Graphene nanoplatelets/hydroxyapatite in PMMA composites for enhanced electrical properties

doi:10.21203/rs.3.rs-2742694/v1

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Graphene nanoplatelets/hydroxyapatite in PMMA composites for enhanced electrical properties

https://doi.org/10.21203/rs.3.rs-2742694/v1

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published 28 May, 2023

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In this article, the casting method was used to prepare PMMA/hydroxyapatite nanocomposite films incorporated with contents graphene nanopalates (Gnp) of nano-size with combined loadings ranging from 0.5 to 1.5 weight %. The nanocomposite was characterized using Fourier transforms infrared (FTIR) spectroscopy, and. Scanning Electron Microscopy (SEM) analysis of the prepared sample, thermal conductivity, and the electrical properties at (1-10MHz) of the samples.

The results for FT-IR, and SEM showed that the resulting material had a low agglomerated state, with multiple wrinkles of graphene flakes in the matrix of the PMMA. The thermal conductivity increased and improvement between (0.05–1.82) w/m.k and the electrical properties of nanocomposites revealed a significant improvement with increasing the amount of graphene also that exponent s between (1.25 < s < 1.35).

The values of real part ɛ' and imaginary part ɛ’’ were reduced at the lower frequency and became constant at high frequency attributed to the relaxation time. The values of ε″ are high at low frequencies and it is decrease with increase frequencies due to polarization effects or to the dipoles not begins to follow the field variation at higher frequencies. The increase in tan δ with increase in Gnp content due to interfacial polarization mechanism occurred in the films corresponding to frequencies.

hydroxyapatite

graphene nanopalates

thermal conductivity

electrical conductivity

Polymethylmethacrylate (PMMA) is a transparent rigid thermoplastic polymer that is widely used as a shatter-proof replacement for glass. Due to its many technical advantages over other transparent polymers. It is often used, in a sheet form, as light weight or shatter-resistant alternative to glass [1]. PMMA is frequently used because of its moderate physical and mechanical properties, easy processing, and low cost. Non-modified PMMA behaves in a brittle manner when under a load, especially under an impact force, and is more prone to scratching than conventional inorganic glass, while modified PMMA is capable to achieve high scratch and impact resistance under some condition[2]

Hydroxyapatite (HA, Ca₁₀(OH)₂(PO₄)₆) possesses chemical and crystallographic similarities to inorganic components of the bone matrix and the teeth [3] with excellent osteoconductivity and osteoinductivity. It has been clinically used as bioactive coatings on dental and orthopedic implants, enabling the adhesion and proliferation of osteoblast cells on the prosthetic surface, and resulting in biological fixation between bone tissues and the implant [4]. However, one primary limitation, when used under major load bearing, is its poor mechanical properties, such as low fracture toughness and tensile strength [5].

Graphene nanoplates is only one atom thick and thus has attracted interest in the field of materials science and condensed matter physics [6]. It is a two-dimensional sheet of sp² bonded carbon arranged in a honeycomb lattice and is the building block of carbon allotropes like zero-dimensional fullerenes, one-dimensional carbon nanotubes (CNTs) and three-dimensional graphite [7]. It is potentially proved that graphene and its derivatives are used in many applications like super-capacitors, solar cells, batteries, biomaterials and bio sensing due to their exclusive physicochemical properties, good mechanical, thermal, electrical conductivity and high surface area [8].Graphene has a large specific surface area, thus the protein absorption capacities of these materials will be higher when compared to the other nanomaterials including solar cells, electrical devices, IR-windows, microwave absorption panels, and sensors [9].

Tripathi et al.[10] have studied the effects of filler incorporation techniques on the electrical and mechanical properties of reduced graphene oxide (RGO)-filled poly(methyl methacrylate) (PMMA) nanocomposites. Composites were prepared by three different techniques, viz. in situ polymerisation of MMA monomer in presence of RGO, bulk polymerization of MMA in presence of PMMA beads/RGO and by in situ polymerization of MMA in presence of RGO followed by sheet casting ranging 0.1 to 2% w/w) of RGO on the electrical, thermal, morphological and mechanical properties of PMMA .

Elham Aram et al. [11] have used Poly(methyl methacrylate) (PMMA)/poly(ethylene oxide) (PEO) (90/10) nanocomposites containing various amounts of graphene nanoplatelets were fabricated by solution method and then the effects of graphene concentration on morphology, thermal, mechanical, and electrical properties of the nanocomposites were investigated. Characterization by electron microscopy and X-ray diffraction of the nanocomposites showed a relatively good dispersion of graphene sheets in the polymer matrix. The results indicated that thermal stability, glass transition temperature, and mechanical properties of PMME/PEO blend improved by increasing graphene concentration. The electrical properties of polymer nanocomposites revealed a significant improvement with increasing the amount of graphene and the percolation threshold was about 3.33 wt% of graphene

H.M. Alhusaiki-Alghamdi [12] used the casting method to prepare PMMA/PCL nanocomposite films incorporated with low contents graphene oxide (GO) nanoparticles. The dispersion of GO acted as reinforcing in the PMMA/PCL blend and hence improving the mechanical and electrical properties of the samples. The values of ε' and ε'' were reduced at the lower frequency and became constant at high frequency attributed to the relaxation time. The AC electrical conductivity was increased.

The main purpose of the present work is to prepare PMMA/HA/Gnp using casting preparation method, and to investigate the structure, thermal conductivity, and electrical properties to understand the effects of Gnp on the structure formation and crystallization behaviors of the PMMA/HA blend.

PMMA/HA blend prepare with weighted 80/20 (2wt%) by using electronic balance of four digits type (Sartorius H51) and then dissolved in chloroform to obtain solution of PMMA/HA by slowly in 60 ◦C for 2 hours warming until the solution become viscous using magnetic stirrer hot plate then cast on the glass plates in room temperature for 24 hour to ensure complete solvent removal.

PMMA/ HA/Graphene nanocomposite films were prepared by many steps a weight percent of nanoparticles were used with different weight percentages (0.5, 1, and 1.5 wt %). Initially graphene was swollen in chloroform by mixing for 2 hours while PMMA/HA dissolved in chloroform then nano graphene solution were mixed by shearing mixer at 800 rpm for one hour to have good distribution and less agglomeration. After two solutions were mixed for an hour and sonication process was again introduced in order to improve dispersion of nano filler in the polymer matrix .Then cast on the glass plates and then kept at 60 C° in the vacuum oven for 24 hour to ensure complete solvent removal.

Characterizations: The surface morphology of graphene nanoplates was observed with AFM micrographs as shown in Fig (1). It emerges that average diameter 59.22 nm for Graphene nanoplates.

Thickness: Determination of thickness of PMMA/HA and PMMA/HA/Gnp composites calculated by electronic digital micrometer to measure the thickness of composites was approximately 115 µm .

Fourier Transform Infrared (FTIR) Analysis: The infrared spectra were recorded with FTIR -7600 in range 400 to 4000 cm^-1.

SEM Scanning Electron Microscopy: The morphology of the films was characterized by scanning electron microscope, operating at 200 kV accelerating voltage. The surface of the samples was coated with a thin layer of gold by the vacuum evaporation technique to minimize sample charging effects due to the electron beam.

Thermal conductivity :-Thermal conductivity coefficient was calculated to the data that measurement by using the lee^'s disk {manufacture by Griffin and George / England}, thermal conductivity coefficient was calculated by using the following equation [13]

K[T_B-T_A/d_s] = e[ T_A+ 2/r[d_A+d_S/4] T_A+ 1/2r (d_ST_B)…….1

H=IV=πr²e(T_A+T_B)+2πre[d_AT_A+(1/2)d_S(T_A+T_B)+d_BT_B+d_CT_C] ….2

Where K: Thermal conductivity Coefficient ,e: Represents the amount of thermal energy passing through unit area per second disk material, H:Represents the thermal energy passing through the heating coil unit of time , d:Thickness of the disk (mm) , r: radius of the disk(mm), d_S: Thickness of the sample(mm) , T: temperature of the disk(^ᵒc).

A.C conductivity: The A.C conductivity σac (ω) was calculated by using the relation[14]:

σtot( ω) = σac(ω) +σdc ............3

σac(ω)=σt – σd.c =Aω ^s ………….4

Where σdc is the D.C. conductivity. (A) is a constant independent on temperature, (ω =2*π*f) and (s) is the frequency exponent.

The dielectric permittivity of a material (ε) is considered a complex quantity with a real part (εr) and imaginary part (εi ) and is given by Eq.5 [14, 15]

ε = εr + εi …………………………… .5

The values of the real and imaginary parts of dielectric permittivity εr and εi are calculated from the value of capacitance measured in parallel mode (Cp) and the loss tangent (tan δ). The values of Cp and tan δ are measured for the room temperature and frequency range of 10kHz–100MHz. The values of εr and εi are calculated according to the following Eq.(6) and (7) :

ε´ = Cp d εo A …………………6

ε´´ = ε´ tan(δ) where δ =90 – φ ………………….7

tan δ= ɛ´´/ɛ´ …………………..8

where εo is the permittivity of free space, and d and A are the sample’s thickness and cross-section area, respectively.

The FTIR spectrum of PMMA HA peak at 1731 cm^− 1 appeared due to the presence of ester carbonyl group stretching vibration. The broad peak ranging from 1260 − 1000 cm ^− 1 can be explained owing to the C-O (ester bond) stretching vibration. The band from 950 − 650 cm^− 1 is due to the bending of C-H. The peak ranging from 3100 − 2900 cm-cm ^− 1 is due to the presence of stretching vibration and the band at 3000 cm^− 1 is assigned to CH3 stretch vibration. A very strong band appeared at 1735 cm^− 1 belongs to the carbonyl group. Band at 2940 cm^− 1 is from –CH2 stretch vibration. The C-O-C peak at 1254, 1200 cm^− 1 and an intense phosphate peak is found is found at 1040 cm^− 1. The additional phosphate group bands at 810 cm^− 1 and 757 cm^− 1. Fourier transform infrared spectroscopy (FTIR) is a widely used analytical technique that is routinely applied to the characterization of biomaterials. Hydroxyl is observed at 3569 cm^− 1 in the spectra of synthetic commercial hydroxyl apatite. The broad peak ranging from 3200–3600 cm^− 1 can be explained owing to O-H group vibration. The band at 1450 cm^− 1 is assigned to the CO3 2- stretching. An intense PO4 3- peak appeared at 1048 cm^− 1. Additional phosphate group bands are found in the region 963, 875, 633 and 472 cm^− 1, a sharp peak of OH stretch vibration band appeared at 3570 cm-1 and a less intense CO3- peak appeared at 1450 cm^− 1. An intense PO4 3- peak appeared at 1048 cm^− 1. The C-O-C peak at 1254, 1200 cm-1 and an intense phosphate peak is found is found at 1040 cm^− 1. The group bands at 810 cm-1 and 757 cm^− 1 that agree with Krithiga G. et al. [16]

In PMMA/HA/1.5% Gnp composites shows the spectrum of Graphene clearly shows oxygen possessing groups at 1054, 1223, 1395, 1622, and 1729 cm^− 1. These correspond to the C − O stretching vibration, C − OH stretching vibration, C − O−H deformation vibration, C − C stretching vibration, and CO stretching vibration of COOH groups.the presence of graphene nanoplates sheets by the emergence of clear absorption bands of methylene (CH2) groups nearly around 2854 and 2918 cm^− 1. The stretching band of pure HAP peaks shifted from 1035 to 1029 cm^− 1 due to the interaction of HAP with Gnp. This indicates the formation of strong hydrogen bonding between the HAP and Gnp sheets that agree with H.M. Alhusaiki-Alghamdi [12]

SEM image of the PMMA/HA blend shown in Fig. (3) evaluation indicates the formation of uniform and solid nanofibers with random orientations.

In PMMA/HA/1.5 Gnp consisted of thin flakes, with a well-defined few-layer structure. Note the wrinkled surface, which could play an important role in enhancing electrical application

Thermal Conductivity Of Pmma/ha/gnp Nanocomposites

In thermal conductivity of PMMA/HA loaded with graphene nanoplates in varying proportions, the PMMA/HA acquired thermal conductivity of 0.05 Wm^− 1K^− 1 for PMMA without graphene shown in Table (1).

The experimental results also showed that the thermal conductivity of the samples increased in general with the percentage (0.5–1.5%) of graphene nanoplates in the composite. This is attributed to the increase in conductive pathway and network density with increased number of filler particles [8].

It has been observed that the incorporation of carbon-based nanomaterials significantly increases the thermal conductivity of different polymeric-based materials. Considering PMMA an increase in thermal conductivity could be advantageous in terms of heat dissipation during the polymerisation reaction, potentially reducing the risk of thermal necrosis. The conductivity of the Gnp is improved as it undergoes treatment with heat, light, and chemical reduction, and the majority of graphene characteristics can be restored in this manner. The smaller contrast in thermal conductivity of polymer between (0.1-1) W/m.K and that increased the thermal conductivity of composites because thermal conduction can be achieved by phonons and electrons. However, the PMMA and hydroxyapatite are an insulator which means the electrons will not play an important role in thermal conduction. The physics of phonons (the main heat carriers in graphene) has been shown to be substantially different in 2-D crystals, such as graphene because of graphene sheets may provide lower interfacial thermal resistance and thus produce highly-improved conductivity for polymer composites even impart significant anisotropy to the thermal conductivity of the polymer composite due to the measured in-plane thermal conductivity as much as ten times higher than the cross-plane conductivity[17]

Table (1): Thermal conductivity values of PMMA, PMMA/Gnp composites

Sample	Thermal conductivity W/m.Kº
PMMA/HA	0.05
PMMA/HA/0.5 Gnp	0.10
PMMA/HA/1 Gnp	0.21
PMMA/HA/1.5 Gnp	1.82

In Figures (4 &5) show the electrical conductivity of the polymer blend PMMA/HA due to charge carriers build up and for PMMA/HA/Gnp the A.C. hopping conduction is possible to distinguish different characteristic regions of frequency. At extremely low- and low frequencies, the ac conductivity is practically constant; then, there is a region of frequencies, where the conductivity increases strongly with frequencies. Figures (4) can be shown that the conductivity obeys the empirical law of frequency dependence given by the power law of the form: σ_AC(ω) = Aω^s[18]. The variation of the exponent s with temperature gives information on the specific mechanism involved and the value of s was found to be 1.25 < s < 1.35 as shown in Ttable(2) below.

Table (2): the value of exponent s factor of PMMA/HA, PMMA/HA/Gnp composites

Sample	S
PMMA/HA	1.3079
PMMA/HA/0.5Gnp	1.305
PMMA/HA/1Gnp	1.2534
PMMA/HA/1.5Gnp	1.3067

In the case of the transport in disordered media, the low – frequency conductivity has the same frequency dependence as already observed in the all PMMA/AH/Gnp samples, which characterizes a process of hopping conduction.

Results of dielectric constant for with frequency (f) at room temperature for different types of samples (PMMA/HA, PMMA/HA/0.5Gnp, PMMA/HA/1Gnp & PMMA/HA/1.5Gnp) are illustrated in Fig. (6).

It shows in Fig. (6) that the dielectric constant ε´ decreases with increasing frequency and increases with increasing with the addition of graphene to PMMA at low frequencies, where the reason for this is due to the great contribution of graphene in the process of electric polarization, which in turn increases the dielectric values. This interpretation also applies to the addition of the HA to the samples. At higher frequencies, charge carriers are unable to follow the rapid changes in the applied electric field, resulting in low values of permittivity. Decrease of dielectric constant with the applied electric field frequency can be explained based on several types of polarization (ionic, orientation, and electronic). The ionic polarization due to the application of an electric field on a material induces a displacement of the positive ions relative to the negative ions. this polarization of sample is related to the structure of the material. Under an applied field, the permanent dipoles of the molecules are oriented in the direction of the field[19]. The electronic polarization is due to the displacement of the electron cloud of the atom with respect to its nucleus, which represent the electronic polarization. The last one, electron polarization is due to a relative displacement of the nucleus of the atom relative to all the electrons that surround it. This type of polarization is established in a very short time and remains sensitive up to high frequencies.

The variations of dielectric losses ε´´ with frequency at different samples are shown in Fig. (7). It can be seen that the dielectric loss of the composites exhibits the strong frequency dependence. The dielectric loss increases slowly in the low-frequency range, followed by a quick decrease in the high frequency range. The dielectric loss of the composites follows the dissimilar trend with frequency as the dielectric constant because the samples behave as a capacitor at low frequency and Omic behavior at high frequency. This interpretation applies to the relationship between Tan δand frequency because the values of Tanδ are related to the values of the dialectical Loss as in the Fig. (8).

The impedance is a complex function of frequency, consist of real part of impedance reflects Ohmic resistance of the sample whereas imaginary par accounts for non-Ohmic resistance for example capacitance reactance. Figures (9) shows the relation between the impedance and frequency, it observed that the impedance decreases rapidly in low frequency range. The reason for this is the relationship between them (Z = 1/wc),where the sample becomes as open circuit to the A.C. current[20].

The incorporation of Gnp to PMMA/HA at a loading level of 0.5-1-5 wt. % has potential for use in electrical devices, IR-windows, microwave absorption panels, and sensors. The addition of Gnp increases and enhances the thermal and electrical conductivity due to charge carriers build up. The values of ε´, ε´´, Tan δ are high at low frequencies and it is decreased with increase frequencies due to polarization .

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No competing interests reported.

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Journal Publication

published 28 May, 2023

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Editorial decision: Major revision
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07 Apr, 2023
Reviewers agreed at journal
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You are reading this latest preprint version

Graphene nanoplatelets/hydroxyapatite in PMMA composites for enhanced electrical properties

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Abstract

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Introduction

Experimental Work

Results And Discussion

Thermal Conductivity Of Pmma/ha/gnp Nanocomposites

Conclusion

References

Additional Declarations

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