Comparative Performance Study of Acidic Pumice and Basic Pumice Inclusions for Acrylonitrile–Butadiene–Styrene-Based Composite Filaments

Abstract

This study aims to evaluate the effective use of porous pumice powder as an additive in acrylonitrile–butadiene–styrene (ABS)-based composite materials. The influence of pumice addition on mechanical, thermomechanical, thermal, and physical properties of ABS filaments was reported. Two types of pumice, namely acidic pumice (AP) and basic pumice (BP), were melt compounded with ABS at loading levels of 5%, 10%, 15%, and 20% by weight using the melt extrusion preparation method. Composites were shaped into dog bone test specimens by the injection molding process. The physical properties of pumice powders were investigated by particle size analysis and X-ray spectroscopy techniques. Mechanical, thermomechanical, thermal, melt flow, and morphological behaviors of ABS/AP and ABS/BP composite filaments were proposed. According to test results, pumice addition led to an increase in the mechanical response of ABS up to a filling ratio of 10%. Further inclusion of pumice caused sharp reduction due to the possible agglomeration of pumice particles. Composites filled with AP yielded remarkably higher mechanical performance in terms of tensile, impact, and hardness strength compared with BP-loaded composites. According to thermal analyses, ABS exhibited higher thermal stability after incorporation of AP and BP. Pumice addition also resulted in raising the glass transition temperature of ABS. Melt flow index (MFI) findings revealed that addition of two types of pumice led to an opposite trend in the melt flow behavior of ABS filaments. Homogeneous dispersion of pumice particles into the ABS matrix when adding low amounts, as well as reduction in dispersion homogeneity with high amounts, of AP and BP was confirmed by scanning electron microscopy (SEM) micrographs.

Introduction

Polymers are materials of unlimited potential and they are addressing the challenges in numerous industrial fields. Weight saving and cost reduction are the main driving factors for compounding polymers with natural minerals. Developing composite materials plays a key role in addressing these considerations at all levels of production areas. The effective use of natural minerals as additives for several polymers is influenced by some parameters such as content, size, shape, and dispersion homogeneity of mineral particles.^1–4 Mineral additives provide property enhancements for polymer composites by tuning these parameters systematically.

Pumice is a pozzolanic mineral with a sponge-like anatomy. The Cappadocia region in Türkiye has a significant pumice reserve, which is ∼3 billion tons.⁵ Pumice is found in various deposits worldwide, other than in Türkiye, such as in Italy and Greece.^6,7 Although there are several types of pumice classified according to the region of deposits, they are generally divided into two types: acidic pumice (AP) and basic pumice (BP). The major distinction between these two types is linked to their silica composition, in which white-colored AP contains a higher silicate amount compared with black-colored BP.

BP contains iron and magnesium-rich komatiitic tuff, whereas these elements are not found in AP.⁸ Due to the high porosity and low density of pumice, it is mostly used in manufacturing of lightweight building materials as well as for water purification and catalysis support purposes, owing to its heavy metal removal capacity.^9–14 Additionally, phase change materials can be produced for use in food packaging with the help of the porous structure of pumice.¹⁵ Furthermore, pumice incorporation yields a positive effect on the drug release behavior of polymer-based composites in biomedical applications.¹⁶

Research attempts regarding the use of pumice as an additive for several polymers were conducted according to the literature. In this regard, polyolefins, which are widely used engineering plastics, were compounded with pumice by the melt mixing method.^17,18 Research works dealing with polyaniline involving pumice powder were reported by Gok et al¹⁹ and Yılmaz et al.²⁰ They revealed that the thermal stability of polyaniline was increased with the addition of AP without losing conductivity at elevated temperatures.

The effect of pumice inclusion on the mechanical and flame-retardant performance of solution-blended epoxy-based composites was studied by Fleischer and Zupan²¹ and Koyuncu.²² According to their findings, pumice particles enhanced the stiffness and fire resistance of the epoxy matrix. Another work related to the polymer/pumice composite system was reported by Akkaya, in which the feasibility of uranium and thorium adsorption on pumice-filled poly(hydroxyethyl methacrylate) composites was evaluated.²³

Biodegradable polylactide containing pumice minerals was prepared by Dike using a melt extrusion process.²⁴ In his work, pumice addition led to an increase in the mechanical properties of composites. Yavuz et al investigated the effectiveness of polyacrylonitrile/pumice composites for adsorption of metal ions from aqueous solutions.²⁵ They found that the pumice-loaded composite can be utilized as a low-priced adsorbent for removal of metal ions from aqueous media.

Pumice inclusion yielded improvement in sound and thermal insulation performance of polyurethane-based composites according to the work conducted by Soyaslan.²⁶ Pumice powder was also compounded with other thermoplastic polymers by a melt blending technique, including polyvinylpyrrolidone,²⁷ polyvinylalcohol,^28,29 poly β-hydroxybutyrate,³⁰ and polyphenylene sulfide,^31,32 according to the literature survey.

Acrylonitrile–butadiene–styrene (ABS) is a valuable engineering plastic that is widely used in industrial fields, including construction applications, owing to its high level of mechanical and chemical resistance besides the ease of processability. ABS is usually used as an impact modifier to enhance the toughness of thermoplastics, including polyamide,^33–35 polycarbonate,^36,37 and polybutylene terephthalate.^38,39 Recent progress in additive manufacturing technology led to an increase in attention to ABS-based filaments since this polymer is the most preferred thermoplastic for development of three-dimensional (3D) printed parts.^40–43

This present study aimed to compare AP and BP based on their reinforcing effect on the mechanical, thermal, and morphological behavior of ABS-based composite filaments. This work is the first research attempt regarding the use of pumice with the ABS matrix based on a literature review related to characteristic properties of AP and BP minerals. The melt mixing method was preferred since this process is widely applied in industrial fields, in addition to providing a similar processing methodology with additive manufacturing technology.

In this regard, composite filaments were manufactured using the melt compounding technique. Test samples were shaped by the injection molding process to obtain mechanical test data with fewer errors compared with the fused deposition modeling process, stemming from voids in 3D printed test specimens.^44–46 Melt flow index (MFI) measurements of composites were carried out since this parameter gives experimental data related to the operating conditions of the additive manufacturing process.

Methodology

Materials

The commercial ABS polymer was purchased from Lanxess AG (Cologne, Germany) with the trade name Lustran M203FC. AP and BP were obtained in powder form and they were supplied by Yoltas Pumice Products AS (Nevşehir, Türkiye) and Bereketli Mining (Adana, Türkiye), respectively. The chemical composition of pumice powders is displayed in Table 1.

Table 1.

Chemical Composition and Elemental Analysis of Pumice Samples

Content	AP (%)	BP (%)
SiO2	66.8	46.2
Al2O3	9.0	18.7
Fe2O3	7.0	10.3
SO3	5.0	0.1
PbO	3.7	—
ZnO	2.4	—
K2O	1.8	2.1
MnO	1.5	0.1
CuO	1.0	—
MgO	0.6	5.8
Sb2O3	0.3	—
BaO	0.3	—
P2O5	0.3	0.7
TiO2	0.2	2.2
As2O3	0.1	—
CaO	0.1	7.7
Na2O	—	5.9
Si	41.32	29.07
N	0.72	0.78
O	45.57	46.04
Fe	0.19	2.01
Na	1.07	0.73
Mg	0.14	4.46
Al	4.25	4.40
Cl	0.02	—
Ca	6.74	12.50

AP, acidic pumice; BP, basic pumice.

Preparation of composite filaments

ABS pellets and pumice powders were dried at 80°C in a vacuum oven for 3 h to avoid possible moisture content before the production stage. ABS/AP and ABS/BP were mixed manually before the extrusion process with a microcompounder (MC15HT; Xplore Instruments, Sittard, The Netherlands) at 230°C for 5 min at a mixing rate of 100 rpm. The composition of AP and BP in composite samples varied: 5%, 10%, 15%, and 20% by weight.

Produced composite filaments have a diameter of 3 mm. Dog bone-shaped specimens with dimensions of 7.4 × 2.1 × 80 mm³ were prepared using a laboratory-scale injection molding device (Microinjector; Daca). An injection temperature of 240°C and injection pressure of 800 kPa were applied during the molding process. In addition to the filament form of ABS and its composites obtained from the extrusion process, injection-molded dog bone test specimens are displayed in Figure 1.

FIG. 1.

The representative image of ABS and composites in molded and filament forms. ABS, acrylonitrile–butadiene–styrene. AP, acidic pumice; BP, basic pumice.

Characterization methods

Particle size distribution of pumice powders was investigated using a wet method with the Malvern Mastersizer 2000 particle size analyzer. The elemental composition of AP and BP samples was characterized by the X-ray fluorescence technique utilizing the PANalytical Axios advanced device. The energy-dispersive X-ray characterization method was applied to both pumice samples to evaluate the surface chemistry of powders using the energy-dispersive X-ray spectroscopy (EDS) mode of Carl Zeiss field-emmision scanning electron microscopy.

The Lloyd LR30K universal tensile test machine was utilized to investigate tensile properties of composites using a 5 kN load cell and 5 cm/min as the crosshead speed. Charpy impact tests were performed with the test speed of 3.5 m/s and pendulum of 4 J with the Coesfeld MT impact tester. Shore hardness measurements were carried out using a ZwickRoell R5LB041 hardness device. Thermal analyses were conducted using the Netzsch Jupiter STA449 F3 differential scanning calorimeter (DSC)/thermal gravimetry (TG) device.

Test parameters, including a temperature range of 30–650°C, heating rate of 10°C/min, and a constant nitrogen flow of 50 mL/min, were applied during DSC and thermal gravimetric analysis (TGA) tests. The PerkinElmer DMA 8000 test device was utilized to determine the thermomechanical behavior of composites using the dual cantilever bending mode at the temperature range between −100°C and 100°C with a heating rate of 5°C/min at a constant frequency of 1 Hz. Melt flow measurements were done under a standard load of 2.16 kg at 230°C with Coesfeld MeltfixerLT.

Scanning electron microscopy (SEM) photographs of fractured surfaces of composites were examined using Carl Zeiss FESEM. Density measurements were carried out using the Easy D30 digital density meter (Mettler Toledo). X-ray diffraction (XRD) analysis was performed to evaluate the composition of the BP sample at 40 kV and 30 mA using the Rigaku SmartLab XRD device.

Results and Discussions

Physical and chemical characterization of pumice powders

Particle size distribution curves of AP and BP samples are displayed in Figure 2a and b, respectively. The maxima of the curves indicate particle size values at the highest volume percentage, which were found to be nearly 20 μm for AP and 68 μm for BP. According to test data, average particle size [d(0.5) parameter] values of AP and BP powders were estimated to be 16.5 and 40.2 μm, respectively.

FIG. 2.

Particle size distribution curves of AP (a) and BP (b), elemental analysis of AP (c) and BP (d).

The chemical composition of pumice powders is listed in Table 1. The AP sample was found to be rich in SiO₂ content and predominantly contains metal oxides of Al₂O₃, Fe₂O₃, SO₃, PbO, ZnO, K₂O, and MnO. According to Supplementary Table S1, SiO₂ contamination of BP was found to be lower compared with AP. Conversely, BP contains higher proportions of Fe₂O₃, Al₂O₃, and CaO compared with the composition of AP. In addition to Fe₂O₃ contamination, the presence of MgO at a high level in the BP structure contributes to the magnetic behavior for BP.

The formation of magnetic susceptibility for BP with the presence of MgO in the content has been explained in the literature.^47–50 Additionally, the composition of metal oxide compounds that display magnetic behavior, including MgO and Fe₂O₃, in BP is reported as XRD data in Supplementary Data S1. The P-XRD pattern of the material shows the most notable Bragg peaks of MgO and Fe₂O₃ phases such as 29.74° (012), 36.91° (104), and 44.90° (110) for Fe₂O₃ and 50.70° (200) for MgO.

The surface elemental composition of AP and BP was analyzed by EDS modulated to SEM. The EDS spectra of AP and BP taken from the numerated region given in SEM images (Fig. 2c, d) show that (1) the Si content in AP was found to be higher than that of BP and (2) the BP surface exhibited higher Mg and Ca levels than AP. The surface elemental composition of AP and BP, including other elements, is listed in Table 1.

Mechanical properties of composites

The mechanical test data are summarized in Table 2 and representative stress–strain curves of ABS and pumice-filled composites are illustrated in Figure 3. The tensile strength of unfilled ABS improved with addition of both AP and BP. Composites filled with AP displayed the highest strength for a 10% loading level as a 21% increase was obtained compared with unfilled ABS. In the case of BP-containing composites, a 5% filling ratio yielded the highest tensile strength value with nearly 24% enhancement concerning neat ABS.

Table 2.

Mechanical Test Data of Acrylonitrile–Butadiene–Styrene and Acrylonitrile–Butadiene–Styrene/Pumice Composites

Samples	Tensile strength (MPa)	Elongation at break (%)	Tensile modulus (GPa)	Shore hardness (types A/D)	Impact strength (kJ/m2)
ABS	35.1 ± 0.9	7.3 ± 0.6	0.88 ± 0.2	93/74	13.3 ± 0.4
ABS/5 AP	41.2 ± 0.4	9.0 ± 0.8	0.92 ± 0.5	96/76	10.5 ± 0.2
ABS/10 AP	42.4 ± 0.5	7.4 ± 0.5	1.03 ± 0.3	97/78	10.9 ± 0.1
ABS/15 AP	41.3 ± 0.4	7.1 ± 0.6	1.10 ± 0.5	98/80	5.8 ± 0.1
ABS/20 AP	38.8 ± 0.7	8.8 ± 0.7	0.96 ± 0.4	99/82	5.4 ± 0.1
ABS/5 BP	43.4 ± 0.8	9.6 ± 0.5	0.90 ± 0.2	95/76	9.2 ± 0.3
ABS/10 BP	41.4 ± 0.5	10.1 ± 0.6	0.96 ± 0.3	96/77	9.7 ± 0.2
ABS/15 BP	40.9 ± 0.7	9.1 ± 0.4	0.87 ± 0.2	97/79	7.0 ± 0.2
ABS/20 BP	40.0 ± 0.4	9.9 ± 0.8	0.81 ± 0.3	99/81	6.1 ± 0.1

ABS, acrylonitrile–butadiene–styrene.

FIG. 3.

Stress versus strain curves of ABS and composites involving AP (a) and BP (b).

Further inclusion of AP and BP resulted in a drop in the tensile strength of composites. The percentage strain of ABS shifted to higher levels after addition of pumice powders regardless of their type. According to stress–strain curves in Figure 3, the necking tendency of the ABS polymer disappeared with the incorporation of AP. Conversely, BP-filled composites exhibited necking behavior.

The necking tendency of the polymer is related to its ductile characteristic, in which polymer chains show resistance against tensile deformation during the test. In this case, BP particles promote ductility in the brittle ABS polymer, whereas AP addition caused no effect on the ductility of composites. The reinforcing effect of AP on the tensile modulus of ABS was found to be more obvious than that of BP. Moreover, adding higher amounts of BP led to a remarkable reduction in the modulus value of unfilled ABS.

The shore hardness of neat ABS was found to be improved with AP and BP inclusion, as can be observed in Table 2. The increasing trend of hardness values stayed upward with the pumice content in composites, which may stem from the stiffening effect of incorporated pumice particles.^51,52 ABS/AP composites yielded slightly higher shore hardness results for all of the concentrations compared with composites involving BP.

Impact test results of composites were found to show a different trend according to impact strength values listed and illustrated in Table 2 and Figure 4, respectively. The addition of AP and BP led to remarkable reduction in the impact strength of unfilled ABS. Composites filled with 5% and 10% loading levels of AP produced higher impact energy relative to the same amounts of BP. With the higher silica content of AP compared with BP, ABS/AP composites displayed better impact performance since silica contributes to stiffening of the polymer structure.^22,53–55

FIG. 4.

Impact test results of ABS and composites involving AP (a) and BP (b).

Accordingly, the impact strength of composites exhibited a sharp decrease with higher loading levels of pumice. BP-incorporated ABS showed higher impact performance compared with ABS/AP composites in the case of 15% and 20% loading levels. These findings might be due to the formation of weak contact points between the pumice additive and ABS matrix, which are linked to the lack of reinforcing ability that impacts deformation.^56–58

Dynamic mechanical analysis of composites

The thermomechanical response of ABS and its composites is investigated by the storage modulus and tan δ curves with respect to temperature, as visualized in Figure 5a–d, respectively. The sharp reduction in the storage modulus curve and the peak point of the tan δ curve are indications of the characteristic temperature of glass transition (T_g). At this point, relaxation of polymer chains during thermal transition causes structural phase transformation.^59–61

FIG. 5.

Storage modulus (a, b) and Tan delta (c, d) curves of ABS and composites involving AP (a, c) and BP (b, d).

The storage modulus of composites involving addition of high amounts (15% and 20%) of AP and BP was found to be higher compared with their low contents. This finding may be related to the restriction of chain mobility by high loading levels of additive particles.^62,63 AP and BP yielded nearly identical results based on the storage modulus values. According to tan δ curves of composites in Figure 5c and d, pumice inclusion caused no remarkable effect on the width of the tan δ curve of unfilled ABS.

However, the T_g value of ABS shifted to one unit and two units' higher temperatures by the incorporation of AP and BP, respectively.

Thermal stability of composites

TGA curves of ABS and relevant composites are represented in Figure 6a and b. Thermal analysis data of samples are listed in Table 3. The sharp decrease in the weight loss curve indicates thermal degradation of the polymer structure. As can be seen from the TGA curve of ABS in Figure 6, thermal decomposition of ABS occurred through a single step across the range between 370°C and 460°C, which is linked to thermal degradation of the aliphatic butadiene segment and aromatic styrene portion in the ABS structure.^64–67

FIG. 6.

TGA (a) and DSC (b) curves of ABS and composites.

Table 3.

Thermal Analysis and Density Measurement Data

Samples	Td (°C)	Char (%)	Density (g/cm3)
ABS	420.2 ± 0.3	3.98 ± 0.2	1.042 ± 2 × 104
ABS/5 AP	418.8 ± 0.4	7.91 ± 0.5	1.047 ± 4 × 104
ABS/10 AP	416.8 ± 0.5	13.82 ± 0.3	1.088 ± 7 × 104
ABS/15 AP	415.8 ± 0.3	18.25 ± 0.5	1.122 ± 8 × 104
ABS/20 AP	415.2 ± 0.3	22.31 ± 0.4	1.163 ± 1 × 103
ABS/5 BP	417.5 ± 0.4	8.84 ± 0.2	1.068 ± 5 × 104
ABS/10 BP	416.3 ± 0.5	17.06 ± 0.3	1.103 ± 6 × 104
ABS/15 BP	415.1 ± 0.3	19.22 ± 0.2	1.139 ± 9 × 104
ABS/20 BP	414.7 ± 0.4	22.10 ± 0.3	1.178 ± 8 × 104

Pumice inclusion led to a slight increase in the decomposition temperature of the ABS terpolymer since both pumice types decomposed at relatively higher temperatures than that of ABS. Additionally, the filling ratio of AP and BP also showed a positive effect on the thermal stability of composites, in which the decomposition rate of ABS expanded as the added amount of pumice increased. However, no obvious difference was observed in TGA results between AP and BP based on their same contents.

As an exception, the BP-containing composite exhibited a slightly higher result compared with the composite sample involving AP for the loading level of 10% by weight. The amount of final residue of composites, namely char yield, was found to be higher than unfilled ABS and the amount of remaining residue increased with the concentration of added pumice. ABS/BP samples yielded a slightly higher amount of char yield relative to ABS/AP composites thanks to BP containing more thermally stable inorganic oxides such as iron oxide and magnesium oxide.

Figure 6a and b displays the DSC data of ABS and related composites. The maximum point on the exothermic peak of the DSC curve indicates the thermal decomposition temperature (T_d). According to the DSC curve of ABS, T_d of the unfilled polymer was estimated to be nearly 420°C. Pumice addition caused a reduction in T_d of composites. T_d values reduced as the amounts of AP and BP increased. However, the decomposition rate of ABS, which was obtained from the area through the initial and final shoulder peaks, improved after being compounded with pumice powders.

These findings were in correlation with the TGA result discussed previously.

Density measurements of composites

The density measurements listed in Table 3 imply that pumice-filled composites have higher density values relative to ABS. This finding might be due to penetration of the polymer phase into micropores of the pumice structure. AP addition led to a slight increase in density, whereas improvement of density was found to be more substantial with BP since BP comprises heavier compounds such as metal oxides, Fe₂O₃, Al₂O₃, and MgO, with higher percentages compared with AP, as can be obtained from the chemical composition of pumice powders in Table 1.

Reports have shown that ferric oxide, magnesium oxide, and alumina are high-density oxides as a result of anisotropic grains in their structures.^68–70

Melt flow behavior of composites

MFI is a characteristic parameter for commercial polymers, which provides experimental data regarding the processability and rheological property of plastics. MFI values of unfilled ABS and composites are displayed in Figure 7. AP and BP exhibited opposite trends concerning the melt flow behavior. Enhancement in MFI of unfilled ABS was observed after the addition of AP. In contrast, BP inclusion resulted in a decrease in the MFI of ABS.

FIG. 7.

MFI parameters of ABS and composites involving AP (a) and BP (b).

Surface roughness and porous structure of pumice are key parameters that affect the interactions between the polymer melt and pumice powder. AP inclusion caused an increase in MFI thanks to its porous structure, and conversely, a decrease in MFI was observed after BP addition, which is linked to the higher surface roughness and lower porosity of BP compared with AP.^71–73 The density of additives is another parameter that influences the melt flow behavior of the composite system. The MFI of unfilled ABS reduced with BP inclusion because of its higher density relative to AP.

In other words, the melt viscosity of ABS increased in the case of involvement with BP, whereas AP-containing composites displayed a reduction in the viscosity of ABS.

Morphological characterization of composites

SEM images of the composites are given in Figure 8. Homogeneity of pumice particle dispersion into the ABS phase is clearly seen from SEM images of AP and BP samples with 5% and 10% loading levels. Beyond the 10% loading level, further addition of pumice powders led to inhomogeneous dispersion morphology stemming from agglomeration of regions of AP and BP, as represented by circles in Figure 8.

FIG. 8.

SEM micrographs of composites.

These observations are the visual evidence of optimum results for composites filled with a low amount of AP and BP thanks to establishment of effective interactions between the pumice powder and ABS matrix. Accordingly, high amounts of AP and BP caused deterioration in ABS-pumice interactions due to the tendency of pumice particles to form agglomerates.

Conclusions

This research contributes to an experimental investigation of the integration of two types of pumice minerals as potential reinforcing agents in ABS-based composite filaments. Mechanical characterization implied that incorporation of AP and BP conferred tensile parameters on ABS. The tensile strength of ABS/10 AP and ABS/5 BP samples had the highest result among their composites by reaching 42.4 and 43.4 MPa, respectively.

The brittle ABS copolymer exhibited ductile character thanks to incorporation of pumice particles that caused necking behavior. Shore hardness of neat ABS exhibited an increasing trend with the addition of both pumice types, in which six units improvement in the Shore A parameter of ABS was achieved. AP and BP addition had a negative effect on the impact strength of ABS, especially for their high loading levels.

From the mechanical point of view, AP yielded better results than BP in hardness and tensile modulus values, whereas higher performances were reached in tensile strength, elongation, and impact resistance with the help of BP inclusion compared with AP. The thermal analysis revealed that the glass transition temperature of ABS shifted to higher values with inclusion of AP and BP. Pumice addition promoted thermal stability for ABS regardless of the type by reducing the thermal decomposition rate.

MFI measurements implied that AP and BP display opposite effects on the melt flow property of ABS, in which increased MFI values were obtained by AP inclusion in contrast to reduction in MFI values for BP-filled composites. The differences in density, porosity, and surface roughness parameters of the two pumice types were found to be key factors in this finding. AP and BP addition at low loading levels exhibited dispersion homogeneity into the ABS polymer phase, as confirmed by SEM micrographs.

According to overall results, the highest performances were observed for 5% and 10% loading levels of both additives. Pumice-containing ABS composites can be used effectively in the additive manufacturing process as mechanically strong and low-cost polymeric filaments.

Authors' Contributions

Ü.T. was involved in supervision, formal analysis, writing—original draft, review, and editing. S.T. and M.Z. were involved in formal analysis and experiments. M.D. was involved in formal analysis and writing—review and editing. Süha Tirkeş was involved in experiments.

Author Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for this article.

Supplementary Material

Supplementary Data S1