HDPE/geopolymer composites with improved thermal and acoustic insulation for aerospace applications

Abstract

This work reports high-density polyethylene (HDPE) composites reinforced with geopolymers derived from ladle-furnace slag for aerospace insulation. Composites containing 10–30 wt% geopolymer were melt-processed with in-situ compatibilization, and their thermal and acoustic properties were systematically evaluated. Compared with neat HDPE, the best formulation (20 wt% geopolymer with compatibilization) increased the onset degradation temperature to 412 °C (≈ +52 °C), reduced thermal diffusivity to 0.24 mm² s⁻¹ (≈ −20%), and raised the noise-reduction coefficient to 0.27 (≈ +35%). Microstructural analysis indicated uniform particle dispersion and improved polymer–filler adhesion, which underpin the simultaneous gains in thermal stability and sound absorption. These results demonstrate a lightweight, sustainable route to multifunctional insulation materials based on industrial by-products, with clear potential for aircraft interior applications.

Keywords:
high-density polyethylene; geopolymer; composite; thermal diffusivity; acoustic absorption coefficient

1. Introduction

Environmental pollution remains a major global concern, with industrial effluents posing risks to ecosystems and public health[¹]. To mitigate these effects, waste valorization and circular economy strategies have emerged as essential components of sustainable materials engineering[²]. Among various industrial residues, ladle furnace slag (LFS), a steelmaking byproduct, is a promising precursor for geopolymer synthesis due to its high SiO₂ and Al₂O₃ content[³,⁴]. Geopolymers are inorganic aluminosilicate materials produced by alkaline activation reactions, forming semi-crystalline three-dimensional frameworks that exhibit high compressive strength, low shrinkage, excellent durability, and good thermal stability[⁵,⁶].

High-density polyethylene (HDPE) is a semicrystalline thermoplastic known for its low density, mechanical toughness, chemical resistance, and long service life exceeding 100 years[⁷-⁹]. HDPE-based composites are increasingly used in aerospace and automotive industries owing to their light weight, fatigue resistance, and insulation properties[¹⁰-¹²]. The integration of inorganic fillers such as fly ash, silica, and glass powder has been explored to improve HDPE’s thermal and mechanical performance[¹³-¹⁵]. However, there is still a lack of studies combining HDPE with geopolymeric fillers derived from industrial residues, aimed at simultaneously improving thermal and acoustic insulation performance.

The geopolymerization reaction involves dissolution of aluminosilicate sources, polycondensation, and gel formation, leading to a three-dimensional network composed of Si–O–Al bonds. This process transforms raw slag into an amorphous-to-semicrystalline material with strong covalent bonding and high-temperature resistance[¹⁶-¹⁸]. The resulting matrix exhibits exceptional durability and tunable porosity, which can contribute to improved sound absorption and reduced thermal diffusivity.

Incorporating geopolymer fillers into polymers has been reported to enhance mechanical rigidity, flame retardancy, and barrier properties due to the inorganic network and residual hydroxyl groups capable of interacting with polymer chains[¹⁹,²⁰]. Nonetheless, achieving good dispersion and interfacial adhesion remains challenging. Compatibilizers such as maleic anhydride (MA) and organic peroxides can promote chemical grafting between HDPE and the inorganic filler surface, thereby improving stress transfer and stability under thermal cycling[²¹,²²].

To date, no studies have reported HDPE composites reinforced with geopolymer particles for combined thermal and acoustic insulation. This work addresses that gap by developing sustainable HDPE/geopolymer composites derived from ladle furnace slag, emphasizing the compatibilization strategy and characterization of the resulting materials. The expected outcome is a lightweight, high-performance composite suitable for aerospace interior insulation and other engineering applications, supporting circular economy principles.

2. Materials and Methods

2.1 Materials

High-density polyethylene (HDPE, grade HS 5407, Braskem) was used as the polymer matrix. Geopolymer particles were synthesized from ladle furnace slag (LFS) supplied by USIMINAS (Brazil), targeting applications in thermal and acoustic insulation. All reagents were of analytical grade. Sodium hydroxide (NaOH, 98%) and sodium silicate (Na₂SiO₃, silica modulus Mₛ = SiO₂/Na₂O = 3.3), both purchased from Sigma-Aldrich, were employed as alkaline activators for geopolymer synthesis. The chemical composition of the original slag is summarized in Table 1.

Table 1
Composition of the ladle furnace slag.

Component	FeT	FeO	CaO	SiO2	MgO	MnO	Al2O3	S	ZnO	K2O	Na2O
wt%	53.58	26.42	17.30	7.11	5.35	2.09	3.97	0.68	<0.005	0.26	0.08

The high FeT content corresponds to total iron oxides, whereas FeO indicates the presence of divalent iron typical of reducing steelmaking environments.

These oxide phases, along with SiO₂ and Al₂O₃, serve as essential precursors for geopolymer network formation, promoting the development of calcium–aluminosilicate structures upon alkaline activation.

2.2 Methods

2.2.1 Geopolymer synthesis and composite preparation

Geopolymer pastes were prepared by dry-mixing the slag powder with an activating solution composed of Na₂SiO₃ and NaOH (mass ratio 2.5:1, 8 M NaOH). The paste was cured at 70 °C for 24 h, crushed, and ground in a Retsch ZM200 mill (9000 rpm, 15 min) followed by sieving (<75 µm). The macerated 1.4 geopolymer was selected for composite production due to its fine particle size distribution.

HDPE pellets were cryogenically milled after exposure to liquid nitrogen for 2 h. In situ compatibilization was achieved using 3 wt% maleic anhydride (MA) and 0.5 wt% dicumyl peroxide (DCP) as a free-radical initiator to promote grafting between MA and the HDPE backbone. Composites were produced via melt extrusion in a Haake Minilab micro-extruder at 200 °C, 120 rpm, for 7 min. After extrusion, composite sheets were compression-molded using a Carver hot press at 200 °C and 5 tons for 7 min, followed by cooling under pressure for 5 min in a cold press.

Table 2 details the formulations, with samples coded by the percentage of geopolymer (G), HDPE, and MA (e.g., 1.4.20:77:03). A control sample using untreated slag (E.20:77:03) was also prepared for comparison.

Table 2
Samples and their compositions.

SAMPLE	%G	%E	%HDPE	%MA
Macerated slag		100	-
Sifted slag	-	100	-
HDPE pellet	-		100
Ground HDPE	-	-	100
Maleic Anhydrid (MA)	-	-	-	100
Geo. 1.4 chunk	100	-	-	-
Geo. 1.4 macerated	100	-	-	-
Geo. 1.4 sifted	100	-	-	-
HDPE.00:00:00	-	-	100	-
1.4.20:80:00	20	-	80	-
1.4.10:87:03	10	-	87	3
1.4.20:77:03	20	-	77	3
1.4.30:67:03	30	-	67	3
E.20:77:03	-	20	77	3

• %G = mass fraction of geopolymer (alkali-activated slag); %E = mass fraction of raw slag (escória) used directly as filler; %HDPE = mass fraction of high-density polyethylene matrix; %MA = mass fraction of maleic anhydride compatibilizer. Codes “1.4.x:y:z” denote geopolymer-filled formulations, whereas “E.x:y:z” denote raw-slag-filled formulations.

2.2.2 Characterization techniques

FTIR spectroscopy was performed in ATR mode (Perkin Elmer Frontier FT-IR/FIR, 4000–400 cm⁻¹, 4 cm⁻¹ resolution, 128 scans) to identify chemical interactions and compatibilization evidence.

Thermogravimetric analysis (TGA) was carried out using a Shimadzu DTG-60H analyzer under nitrogen from 25 °C to 1000 °C (10 °C/min). DTG curves were derived to determine T_onset, T_max, T_end, and residual mass.

Scanning electron microscopy (SEM) analyses were conducted using a FEI Quanta 250 FEG operating at 15 kV. Samples were sputter-coated with Au (16 nm, 180 s) using a Leica Ace600 coater. Average particle sizes were measured from 30 particles per image (n=30) using ImageJ software.

Shore D hardness measurements followed ASTM D2240 with five replicates (n=5). Standard deviations were calculated and reported.

Density measurements were performed using a 250 mL pycnometer with ethanol (0.793 g cm⁻³, 20 °C) as the immersion liquid. The sample density was calculated considering the measured masses of the empty pycnometer, the pycnometer with ethanol, and with the sample immersed, following the standard displacement method described in ASTM D792. Five replicates (n = 5) were conducted, and average values with standard deviations were reported.

Thermal diffusivity was measured by Laser Flash Analysis (Netzsch LFA 457, ASTM-E-1461) at 25 °C using 9.75×9.75 mm disks (0.92 g/cm³).

Acoustic absorption coefficient (AAC) was evaluated according to ASTM-E-1050 using an impedance tube equipped with two microphones and white noise between 100 and 3150 Hz. The was obtained as the average of the sound absorption coefficients at 250, 500, 1000, and 2000 Hz, following the ASTM C423 standard. The NRC value was calculated using Equation 1.

$$NRC=\left(\left(\alpha 250+\alpha 500+\alpha 1000+\alpha 2000\right)/4\right)$$ (1)

where, α = is the arithmetic mean of the values found for the acoustic absorption coefficients at a given frequency.

3. Results and Discussion

3.1 FTIR analysis

The FTIR spectra of neat HDPE and its composites (Figure 1) revealed the characteristic absorption bands of polyethylene and confirmed the incorporation of geopolymer particles into the polymer matrix. The main CH₂ stretching vibrations appeared at 2915 and 2848 cm⁻¹, corresponding to asymmetric and symmetric stretching modes of the methylene groups, while the bending vibrations were observed at 1470 and 720 cm⁻¹. A broad band at 3380–3400 cm⁻¹ was attributed to hydroxyl groups, which became more pronounced in the compatibilized composites, indicating the presence of interfacial interactions between the polymer and the inorganic filler.

Figure 1
Fourier transform infrared (FTIR) spectrum of (a) HDPE, ladle furnace slag and geopolymer 1,4; (b) the 1.4:30:67:03 composite and HDPE.

In the geopolymer phase, typical Si–O–Al stretching vibrations appeared around 950–1000 cm⁻¹, consistent with the formation of aluminosilicate networks. A noticeable shift in this band from 963 to 935 cm⁻¹ suggested increased polymer–filler interactions and partial modification of the geopolymer surface due to the grafting reaction. The presence of new absorption at 1715 cm⁻¹ in the compatibilized composites confirmed the formation of carbonyl groups from maleic anhydride (MA) grafting, which improved the interfacial adhesion between HDPE and the geopolymer particles[²³-²⁵].

These findings indicate that the peroxide-initiated MA compatibilization promoted chemical bonding at the interface, resulting in enhanced adhesion and dispersion. Similar behavior has been reported for MA-functionalized HDPE systems containing inorganic fillers[²⁶,²⁷].

3.2 Thermogravimetric analysis (TGA)

The thermal stability of HDPE and its composites was evaluated by TGA and DTG (Figures 2 and 3).

Figure 2
Geopolymer 1,4 and ladle furnace slag. (a) TGA; (b) DTG.

Figure 3
TG (a) and DTG (b) of HDPE and composites manufactured with different concentrations of geopolymer 1,4, without and with compatibilizer.

The main thermal parameters (T_onset, T_max, T_end, and residue) obtained from the thermogravimetric curves are summarized in Table 3. Neat HDPE exhibited a single-stage degradation process starting at 359 °C and peaking at approximately 480 °C, typical of polyethylene decomposition under inert atmosphere[²⁸]. Incorporation of geopolymer increased the onset degradation temperature for all composites, confirming the protective barrier effect of the inorganic phase.

Table 3
Data obtained in Thermogravimetric Analysis (TGA).

SAMPLE	Tonset (°C)	Tmax (°C)	Tend (°C)	Residue (%)
Slag	25.0	-	1000.0	95.1
Geopolymer 1.4	25.0	-	1000.0	84.2
HDPE	359.8	469.2	501.0	4.3
1.4.20:80:00	401.9	457.9	490.1	24.4
1.4.10:87:03	403.6	469.2	508.9	18.8
1.4.20:77:03	412.4	463.1	479.5	71.9
1.4.30:67:03	384.8	485.6	508.9	35.4
E.20:77:03	413.5	451.4	483.2	35.7

The 1.4.20:77:03 composite showed the highest T_onset (412 °C) and residue at 1000 °C (71.9%), far exceeding the expected inorganic fraction (~17%), which can be attributed to the formation of thermally stable calcium–aluminosilicate phases[²⁹,³⁰]. This improvement reflects the efficient dispersion of geopolymer and the formation of a cohesive interfacial layer that restricted polymer chain mobility and limited the diffusion of degradation products.

For the 1.4.30:67:03 sample, although higher filler content could potentially reduce the polymer continuity, the degradation profile remained stable due to the crosslinked and inorganic-rich network. The observed residue at 1000 °C confirmed the persistence of geopolymer structures and their contribution to enhancing the composite’s fire resistance[³¹-³³].

3.3 Scanning electron microscopy (SEM)

SEM micrographs (Figure 4) of the raw ladle furnace slag and the geopolymer confirmed significant morphological transformation after alkaline activation. The slag particles exhibited irregular shapes with sharp edges, while the geopolymer showed smoother and more cohesive agglomerates, characteristic of gel consolidation.

Figure 4
(A) Micrograph (2000x) of ladle furnace slag (a) and geopolymer 1.4 (b). (B) Images (250x) of macerated (a) and sieved 1,4 geopolymer (b).

In the HDPE composites, uniform dispersion of geopolymer particles was observed for the compatibilized 1.4.20:77:03 sample, while the non-compatibilized 1.4.20:80:00 presented visible interfacial gaps. This indicates that the use of MA and DCP improved the filler–matrix adhesion, leading to a more homogeneous microstructure. The improved dispersion was consistent with the FTIR evidence of interfacial bonding.

Particle size analysis (Table 2) showed mean diameters of 91.1 ± 26.0 µm for macerated and 63.4 ± 7.4 µm for sieved geopolymers. The smaller particles favored improved packing, decreased interparticle voids, and enhanced interfacial wetting by the polymer matrix[³⁴]. Such morphological refinement contributes directly to the observed increase in thermal stability and sound absorption.

3.4 Mechanical and physical properties

The Shore D hardness results (Table 4) demonstrated a progressive increase with geopolymer content up to 20 wt%, followed by a slight reduction at 30 wt%. Neat HDPE exhibited 55 ± 2 Shore D, while the 1.4.20:77:03 composite reached 60 ± 2, confirming reinforcement by rigid filler particles. The minor decrease at 30 wt% may be due to particle agglomeration and stress concentration at interfacial voids.

Table 4
Hardness test results.

SAMPLE	MEASUREMENTS					AVERAGE ± SD
	1	2	3	4	5
HDPE	56	56	55	53	48	55 ± 3.2
1.4.20:80:00	61	60	59	59	57	60 ± 1.6
1.4.10:87:03	58	58	58	59	59	58± 0.5
1.4.20:77:03	60	60	63	57	60	60 ± 2.0
1.4.30:67:03	52	60	55	55	50	56 ± 3.7
E.20:77:03	62	62	58	55	50	59± 4.5

The densities of the composites (Table 5) ranged from 1.38 to 2.11 g/cm³, depending on geopolymer content and processing route. The compatibilized 10 wt% composite exhibited slightly lower density, associated with the incorporation of fine pores that improved insulation properties. This microvoid formation was beneficial for sound and heat insulation, as similar behavior has been reported for hybrid polymer–inorganic systems[³⁵,³⁶].

Table 5
Density test results.

DATA USED		m1 (g)	m2 (g)	Vp (cm3)	t	de (g/cm3)
		23.388	43.528	25.397	20 °C	0.793
SAMPLE	m3 (g)	m4 (g)	me (g)	Ve (cm3)	Va (cm3)	da (g/cm3)
HDPE	0.551	43.672	19.733	24.884	0.513	1.074
1.4.20:80:00	0.540	43.782	19.854	25.037	0.361	1.497
1.4.10:87:03	0.549	43.762	19.825	25.000	0.397	1.382
1.4.20:77:03	0.604	43.905	19.913	25.111	0.286	2.110
1.4.30:67:03	0.648	43.990	19.954	25.163	0.235	2.763
E.20:77:03	0.526	43.867	19.953	25.161	0.236	2.231

• m₁ – mass of the empty pycnometer; m₂ – mass of the pycnometer filled with liquid; Vₚ – volume of the pycnometer; t – measurement temperature; d_e – density of the immersion liquid; m₃ – mass of the dry sample; m₄ – mass of the pycnometer with liquid and sample; m_e – equivalent mass of displaced liquid (m₂ + m₃ – m₄); V_e – effective (displaced) volume of the sample; V_a – apparent volume; d_a – apparent density of the sample.

3.5 Thermal diffusivity and acoustic performance

Thermal diffusivity results (Figure 5a) indicated that the incorporation of geopolymer effectively reduced heat conduction through the composite. The diffusivity decreased from 0.30 mm²/s for neat HDPE to 0.23 mm²/s for the 1.4.10:87:03 composite and remained low (0.24 mm²/s) for the compatibilized 1.4.20:77:03 sample. This reduction is attributed to the phonon-scattering effect caused by the dispersed inorganic particles and interfacial microvoids that hinder heat transfer[³⁷]. The overall results confirm the inverse relationship between thermal diffusivity and acoustic absorption, validating the dual insulation functionality of the developed composites (Table 6).

Figure 5
Acoustic Absorption Coefficients of (a) HDPE; (b) composites with geopolymer 1.4 with and without maleic anhydride.

Table 6
Results of the Thermal Diffusivity Test (LFA).

SAMPLE	THERMAL DIFFUSIVITY (m2/s)			AVERAGE	Standard Deviation
	Measure 1	Measure 2	Measure 3
HDPE.00:00:00	0.30	0.29	0.29	0.29	0.01
1.4.20:80:00	0.30	0.30	0.29	0.30	0.01
1.4.10:87:03	0.23	0.23	0.24	0.23	0.01
1.4.20:77:03	0.25	0.24	0.24	0.24	0.01
1.4.30:67:03	0.29	0.28	0.28	0.28	0.01
E.20:77:03	0.38	0.38	0.38	0.38	0.00

Acoustic absorption coefficient (AAC) curves (Figure 5b) showed that neat HDPE reached a maximum absorption of 0.26 at 315 Hz, with its best response between 200–400 Hz, typical of dense thermoplastics with low internal damping. This limited response is associated with vibrational resonance rather than true sound absorption, due to the absence of internal porosity[³⁸].

Among the composites, 1.4.20:77:03 (20 wt% geopolymer and 3 wt% MA) presented the best acoustic performance, with a peak AAC of 0.38 at 315 Hz and superior absorption across most frequencies (Table 7). The addition of geopolymer increased internal friction and multiple reflections of sound waves, while MA improved particle–matrix adhesion, enhancing dissipation efficiency. Conversely, the 1.4.30:67:03 composite (30 wt% geopolymer) exhibited lower AAC values, likely due to particle agglomeration and reduced damping.

Table 7
Most suitable composite for sound insulation under specific frequency conditions.

CASE	PURPOSE OF INSULATION	FREQUENCY RANGE (Hz)
1	Excitation of flow and internal vibration of panels	800 to 2000
2	Turboprop engines	60 to 400
3	Tail-mounted engines (jet aircraft)	100 to 500
4	Wind noise	Above 400
5	Stronger excitation in a twin-engine turboprop aircraft	100 to 500
6	Narrowband internal noise spectrum of an executive jet	Up to 800
7	Noise band in medium-sized commercial jet aircraft with up to 140 passengers	1000 to 1200
8	Noise band in medium-sized commercial jet aircraft with up to 140 passengers	800 to 1800

Table 7 summarizes the frequency ranges relevant to specific aircraft noise sources, confirming that the 1.4.20:77:03 composite is the most suitable for sound insulation in nearly all evaluated cases—except for Case 7 (1000–1200 Hz), where neat HDPE slightly outperformed due to resonance at that band.

The results summarized in Table 8 highlight clear differences in NRC values among the samples[³⁹]. Neat HDPE exhibited limited sound absorption (NRC = 0.20), consistent with its compact and non-porous structure. The 1.4.20:80:00 composite (20 wt% geopolymer, no compatibilizer) showed modest improvement (NRC = 0.23), primarily at 250 Hz, attributed to increased porosity introduced by the inorganic phase.

Table 8
Noise Reduction Coefficient (NRC) values for HDPE/geopolymer composites.

SAMPLE	CAA AVERAGE IN FREQUENCY				NRC
	250.00	500.00	1000.00	2000.00
HDPE.00:00:00	0.25	0.20	0.18	0.19	0.20
1.4.20:80:00	0.29	0.22	0.17	0.24	0.23
1.4.10:87:03	0.25	0.22	0.17	0.28	0.23
1.4.20:77:03	0.32	0.31	0.18	0.28	0.27
1.4.30:67:03	0.28	0.20	0.15	0.22	0.21
E.20:77:03	0.26	0.20	0.15	0.19	0.20

The compatibilized 1.4.10:87:03 composite achieved a similar average (NRC = 0.23), but exhibited enhanced absorption at higher frequencies (2000 Hz), suggesting that maleic anhydride promotes better filler dispersion, improving the dissipation of short-wavelength acoustic waves. The 1.4.20:77:03 composite demonstrated the best overall NRC (0.27), with increased absorption at both 250 Hz and 500 Hz, confirming that proper compatibilization improved matrix–filler interactions and internal friction.

In contrast, the 1.4.30:67:03 composite showed lower NRC (0.21), likely due to excessive stiffness and reduced vibrational damping. The slag-based composite (E.20:77:03) displayed an NRC comparable to neat HDPE (0.20), reinforcing that alkali activation is crucial to convert raw slag into an acoustically functional geopolymer filler.

Overall, the 1.4.20:77:03 composite emerges as the most promising formulation for aerospace noise reduction applications, particularly in the low-to-mid frequency range (250–500 Hz), where cabin comfort and structural damping are most critical.

3.6 Overall discussion

The combined results demonstrate that geopolymer incorporation not only enhanced the thermal and acoustic performance but also improved the mechanical rigidity and thermal stability of HDPE. The MA/DCP compatibilization was essential to achieve homogeneous filler dispersion and efficient load transfer.

The improved performance is explained by a hierarchical structure combining the ductile polymer matrix and rigid, thermally stable geopolymer particles. Such morphology creates multiple scattering interfaces, contributing to lower phonon propagation and higher acoustic damping.

Overall, the developed composites meet the dual requirements of lightweight and multifunctionality, confirming the relevance of ladle furnace slag-derived geopolymers as sustainable fillers for high-performance polymeric insulation materials.

4. Conclusions

This study successfully demonstrates the feasibility of using alkali-activated ladle slag as a functional filler in HDPE matrices. The incorporation of alkali-activated geopolymer fillers significantly enhanced the multifunctional performance of HDPE composites. The compatibilized system containing 20 wt% geopolymer and 3 wt% MA (1.4.20:77:03) presented the most balanced set of properties, combining superior thermal stability, mechanical rigidity, and acoustic insulation while maintaining a low density desirable for aerospace and structural applications. Thermal analysis confirmed the formation of thermally stable calcium–aluminosilicate phases, which delayed degradation and increased residual mass at high temperatures. Morphological observations demonstrated effective filler dispersion and interfacial adhesion promoted by MA/DCP compatibilization, resulting in reduced interfacial voids and improved load transfer.

Acoustic and thermal diffusivity tests revealed a synergistic behavior: as the inorganic phase increased internal scattering and porosity, heat conduction decreased while sound absorption improved, validating the dual-insulation functionality of the composites. Among all formulations, the 1.4.20:77:03 composite exhibited the best overall Noise Reduction Coefficient (NRC = 0.27), confirming its suitability for low- and mid-frequency noise attenuation in aeronautical environments.

In summary, these results highlight the technological potential of ladle furnace slag–derived geopolymers as sustainable, high-performance fillers, enabling the development of lightweight polymeric composites with combined mechanical robustness, thermal protection, and acoustic damping capabilities. This strategy offers a sustainable pathway for valorizing metallurgical residues while advancing next-generation multifunctional materials for aerospace and construction sectors.

6. Acknowledgements

The authors thank CNPq for funding and acknowledge the support of IMA, the Navy Research Institute, the Acoustics and Vibrations Laboratory (UFRJ), and the Army Technological Center (CETx) for their contributions to the experimental work.

• Data Availability:
  All data supporting the findings of this study are available from the corresponding author upon request.
• How to cite:
  Santos, E. M., Weber, R. P., Ramos, F. J. H. T. V., & Marques, M. F. V. (2026). HDPE/geopolymer composites with improved thermal and acoustic insulation for aerospace applications. Polímeros: Ciência e Tecnologia, 36(3), e20260033. https://doi.org/10.1590/0104-1428.20250051

7. References

• ¹ El Alouani, M., Saufi, H., Moutaoukil, G., Alehyen, S., Nematollahi, B., Belmaghraoui, W., & Taibi, M. (2021). Application of geopolymers for treatment of water contaminated with organic and inorganic pollutants: state-of-the-art review. Journal of Environmental Chemical Engineering, 9(2), 105095. https://doi.org/10.1016/j.jece.2021.105095
  » https://doi.org/10.1016/j.jece.2021.105095
• ² Muraleedharan, M., & Nadir, Y. (2021). Factors affecting the mechanical properties and microstructure of geopolymers from red mud and granite waste powder: A review. Ceramics International, 47(10), 13257-13279. https://doi.org/10.1016/j.ceramint.2021.02.009
  » https://doi.org/10.1016/j.ceramint.2021.02.009
• ³ Paul, D., Suresh, M., & Pal, M. (2021). Utilization of fly ash and glass powder as fillers in steel slag asphalt mixtures. Case Studies in Construction Materials, 15, e00672. https://doi.org/10.1016/j.cscm.2021.e00672
  » https://doi.org/10.1016/j.cscm.2021.e00672
• ⁴ Lin, W. Y., Prabhakar, A. K., Mohan, B. C., & Wang, C.-H. (2020). A factorial experimental analysis of using wood fly ash as an alkaline activator along with coal fly ash for production of geopolymer-cementitious hybrids. The Science of the Total Environment, 718, 135289. https://doi.org/10.1016/j.scitotenv.2019.135289 PMid:31839313.
  » https://doi.org/10.1016/j.scitotenv.2019.135289
• ⁵ Hui-Teng, N., Cheng-Yong, H., Yun-Ming, L., Abdullah, M. M. A. B., Ern Hun, K., Razi, H. M., & Yong-Sing, N. (2021). Formulation, mechanical properties and phase analysis of fly ash geopolymer with ladle furnace slag replacement. Journal of Materials Research and Technology, 12, 1212-1226. https://doi.org/10.1016/j.jmrt.2021.03.065
  » https://doi.org/10.1016/j.jmrt.2021.03.065
• ⁶ Koriem, A., Ollick, A. M., & Elhadary, M. (2021). The effect of artificial weathering and hardening on mechanical properties of HDPE with and without UV stabilizers. Alexandria Engineering Journal, 60(4), 4167-4175. https://doi.org/10.1016/j.aej.2021.03.024
  » https://doi.org/10.1016/j.aej.2021.03.024
• ⁷ Shahin, A., Barsoum, I., & Korkees, F. (2021). Analysis of a HDPE flanged connection with a time and temperature dependent constitutive behavior. International Journal of Pressure Vessels and Piping, 191, 104375. https://doi.org/10.1016/j.ijpvp.2021.104375
  » https://doi.org/10.1016/j.ijpvp.2021.104375
• ⁸ Wang, H., Yang, D., Xiong, W., Liu, W., & Qiu, X. (2021). One-pot preparation of hydrophobic lignin/SiO₂ nanoparticles and its reinforcing effect on HDPE. International Journal of Biological Macromolecules, 180, 523-532. https://doi.org/10.1016/j.ijbiomac.2021.03.091 PMid:33745976.
  » https://doi.org/10.1016/j.ijbiomac.2021.03.091
• ⁹ Nguyen, K. Q., Mwiseneza, C., Mohamed, K., Cousin, P., Robert, M., & Benmokrane, B. (2021). Long-term testing methods for HDPE pipe – advantages and disadvantages: A review. Engineering Fracture Mechanics, 246, 107629. https://doi.org/10.1016/j.engfracmech.2021.107629
  » https://doi.org/10.1016/j.engfracmech.2021.107629
• ¹⁰ Khouaja, A., Koubaa, A., & Ben Daly, H. (2021). Dielectric properties and thermal stability of cellulose high-density polyethylene bio-based composites. Industrial Crops and Products, 171, 113928. https://doi.org/10.1016/j.indcrop.2021.113928
  » https://doi.org/10.1016/j.indcrop.2021.113928
• ¹¹ Sadik, W. A., El-Demerdash, A.-G. M., Abokhateeb, A. E. A., & Elessawy, N. A. (2021). Innovative high-density polyethylene/waste glass powder composite with remarkable mechanical, thermal and recyclable properties for technical applications. Heliyon, 7(4), e06627. https://doi.org/10.1016/j.heliyon.2021.e06627 PMid:33889767.
  » https://doi.org/10.1016/j.heliyon.2021.e06627
• ¹² Dubiella, K., & Vicentini, D. (2018). Estudo de laminados de materiais compósitos no transporte aéreo. In 1º Simpósio de Transportes do Paraná / 2º Seminário em Aeroportos e Transporte Aéreo / 2º Urbanidade (pp. 31-40). Curitiba, PR: UFPR. https://doi.org/10.5380/1stpr2018.artcomp03p31-40
  » https://doi.org/10.5380/1stpr2018.artcomp03p31-40
• ¹³ Callister, W. D., & Rethwisch, D. G. (2018). Materials science and engineering: an introduction (10th ed.). Milton: Wiley.
• ¹⁴ Miao, J., Shen, Y., Tao, J., Zeng, X., Liu, S., & Wang, Z. (2023). Design and spraying-preparation of the gradient coatings with various diameters and contents of SiO₂ nano-particles for the enhanced anti-impact and thermal insulation performance. Progress in Organic Coatings, 179, 107491. https://doi.org/10.1016/j.porgcoat.2023.107491
  » https://doi.org/10.1016/j.porgcoat.2023.107491
• ¹⁵ Chauhan, S., & Bhushan, R. K. (2017). Study of polymer matrix composite with natural particulate/fiber in PMC: a review. International Journal of Advance Research. Ideas and Innovations in Technology, 3(3), 1168-1179. Retrieved in 2025, August 10, from https://www.ijariit.com/manuscript/study-of-polymer-matrix-composite-with-natural-particulatefiber-in-pmc-a-review
  » https://www.ijariit.com/manuscript/study-of-polymer-matrix-composite-with-natural-particulatefiber-in-pmc-a-review
• ¹⁶ Sekkal, W., & Zaoui, A. (2023). Thermal and acoustic insulation properties in nanoporous geopolymer nanocomposite. Cement and Concrete Composites, 138, 104955. https://doi.org/10.1016/j.cemconcomp.2023.104955
  » https://doi.org/10.1016/j.cemconcomp.2023.104955
• ¹⁷ Aly, N. M., Seddeq, H. S., Elnagar, K., & Hamouda, T. (2021). Acoustic and thermal performance of sustainable fiber reinforced thermoplastic composite panels for insulation in buildings. Journal of Building Engineering, 40, 102747. https://doi.org/10.1016/j.jobe.2021.102747
  » https://doi.org/10.1016/j.jobe.2021.102747
• ¹⁸ Dönmez Çavdar, A., Tomak, E. D., Boran Torun, S., & Arpaci, S. S. (2021). Accelerated weathering resistance of high-density polyethylene composites reinforced with microcrystalline cellulose and fire retardants. Journal of Building Engineering, 39, 102282. https://doi.org/10.1016/j.jobe.2021.102282
  » https://doi.org/10.1016/j.jobe.2021.102282
• ¹⁹ Gupta, K. K., Chandra, H., Sagar, K., Sharma, K. K., & Devi, D. (2023). Degradation of high density polyethylene (HDPE) through bacterial strain from cow faeces. Biocatalysis and Agricultural Biotechnology, 48, 102646. https://doi.org/10.1016/j.bcab.2023.102646
  » https://doi.org/10.1016/j.bcab.2023.102646
• ²⁰ Salleh, M. N., Aziz, R. A., Shan, C. R., Musa, L., Razak, M. F. S. A., Nabiałek, M., & Jeż, B. (2022). Comparison between the tensile, water absorption and flammability properties of recycled high-density polyethylene/rice husk composite from twin-screw extruder and heated two-roll mill. Archives of Metallurgy and Materials, 67(2), 661-668. https://doi.org/10.24425/amm.2022.137803
  » https://doi.org/10.24425/amm.2022.137803
• ²¹ Lazorenko, G., Kasprzhitskii, A., Yavna, V., Mischinenko, V., Kukharskii, A., Kruglikov, A., Kolodina, A., & Yalovega, G. (2020). Effect of pre-treatment of flax tows on mechanical properties and microstructure of natural fiber reinforced geopolymer composites. Environmental Technology & Innovation, 20, 101105. https://doi.org/10.1016/j.eti.2020.101105
  » https://doi.org/10.1016/j.eti.2020.101105
• ²² Wang, C., Jin, Z., Liu, G., Dong, W., Pang, B., & Ding, X. (2023). Mechanisms of chloride transport in low carbon marine concrete: an alkali-activated slag system with high limestone powder. Journal of Building Engineering, 72, 106539. https://doi.org/10.1016/j.jobe.2023.106539
  » https://doi.org/10.1016/j.jobe.2023.106539
• ²³ Bai, T., Song, Z.-G., Wu, Y.-G., Hu, X.-D., & Bai, H. (2018). Influence of steel slag on the mechanical properties and curing time of metakaolin geopolymer. Ceramics International, 44(13), 15706-15713. https://doi.org/10.1016/j.ceramint.2018.05.243
  » https://doi.org/10.1016/j.ceramint.2018.05.243
• ²⁴ Akarken, G., & Cengiz, U. (2023). Fabrication and characterization of metakaolin-based fiber reinforced fire resistant geopolymer. Applied Clay Science, 232, 106786. https://doi.org/10.1016/j.clay.2022.106786
  » https://doi.org/10.1016/j.clay.2022.106786
• ²⁵ Giannopoulou, I., Robert, P. M., Sakkas, K.-M., Petrou, M. F., & Nicolaides, D. (2023). High temperature performance of geopolymers based on construction and demolition waste. Journal of Building Engineering, 72, 106575. https://doi.org/10.1016/j.jobe.2023.106575
  » https://doi.org/10.1016/j.jobe.2023.106575
• ²⁶ Vahidi, G., Bajwa, D. S., Shojaeiarani, J., & Stark, N. M. (2022). Experimental investigation into the direct feeding of coupling agent, cellulose nanocrystals, and nano zinc oxide in high-density polyethylene. Composites Part C: Open Access, 8, 100287. https://doi.org/10.1016/j.jcomc.2022.100287
  » https://doi.org/10.1016/j.jcomc.2022.100287
• ²⁷ Donmez Cavdar, A., Kalaycioglu, H., & Mengeloğlu, F. (2016). Technological properties of thermoplastic composites filled with fire retardant and tea mill waste fiber. Journal of Composite Materials, 50(12), 1627-1634. https://doi.org/10.1177/0021998315595113
  » https://doi.org/10.1177/0021998315595113
• ²⁸ Sarfraz, M. (2016). Upgrading electrical, mechanical, and chemical properties of CNTs/Polybond® nanocomposites: pursuit of electroconductive structural polymer nanocomplexes. International Journal of Polymer Science, 2016(1), 2396817. https://doi.org/10.1155/2016/2396817
  » https://doi.org/10.1155/2016/2396817
• ²⁹ Xu, B., & Yi, Y. (2022). Treatment of ladle furnace slag by carbonation: carbon dioxide sequestration, heavy metal immobilization, and strength enhancement. Chemosphere, 287(Pt 3), 132274. https://doi.org/10.1016/j.chemosphere.2021.132274 PMid:34562709.
  » https://doi.org/10.1016/j.chemosphere.2021.132274
• ³⁰ Rashad, A. M., Khafaga, S. A., & Gharieb, M. (2021). Valorization of fly ash as an additive for electric arc furnace slag geopolymer cement. Construction & Building Materials, 294, 123570. https://doi.org/10.1016/j.conbuildmat.2021.123570
  » https://doi.org/10.1016/j.conbuildmat.2021.123570
• ³¹ Cong, P., & Mei, L. (2021). Using silica fume for improvement of fly ash/slag based geopolymer activated with calcium carbide residue and gypsum. Construction & Building Materials, 275, 122171. https://doi.org/10.1016/j.conbuildmat.2020.122171
  » https://doi.org/10.1016/j.conbuildmat.2020.122171
• ³² Joseph, M., Anugop, B., Vijesh, K. R., Balan, V., Nampoori, V. P. N., & Kailasnath, M. (2022). Morphology and concentration-dependent thermal diffusivity of biofunctionalized zinc oxide nanostructures using dual-beam thermal lens technique. Materials Letters, 323, 132599. https://doi.org/10.1016/j.matlet.2022.132599
  » https://doi.org/10.1016/j.matlet.2022.132599
• ³³ Atef, M., Bassioni, G., Azab, N., & Hazem Abdellatif, M. (2022). On the acoustical performance of eco-friendly cementitious composite with recycled fine rubber particles. Construction & Building Materials, 325, 126830. https://doi.org/10.1016/j.conbuildmat.2022.126830
  » https://doi.org/10.1016/j.conbuildmat.2022.126830
• ³⁴ Lima, J. E. S., Assumpção, T. A. A., Azeredo, E. A., & Macedo, T. L. (2017). Estudo preliminar de reforço de material polimérico por meio de fibras de carbono. Revista Caleidoscópio, 9(1), 23-29. Retrieved in 2025, August 10, from https://ojs.eniac.com.br/index.php/Anais/article/view/451/542
  » https://ojs.eniac.com.br/index.php/Anais/article/view/451/542
• ³⁵ Coates, J. (2000). Interpretation of infrared spectra: a practical approach. In R. A. Meyers (Ed.), Encyclopedia of Analytical Chemistry (pp. 10815-10837). Chichester: Wiley. https://doi.org/10.1002/9780470027318.a5606
  » https://doi.org/10.1002/9780470027318.a5606
• ³⁶ Stuart, B. (2021). Infrared spectroscopy: Fundamentals and applications (2nd ed.). Chichester: Wiley.
• ³⁷ American Society for Testing and Materials – ASTM (2022). ASTM E1461-22: standard test method for thermal diffusivity by the flash method. West Conshohocken: ASTM.
• ³⁸ American Society for Testing and Materials – ASTM (2022). ASTM E1050-22: standard test method for impedance and absorption of acoustical materials using a tube, two microphones, and a digital frequency analysis system. West Conshohocken: ASTM.
• ³⁹ American Society for Testing and Materials – ASTM (2022). ASTM C423-22: standard test method for sound absorption and sound absorption coefficients by the reverberation room method West Conshohocken: ASTM.

Edited by

• Associate Editor:
  José A. C. G. Covas

Data availability

All data supporting the findings of this study are available from the corresponding author upon request.

Publication Dates

• Publication in this collection
  03 Aug 2026
• Date of issue
  2026

History

• Received
  10 Aug 2025
• Reviewed
  22 Oct 2025
• Accepted
  04 June 2026