Research ArticleAdditive manufacturing of CNTs/PLA composites and the correlation between microstructure and functional properties
Introduction
The surging field of polymer bonded carbon nanotubes (CNTs) has provided promising opportunities for transferring inherent properties of CNTs into macroscopic applications in composite materials [[1], [2], [3]], sensor [4,5], electric drive technology [6], and thermal insulator [7], etc. The incorporation of CNTs into polymer matrix has guaranteed great potential development of super-strong and super-stiff polymer-based composites. In addition, according to the modification processes [8,9], it is a well-known strategy to employ CNTs as filler for reinforcing polymer matrix for fabrication of functional composites, such as unique electric, light and thermal properties [3]. However, the main barriers for CNTs as filler particles are the dispersion and alignment in polymer matrix [5]. CNTs can be bundled and intertwined together and form bulk block in polymer matrix due to the high length-diameter ratio and anisotropic properties [8]. This may weaken the reinforcement function and dispersity of CNTs in polymer matrix, and further decrease the stability and other properties of composite. The selection of proper polymer matrix and decoration of CNTs surface [9] are the two main ways to solve the problem. The decorated CNTs with a low loading, which dispersed relatively homogenous in the polymer matrix, can be fabricated by solution casting, in situ polymerization or ultrasonication for a long time [10].
Poly(lactide) (PLA) is one of the most promising environment-friendly polymers, which possesses attractive mechanical properties, renewability, biodegradability and relatively low cost [11]. Although PLA has these merits, it is brittle with low impact strength, thermal and electric properties, representing the main limitations for the sustainable development in industries [8]. The addition of CNTs filler into PLA matrix is one of the most significant strategies to improve the performance. The most straight forward method remains the direct melt-extrusion blending [8] of CNTs with PLA matrix via twin-screw extruder or single screw extruder. It is reported that the dispersion extent of CNTs within PLA matrix using extrusion technology is affected by the melt-mixing conditions largely, including different screw profile, temperature profile, rotation speed and so on [12]. Murr et al. [13] mixed CNTs and PLA physically and then the mixture was extruded by using a counter-rotating twin-screw mini-extruder. The addition of CNTs can obviously improve the PLA properties due to the strong interfacial interaction between the CNTs surface and the PLA chains. Villmow et al. [14] also prepared graphene nanoplatelet/PLA composite via melting process by using an internal mixer. The results indicated that the incorporation of graphene nanoplatelet improved the crystallinity from 29.6 %–41.9 %, thermal stability, Young’s modulus, and electrical conductivity of PLA. According to the previous [15], the introduction of CNTs into PLA matrix helps to form electrospun fibers made of PLA. It is suggested that the CNTs/PLA composite may be used as raw materials in other fabrication methods, such as electrospun, and three-dimension (3D) printing [16,17]. Moreover, the CNTs/PLA composite may be significantly applied in scaffold for tissue, water treatment, textile, packaging and even flexible electronic devices [[18], [19], [20]]. Thus, it is significant to prepare CNTs/PLA composite-based molding with different functions to broaden their application.
For preparation of CNTs/PLA composite, 3D printing may be a significant process due to the ease of adoption, oriented fabrication, and minimization in material waste [8]. It is a recently developed additive manufacturing (AM) method consisting in the “process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing methodologies”, which is totally different from 2D printing [1,21,22]. It holds the potential application in surgical planning, plastic-based car interior components, metallic structural parts for airplane, inert and hard implants, metal AM for injection molding, spare parts for machines, lighting and other home decoration products, 3D-printed textiles, affordable houses, and 3D-printed confectionery [23]. Among these applications, there are still some barriers hampering 3D printing until now, such as limited performance of 3D-printing materials, inadapted textile CAD data, insufficient qualification and certification of 3D-printing materials and processes, and lack of precision, scalability issues. Therefore, the materials preparation and characterization processes play the key role for the development of 3D-printing. Zhang et al. [24] developed a novel 3D printing technique by integrating 3D printing ice and freeze casting to print graphene aerogels via multinozzle drop-on-demand inkjet with freeze casting to prepare functional graphene aerogels architecture. Guo et al. [25] devoted to the preparation of PLA/MWCNTs nanocomposite with high electrical conductivity for application in 3D liquid sensor. The unique helical configuration was constructed, presenting an excellent sensitivity and selectivity even for a short immersion into solvents. Chizari et al. [26] reported a novel highly conductive CNTs/PLA nanocomposites used as 3D printable conductive inks for fabrication of conductive sensors. According to the previous [1,24,26], works mainly focus on the preparation of 3D printing functional materials with unique properties, such as electrical conductivity, and special structure, magnetic property. Little literature has been devoted to the thermal behaviors and stability for CNTs/PLA composite.
In this research, we focus on the thermal properties of PLA and CNTs composites. A simple process has been developed by combination of melt-extrusion and 3D printing methods to prepare CNTs/PLA composite materials and their molding. The variation of thermal stability of 3D printing materials before and after printing process was investigated. Meanwhile, in order to achieve a well alignment of CNTs in PLA matrix when preparing CNTs/PLA composite, the CNTs and PLA mixture were stretched along one direction via melt-extrusion method. Then, the CNTs/PLA composite was printed with a 3D printer to fabricate the object from the digitally designed 3D model. The electrical, morphology and crystallinity were also studied in this research.
Section snippets
Materials and the preparation of samples
Polylactic acid (PLA) pellets (No. 3052D) were purchased from NATUREWORKS LLC. Multi-walled carbon nanotubes (CNTs) were purchased from Beijing BOYU GAOKE New Materials Co., Ltd. China. The diameter is in 10−40 nm and length is about 10−30 μm. Both the PLA and CNTs were used without further purification. The dry-mixed CNTs and PLA in a polyethylene bottle, and then the mixture was extruded by using a twin-screw extruder (Nanjing Hone Machinery & Electricitron Co, Ltd) with a length-to-diameter
The samples information and 3D printed parameters setting
In this work, the PLA and CNTs composites were prepared before and after 3D printing processes. The 3D printing process is depicted in Fig. 1. To investigate the properties of PLA, CNTs/PLA composite before and after 3D printing, four samples were employed, including PLA, CNTs/PLA composite, and two CNTs/PLA 3D printed objects. The CNTs/PLA composite was prepared by extruding the CNTs and PLA mixture in Section 2.1. The two 3D printed objects were prepared by printing CNTs/PLA composite with
Conclusion
In summary, the CNTs/PLA composites were prepared via the simple process in combination of extrusion and 3D printing processes. The CNTs has been largely aligned in PLA matrix observed in SEM and TEM. Raman results indicate that 3D printing process is helpful to remove the impurities, oxygen-containing functional groups or amorphous carbon with thermal annealing. The increasing content of CNTs loading in CNTs/PLA composites enhances the degree of crystallinity slightly due to the presence of
Acknowledgements
This work was financially supported by the National Natural Science Foundation of China (Nos. 51802259 and 51772243), the China Postdoctoral Science Foundation Funded Project (No. 2019M663785), the Natural Science Foundation of Shaanxi (No. 2019JQ-510), Xi’an and Xi’an Beilin District Programs for Science and Technology Plan (Nos. 201805037YD15CG21(18) and GX1913), the Promotion Program for Youth of Shaanxi University Science and Technology Association (No. 20190415), and the Fund of Key
References (42)
- et al.
Compos. Part B
(2016) - et al.
J. Mater. Sci. Technol.
(2018) - et al.
J. Mater. Sci. Technol.
(2020) - et al.
Prog. Org. Coat.
(2020) - et al.
Compos. Part B
(2018) - et al.
Prog. Polym. Sci.
(2013) - et al.
Prog. Mater. Sci.
(2019) J. Mater. Sci. Technol.
(2016)- et al.
Polymer
(2008) - et al.
J. Mater. Sci. Technol.
(2018)
Compos. Part B
Prog. Polym. Sci.
Appl. Surf. Sci.
J. Mater. Sci. Technol.
Compos. Part A
Compos. Part A
Waste Manage.
Polymer
Compos. Sci. Technol.
Prog. Org. Coat.
Environ. Res.
Cited by (49)
Infill strategies for improving the impact behavior of polymer composites utilizing statistical and thermal analysis
2024, International Journal of Polymer Analysis and CharacterizationDevelopment, Physiochemical characterization, Mechanical and Finite element analysis of 3D printed Polylactide-β-TCP/α-Al<inf>2</inf>O<inf>3</inf> composite
2023, Journal of the Mechanical Behavior of Biomedical MaterialsAtom-economic synthesis of an oligomeric P/N-containing fire retardant towards fire-retarding and mechanically robust polylactide biocomposites
2023, Journal of Materials Science and TechnologyA facile and clean strategy to manufacture functional polylactic acid bead foams
2023, Materials Today CommunicationsAging phenomena of backsheet materials of photovoltaic systems for future zero-carbon energy and the improvement pathway
2023, Journal of Materials Science and Technology