Effect of chicken feather and boron compounds as filler on mechanical and flame retardancy properties of polymer composite materials

Abstract

Sustainable utilisation of solid waste has been influenced by the increasing population of the world. Benefits of using solid waste based on natural fibre in polymer material are biodegradability and cost effectiveness. In poultry farms, chicken poultry, one of the slaughterhouse wastes is confronted with 30 10⁶ kg of waste per year in Turkey. The evaluation of this waste, which is quite rich in keratin, is extremely important both for the solution of the waste problem and for maintaining a clean environment, bringing this valuable material to the economy. These fibres are stable, durable and biodegradable because they have a crystalline structure. However, this valuable waste will have a positive effect when used together with boron minerals, which both increase the mechanical properties, flame retardancy and biodegradation of composite material. In this study, it is the aim to manufacture superior polyester-based composite materials reinforced with three kinds of boron minerals, such as boron oxide, borax pentahydrate, borax decahydrate and fibres recycled from waste chicken feathers. The effect of different filling ratios of filling materials on the mechanical and physical properties of composite materials was examined. Flame retardancy properties of the composites with best mechanical results were investigated. After pouring by means of the pre-casting process, the water absorption and swelling thickness of final products, as well as density, bending strength, flexural modulus, limiting oxygen index, thermogravimetric analysis and scanning electron microscope analysis, was performed. Mixing prescriptions and conditions with the best properties were determined.

Keywords

Polymer matrix composites boron waste chicken feather flame retardancy mechanical properties physical properties

Introduction

Studies on poultry feathers focuses on protecting the environment. In literature, short fibre composites based on agricultural waste have increased more recently. These fibres are generally more environmentally friendly and relatively easier to obtain at lower densities than inorganic fibres (Barone and Schmidth, 2005). Beside these superior properties, the flame retardants of composites are also important to provide safety necessity of the products. Fire retardants are chemicals that increase the temperature to above normal and literally increase the ignition point of the materials. This limit varies as a function of the retarder, but in any case, it tries to reduce the risk of fire (Oliwa et al., 2016). Recently, biochar, wool, calcium carbonate with diammonium phosphate, etc., was used to bring a flame retardant property to composite materials (Das et al., 2016, 2017; Shuarty et al., 2012). The effect of zinc borate, boric acid and boric oxide on the flammability of epoxy resin containing red phosphorus was investigated by Doğan and Unlu. According to the limiting oxygen index (LOI) values and thermal gravimetric analysis (TGA) results, the boron compounds showed a good effect by increasing char yield in the condensed phase (Doğan and Unlu, 2014). Yang et al. also proved that contribution of boron to epoxy composites was successful to form swollen and glassy char layers with a barrier effect on providing free radicals (Yang et al., 2016). Bansal and Singh reported the flame retardation characterisation of chicken feather fibre (CFF) and extracted residue powder from fish. Epoxy resin was used as a matrix material with chicken feather as a filler in a micro-sized particulate. They obtained that use of 5% of chicken feather improved the flammability properties of epoxy resin composites based on weight loss rate versus linear burning rate (Bansal and Singh, 2016). Beside flame retardancy of composites, there are also several studies on mechanical properties of composites reinforced with chicken feather. In the study of Barone and Schmidt, mechanical properties of polyethylene reinforced with chicken feathers were obtained. The results show that improvement of a polymer matrix can be provided with keratin feather fibre. According to their mechanical analysis there is an observed increase in flexural modulus when the keratin feather fibre loading increased (Barone and Schmidth, 2005). Cheng et al. also concluded in their study that chicken feathers had a positive effect on mechanical properties of composites. They used poly lactic acid (PLA) as a polymer matrix and CFF as filler. Owing to the CFF reinforcement, the flexural modulus of the CFF/PLA composites were significantly higher than that of pure PLA (Cheng et al., 2009). Huda and Yang researched the mechanical and acoustical properties of composites manufactured from a ground chicken quill and polypropylene (PP) matrix. They studied some parameters, such as a concentration of ground chicken quill, holding temperature and density. Jute–PP composites were compared with chicken quill–PP composites according to their mechanical and acoustical properties. They found that quill showed better compatibility with a PP matrix. In general, jute and chicken quill revealed similar flexural strength, while chicken quill showed better noise adsorption compared with jute composites. Noise reduction coefficient of ground quill composites were 71% higher than jute composites (Huda and Yang, 2008). Acda showed the availability of waste chicken feathers as reinforcement in cement-bonded composites. Composite boards, including a various amount of waste chicken feather, cement, sand and chemical admixtures, were manufactured. Boards with 5% to 10% fibre and/or ground feather by weight had better strength and stability compared with commercial wood fibre–cement composites. After 1 day it was concluded that higher amounts of feather caused higher water absorption and thickness swelling (Acda, 2010). Winandy et al. investigated the potential of CFF in wood MDF composites. They used phenol formaldehyde resin as a matrix and chicken feather as a reinforcement in the amount of between 20% to 95%. They significantly concluded that physical properties of feather fibre–wood fibre mixtures had an improvement in properties of thickness swelling and water absorption compared with control panels, likely owing to the keratin that has hydrophobic character in the chicken feather (Winandy et al., 2003). Ghani et al. used polyethylene grafted maleic anhydride (PEgMAH) as a coupling agent in production of low-density polyethylene (LDPE)/CFF composites. They investigated the effect of a coupling agent on tensile properties, structural property, thermal degradation and swelling thickness. LDPE/CFF/PEgMAH composites showed better tensile strength, elastic modulus and final decomposition temperature. From scanning electron microscope (SEM) images they obtained the grafted maleic anhydride, which played an important role in providing good adhesion between matrix and fibres. Chicken feather fibres were dispersed well in the polymer matrix (Ghani et al., 2013). To our knowledge, this is the first study investigating the flammability properties of polyester composites reinforced with chicken feather and boron minerals.

Our recently published study of polymer composites reinforced with waste marble dust and fibres from chicken feathers showed that the properties of natural fibre reinforced composites can be influenced by fibre content and/or the amount of filler (Akpinar Borazan and Gokdai, 2017). Therefore, the objective of this study was to improve the properties of polyester composites containing chicken-feather fibre and investigate the effect of the incorporation of boron compounds on the mechanical and flammability properties of the feather fibre/polyester composites. As a result of the study, the environmental problems caused by chicken feather waste might be reduced, and also value added to feather fibre/polyester composites by adding boron compounds were produced.

Materials and method

Materials

In this study, composite materials were produced from polyester resin (Polipol 383-G, Poliya Composite Resins and Polymers Inc., density of 1.076 ±0.05 g cm⁻³ as a standard ISO 1675), waste chicken feather obtained from a poultry in Turkey and three kinds of boron minerals supplied by Eti Maden in Turkey. Boron oxide (density of 1.84 g cm⁻³, particle size 0.315 mm), borax decahydrate (density of 1.71 g cm⁻³, particle size 1.180 mm), borax pentahydrate (density of 1.81 g cm⁻³, particle size 1.180 mm) and waste chicken feather were used as reinforcement. Methyl ethyl ketone peroxide (MEKP) was a hardener (Butanox™ M-60, AkzoNobel Products) and Cobalt 1% solution as a promoter was used in the curing of polyester resins. Polypropylene graft maleic anhydride (Aldrich Chemistry) was used as a coupling agent.

Pretreatment of chicken feathers

A pre-treatment was required to stabilise and transform chicken feathers into a stable technical material. First, chicken feathers were washed with water. Afterward, quill was separated from barbs and cut into small pieces. Finally, last drying was again in oven at 105 °C, for 2 hours. Moisture of clean feather fibres was decreased to 10%.

The boron minerals that have more than 10% moisture were dried in a drying oven at 40 °C to provide moisture of less than 10%. Finally waste chicken feathers were ground respectively in a precision grinder (Fritsch- Pulverisette9, GmbH) equipped with a sieve (Fritsch, Analysette 3).

Composite preparation

The polyester matrix was compounded, respectively, with reinforcement fillings in different ratios by volume. The raw material formulations and the prescription for composite production is given in Table 1.

Table 1.

Ratio of materials used for composite manufacture.

Sample Code	F[v/v %]	B1[v/v %]	B2[v/v %]	B3[v/v %]	P[v/v %]
B1P	–	8	–	–	92
B2P	–	–	8	–	92
B3P	–	–	–	8	92
FF1P	5	–	–	–	95
FF2P	7	–	–	–	93
FF3P	8	–	–	–	92
FF1B1P	5	8	–	–	87
FF2B1P	7	8	–	–	85
FF3B1P	8	8	–	–	84
FF1B2P	5	–	8	–	87
FF2B2P	7	–	8	–	85
FF3B2P	8	–	8	–	84
FF1B3P	5	–	–	8	87
FF2B3P	7	–	–	8	85
FF3B3P	8	-	-	8	84

F: chicken feather; B1: boron oxide; B2: borax pentahydrate; B3: borax decahydrate; P: polyester.

[v/v %] refers the volume percentage of each component in composite preparation.

Polyester resin and reinforcement materials were first mixed in the given ratios using a speed of 700, 1200 and 1700 r min⁻¹ (Stuart scientific mechanical stirrer), 5 min cycle time for each. After the accelerator and hardener were added to the mixture, the mixture was poured into a mould. Composites remained in the mould for 2 hours, then removed from the mould and were kept at room temperature for 1 day. Later they were held at 110 °C for 2 hours in an oven (Binder, Germany).

Characterisation of composites

Three-point bending tests were carried out according to EN ISO178 at a bending speed of 2 mm min⁻¹ in Shimadzu AG-IC Test Machine to determine flexural strength and modulus of composites. Five samples of each group were tested and average values were reported. The bending measurements were performed at ambient conditions (23 ±2 °C). Determination of the mechanical properties of polyester composites in the form of rectangular bars (100 mm × 10 mm × 4 mm; length × width × thickness) were used for measurement.

Density measurements of the composite specimens were done according to the Archimedes’ Principle (ASTM D570 standard). The physical properties examined were bulk density, thickness swelling, open porosity and water absorption. These tests were carried out with test sample sizes of 5 × 5 cm.

The flame retardancy properties of composite materials were carried out according to ASTM D2863 (2013) standard (Dynisco Polymer Test LOI Limiting Oxygen Index Chamber). This standard covers the methods used to determine the minimum oxygen concentration required to be present in nitrogen–oxygen mixtures for the continuation of the flushes of the test specimens in the upright position under certain test conditions. In principle, a small test sample is placed vertically into a transparent chimney passing through a mixture of oxygen and nitrogen up through it. The top of the test sample is ignited, followed by the burning behaviour of the test sample, and the duration of the burn or the duration of the burning test sample is compared with predetermined threshold values for such combustion. Experiments using a series of test samples at different oxygen concentrations predict the smallest oxygen concentration value required for continuation of the burn (Ayar et al., 2014). The results are given in terms of the oxygen index value (ASTM D2863-13).

Thermal properties of the composite samples were carried out by using Setaram LabSys Evo analyser. Five to 9 mg of measured composite was kept in an alumina crucible under a nitrogen atmosphere with a flowrate of 20 ml min⁻¹ by raising its temperature from 20 °C to 800 °C in steps of 20 °C min⁻¹. The surface morphology of the composites was determined by using a field emission SEM (Zeiss Supra 40VP). Images were taken from the fracture surface of the composites.

Results and discussions

Mechanical properties of composites

In order to investigate the effects of boron compounds on mechanical properties of the rising volume of chicken feather/polyester composites, the flexural strength and modulus value of boron/polyester composites were evaluated in the range from 48.73 MPa to 73.61 MPa and 3203.26 MPa to 3954.22 MPa, respectively. In this range, the highest reinforcing effect of the boron compounds was determined with boron oxide.

Figure 1 shows the flexural strength and modulus value of waste chicken feather powder/boron compounds polyester composites. When increasing the volume content of the waste chicken feather powder from 5 to 8 v%, the bending properties increased, whereas boron compounds reduced the flexural strengths and modulus for all composite samples. Boron oxide filler, however, had the highest impact on the flexural strength and modulus of the composite samples (FF3B1P: 58.31 MPa flexural strength, FF1B1P:3848.35 MPa flexural modulus).

This is because of the anhydrous structure of boron oxide, while the other compounds consist water molecules in their formulas (B2; borax pentahydrate, Na₂B₄O₇. 5H₂O, B3; borax decahydrate, Na₂B₄O₇. 10H₂O). Water molecules led to micro voids at the interface between the polymer and fibres; these voids caused a decrease in mechanical properties (Arrakhiz et al., 2013). Bending properties of each chicken feather/boron compounds were investigated. When graphs were evaluated, it could be clearly seen that chicken feather filler only improved the boron oxide strength. The composites with other boron compounds (B2 and B3) and also chicken feather had lower strength values than the FFB1P composite series. The highest value of flexural modulus belongs to chicken feather/polyester composites of nearly 3600 MPa.

In general, increasing amounts of chicken feather provided better flexural strength. Nagaraja Ganesh and his colleagues show similar results in their study. It was observed that the resistance of bending gradually increased with the loading of excess of CFFs (NagarajaGanesh et al., 2012). We can see from Figure 1 that all kinds of boron doped chicken feather composites have higher flexural modulus values. It can be concluded that boron oxide in particular improved the composite resistance to being deformed elastically.

Physical properties of composites

The physical properties of composites are very important for the determination of their usage areas. Table 2 shows the physical properties of composite materials, such as bulk density, open porosity, thickness swelling and water absorption.

Table 2.

Physical properties of composite materials.

Sample code	Bulk density (g/cm³)	Open porosity (%)	Thickness swelling (%)	Water absorption (%)
B1P	1.241 ±0.002	0.664 ±0.062	3.510 ±0.082	0.535 ±0.030
B2P	1.190 ±0.005	1.911 ±0.048	1.466 ±0.065	1.607 ±0.038
B3P	1.164 ±0.066	3.683 ±0.055	1.690 ±0.024	3.278 ±0.025
FF1P	1.174 ±0.003	0.594 ±0.095	0.662 ±0.020	0.506 ±0.040
FF2P	1.164 ±0.010	0.897 ±0.080	1.716 ±0.035	0.771 ±0.055
FF3P	1.157 ±0.003	1.153 ±0.085	2.665 ±0.040	0.999 ±0.045
FF1B1P	1.226 ±0.006	0.647 ±0.064	3.448 ±0.058	0.528 ±0.020
FF2B1P	1.221 ±0.014	0.709 ±0.028	3.453 ±0.042	0.585 ±0.050
FF3B1P	1.211 ±0.005	0.954 ±0.018	4.882 ±0.056	0.789 ±0.065
FF1B2P	1.213 ±0.004	0.122 ±0.075	2.276 ±0.018	0.100 ±0.048
FF2B2P	1.203 ±0.001	0.700 ±0.086	2.564 ±0.020	0.581 ±0.032
FF3B2P	1.165 ±0.035	1.880 ±0.045	2.753 ±0.025	1.627 ±0.030
FF1B3P	1.202 ±0.001	1.170 ±0.040	1.982 ±0.036	0.974 ±0.020
FF2B3P	1.174 ±0.026	0.556 ±0.020	2.372 ±0.050	2.448 ±0.035
FF3B3P	1.168 ±0.001	0.333 ±0.025	3.775 ±0.062	2.878 ±0.042

Among the composites, B3P has the highest water absorption value. It was thought this was because of the high amount of water molecules in borax decahydrate. Increasing the amount of chicken feather led to increasing of open porosity in composites as was proved with SEM images of composite samples. Bansal et al. also showed that increasing w% of chicken feather caused water absorption to increase as the voids in epoxy composites were raised (Acda, 2010; Bansal et al., 2016). We can conclude that water absorption values show compliance with swelling thickness and open porosity values, except for the FFB3P series. Open porosity and water absorption increased with an increasing amount of chicken feather in other boron composites, while open porosity decreased in the borax decahydrate series. It was thought because of the maximum water absorption capability of decahydrate owing to the high amount of water molecules in its structure. While the composites swelling and open porosities in composite structure increased, their capability of water absorption increased. For all composites, bulk density values decreased with the increasing amount of fillers.

Flame retardancy properties of composites

Flame retardancy properties of composites that give the best mechanical properties were obtained according to ASTM D 2863 standard. LOI values of three samples with better mechanical and physical properties are 19 for B1P, 19 for FF3P and 24 for FF3B1P. Images of burned samples given in Figure 2 show the combustion performances in the determined oxygen and nitrogen ratios at the end of 180 s. Numbers below the photographs represent the combustion states of the composite samples at different oxygen and nitrogen ratios. For example, when the 19 LOI value was used in the B1P sample, the sample was not flammable at the end of 180 s. But when the 20 LOI value was used, in other words the amount of oxygen was increased, the sample burned at the end of 180 s. This means that the LOI value for the B1P sample is 19, the sample will flash on the oxygen values given above. It is known that if the composite sample has a higher LOI value, it means it has a more stable behaviour in flame and duration to burn it completely is longer. From Figure 2 it can be observed that polyester composites reinforced with boron oxide and chicken feather have higher LOI values than the others. While B1P and FF3P burned at lower oxygen levels, the FF3B1P series achieved higher oxygen percentages.

Boron oxide can be used as a flame retardant in many manufacturing processes. From these results it can be concluded that the use of chicken feather and boron oxide together increased the flame retardant property by 26%.

TGA analysis of composites

Thermal stability results of composite samples that were exposed to LOI tests were given by thermogravimetric, derivative thermogravimetric and differential thermal analysis in Figure 3. The top curve refers to thermogravimetric, the bottom curve refers to differential thermal analysis and the middle one mentions the derivative thermogravimetric curve of composite samples.

According to the results, it can be indicated that when boron oxide filler was used with chicken feather, the residual mass value increased from 8.74% to 20.67%. These results are also compatible with the LOI test results, as boron oxide gives a flame retardancy to composites. This can be explained by the fact that B₂O₃ is known as hard glass and the crystal structure begins to deteriorate at 300 °C, and a series of sub-oxides are produced by partial melting until full fusion is reached at 700 °C. As boron oxide is anhydrous it can behave as a blowing agent that provides a ‘glue’ to keep the combustion char and provide structural unity to the char (Jimenez et al., 2006). Flame retardant property is owing to the effect of not only the boron oxide but also the chicken feathers. The thermal stability of the FF3B1P composite is enhanced by chicken feather reinforcements that act as a barrier for better thermal insulation and inhibit the penetration of volatile corrosion products (Cheng et al., 2009). When the thermal decomposition graphs (Figure 3) are examined the TGA results indicate a slight decrease in the thermal degradation temperature of FF3B1P composite with a boron oxide loading of 8% vol. In graphs, it can be analysed that the first stage is related to a small weight loss because of the dehydration that belongs to a temperature between 150 °C and 250 °C (Akpinar Borazan and Gokdai, 2018). At the second stage, main evaporation reactions occur at nearly 320 °C–350 °C where most of the sample weight is lost as volatile matter. There was no significant change between 460 °C–800 °C that would affect the mechanical and physical properties.

Morphological analysis of composites

Figure 4 shows the SEM images of these three composite samples. Chicken feather barbs were located in the voids in FF3P and FF3B1P composites. Filler cracking was observed in Figure 4(a1) and (a2) in the B1P series. The cracked surface occurred especially in boron oxide/polyester composites. Significantly, Figure 4(b1) and (b2) fillers are uniformly distributed in the polyester matrix from large to fine. In Figure 4(c1) and (c2) it is clear that the surface around the filler materials have been covered with a polymer matrix. This case showed that they can easily have a good adhesion between the polymer and fibres in the composite structure. Good adhesion mainly affected the mechanical properties of the polymer matrix, such as flexural strength and modulus, in a positive way (Uygunoglu et al., 2015).

The central part of the chicken feather is called rachis, which is connected with the barbs. These chicken barbs have the length, strength and flexibility that make them convenient as natural protein fibres (Reddy and Yang, 2007). As seen from Figure 4, the chicken feather barbs have a unique cross-section that cannot be observed in any other protein fibres. These chicken barbs are soft and readily can absorb water (Akpinar Borazan and Gokdai, 2017). Addition of boron oxide improved the connection of the waste chicken feather with polyester and it filled the voids in the structure and gave the composite a high strength.

Conclusions

This study investigated the effect of the incorporation of boron compounds to feather fibre on enhancing the mechanical and flame-retardant properties of polyester composites. According to some mechanical and physical properties of the composites, it can be concluded that boron oxide had a better contribution to bending properties of composites. Especially, flexural modulus of the blends, both feather fibre and boron oxide/polyester composites, were higher than the feather fibre/polyester composites. When three kinds of boron minerals were compared it was indicated that boron oxide was more compatible with waste chicken feather in polymer composites. In results of LOI tests and TGA analysis it was clearly noted that boron oxide improved the flame retardancy properties of polyester with a gain of 26%. Based on physical test results, when the feather fibre loading level increased from 5 to 8%, the open porosity and water absorption percentage increased and bulk density decreased. Moreover, it is recommended that a combination of higher feather fibre loading with boron oxide in polyester composite would be more ideal if flame retardancy is the main concern for application of the polymer blends.

Footnotes

Acknowledgements

We would like to thank Bilecik Seyh Edebali University Scientific Research Project (No: 2016-02.BSEÜ.03-05) for their support.

Declaration of conflicting interests

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

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

A Akpinar Borazan

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