVD-SiC coating considerably improves the mechanical strength, oxidation resistance and thermal diffusivity of the material.     

A modified creep model of polylactic acid (PLA-max) materials with different printing angles processed by fused filament fabrication

The creep behavior caused by the viscous mechanical effect of biodegradable polylactic acid (PLA-max) material is of great significance to its application. To better understand the creep properties of PLA-max materials processed by fused filament fabrication, the effects of printing parameters including printing angle and layer thickness on them are studied theoretically and experimentally. The experimental results show that within the range of loading stress and loading time, the creep deformation of the PLA-max material decreases with the increase of the printing angle or the decrease of the layer thickness. The experimental results are processed and analyzed, and a modified Burger model is proposed to quantitatively analyze the creep deformation of PLA-max. In this modified Burger model, the four parameters are functions of printing angle and stress level. The modified model can accurately calculate the creep deformation of the specimen at other printing angles, which provides an important reference for the design of functional structures with specific mechanical properties.     

Effect of silane coupling on the properties of polylactic acid/barium ferrite magnetic composite filament for the 3D printing process

Poly(lactic acid) (PLA)/barium ferrite (BaFe₁₂O₁₉) with different composition ratios was fabricated by magnetic composite filaments using an extrusion process for a 3D printer. The silane modified surface of BaFe₁₂O₁₉ was studied to observe the effect on the mechanical, morphology, thermal, and magnetic properties of magnetic composite filaments. The results showed that the silane treated surface BaFe₁₂O₁₉ not only enhanced the mechanical properties of magnetic composite filaments, but also improved adhesion and homogeneity between the BaFe₁₂O₁₉ filler and PLA matrix. Moreover, the thermal and magnetic properties of magnetic composite filaments were not obviously changed after adding silane treated surface BaFe₁₂O₁₉. The achievement of the magnetic composite filaments preparation with silane treated surface BaFe₁₂O₁₉ for the 3D printing process could become a guideline to develop and design other magnetic composites products in the near future.     

Influence of irradiation parameters on the curing and interfacial tensile strength of HAP printed part fabricated by SLA-3D printing

In this paper, the curing and the interfacial tensile strength of a hydroxyapatite (HAP) printed part, fabricated by stereolithography (SLA), are systematically evaluated. First, a stable HAP paste was developed with a viscosity suitable for SLA-3D printing. In the curing process of SLA-3D printing, an evident laser removal phenomenon occurred on the upper surface of the cured HAP paste, which was not mentioned in other studies. Therefore, the influence of irradiation parameters on the curing characteristics of HAP paste was investigated, while a modified critical laser exposure inequation was established, to derive the curing range of HAP paste under a UV spot. Next, the influence of irradiation parameters on the interfacial tensile strength of HAP printed part was tested and analyzed in detail. Ideally, the laser removal site formed on the cured surface would increase the contact area with the next layer and facilitate a stronger mechanical bond between layers.     

Optimized preceramic polymer for 3D structured ceramics via fused deposition modeling

3D structured ceramics stemmed from preceramic polymers via additive manufacturing have attracted much attention recently. However, these polymers with high ceramic yield are so brittle that extrusion-based additive manufacturing techniques are hardly able to be utilized for assembling 3D structures. Herein, we developed a strategy to prepare feedstocks for these manufacturing techniques, i.e., utilizing a small amount of thermal-plastic polymer to optimize the preceramic polymer while good compatibility is required between the two polymers to ensure a homogeneous mixture. Polycarbosilane and polypropylene were selected as the representative materials. Polypropylene occupied a small proportion (≤5wt.%) and significantly improved the formability of the precursor. Three-dimensional SiC were obtained via fused deposition modeling combined with crosslinking and pyrolysis. The SiC ceramic filaments showed a mean tensile strength of 471 MPa. The strategy is also applicable to a large field of ceramic systems with corresponding precursor, such as sialon ceramic and multicomponent Si-based ceramics.     

聚乳酸增韧研究进展

总结了聚乳酸增韧改性方面的最新研究进展,为新型聚乳酸复合材料的研究开发提供理论依据;概述了共混、复合、共聚、交联、增塑以及添加成核剂等几种增韧技术,并比较了不同增韧方法的特点;通过对合成方法的改进以及进行共混、共聚、复合及增塑等改性,可以显著改善聚乳酸材料的力学性能并同时保持耐热性和降解性能不受影响;开发更加高效的增韧改性剂,增加其与聚乳酸分子链间的界面相互作用并提高复合材料的冲击性能已成为研究工作的努力方向。从微观分子尺度上对聚乳酸进行增韧改性以及设计绿色合成路线仍是目前研究工作的重点。