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Abstract

As a natural plant material with unique porous structure, loofah is used in many fields, but there are still defects in fire safety performance in that its flammability. The melamine-modified flame retardant loofah composites (M-FR-PL) were prepared by impregnation baking method. The experimental synthesis conditions were optimized by L9 (3⁴) orthogonal design. The flame retardancy, heat release rate (HRR), thermal stability and smoke density of the composites were analyzed. M-FR-PL6 prepared under the optimum experimental conditions had good properties: the adsorption rate of flame retardant (AR, %) was 6.8%, the limiting oxygen index (LOI, %) reached 27.5%, the vertical combustion level reached V-0, and the amount of residual char was 17.2% higher than that of loofah. The flame retardant mechanism of M-FR-PL6 was thoroughly discussed by various characterization methods. The peak of the HRR curve of M-FR-PL6 declined compared with loofah, indicating the loofah after melamine flame-retardant treatment has good flame retardancy and smoke suppression properties.

Keywords

Biomass flame retardant loofah melamine orthogonal design

Introduction

Loofah is a kind of natural and renewable plant fiber with properties such as unique porous structure, toughness, wear resistance and good elasticity. Loofah is used in the fields of packaging, sound and heat insulation, building and home decoration, adsorption materials and so on.^1–5 However, loofah is flammable and can quickly reach the heat release peak. After ignition, it can release a lot of heat and flue gas,^6–8 which limits the application of loofah in many fields. Therefore, it is of great significance to explore how to reduce its fire risk. With the popularization and use of environment-friendly and renewable resources, environmental friendly and halogen-free flame retardants have gradually become the focus of attention.^9–11 Among them, nitrogen-based flame retardants with high nitrogen content can not only release inert gas and combustible gas in dilution air during pyrolysis, but also be effectively applied to the research of flame retardant materials.^12,13

Melamine is a typical nitrogen-based halogen-free flame retardant containing high N element. The thermal decomposition of melamine can produce inert gases such as NH₃ and dilute the combustible gases in the system to achieve the effect of flame retardation.^14,15 The natural fibers are usually pretreated before surface modification. Alkali treatment is often used to remove not only the colloid and wax on the surface, but also the lignin and hemicellulose inside natural fibers.^16,17 Alkalization can change the chemical content of the fiber by breaking the hydrogen bond in the structure of the wood fiber, so as to remove hemicellulose, pectin, wax and lignin during the separation of the fiber bundle in the micro fiber.^18,19 The density of the pretreated fiber increases and the structure is closer, which is conducive to improve the mechanical properties of the material. High cellulose content and low hemicellulose after pretreatment can also improve the thermal stability of the fiber.^20–22

To improve the flame retardant performance of loofah, the flame retardant loofah composites were prepared by impregnation baking method using melamine as the flame retardant. Scheme 1 presents the preparation process. The optimal experimental preparation conditions were determined by orthogonal design method. The flame retardant, thermal stability and smoke suppression properties of the composites were studied by various characterization methods, and the possible mechanisms of flame retardant and smoke suppression were discussed.

Scheme 1.

Experimental flowchart.

Materials and methods

Materials

Loofah was grown in Nanning, Guangxi. Sodium hydroxide, 30% hydrogen peroxide, phosphoric acid and melamine were purchased from Sinopharm Chemical Reagent Co., Ltd. (China). Sodium hydroxide and 30% hydrogen peroxide were used for loofah pretreatment.

Pretreatment of loofah

Firstly, the dust and impurities of loofah were washed with distilled water, and then dried at 80.0°C for 12.0 h to constant weight. Then, the dried loofah was crushed with a pulverizer, and the loofah was stored in a dry environment. A certain amount of loofah was put into 10%NaOH solution (loofah bath ratio (LBR) was 1:50), and then treated at 98.0° C for 4.0 h. After the reaction, took out the loofah and rinsed it with distilled water until it became neutral. Then 2.0 g/L H₂O₂ solution was added into the mixture ((LBR was 1:50), refluxed at 80.0° C and mixed for 4.0 h. Finally, the resulting product cooled to room temperature was collected by filtration and multiple washes with distilled water, and then it was dried to constant weight at 80°C and called as pretreated loofah (PL).

Preparation of melamine flame retardant loofah material (M-FR-PL)

PL was flame retardant treated by impregnation baking method. First, a certain amount of melamine and phosphoric acid (molar ratio of 1:3) were added into distilled water so that it can be completely dissolved at a certain temperature. Record the above mixed solution as A. Then, a certain amount of PL was added into the mixture A according to LBR. Then the whole system was condensed and refluxed, and the temperature of the system was maintained at a certain temperature through constant temperature heating of the magnetic stirrer. After the reaction, the product was centrifugally rinsed with absolute ethanol and vacuum desiccation at 60°C overnight to obtain M-FR-PL. The detail experimental conditions are shown in Table 1. In order to optimize the synthesis conditions of the experiment, four important factors affecting the flame retardancy of M-FR-PL were studied, including the mass concentration of melamine (ρ_m, g/L), loofah bath ratio (LBR), reaction temperature (T_r, °C) and reaction time (t_r, h). The adsorption ratio (AR, %) and LOI of the flame retardant loofah composites were determined as the reference conditions of the orthogonal design. AR was defined as the ratio of the mass difference before and after the flame retardant treatment of PL to the mass of PL, as shown in equation (1). L₉(3⁴) orthogonal design was used to optimize the preparation conditions of loofah flame retardant treatment. Table 2 shows the specific parameters of 9 groups of orthogonal tests. Each group of experiments was carried out twice, and finally the average value was taken. As shown in Scheme 1 of the experimental flowchart.

AR = \frac{m_{1} - m_{0}}{m_{0}} \times 100

(1)

m_{0}

(g) was the mass of PL, and

m_{1}

(g) was the mass of M-FR-PL.

Table 1.

Experimental factors and levels in orthogonal design.

Levels	Factors
Levels	A (ρ_m/g·L⁻¹)	B (LBR)	C (T_r/°C)	D (t_r/h)
1	2.0	1:50	80.0	1
2	6.0	1:75	90.0	2
3	10.0	1:100	100.0	3

Table 2.

The orthogonal design layout and results of adsorption rate (AR) and limiting oxygen index (LOI).

samples			A (ρ_m/g·L⁻¹)	B (LBR)	C (T_r/°C)	D (t_r/h)	AR/%	LOI/%
M-FR-PL1			2.0	1:50	80.0	1.0	−1.9	19.8
M-FR-PL2			2.0	1:75	90.0	2.0	0.5	19.8
M-FR-PL3			2.0	1:100	100.0	3.0	−0.5	19.4
M-FR-PL4			6.0	1:50	90.0	3.0	2.4	24.8
M-FR-PL5			6.0	1:75	100.0	1.0	2.8	25.5
M-FR-PL6			6.0	1:100	80.0	2.0	6.8	27.5
M-FR-PL7			10.0	1:50	100.0	2.0	4.5	26.2
M-FR-PL8			10.0	1:75	80.0	3.0	3.5	26.4
M-FR-PL9			10.0	1:100	90.0	1.0	4.0	25.5
Range analysis results	AR	K ₁	−0.6	1.7	2.8	1.6
		K ₂	4.0	2.2	2.3	3.9
		K ₃	4.0	3.5	2.3	1.8
		R	4.6	1.8	0.6	2.3
	LOI	K ₁	19.7	23.6	24.6	23.6
		K ₂	25.9	23.9	23.4	24.5
		K ₃	26.0	24.1	23.7	23.5
		R	6.4	0.5	1.2	1.0

Characterization

Fourier transform infrared (FTIR) spectra were performed on a Spectrum One Autoima spectrometer (Nicolet 50, Thermo Scientific Company) in the range of 4000–400 cm⁻¹.

X-Ray photoelectron spectroscopy (XPS) was carried out using a K-Alpha XPS analyzer (Thermo Scientific, USA), with Al Kα excitation radiation (hυ = 1486.6 eV) in ultrahigh vacuum conditions.

The limiting oxygen index (LOI) test was performed by an oxygen index instrument ZY6155A (Dongguan Zhongnuo Quality Inspection Equipment Co. Ltd, China). According to ASTM D-2863 standard, the LOI value of the samples were tested, and the samples were prepared with a die at 36.0 MPa, with a size of 80.0 mm × 6.0 mm × 3.0 mm. Then, adjusted the proportion of nitrogen and oxygen, ignited the top of the sample. The samples’ LOI were measured for 3 times and the average value was calculated.

The vertical burning (UL-94) test was performed using a vertical burning tester (ZY6017, Dongguan Zhongnuo Quality Inspection Equipment Co. Ltd, China). The samples were prepared with a die at 36.0 MPa, with sample dimensions of 80.0 mm × 13.0 mm × 3.0 mm. Then according to ASTM D-3801 standard the UL-94 values of the samples were measured 3 times and the average value was calculated.

Thermogravimetric analysis(TG) of the composites was carried out by thermogravimeter (TG 209 F1, Netzsch Scientific Instruments Trading (Shanghai) Co. Ltd, China). Under the nitrogen conditions, the gas flow rate of thermogravimeter was 40.0 mL/min, the sample dosage was between 3.0 mg and 5.0 mg, the heating rate was 10°C/min and the heating temperature was from 40°C to 800°C.

The combustion behavior of the samples was studied by a microscale combustion calorimeter (MCC, Suzhou Yangyi Volch Testing Technology Co. Ltd, China). About 5.0 mg sample was heated from 100 to 700°C at a heating rate of 0.5°C/s in a mixed stream of oxygen (20 cm³/min) and nitrogen (80 cm³/min).

Residual char analysis tests were performed on a SUPRA-55 (Carl Zeiss AG, Germany) Scanning Electron Microscope (SEM). The scanning accelerating voltage was 5 kV to investigate the morphologies of the residual char after complete combustion.

The smoke density was measured by using smoke density chamber (ZY6166B, Dongguan Zhongnuo Quality Inspection Equipment Co. Ltd, China) according to GB-T 8624-2007. The smoke generated (flameless combustion mode) during the combustion process of the samples was measured by the change of light intensity.

Results and discussion

Analysis of orthogonal experiment

To investigate the effects of the melamine adsorbed onto loofah surface on LOI variation, the following four factors were considered for synthesis optimization of M-FR-PL: the mass concentration of melamine (ρ_m, g/L), loofah bath ratio (LBR), reaction temperature (T_r, °C) and reaction time (t_r, h). The experimental layout of L₉(3⁴) and results of AR and LOI for M-FR-PL samples are shown in Table 2. The LOI values of raw loofah and PL were 16.0% and 17.0% respectively. Range analysis method was used to analyzed the experimental data in Table 2. The subscript K represents a level of the factor. The range value of the four factors was determined by subtracting the minimum value from the maximum value of K. The larger the range, the more important the coefficient was.²³ The AR values of M-FR-PL1 and M-FR-PL3 in Table 2 were negative, which may be due to the dissolution of cellulose in water under acidic conditions and the experimental loss. The range analysis results were similar with AR and LOI. The results showed that the influence degree of various factors on the AR and LOI was as following: ρ_m > t_r > LBR > T_r. According to the K value analysis and combined with the actual situation: the minimum temperature for the complete dissolution of melamine and phosphoric acid in the aqueous solution was 80.0°C; since changes in LBR have little effect on the results, it was of little practical significance to further reduce LBR. Therefore, the experimental conditions for obtaining the best AR and LOI were as follows: 6.0 g/L of ρ_m, 1:100 of LBR, 80.0°C of T_r, 2.0 h of t_r. That was A2B3C1D2, which was the experimental condition of M-FR-PL6. Under the optimum experimental conditions, the quality of each component of the material prepared in this experiment was: 10 g of loofah, 6 g of melamine, 1:100 of LBR, 80.0°C of T_r, 2.0 h of t_r. After melamine flame retardant modification, compared with PL, the LOI of M-FR-PL6 was increased by 10.5% and the flame retardant performance of M-FR-PL was significantly improved. Due to the thermal decomposition of melamine to produce inert gas and dilute the oxygen around the sample, it can be quickly extinguished when igniting sample M-FR-PL6 in air, which plays the role of gas-phase flame retardant.²⁴ The other properties of M-FR-PL6 will be shown in the following sections.

FT-IR and XPS analysis

The FT-IR spectra of melamine, PL and M-FR-PL are presented in Figure 1. The peak at 3469 and 3419 cm⁻¹ were ascribed to antisymmetric stretching vibration peaks of NH₂ bonds; the absorption peaks at 3410 and 1653 cm⁻¹ were attributed to the stretching vibration peaks of N-H and bending vibration peaks of N-H respectively. In addition, the peaks at 1555 and 1467 cm⁻¹ occurred because of the skeleton vibration peaks of triazine ring.²⁵ The M-FR-PL modified by melamine retained the characteristic peak of PL and appeared the characteristic peak related to melamine. From these characteristic peaks, it can be inferred that the chemical structure of the compound is basically consistent with that of PL.

Figure 1.

FT-IR spectra of melamine, PL and M-FR-PL6.

As shown in Figure 2 and Figure 3, the XPS of PL and M-FR-PL and narrow-band spectra of C1s, O1s and N1s also proved that melamine successfully modified loofah. From Figure 2, both PL and M-FR-PL contained two obvious O1s and C1s characteristic peaks. However, after melamine flame retardant modified loofah, M-FR-PL6 has a new peak attributed to N1s at 399.08 eV. The appearance of nitrogen-containing groups shows that melamine had been successfully attached to the surface of loofah complex. It can be seen from Figure 3, the N1s spectrum of M-FR-PL6 shows two peaks at 397.7 and 398.7 eV (Figure 3(e)), which are ascribed to N and C-NH₂ in the melamine ring, respectively. The results show that melamine is successfully loaded on loofah surface.

Figure 2.

XPS full spectrum of PL and M-FR-PL6.

Figure 3.

XPS narrowband spectra of PL and M-FR-PL6: (a)C1s and (b)O1s narrowband spectra of PL respectively; (c)C1s, (d)O1s and (e)N1s narrowband spectra of M-FR-PL6 respectively.

The vertical burning (UL-94) analysis

The vertical combustion tests were carried out on loofah, PL and the 9 samples of orthogonal experiments. Results are listed in Table 3. t₁ was the time required for the sample to leave the fire source until it extinguishes itself after being ignited for the first time. t₂ was the time required for the sample to extinguish itself after being ignited for the second time and leaving the fire source. The total combustion time (t₁ + t₂) was summarized by the two burning times of the sample. Since the samples of loofah, PL and M-FR-PL1 to M-FR-PL3 could not self-extinguish in the air, they have no test level. Samples from M-FR-PL4 and M-FR-PL5 reached V-1 level, and samples from M-FR-PL6 to M-FR-PL9 reached V-0 level. Among the samples, M-FR-PL6 prepared under optimal condition had the shortest combustion time, and it could extinguish itself instantly when ignited in the air. The results confirmed that M-FR-PL6 achieved the best flame-retardant performance. After observation of the combustion process of M-FR-PL6 sample (as shown in Figure 4), the total damage length was only 15 mm (the total length of the sample before vertical combustion test was 80 mm), which was caused by an external fire source. The inert gas released by the thermal decomposition of melamine dilutes the surrounding oxygen in time to extinguish the flame. The other parts only burn on the surface, and there was no sign of combustion inside, which can also reflect the good flame retardant performance of M-FR-PL6. Also, the results demonstrated that there was a negative correlation between AR and the total combustion time (t₁ + t₂), that was, the higher the AR, the shorter the total combustion time after leaving the fire source. Therefore, increasing the AR of flame retardant will be conducive to improve the flame retardant performance of loofah. The results also lay a foundation for future experimental investigations.

Table 3.

Vertical burning (UL-94) results including adsorption rate (AR).

Samples	t₁/s	t₂/s	t₁+t₂/s	Dropping	UL-94	AR/%
loofah	—	—	—	No	No level	—
PL	—	—	—	No	No level	—
M-FR-PL1	—	—	—	No	No level	−1.9
M-FR-PL2	—	—	—	No	No level	0.5
M-FR-PL3	—	—	—	No	No level	−0.5
M-FR-PL4	8	38	46	No	V-1	2.4
M-FR-PL5	5	29	34	No	V-1	2.8
M-FR-PL6	1	1	2	No	V-0	6.8
M-FR-PL7	1	9	10	No	V-0	4.5
M-FR-PL8	1	3	4	No	V-0	3.5
M-FR-PL9	4	17	21	No	V-0	4.0

Figure 4.

Sample M-FR-PL6 before and after combustion: (a)before and (b)after.

Thermogravimetric analysis

The TG and DTG profiles of loofah, PL and M-FR-PL6 are displayed in Figure 5. The initial thermal decomposition temperatures (T_5%), the 50 wt% weight loss temperatures (T_50%), and the temperature (T_max) at the maximum decomposition rate (R_max) are summarized in Table 4. The value of T_max is determined from the point where the slope of the thermogravimetric curve changes sharply. The T_5wt%, T_50wt%, T_max and R_max results of PL were all lower than those of loofah. The results indicated that the removal of gum and wax from loofah reduced the thermal stability of loofah and the maximum decomposition rate. The alkali treated loofah will be benefit for melamine adsorption after the removal of lignin, hemicellulose and waxy substances from the fiber.²⁶ The T_5wt% of M-FR-PL6 was less than that of loofah, and T_50wt% was greater than that of loofah. This showed that the thermal decomposition rate of M-FR-PL6 was reduced compared with loofah. The TGA results indicated that the initial decomposition temperature of M-FR-PL6 was lower than loofah and PL. It might be contributed to the thermal stability of P-O-C was lower than that of C-C.²⁷

Figure 5.

Thermogravimetric analysis curves of samples: (a)TGA and (b)DTG.

Table 4.

Thermogravimetric analysis results.

Samples	T_5wt%/°C	T_50wt%/°C	T_max/°C	R_max/wt% °C⁻¹	Residual char at 800°C/wt%
loofah	247.0	361.0	366.0	13.81	19.53
PL	234.0	355.0	362.0	11.86	13.52
M-FR-PL6	215.0	414.0	296.0	9.87	36.74

There may be preferential decomposition of phosphorus containing components in flame retardants, which can promote the formation of char layer.²⁸ The final residual char ratio was M-FR-PL6 > loofah > PL. The final residual char ratio of M-FR-PL6 was 17.2% higher than loofah and 23.2% higher than PL. Melamine could promote the formation of residual char during the thermal decomposition process, and generate nitrogen gas, which takes away part of the heat while blocking the oxygen supply.²⁹ The final residual char ratio of PL was lower than that of loofah, which was due to the removal of the gum and lignin in the loofah.

Microcalorimetric analysis

MCC was used to further evaluate the combustion parameters of the sample (Table 5), including heat release rate (HRR), peak heat release rate (PHRR), temperature at peak heat release rate (TPHRR), heat release capacity (HRC) and total heat release (THR). THR is another parameter to evaluate the heat release of materials, and in this case, the change of THR showed a similar trend as that of HRR. The HRR curve is shown in Figure 6. Compared with loofah, the HRC and THR of PL decreased slightly. It showed that the removal of wax and gum from loofah was helpful to reduce the heat release level of the material. The HRC and THR of M-FR-PL6 decreased by 40.5% and 56.7% respectively. It made clear that the introduction of melamine could greatly inhibit the heat release capacity of loofah and reduced its total heat release. The exothermic peak shifted to lower temperature range might be due to the decomposition effects of melamine. And the exothermic peak of M-FR-PL6 was narrower, meaning that the stable char layer was formed in less time at the temperature. MCC results showed that the heat release level of the melamine-modified loofah composite was significantly reduced, and the fire safety performance of the composite was effectively improved.³⁰

Table 5.

Microscale combustion calorimeter (MCC) data of the samples.

Samples	HRC/J·g⁻¹ K⁻¹	THR/kJ·g⁻¹	PHRR/W·g⁻¹	T_PHRR/°C
loofah	227.0	13.4	218.2	372.4
PL	184.0	11.1	185.2	351.8
M-FR-PL6	135.0	5.8	139.0	290.0

Figure 6.

Heat release rate curves of samples.

SEM analysis

The digital photo of loofah and its fiber structure is shown in Figure 7, the density distribution of fibers is uneven and the diameter is different. The presence of lumen in the loofah indicates that the porosity of the sample increases when the number of cellulose increases.³¹ The SEM micrographs of loofah, PL and M-FR-PL6 are shown in Figure 8. The surfaces of loofah were relatively smooth with shallow grooves Figure 8, The structure is attributed to the colloid, wax and other substances existed in the outer layer. The SEM micrographs indicate that alkali treatment made the surface of the loofah smoother.³² From Figure 8 (c) the melamine particles attached to the fiber surface were clearly and confirmed the successful preparation of flame-retardant loofah composites.

Figure 7.

Digital photos of loofah and its fiber structure.

Figure 8.

SEM of (a)loofah, (b)PL and (c)M-FR-PL6.

The SEM images of residual char after samples combustion are displayed in Figure 9. The residual char surface of loofah after combustion was wavy, with many holes and relatively loose distribution. Although the residual char pores of PL were reduced, the problems of uneven and loose surface still exist. The removal of gum, wax, hemicellulose and lignin from loofah can improve the surface morphology of loofah fibers.³³ The residual char surface of M-FR-PL6 was more smooth and dense. There were many closely packed continuous char layers. The triazine ring existed in melamine was used as a starting char point, which could quickly form the residual char of the polymerized aromatic ring and the polymerized nitrogen heterocyclic ring. The tightly stacked char layer could well isolate oxygen and heat and improve the flame retardancy of M-FR-PL6. Thus, on the basis of the aforementioned results of FTIR, XPS, MCC, TG and SEM analyses, a possible mechanism of the flame retardancy of M-FR-PL is presented in Figure 10. The addition of melamine flame retardant improved the flame-retardant performance of the flame-retardant loofah composites.

Figure 9.

SEM diagrams of residual char of samples: (a) loofah, (b) PL, and (c) M-FR-PL6.

Figure 10.

Mechanism of the flame retardancy of M-FR-PL6.

Smoke density analysis

Loofah will produce a lot of smoke when burning, which was also one of the fire risk factors. Therefore, loofah, PL and M-FR-PL6 samples were selected to analyze the smoke density test under flameless conditions. The smoke generated by loofah, PL and M-FR-PL at 600°C were determined. The transmittance at 4 min and maximum specific optical density (Ds_max) were compared and analyzed (Table 6). The variation curves of the samples’ transmittance were shown in Figure 11. The flue gas release rate of loofah was fast, that the transmittance at 4 min was only 6.2% and Ds_max was 159.7. The flue gas release rate of loofah decreased after pretreatment. Compared with loofah, the transmittance at 4 min of PL increased by 61.4%, while Ds_max decreased by 129.1%. It may be attributed to the removal of gum and wax on the surface of loofah after alkali treatment. At the beginning of heating PL could immediately produce smoke, while loofah produced smoke until 55 s later. This might be the colloid and wax on the surface of natural fiber need higher heat to decompose than cellulose. This also proved the removal of colloid and wax on loofah after pretreatment.^34,35

Table 6.

Smoke density analysis results.

Samples	transmittance at 4 min/%	Ds _max
loofah	6.2	159.7
PL	67.6	30.6
M-FR-PL6	60.4	31.3

Figure 11.

Transmittance curves of samples.

Melamine is a kind of gas phase flame retardant, and the function of the gas phase flame retardant is mainly to remove active free radicals (such as H•, OH• and O•) that contribute to flame propagation.³⁶ This effect can also inhibit the oxidation reaction of the smoke precursor formed during combustion and be beneficial to the decrease of smoke production of M-FR-PL6. Compared with PL, the transmittance at 4 min of M-FR-PL6 decreased by 7.2%, while Ds_max increased by 0.70. Moreover, M-FR-PL6 possessed a slower smoke release rate compared with PL, which also reflect a good smoke suppression performance.³⁷

Conclusions

The melamine-modified flame retardant loofah composites were prepared by impregnation baking method and the orthogonal design method was used for optimization of the experimental preparation conditions. The following four factors: the mass concentration of melamine (ρ_m, g/L), loofah bath ratio (LBR), reaction temperature (T_r, °C) and reaction time (t_r, h) were discussed. The adsorption amount of melamine has great effect on the flame retardancy of the composites. The results showed that the loofah prepared under the following optimum experimental conditions (M-FR-PL6) had optimal flame retardant performance: ρ_m was 6.0 g/L, LBR was 1:100, T_r was 80.0 °Cand t_r was 2.0 h. Compared with loofah, the flame retardant performance of M-FR-PL6 was significantly improved: LOI was increased by 11.5%, UL-94 reached V0, and the value of Ds_max decreased by 128.4. Meanwhile, MCC results indicated that the heat release of loofah was significantly reduced after melamine modification. M-FR-PL6 could form a dense char layer to isolate oxygen and inhibit flame spread during the combustion process. The melamine-modified loofah composites possessed good flame retardancy and smoke suppression performance, which will be beneficial for its application in fire-proof building materials, household products, thermal insulation materials and other fields in the future. In this study, since the limitation of flame-retardant adsorption onto loofah, it is difficult to further improve the flame retardant performance by increasing the flame-retardant concentration.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research was financially supported by the National Natural Science Foundation of China (No.21878026), Beijing Key Laboratory of Quality Evaluation Technology for Hygiene and Safety of Plastics (QETHSP2021008), 2020 Industrial Technology Foundation Public Service Platform Project (2020-0107-3-1), Postgraduate Research & Practice Innovation Program of Jiangsu Province (KYCX21_2881, KYCX20_2585), Jiangsu Province University Blue Project, and Project of Higher Education Reform in Jiangsu Province (2019JSJG022).

ORCID iD

Hongxiang Ou

References

Liu

Zhao

Jin

, et al. Production of fumaric acid by immobilized Rhizopus arrhizus RH 7-13-9# on loofah fiber in a stirred-tank reactor[J]. Bioresour Technol 2017; 244: 929–933.

Sun

Zhang

, et al. The highly enhanced Cr(VI) photoreduction removal by oxalic acid coordinated with iron-loaded waste Loofah[J]. Environ Res, 2021: 112456. DOI: 10.1016/j.envres.2021.112456.

Sari

Suteja

R A Ilyas

, et al. Characterization of the density and mechanical properties of corn husk fiber reinforced polyester composites after exposure to ultraviolet light[J]. Funct Composites Structures 2021; 3: 034001. DOI: 10.1088/2631-6331/ac0ed3.

Ilyas

Zuhri

MYM

Aisyah

, et al. Natural fiber-reinforced polylactic acid, polylactic acid blends and their composites for advanced applications[J]. Polymers 2022; 14(1): 202. DOI: 10.3390/polym14010202.

Zeng

Liu

, et al. Modified natural loofah sponge as an effective heavy metal ion adsorbent: Amidoxime functionalized poly(acrylonitrile-g-loofah) [J]. Chem Eng Res Des 2019; 150: 26–32.

Wang

Chen

Jiang

, et al. Facile and green synthesis of reduced graphene oxide/loofah sponge for Streptomyces albulus immobilization and ε-Poly-L-lysine production[J]. Bioresource Technology, 2021, 126534.

Ilyas

Zuhri

MYM

Aisyah

, et al. Corn husk fiber-polyester composites as sound absorber: nonacoustical and acoustical properties[J]. Polymers 2022; 14(202). DOI: 10.3390/polym14010202.

Mahardika

Abral

Anwar Kasim

, et al. Production of nanocellulose from pineapple leaf fibers via high-shear homogenization and ultrasonication[J]. Fibers 2018; 6(28). DOI: 10.3390/fib6020028.

Ming

Yuan

, et al. Novel eco-friendly flame retardants based on nitrogen–silicone schiff base and application in cellulose[J]. ACS Sustain Chem Engeering 2020; 8: 290–301.

10.

Koedel

Callsen

Weise

, et al. Investigation of melamine and DOPO-derived flame retardants for the bioplastic cellulose acetate[J]. Polym Test 2020; 90: 106702. DOI: 10.1016/j.polymertesting.2020.106702.

11.

Czlonka

Strakowska

Strzelec

, et al. Melamine, silica, and ionic liquid as a novel flame retardant for rigid polyurethane foams with enhanced flame retardancy and mechanical properties[J]. Polym Test 2020; 87: 106511. DOI: 10.1016/j.polymertesting.2020.106511.

12.

Song

Liu

Fan

, et al. Sustainable, high-performance, flame-retardant waterborne wood coatings via phytic acid based green curing agent for melamine-urea-formaldehyde resin[J]. Proress in Oranic Coatins 2022; 162: 106597. DOI: 10.1016/j.porgcoat.2021.106597.

13.

Wang

, et al. Modification of diatomite with melamine coated zeolitic imidazolate framework-8 as an effective flame retardant to enhance flame retardancy and smoke suppression of rigid polyurethane foam[J]. J Hazard Mater 2019; 379: 120819. DOI: 10.1016/j.jhazmat.2019.120819.

14.

, et al. Flame-retardant ethylene vinyl acetate composite materials by combining additions of aluminum hydroxide and melamine cyanurate: Preparation and characteristic evaluations[J]. J Colloid Interf Sci 2021; 589: 525–531.

15.

Zhang

, et al. Highly efficient replacement of traditional intumescent flame retardants in polypropylene by manganese ions doped melamine phytate nanosheets[J]. J Hazard Mater 2020; 398: 123001. DOI: 10.1016/j.jhazmat.2020.123001.

16.

Harini

Mohan

. Isolation and characterization of micro and nanocrystalline cellulose fibers from the walnut shell, corncob and sugarcane bagasse[J]. Int J Biol Macromolecules 2020; 163: 1375–1383.

17.

Sari

Wardana

ING

Irawan

, et al. Characterization of the chemical, physical, and mechanical properties of naoh-treated natural cellulosic fibers from Corn Husks[J]. J Nat Fibers 2018; 5(4): 545–558.

18.

Syafri

Jamaluddin Sari

, et al. Isolation and characterization of cellulose nanofibers from Agave gigantea by chemical-mechanical treatment[J]. Int J Biol Macromol 2022; 200: 25–33.

19.

Loganathan

Sultan

MTH

Ahsan

, et al. Characterization of alkali treated new cellulosic fibre from Cyrtostachys renda. [J] 2020; 9(3): 3537–3546.

20.

Karimah

Ridho

Munawar

, et al. A comprehensive review on natural fibers: technological and socio-economical aspects[J]. Polymers 2022; 13(24): 4280. DOI: 10.3390/polym13244280.

21.

Zheng

Zhang

Guo

, et al. Isolation and characterization of nanocellulose with a novel shape from walnut (Juglans Regia L.) shell agricultural waste[J]. Polymers 2019; 11(7): 1130. DOI: 10.3390/polym11071130.

22.

Singh

Pahal

Ahuja

. Isolation and characterization of microfibrillated cellulose and nanofibrillated cellulose with “biomechanical hotspots” [J]. Carbohydr Polym 2020; 234: 115827. DOI: 10.1016/j.carbpol.2020.115827.

23.

Tan

Niu

, et al. Enhancement of the stability of biosorbents for metal-ion adsorption. Ind Eng Chem Res 2015; 54: 6100–6107.

24.

Naik

Fontaine

Samyn

, et al. Melamine integrated metal phosphates as non-halogenated flame retardants: synergism with aluminium phosphinate for flame retardancy in glass fiber reinforced polyamide 66[J]. Polym Degrad Stab 2013; 98: 2653–2662.

25.

Zhang

Shi

, et al. N, P-codoped carbon networks as efficient metal-free bifunctional catalysts for oxygen reduction and hydrogen evolution reactions[J]. Angew Chemie-International Edition 2016; 55(6): 2230–2234.

26.

Syafri

Jamaluddin Wahono

, et al. Characterization and properties of cellulose microfibers from water hyacinth filled sago starch biocomposites[J]. Int J Biol Macromol 2019; 137: 119–125.

27.

Fan

Feng

Zhang

, et al. Synergistic effects of aluminium hypophosphite on the flame retardancy and thermal degradation behaviours of a novel intumescent flame retardant thermoplastic vulcanisate composite. Plast[j] Plastics Rubber Composites 2019; 48: 270–280.

28.

Jiang

Jin

Park

. Synthesis of a novel phosphorus-nitrogen-containing intumescent flame retardant and its application to fabrics[J]. J Ind Eng Chem 2015; 27: 40–43.

29.

Rao

, et al. Flame-retardant flexible polyurethane foams with highly efficient melamine salt[J]. Ind Endineering Chenistry Res 2017; 56(25): 7112–7119.

30.

Chaudhari

Kwon

Moon

, et al. Melamine-modified silicotungstic acid incorporated into the polyvinyl alcohol/polyvinyl amine blend membrane for pervaporation dehydration of water/isopropanol mixtures. Vacuum 2018; 147: 115–125.

31.

Singh

Pahala

Ahuja

32.

Matea Perić

Robert Putz

Paulik

. Influence of nanofibrillated cellulose on the mechanical and thermal properties of poly (lactic acid) [J]. Eur Polym J 2019; 114: 426–433.

33.

Sari

Setyawan

Thiagamani

SMK

, et al. Evaluation of mechanical, thermal and morphological properties of corn husk modified pumice powder reinforced polyester composites[J]. Polym Composites 2022; 43: 1763–1771.

34.

Basak

Ali

. Fire resistant behaviour of cellulosic textile functionalized with wastage plant bio-molecules: a comparative scientific report[J]. Int J Biol Macromolecules 2018; 114: 169–180.

35.

Liu

Zhao

Chen

, et al. Eco-friendly synergistic cross-linking flame-retardant strategy with smoke and melt-dripping suppression for condensation polymers[J]. Composites Part B 2021; 211: 108664. DOI: 10.1016/j.compositesb.2021.108664.

36.

Salmeia

Fage

Liang

, et al. An overview of mode of action and analytical methods for evaluation of gas phase activities of flame retardants. Polymers 2015; 7(3): 504–526.

37.

Wang

, et al. Ecofriendly flame-retardant cotton fabrics: preparation, flame retardancy, thermal degradation properties, and mechanism[J]. ACS Sustain Chem Eng 2019; 7(3): 19246–19256.

Research on preparation and flame retardancy of melamine-modified flame retardant loofah composites

Abstract

Keywords

Introduction

Materials and methods

Materials

Pretreatment of loofah

Preparation of melamine flame retardant loofah material (M-FR-PL)

Characterization

Results and discussion

Analysis of orthogonal experiment

FT-IR and XPS analysis

The vertical burning (UL-94) analysis

Thermogravimetric analysis

Microcalorimetric analysis

SEM analysis

Smoke density analysis

Conclusions

Footnotes

Declaration of conflicting interests

Funding

ORCID iD

References