Preparation And Performance Characterization

Published Date: 02 Nov 2017

Soft polymer composite (SPC) was prepared by by mixing polyvinyl alcohol (PVA) host system with conducting carbon black (CCB) as single nano entity (SNE) and CCB+Montmorillonite (MMT) clay as mixed nano entities (MNE). The impact of filler demonstrated the ‘destroyed crystalline phase’ (DCP) to amorphous phase. The destroyed crystalline phases are also evident from XRD spectra where interplaner distance decreased. Addition of MNE resulted in inhibition of foreign bond formation and also prevented stretching and bending of substrate molecules detected by Fourier Transform Infrared (FTIR) spectroscopy. Soft morphology of SPC was viewed by optical and scanning electron microscopy. Improvement of glass transition temperature (Tg), Young’s modulus and AC conductivity was observed which can be corelated as a function of SNE and MNE loading.

Keywords: soft polymer composites, conducting carbon black, single nano entity, mixed nanoentity.

INTRODUCTION

The performance and properties of polyvinyl alcohol (PVA) as function of molecular weight and its compatibility for various applications such as in in composite form is demonstrated.[1-4] PVA is unique, water soluble polymer having low PH affinity.[5] Research on filler based polymers has been of much scientific interest for various applications.[6-9 ]Conducting carbon black has unique property of high surface-area-to-volume ratio which can be useful to modify the virgin polymer system. It is useful in pigments and as a reinforcing filler in automobile tires. It reduces thermal damaging of rubbers and improves life of rubbers. It has good mechanical strength. Hence it is the choice of material community.[10] CCB inducted polymer composite pressure capacitance sensor, working on the principal of decrease in composite entire volume as a function of compression due to volume fraction of filler. This is due to CCB conducting chains, which dominate the conductivity of the composite. The net effect was an increase in capacitance or decrease in resistance under external stimuli of pressure.[11] The modern electronic devices need electromagnetic shielding (EMI). This can be achieved by carbon allotropes which have lighter weight, easy moldability and processability.[12]

The mixed carbon allotropes such as graphene, multi-wall carbon nanotubes, carbon black, and graphite powder proved conductivity 103S/cm which was ten times better then CCB. The bulk conductivity depends basically on the packing density of powder compaction of different carbon allotropes which may be optimized.[13] CCB as a single nano entity (SNE) in composite form demonstrated the improved properties. Clay modifies the virgin polymer by offering whiteness, better translucency, reduction of fire slag, low iron and titania enable to improve host system.[14] The Intercalated clay nano particles were dispersed in a continuous polymeric matrix. Intercalation is the process of insertion of a molecule between two other molecules (or groups). It will improve several physical properties such as thermal, electrical and mechanical properties of host material.[15] The clay inducted host polymer system show morphological softness and modifies several physical properties.[16] It was motivation to understand the overall impact performance of soft polymer composite (SPC) by inducting single nano entity (SNE) and mixed nano entity (MNE). Reduction in the interlayer spacing due to combination of CCB as SNE, CCB+MMT as MNE disclosed in the present investigation. The issues related to to phase transformation of soft polymer composite (SPC) which are corelated to the modified structure of host PVA moiety as a function of SNE and MNE loading are adressed.

Experimental

Materials

PVA powder of grade RS-2117 (Lot No.484649) made by Kuraray Japan, Kurray Exceval and supplied by Associated Agencies, Mumbai. CCB powder N991 Thermax supplied by sepulcher Brothers (India) Pvt. Ltd. Chennai. Clay MMT Halloysite was procured from Imerys, New Zealand.

Synthesis of SPC

All samples were prepared using solution blending technique. The varying weight proportions of PVA as a host polymer system with different weight % of CCB and CCB+MMT is shown in Figure (1a) Figure (1b). The sample codes and proportions are given in Table 1. The total weight of PVA+filler was taken as 2gm and weight of PVA and filler was adjusted according to the proportions by its weight. PVA was dissolved in 40 ml water by heating at 80oC. Further, CCB and CCB+MMT were dispersed in the mixture by the magnetic stirrer. The resulting solution was then cast into galvanized iron plates (15cmX15cm) covered by inert high density polyethylene film. These plates were then kept in a hot air chamber at 45oC for a period of 24 hours for evaporation of the solvant. The dry composite films were then peeled off for further characterization.

Characterization

Fourier transform infrared (FTIR) spectroscopy of the SPC was performed with an attenuated total reflection FTIR spectrophotometer (Paragon 500, PerkinElmer, Beaconsfield, United Kingdom) in the wave-number range of 500–4000 cm-1 with a resolution of 4 cm-1. The FTIR spectra were taken in the transmittance mode.

The wide angle X-ray diffraction of the SPC was recorded using Cu Kα radiation of wavelength λ = 1.54060Ao with a graphite monochromator produced by Bruker AXS D8 focus advance X-ray diffraction meter (Rigaku, Japan, Tokyo) with Ni- filtered. The scans were taken in the 2θ range from 4 to 80o with a scanning speed and step size of 1o/mm and 0.01o respectively.

Optical polarizing microscope was used to record the phase morphology of SPC by using Carl Zeiss AX10 vision LE optical microscope. All the measurements were carried out at 25oC.

The Quanta 200 FEG scanning electron microscope (SEM) of versatile high resolution was used to understand SPC morphology.

The thermal analysis of the SPC was carried out using differential scanning calorimetry (DSC-TA Q100). The sample was heated upto 400oC at a heating rate of 10oC/min, under nitrogen atmosphere.

The mechanical properties of SPN were tested on a Lloyd LR10K Universal tensile machine (Lloyd Inst. Ltd, Hampshire, England). A thin film 8 cm long and 1 cm wide (ASTM D 638) was gripped between the two jaws of the tensile machine. The crosshead speed was kept at 5 mm/min. The average value was calculated from a set of at least 10 repeats.

The AC conductivity of SPN was carried out by using Waynn Kerr Impedance Analyzer 6200B, UK, under 20Hz to 20MHz frequency range.

Role of fillers with polymer moiety

CCB known as Thermal Carbon Black (TCB) often referred as MT black. It is derived from natural gas and it is one of the purest forms available of carbon. It has a larger particle size and the lowest degree of aggregation or structure. It is highly useful based on its unique properties include applications in rubber, metallurgy, plastics, insulation, concrete and graphite. In the present polymer system it modifies the structure and properties to a great extent. The MMT- nano clay commercially known as halloysite which offers whiteness, high translucency, reduction of fire slag, low iron and titanium. The filler effect of MNE (combination of both CCB and MMT) demonstrates the DCP.

Results and discussion

FTIR spectroscopy of SPC

The chemical structural characterization was carried out by using the FTIR. The FTIR spectroscopy is carried out in the range of wave numbers 500 to 4000 cm-1. This range can be divided into two broad parts 4000-1500 cm-1 functional group region, arising from absorption by characteristic functional groups present in the sample and 1500- 400 cm-1 - Fingerprint region which arises from complex deformation of substrate molecules. FTIR of virgin PVA film shown in Figure 2 (a) demonstrate a broad peak at 3329 cm-1 corresponding to alcoholic –OH stretch or H bond stretch or a combination of both. The peak between 2900-2800cm-1 corresponding to -CH2 asymmetric stretch. The peaks between 1800 and 1700 cm-1 represent -C=O (ketonic or aldehyde groups) stretch. Those peaks between 1400-1300 cm-1 corresponds to the scissoring and bending of –CH2 molecules. The final major peaks are between 1200- 1000 cm-1 representing –C-O- bond (alcoholic) stretch. Figure 2 ( b - d) shows FTIR spectroscopy of composite film of CCB inducted PVA, only with CCB (sample codes CCB 1, 2, 3). The comparatively deviations in the FTIR spectra of composite was seen compare to pure samples. The peak around 3330 cm-1 was considerably broader than that in pure sample showing greater prevalence of –OH bond stretch. Peaks between 2900-2800 cm-1 exhibit greater absorbance. A similar trend was observed in the subsequent characteristic peaks. No significant new peaks were obtained. Change was only observed in the absorbance and broadness of peaks. The higher absorbance and broadness of peaks can be attributed to a greater percentage of carbon in the sample which resulted in greater bond formation. Figure 2 (e - g) shows FTIR spectra of the samples dispersed with both CCB and MMT (sample codes MMT 1, 2, 3). A trend opposite to that of the CCB sample was observed. The peak around 3330 cm-1 was narrower than that of pure sample and also showed lesser absorbance. No new peaks were seen and all characteristic peaks had lesser broadness and absorbent than pure sample. This implies that the addition of MMT in the samples resulted in inhibition of foreign bond formation and also prevented stretching and bending of substrate molecules.

Structural Characterization of SPC

Structural modification was confirmed by using XRD. XRD of SNE and MNE is shown in Figure 3. Figure 3 shows XRD spectra of ( a) virgin PVA (b) CCB1% (c) CCB 1.5% (d) CCB 2% (e) MMT-2 (f) MMMT-3 (g) MMT-4. The intensity of the diffraction peak increased with an increase in the CCB and CCB+MMT loading %. The major portion of the composite consists of the host polymer PVA. However, the similar pattern of XRD was observed in all the composites with different CCB and CCB+MMT loading%. The interplaner distance of composites evaluated by using Bragg’s diffraction equation and tabulated in Table 2.[17-20]The effect of CCB% inducted PVA demonstrate a decrease in interplanar spacing in the range of d = 0.0422Ao. The additional incorporation of MMT as MNE demonstrates decrease in the interplanar spacing in the range of d = 0.0547A.

Optical Microscopy of SPC

Optical microscopy is crucial in polymer composite due to inexpensive and fast method for batch quality control of particulate products before further manufacturing based on filler transparency and refractive index.[21] It is also useful to find the apparent connection between polymer-ceramic-metal systems as a function of filler[22] and to identify the effect of reinforcing entities such as epoxy with glass fibers.[23] Optical images shown in Figure 4 (a-d) represents SNE loaded 0.5 to 3% indicating its presence in the PVA system. From Figure 4 (e-h) which shows the optical images of MMT-1 to MMT-4 (MNE), clearly indicate that the homogeneous dispersion was achieved in comparison to CCB with polymer system only. The interrupted corona formation indicates more brightness due to MMT, which minimizes the presence of PVA and CCB system. It is well understood that the optical microscopy completely reveals the phase transition of virgin polymer from crystalline to amorphous due to SNE and MNE fillers.

Scanning electron microscopy of SPC

Microstructure of CCB loaded 3% and CCB+MMT (1.5+1.5%) inducted composite films was tested with scanning electron microscopy and the images are shown in Figure 5. SEM images reveal the morphology of CCB inactive surface chemistry relatively free of organic functional groups resulting in superb chemical and heat resistance.[24 ] Nano entity CCB occupied PVA network and the varying resolution image confirmed the filler aggregates may be due to association with PVA. The CCB+MMT incorporated PVA composites show bright and bulky aggregation and more smooth morphology at 40X resolution. Phase conversion of this pristine composites exhibit change in phase from crystalline to amorphous due to destroying crystalline orientation which is also verified by XRD results.

Thermal properties of SPC

Differential Scanning Calorimetry (DSC) is one of the most frequently used techniques in the field of thermal characterization of solids.[25] Thermogram of CCB and MMT inducted PVA composites are shown Figure 6 (a-f). The heating temperature rate of 10oC maintained for all the samples. Thermogram of pure PVA film shown in Figure 6 (a). The glass transition temperature of water soluble PVA resin was observed 48.7oC, with rubbery phase 80.60C and its melting at 197.9oC. Interestingly the MMT 1 sample demonstrates improvement over Tg by 31.8oC with respect to pure PVA. Further increase in MMT loading, decreases the Tg gradually as shown in the Figure 6 (b-e) for different % loading of CCB+MMT. It may due to the phase separation of inducted MNE. The MMT1 and MMT2 samples do not show rubbery phase. However, only for MMT3 and MMT4 samples exhibit rubbery phase in the range of maximum Tm = 1 to 2oC as shown in Figure 6(d) and Figure 6 (e) respectively. Glass transition temperature decrease at higher loading of. The elaborate trend of Tg, Tc and Tm as a function of loading MNE shown in Table 3. The effect of MNE loading exhibit unique thermal properties.[26]

Mechanical properties of SPC

The SNE filled SPC demonstrates significant effect on the mechanical properties of PVA. The improvement in mechanical strain observed in 1% CCB inducted composite. The tensile strength improves very strongly for the 2% CCB inducted composite. It may be due to strong interaction between filler and the polymer. The plots of mechanical propertie are shown in Figure 7 (a, b). However, improvement in the tensile strength of 2% inducted MMT was observed. In comparison to MNE filler, SNE is more effective and exhibit good mechanical strength as shown in Figure 7 (c). The tensile strength dominance may arise due to proper dispersion of CCB and MMT in an exact ratio. [27]As shown in Figure 7(d), MMT-2 sample demonstrates tensile strength of about 4 Mpa. Exceptional improvement of Young’s modulus and tensile strain at break was observed in the sample MMT-2 shown in Figure 7 (e,f).

AC conductivity of SPC

All the electrical measurements were carried out at 27oC by using an impedance analyzer. AC conductivity of SNE and MNE is shown in Figure 8 (a,b). The significant effect of SNE as a filler was found at 50Hz and 100 KHz. The AC conductivity is directly proportional to the SNE loading concentration. Three samples of MNE were tested for AC conductivity. The conductivity of MNE observed at lower frequency increased (for MMT-1), whereas an increase in MNE decreases the trend (sample MMT-2). For further increase in MNE % again improve the conductivity (sample MMT-3). This variation may be due to variation in MNE composition.The SPC prepared by loading SNE and MNE exhibit different trend of AC conductivity.[28-32]

Conclusions

In the present investigation, SPC was prepared by solution casting method .The chemical and structural modification were confirmed by FTIR and XRD. The decrease in interplanar distance was observed which can be correlated by optical microscopy. The destroyed crystalline phases of the composite was observed which may be due to presence of CCB and CCB+MMT in PVA. The improvement in glass transition temperature as a function of loading of the MNE% indicate vanishing of rubbery phase of (MMT-2, MMT-3 samples). Mechanical strength and Young’s modulus for MMT-2 dominates as compare to SNE. Improvement in electrical AC conductivity of SNC is inducted with MNE was different then SNE loading. Overall the impact performance of MNE observed better to that of pristine SPC. Furthermore, these properties may be implemented for various applications in packaging and biomedical sectors.

Acknowledgements

The authors are highly thankful to Sophisticated Analytical Instrumental facility (SAIF) at Indian Institute of Technology, Madras, India for providing thermal and electron microscope facility. Authors also wish to thank Dean of School of Advanced Science at VIT University, Vellore, India, for providing in house facilities under summer research scheme.