THERMO-ELECTRICAL CHARACTERIZATION OF SMART BIO COMPOSITE MATERIAL (PLA-G-CF)

these novel composites can be used as filament material in commercial FDM devices without requiring modification. According to the the printed part quality, functionalities, and applications based on the printed PLA-CF-G composite needed to be further exploited.

Biodegradable and Bio-compactable characteristics of Polylactic Acid (PLA) attracted the attention for numerous biomedical applications. Numerous tissue engineering problems, restoration of weakened or damaged tissues have been reported by using PLA and its copolymers due to their biocompatibility and distinctive mechanical and electronic properties. Similarly, biomedical application of Graphene and Carbon fiber can be exposed with significant potential. Therefore, use of graphene and carbon fiber blend to PLA can positively impact, accelerate and can provide very high influence in tissue engineering, regenerative medicine and other biomedical sectors. In this research study, a screw extruder is used to synthesis PLA-G-CF polymer composite filaments of various nano and micro particles with different particle morphology as reinforcement to PLA matrices. Polylactic Acid (PLA) has been used as matrix material and Graphene and Carbon fiber particles used as reinforcement. These polymer composite filaments are then used for Additive Manufacturing to fabricate medical components. The aim of this work was to investigate a potential method of preparing and processing biodegradable Polylactic Acid (PLA), Graphene and Carbon fiber (CF) through 3D Printing (FDM) Technology. In this research, the capability to use materials with conductive properties are also investigated which may lead to a new generation of 3D smart material. Synthesized composite filaments were characterized through Scanning Electron Microscope (SEM), Differential Scanning Calorimetry (DSC), Tensile Test and Fatigue Test. Among the various blend proportions considered in this work, 80/20% PLA-G-CF blend exhibited the highest elongation and impact strength. Diffe-rential Scanning Calorimetry (DSC) showed the influence of Graphene and Carbon fiber content on glass transition temperature (Tg), melting temperature and degree of crystalline of PLA-G-CF blends. Based on their characterization properties, PLA-G-CF Composite material can focus on various biomedical applications such as scaffolds, implants, drug delivery, cancer therapy, biological imaging etc.
Today, the environmental pollution has become a great concern and evil due to the high impact of plastic wastes in daily use. One of the possible solutions to this problem is to replace the commodity synthetic polymers with a biodegradable and ecco-polymers which are readily susceptible to microbial action. Among them, bio-based and biode-gradable polymers, Polylactic Acid (PLA) has been attracting much attention due to its mechanical properties resembling that of present day commodity plastics such as PE, PP and PS. Pure PLA is usually colorless and glossy thermoplastic polymer with similar properties as that of polystyrene. It can be processed using injection-molding, compres-sion-molding, extrusion, thermoforming etc (Garlotta et al., 2002). Polylactic acid (PLA) polymers are synthesized and obtained from renewable agricultural resources by polymerization of lactide, which is the cyclic diester of lactic acid (Milena et al., 2014). PLA has high modulus, reasonable strength, excellent flavor and aroma barrier capability, good heat seal ability and can be readily fabricated, The tensile strength gained from PLA structures ranges from 15. . Hence, various medical devices have been prepared from different PLA types including degradable sutures, drug releasing micro-scale particles, nano-particles, and porous scaffolds for cellular applications (Rasal et al.,2016).Despite these desirable features, several drawbacks tend to limit its widespread applicability such as high cost, lower mechanical properties, and narrow processing windows (Dedenaro et al., 2016). Thus in order to broaden the applications of PLA, material properties and process ability has to be improved by blending with some higher grade biocompatible material. Even though, PLA polymers have a numerous limitations, significantly, thermal and mechanical properties, its tensile strength and elastic modulus are comparable, but poor toughness limits its use in applications at higher stress levels. For instance, when Polylactic acid interference screws were used for graft fixation during anteriorcruciate ligament (ACL) reconstruction, the devices were reported to be mechanically weaker than their metallic counterparts and often fractured during implantation (Rasal et al.,2016) . Its biodegradation rate is considered to be quite slow, which depends on its crystalline and molecular weight of the material (Dedenaro et al., 2016). Polymer blends as composites are the one of the convenient approaches to tailor the ma-terial properties at low processing cost. Polymer blending is a method for obtaining properties that the individual do not possess and has been widely used for various kind polymers. Blending of PLA with other polymers offers the possibility of improving the degradation rate, permeability characteristics, thermal and mechanical properties. The objective of this research is to produce different blends of PLA, Graphene and Carbon fiber and to investigate the mechanical and chemical characterization. The research also reports natural jute fibers with PLA matrix that results in high 428 ductility instead of tensile strength, as compared to carbon fibers' reinforced parts. Therefore, the brittle carbon fibers and graphene provide high strength and natural fibers exhibiting low brittleness attain higher ductility. The non-treated carbon fibers and graphene with PLA matrix depicted the highest flexural strength of 335 MPa (Matsuzaki et al., 2016). In Rangisetty and Peel's study, they investigated the mechanical properties of the composite materials produced by FDM process. As filament materials, they used PLA, PLA/CF, ABS, ABS/CF, PETG and PETG/CF filaments from commercial products. As the result of study, rigidity of all the fiber reinforced composites were increased, but surprisingly the tensile strengths were decreased probably due to very short fiber lengths (Rangisetty et al., 2016).
Additive manufacturing (AM) or 3D printing is the next generation manufacturing tech-nology that allows manufacturing of complex parts without requiring specialized tooling (Hsiao et al., 2018). Additive manufacturing (AM) is a bottom to up process, creating ob-jects directly from material deposition layer by layer in a controlled manner. Because of this unique approach, AM allows to manufacture complex shaped parts with minimum material wastage and energy consumption (Diegel et al., 2006). FDM/FFF is one of the most prominent and prevalent AM Technology due to its devices simplicity and wide availability of materials. In

Preparation of PLA Composite Filament:
PLA is mixed mechanically with reinforcement powder and then is melt compounded using the screw. This method is widely used for preparing thermoplastic nano-composite. For the filament extrusion process, the PLA composite with 1.5 to 2 wt.% of reinforcement content was mixed to 98 to 98.5 wt.% of pure PLA granules. This mixture was then melted and extruded using the screw extruder. The extrusion temperatures ranged from 180°C to 220°C from the hopper to the die. Thus, the 1.75mm diameter filament was produced and collected for the 3D printing test. Figure 1 demonstrates the equipment setup for preparing the PLA Composite filament by the melt extrusion process.

Fabrication of PLA-TPU/ABS/G/CF Composite Filaments:
The process starts feeding the hopper with the PLA and TPU/ABS/Graphene/Carbon fi-ber granules or pellets in a proportionate condition. The screw extrusion pushes and breaks the granules due to the thermal condition provided by the induction coils. The ex-trusion process continues until the material comes out of the nozzle in the form of wire. The screw extrusion is utilized for the filament composite production.
The main part of the extruder is a barrel containing a screw (also sometimes referred to as an -auger‖, which is connected to a heater towards its far end. On the other end, the screw is connected to an electric motor which will, via mechanical action, transport the so-called resin pellets through the barrel towards the heater. Pellets are gravityfed continuously from a hopper (a kind of feeding funnel). As the motor is continuously driving the auger, the resin pellets are pushed into the heater. The thermoplastic granules will soften and melt because of the heat generated and are then pushed mechanically through a die. Pushing the soft thermoplastics through the die will cause it to form a continuous filament strand with the diameter of the diameter (1.75mm). This process is called extrusion, hence the term -extruder‖.

DSC Studies of the Produced Filaments:
Differential scanning calorimetry (DSC) is one of the thermal analysis methods. It is used for measuring thermal flow difference between the sample and the reference material during the exposure of the sample to a controlled temperature and atmosphere. Thermal properties of pure PLA, PLA Flexible, PLA Hard and PLA-G-CF blend were obtained from their DSC thermographs. This study has ability to monitor the transformations in the solid state, phase changes and to determine the thermodynamic parameters during the controlled heating and cooling of the sample.
The samples of the weight of about 10 mg were put in an aluminium bowl, sealed by a press and then placed in a DSC testing device where glass transition temperature, melting temperature, crystallization temperature etc were determined. The parameters that can be determined by DSC analysis are glass transition temperature, crystallization temperature, melting temperature, polymer crystallinity percentage, specific heat capacity, transformation enthalpy and many others. The variation of glass transition temperature, cold crystallization temperature and melting temperature are briefed in the graph given below. For all of the produced filaments, results of the DSC studies were shown in Figure. According to results Pure-PLA granules and PLA-CF-G shows a glass transition temperature (Tg) around of 170.5 °C and 116 °C. It can be seen in Figure 4 that first transition of PLA-CF-G is at −116 °C and it represents the glass transition temperature. Next transition is in the interval from 0 to 70 °C and it represents PLA-CF-G melting. Endothermic 431 peak of melting is at 65.6 °C. Third transition is cold crystallization of PLA in the interval from 110 °C to 364.9 °C. Exothermic peak of cold crystallization is at 300 °C. This result suggests that the addition of Graphene and Carbon fiber to the PLA mixture does not significantly affect the mobility of the polymer in the polymer network. Visible changes are present in the cold crystallization temperature and enthalpy of crystallization for all measured samples. The values are shifted to lower points after addition of higher fibre concentration, which is common for composite materials.
TGA Analysis or Thermo Gravimetry: TGA analysis measures the amount of weight change of a material, either as a function of increasing temperature, or isothermally as a function of time, in an atmosphere of nitrogen, helium, air, other gas, or in vacuum. TGA analysis can be interfaced with a mass spectrometer RGA to identify and measure the vapors generated, though there is much greater sensitivity when the mass spectroscopy heating is performed in an ultrahigh vacuum system.
TGA determines temperature and weight change of decomposition reactions, which often allows quantitative composition analysis and also used to determine water content or the residual solvents in a material. This analysis is used as one of the several complementary techniques for identification of an unknown polymer composite content. XPS identified the composition of the reinforcements and revealed the presence of PLA composite as residues of a lower temperature TGA run than the high temperature run shown below. TGA was then performed on the material to find the weight percent of each material. The sample was heated from room temperature to 400°C at a rate of 5°C/min in air. The TGA curve (below) is labeled in terms of the identity of the components.

Thermo-Electrical characterization of Smart material:
The research also concentrates on employing electrical conductive materials in the composites to obtain a smart material. It is possible to 3D print active or passive elements that are printed on their own same materials. In this study, Commercial Polylactic acid (PLA) and FDM represent a benchmark to understand which the real potentialities of smart objects 3D printing are. PLA-G-CF Composite conductive filament has been characterized in terms of resistivity. Then a resistance vs temperature characteristic of this material was attained, which are a new class of low cost materials that promise to substitute metals and semiconductors, opening the way to a new generation of 3D printed smart objects. The results of the conductive PLA-G-CF Composite thermo-electrical characterization indicate that this material is not only exploitable for its electrical conductivity, but also for its significant variation as a function of temperature. Future investigations will be focused on more complex objects in which the PLA-G-CF conductive smart composite in 3D pattern which can be employed for both temperature sensing and electrical pulse sensing.

Conclusion:-
Fused filament fabrication (FFF) is a promising additive manufacturing (AM) technology due to its ability to build thermoplastics parts with advantages in the design and optimization of models with complex geometries, great design flexibility, recyclability and low material waste. This technique has been extensively used for the manufacturing of conceptual prototypes rather than functional components due to the limited mechanical properties 432 of pure thermoplastics parts, new 3D printing filament from PLA-Graphene-Carbon fiber composite was successfully prepared by solution mixing and followed by melted extrusion using a screw extruder. Characterization results shows that these novel composites can be used as filament material in commercial FDM devices without requiring modification. According to the results; 1. The graphene and Carbon fiber reinforced PLA composite filaments for FDM type 3D printer were produced through a twin screw extruder between 190oC -220oC without degradation of the matrix. 2. Thermal properties of neat PLA and PLA-CF-G blends were obtained from their DSC thermographs. DSC studies showed that produced filaments were compatible with commercial 3D printers because of having lower Tg values. However, a Melt Flow Index (MFI) should be applied on the composite polymers for determining exact processing temperature. 3. The solvent system improved the Graphene and Carbon fiber dispersion capability in the PLA matrix. 4. Graphene and Carbon fiber dispersion improved the thermal properties of the PLA-CF-G composite. 5. SEM microstructure of fracture surfaces indicated PLA-CF-G demonstrated a higher-porous surface with the presence of dispersed Carbon fiber and Graphene flakes embedded in the PLA matrix. The smaller size and the more uniform distribution of Carbon fiber and Graphene were the critical keys for enhancing the mechanical behavior and for the thermal diffusivity of the composite. 6. During the extrusion process, the nano composite filaments need to be fabricated-granulated for a couple cycles to achieve well dispersion of the reinforcement particles in the PLA matrix. 7. Improving mechanical properties verified the feasibility of 3D printed PLA-CF-G for potential use in engineering applications. The tensile strength and Young's modulus of PLA were enhanced naturally by adding Carbon fiber and Graphene. Besides, the elongation at break decreased and needed to be further improved.
Our study demonstrated one of the active attempts to print PLA-CF-G based composite using FFF 3D printing process directly. However, the printed part quality, functionalities, and applications based on the printed PLA-CF-G composite needed to be further exploited.