Tensile and flexural properties of polypropylene composites filled with highly effective flame retardant magnesium hydroxide

Accepted Manuscript Tensile and flexural properties of polypropylene composites filled with highly effective flame retardant magnesium hydroxide Ji-Zhao Liang PII:

S0142-9418(17)30151-4

DOI:

10.1016/j.polymertesting.2017.03.014

Reference:

POTE 4961

To appear in:

Polymer Testing

Received Date: 8 February 2017 Accepted Date: 13 March 2017

Please cite this article as: J.-Z. Liang, Tensile and flexural properties of polypropylene composites filled with highly effective flame retardant magnesium hydroxide, Polymer Testing (2017), doi: 10.1016/ j.polymertesting.2017.03.014. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Material Properties

Tensile and Flexural Properties of Polypropylene Composites Filled

Ji-Zhao Liang

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with Highly Effective Flame Retardant Magnesium Hydroxide

Research Division of Green Function Materials and Equipment School of Mechanical and Automotive Engineering

ABSTRACT

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South China University of Technology, Guangzhou 510640, P.R. China

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The reinforcing effects of highly effective flame retardant magnesium hydroxide (FMX) content on the tensile and flexural properties of filled polypropylene (PP) composites were investigated within the FMX weight fraction range from 5 to 60

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wt.%. It was found that the Young’s modulus and flexural modulus increased approximately linearly while the tensile yield strength and tensile fracture strength decreased slightly with increasing the FMX weight fraction. When the FMX weight

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fraction was lower than 20%, the tensile elongation at break decreased considerably,

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and then decreased slightly; the flexural strength increased when the FMX weight fraction was lower than 30%, and then decreased slightly. The tensile properties increased with increasing rate of tension. Moreover, the tensile yield strength of the composites was estimated using an equation proposed in previous work, and good agreement was shown between the predicted and the measured data. Key words: polymer-matrix composites; mechanical properties; stress/strain curves; strength; elastic properties. __________________ 1

ACCEPTED MANUSCRIPT Corresponding author. E-mail address: [email protected] 1. Introduction For flame retardant polymer composites, both retardant and mechanical

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properties are important. Polypropylene (PP) is one of general thermoplastics used extensively in industry, agriculture and daily life due to the good insulation properties, small dielectric constant, good stress crack resistance and chemical resistance.

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However, owing to some defects such as poor flammability resistance and relatively

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low mechanical strength, the applications of PP resin have been limited [1-4]. In order to broaden the scope of application, PP is often loaded with flame retardants to enhance the flame-retarding ability. Recently, extensive attention has been paid to the flame retardant properties of PP [5-7]. Magnesium hydroxide [Mg(OH)2] is one of the

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flame retardants used extensively in the polymer industry [7-12]. Titelman and Gonen [7] studied the discoloration of PP-based compounds containing magnesium hydroxide, they found that compounding Mg(OH)2 with polymers leads to the

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formation of various colors ranging from light grey to rather dark beige. Sangcheol

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[10] researched the flame retardancy and smoke suppression of magnesium hydroxide filled PP composites. The results showed that the flame retardancy developed by magnesium hydroxide could effectively be increased by the additional incorporation of zinc borate and talc.

The flame retardant properties of flame retardant polymer composites can be improved with higher content of metal hydroxide flame retardant such as Mg(OH)2 and aluminum hydroxide [Al(OH)3], but the mechanical properties of the composites

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ACCEPTED MANUSCRIPT are usually weakened in this case, especially tensile strength and flexural strength [13, 14]. Liang and Li [13] investigated the effects of Mg(OH)2 content on the impact fracture toughness of PP/Mg(OH)2 composites, the results showed that the V-notched

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Izod impact strength of the PP/Mg(OH)2 composites increased non-linearly with increasing the filler weight fraction up to 15 wt.%, and then decreased slightly. It is, therefore, quite meaningful to develop highly effective flame retardant such that the

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retardant properties of polymer composites can be significantly improved even in the

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case of low content of the metal hydroxide flame retardant. Highly effective flame retardant magnesium hydroxide (FMX) is a new type of magnesium hydroxide with better flame retardant effect than that of general Mg(OH) 2 [15, 16]. However, there have been relatively few studies on the tensile properties and flexural properties of

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PP/FMX composites. The objectives of this study are to measure the tensile and flexural properties including Young’s modulus, tensile strength, flexural modulus and strength of PP/FMX composites, and to investigate the effects of the FMX content

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and rate of tension on the mechanical properties of these composites, to be beneficial

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to understand the reinforced mechanisms of the PP/FMX composites.

2. Experimental

2.1 Raw materials

The major raw materials were a polypropylene (PP) and a high effective flame retardant magnesium hydroxide (FMX). PP with trade mark CJS-700G was used as the matrix resin, which was supplied by the Guangzhou Petrochemical Works in

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ACCEPTED MANUSCRIPT Guangdong province (Guangzhou, China). The density in the solid state was 910 kg/m3 and melt flow rate (230oC, 2.16kg) was 10 g/10min. The FMX with trade-mark FMX-507 was supplied by the Jinge Fire-Fighting Materials Co., Ltd. (Foshan city,

of the FMX are summarized in Table 1.

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China), with mean diameter of 1.74µm. The main compositions and basic properties

Table 1 Main compositions and basic properties of FMX

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2.2 Preparation

Values ≥64 2.40 2.50 340 30±2 9-11 ≥93.0 ≤1.0 2

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Properties MgO content (wt.%) Specific gravity (g/cm3) Mohs hardness Loss of coolant temperature (oC) Thermal weight loss (%) PH value The white degree (%) Moisture (%) The heat absorption at decomposition (kJ/g)

The FMX particles were compounded with the PP in a high speed mixer, model

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CH-10DY, supplied by the Beijing plastics machinery factory (Beijing, China), and then the mixtures were melt blended by means of a co-rotating twin-screw extruder in

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the temperature range from 165 to 180oC and a screw speed 200 rpm to produce the PP/FMX composites. The extruder model SHJ-26 was supplied by the Nanjing Chengmeng machinery Ltd. Co. (Nanjing, China). The screw diameter was 24.5 mm, and the screw length-diameter ratio was 40. Finally, the extrudate was granulated. The FMX weight fractions were separately 5, 15, 30, 45 and 60 wt.%. The granules were dried at 80oC for 5 hours before fabrication of the specimens. The specimens for tensile and flexural tests were molded using a plastics injection machine (model

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ACCEPTED MANUSCRIPT UN120A) supplied by the Yizumi machinery Co. Ltd. (Foshan, China). The specimens for the tensile tests were dumbbells with width and thickness of 10 mm and 4 mm, respectively, while the specimens for the flexural tests were 80×10×4 mm.

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2.3 Instruments and methodology The tensile tests of the PP/FMX composites were conducted at room temperature by means of a universal materials testing machine (model CMT4104) supplied by the

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Newsans Co. Ltd. (Shenzhen, China) according to the ISO 527-1-. The cross-head

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speeds for the tensile test were 10, 50 and 100 mm/min to investigate the influence of the rates of tension on the tensile properties of the composites. The flexural properties of the PP/FMX composites were also measured at room temperature by means of the universal materials testing machine. The flexural tests were conducted according to

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ISO 180/1A, with a cross-head speed of 2 mm/min. Each group of specimens contained 5 pieces, and the average values of the measured tensile and flexural

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properties were used in the reported data.

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3 Results and discussion 3.1 Tensile properties

3.1.1 Tensile stress versus strain curves Figure 1 shows the tensile stress versus tensile strain curves of the PP/FMX

composites when the rate tension was 10 mm/min. It can be seen that the maximum tensile strength and the tensile strain at break decrease with increasing FMX weight fraction ( ϕ f ). This indicates that the tensile strength and the tensile ductility of the

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ACCEPTED MANUSCRIPT composites are weakened due to loading FMX into the PP resin. Figure 2 presents the tensile stress versus tensile strain curves of the PP/FMX composites when the rate of tension was 50 mm/min. It can be observed that the values of the maximum tensile

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strength and the tensile strain at break decrease with increasing the FMX weight fraction, but the values of the maximum tensile strength are somewhat higher than those of the results shown in Figure 1. Figure 3 displays the tensile stress versus

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tensile strain curves of the PP/FMX composites when the rate of tension was 100

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mm/min. Similar to the results shown in Figures 1 and 2, the values of the maximum tensile strength and the tensile strain at break decrease with increasing the FMX weight fraction, but the values of the maximum tensile strength are somewhat higher than those of the results shown in Figures 1 and 2. This shows that there is a

composites.

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significant influence of the rate of tension on the tensile strength of the PP/FMX

3.1.2 Relationship between Young’s modulus and FMX content

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Young’s modulus is an important parameter for characterizing the stiffness of

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materials under tensile load. Figure 4 illustrates the relationship between the Young’s modulus of the PP/FMX composites and the FMX weight fraction. It can be seen that Young’s modulus increases almost linearly with increasing FMX weight fraction. It is generally believed that the movement of macromolecular chains of polymer matrix is blocked by the inorganic particles, as well as the physical crosslink points between the filler particles and the macromolecular chains of the matrix. In addition, the inclusions play a role of the skeleton in the polymer matrix. Hence the stiffness of the PP/FMX

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ACCEPTED MANUSCRIPT composites is improved, leading to increasing the Young’s modulus with increasing the FMX weight fraction. In other words, the blocking effect and the skeleton effect are two of the major reinforcing mechanisms of inorganic particulate-filled polymer

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composites [17-19]. Moreover, PP is a semi-crystalline resin, and the inorganic particles could play a role of heterogeneous nucleation in the matrix [20]. The crystal type and degree of crystallinity of the PP will be changed by addition of the inorganic

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particles, resulting in variation of the stiffness of the composites. It can also be seen in

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Figure 4 that the values of the Young’s modulus increase approximately linearly with increasing rate of tension at the same FMX weight fraction. It was found through further analysis that the relationship between the Young’s modulus of the PP composites and the FMX weight fraction under these experimental conditions can be

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expressed by the following equation: Et = λ0 + λ1ϕ f

(1)

where Et is the Young’s modulus, ϕ f is the filler weight fraction, λ0 and λ1 are

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parameters related to the tensile properties. Parameter λ1 presents the sensitivity of

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the Young’s modulus to the filler concentration for the composites. The values of

λ0 and λ1 can be determined using linear regression analysis method from the measured data. The values of λ0 and λ1 of the composites under the experimental conditions are listed in Tables 2. It was found that the values of the linear correlation coefficient are higher than 0.98. Table 2 Values of parameters λ0 and λ1 Rate of tension (mm/min)

λ0

λ1

Rt

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2.7654

0.0546

0.9828

50

3.0825

0.0535

0.9843

100

3.9212

0.0385

0.9925

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3.1.3 Dependence of tensile strength on FMX content

It is generally believed that the tensile strength of polymer composites depends, to great extent, up on the interfacial adhesion between the filler and the matrix. The

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better the interfacial adhesion, the higher is the tensile strength of polymer composites.

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Tensile strength includes tensile yield strength and tensile fracture strength. Figure 5 presents the dependence of the tensile yield strength of the PP composites on the FMX weight fraction. It can be seen that the tensile yield strength decrease slightly with increasing the FMX weight fraction. The reason could be that the interfacial

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adhesion between the FMX particles and the PP matrix is not weak, and the interface can transfer effectively somewhat tensile load in this case, resulting in reducing

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slightly the tensile yield strength with increasing the filler concentration [18, 19]. In addition, the values of the tensile yield strength increase with increasing rate of

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tension under the same FMX weight fraction. Figure 6 shows the dependence of the tensile fracture strength of the PP/FMX

composites on the FMX weight fraction. It can be observed that the values of the tensile fracture strength decrease slightly with increasing the FMX weight fraction. This could also be attributed to the relatively good interfacial adhesion between the FMX particles and the PP matrix in addition to the PP matrix strength. Furthermore, the values of the tensile fracture strength also increase with increasing the rate of

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ACCEPTED MANUSCRIPT tension under same FMX weight fraction. It is also seen in Figures from 4 to 6 that the Young’s modulus, tensile yield strength and tensile fracture strength of the PP/FMX composites increase with

that

the

mechanical

behavior

of

polymeric

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increasing rate of tension at the same FMX weight fraction. It is generally believed materials

obeys

the

time-temperature equivalent principle. Thus, at a given temperature, the mechanical

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strength would increase with increasing deformation rate. Consequently, the values of

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Young’s modulus, tensile yield strength and tensile fracture strength of the PP/FMX composites increase with increasing rate of tension.

3.1.4 Correlation between tensile elongation at break and FMX content

Figure 7 presents the correlation between the tensile elongation at break of the

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PP/FMX composites and the FMX weight fraction. It can be seen that the tensile elongation at break decreases quickly when the FMX weight fraction is lower than 20 wt.%, and reduces slightly with increasing FMX weight fraction. The reason could be

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that the loading of the FMX particles would reduce, to certain extent, the integrity of

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the PP matrix, the ductility of the PP/FMX composites would be weakened, leading to decreasing tensile elongation at break. Moreover, the tensile elongation at break increases with increasing the rate of tension under the same FMX weight fraction. 3.2 Flexural properties 3.2.1Flexural stress versus strain curves

Figure 8 displays the flexural stress versus flexural strain curves of the PP/FMX composites. With increasing flexural strain, the flexural stress increases before

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ACCEPTED MANUSCRIPT reaching the maximum value. In addition, the values of the maximum flexural stress of the composite systems are higher than that of the unfilled PP resin, especially at lower filler content. This indicates that the loading of the FMX into the PP resin can

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enhance the flexural strength of the composites, especially at low flexural strain. 3.2.2 Relationship between flexural modulus and FMX content

Figure 9 presents the relationship between the flexural modulus of the PP/FMX

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composites and the FMX weight fraction. It can be seen that the flexural modulus

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increases approximately linearly with increase of the FMX weight fraction, and the relationship between them can be expressed by the following equation: E f = α + βϕ f

(2)

where E f is the flexural modulus, ϕ f is the filler weight fraction, α and β are the

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parameters related to the flexural properties. Parameter β characterizes the sensitivity of the flexural modulus of the composites to the filler concentration. The values of

α and β can also be determined using a linear regression analysis method from the

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measured data. The values of α and β of the composites under the experimental

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conditions are listed in Tables 3. It can be seen that the values of the linear correlation coefficient are greater than 0.98. Table 3 Values of parameters α and β

α

β

Rf

1677.9711

35.6203

0.9816

3.2.3 Dependence flexural strength on FMX content

Figure 10 shows the dependence of the flexural strength of the PP/FMX

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still higher than that of the unfilled PP resin. This illustrates that the flexural strength of the PP composites can be enhanced with the filler particles, especially in the case of lower FMX concentration. The reason could be that, when the specimen is under

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action of bending load, its top side will be subjected to compressive stress while the

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bottom side will be subjected to tensile stress. In the case of lower filler concentration, the tensile strength of the PP/FMX composites only decreases slightly (see Figure 5), while the stiffness of the composites increases significantly (see Figures 4 and 9); as a result, the flexural strength PP/FMX composites increases correspondingly. In the

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case of higher filler concentration, although the stiffness of the composites still increases (see Figures 4 and 9), the tensile strength decreases significantly (see Figure 5); as a result, the flexural strength of the PP/FMX composites decreases slightly.

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3.3. Prediction

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3.3.1 Prediction of tensile yield strength

As stated above, the tensile strength of polymer composites is related closely to

the interfacial adhesion status between the filler and the matrix. Therefore, how to access the interfacial adhesion status is a key for estimation of the tensile strength. In the case of good adhesion at the interface between the inclusions and the matrix, the tensile yield strength ( σ yc ) of polymer composites filled with sphere shape rigid particles can be estimated using the following equation [17-19]:

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ACCEPTED MANUSCRIPT 

2



σ yc = σ ym 1 − 1.21sin 2 θφ f3  

(3)



where φ f is the filler volume fraction, θ is the interfacial adhesion angle. In general, the smaller the θ value, the better is the interfacial adhesion between the filler and the

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matrix. When θ is equal to zero, the interfacial adhesion is good. In this case, σ yc is equal to σ ym .

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. The estimations of the tensile yield strength of the PP/FMX composites using Eqn. (3) are shown in Figure 11 when the rate of tension is 50 mm/min. The

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estimations are then compared to the experimental measured data of the composites, the results are also shown in Figure 11. Here, the value of the θ is about 50o determined by means of Eqn. (3) from the experimental data, and the filler volume fraction can be determined by the following expression [20]:

ϕf ϕ f (1 − χ ) + χ

χ=

ρf ρm

(4)

(5)

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φf =

where ρ f and ρ m are the density of the composite and resin matrix, respectively.

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Here, the densities of the PP resin and the FMX are 910kg/m3 and 2400 kg/m3, respectively.

It can be seen in Figure 11 that the values of the predicted tensile yield

strength by means of Eqn. (3) are close to the measured data from the PP/FMX composites. Moreover, the interfacial adhesion angle is 50 degrees under experimental conditions; as stated above, which means that the interfacial adhesion between the filler particles and matrix is good in this case. 12

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There have been various equations for Young’s modulus of polymer composite materials such as the mingling rule, Einstein equation, Guth equation, Liang’s

equation as follows:

9π (E f − Em )φ f2 / 3 16

(6)

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Et = Em + 3

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equation, etc [19]. Recently, Liang and Ma [21] proposed a new Young’s modulus

where Em and E f are the Young’s modulus of the matrix and the filler, respectively.

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For sphere particle filled polymer composites, the Young’s modulus can be estimated by means of the Einstein equation [22]: Et = Em (1 + 2.5φ f )

(7)

Guth et al. [22] modified the Einstein equation through including a second order

(

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power of φ f , and proposed the following expression

Et = Em 1 + 2.5φ f + 14.1φ f2

)

(8)

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The Young’s modulus of the FMX particles is difficult to measure under general conditions. In this study, the Young’s modulus of the PP/FMX composites is estimated

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using Eqns. (7) and (8) when the rate of tension is 50mm/min, and then the estimations are compared with the measured data, as shown in Figure 12. It can be seen that, when the FMX volume fraction is lower than 25 %, the predictions from the two equations are close to the measured data of the Young’s modulus of the PP/FMX composites; when the FMX volume fraction is higher than 25 %, the measured data of the Young’s modulus of the PP/FMX composites are close to the predictions from Eqn. (7), while the difference in the Young’s modulus between the predictions from Eqn. (8) 13

ACCEPTED MANUSCRIPT and the measured data increases with increasing FMX volume fraction. 3.3.3 Discussion It is generally believed that the mechanical properties of polymeric composites

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depend closely, not only on the interface between the filler particles and the polymer matrix, but also on the dispersion state of the inclusions in the matrix under given conditions. In previous work, Liang and Li [13] examined the interface between the

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FMX particles and the PP matrix, and the dispersion status of the FMX particles in the

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PP matrix by means of a scanning electron microscope. Figure 13 is the SEM photograph of the specimen fracture surface of the PP/FMX composite with the filler weight fraction of 35 %, Figure 14 is the SEM photograph of the specimen fracture surface of the PP/FMX composite with the filler weight fraction of 45 %. It can be

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seen that the dispersion or distribution of the FMX particles in the matrix is roughly uniform, and the interface adhesion between the FMX particles and the matrix is good. Thus, the Young’s modulus and the flexural modulus of the composites increase with

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increasing FMX weight fraction (see Figs. 4 and 9), and the tensile strength decreases

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slightly with increasing FMX weight fraction (see Figs. 5 and 6). In addition, the mechanical properties of crystalline polymeric materials depend,

to great extent, on the type and size of crystals as well as degree of crystallinity. Flame retardant particles can play a role of nucleation agent in polymer matrix under given conditions, leading to variation of the type and size of crystals as well as degree of crystallinity [23]. In general, the stiffness of polymer composites increases with increasing degree of crystallinity [24]. Thus, the increase of the degree of crystallinity

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ACCEPTED MANUSCRIPT due to the role of nucleation agent of the FMX in the PP matrix could be another reason for increasing the Young’s modulus and flexural modulus of the PP/FMX

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composites.

4 Conclusions

There were certain reinforcing effects of the FMX content on the tensile and

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flexural properties of the filled PP composites within the FMX weight fraction range

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being from 5 to 60wt.%. The results showed that the Young’s modulus increased approximately linearly while the tensile yield strength and the tensile fracture strength decreased slightly with increasing FMX weight fraction. When the FMX weight fraction was less than 20%, the tensile elongation at break decreased obviously, and

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then reduced slightly with an increase of the FMX weight fraction. Moreover, the Young’s modulus, tensile yield strength, tensile fractured strength and tensile elongation at break increased with increasing rate of tension. The flexural modulus

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also increased almost linearly with increasing the FMX weight fraction; while the

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flexural strength increased when the FMX weight fraction was lower than 30%, and then decreased slightly with an increase of the FMX weight fraction. The tensile yield strength of the composites was estimated using Eqn. (3)

proposed previously, and good agreement was shown between the predictions and the measured data, and the good interfacial adhesion between the filler and the matrix. Furthermore, the Young’s modulus of the composites was predicted separately by means of the Einstein and Guth equations. When the FMX volume fraction is lower

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ACCEPTED MANUSCRIPT than 25 %, the predictions were close to the measured data.

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Captions of Figures Fig.1 Tensile stress versus strain curves at rate of tension 10mm/min. Fig.2 Tensile stress versus strain curves at rate of tension 50mm/min.

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Fig.3 Tensile stress versus strain curves at rate of tension 100mm/min. Fig.4 Relationship between Young’s modulus and FMX weight fraction. Fig.5 Dependence of tensile yield strength on FMX weight fraction.

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Fig.6 Dependence of tensile fracture strength on FMX weight fraction.

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Fig.7 Correlation between tensile elongation at break and FMX weight fraction. Fig.8 Flexural stress versus flexural strain curves.

Fig.9 Relationship between flexural modulus and FMX weight fraction. Fig. 10 Dependence of flexural strength on FMX weight fraction.

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Fig. 11 Comparison between estimated tensile yield strength and measured data at rate of tension 50 mm/min.

Fig. 12 Comparison between estimated Young’s modulus and measured data at rate of

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tension 50 mm/min.

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Fig. 13 SEM photograph of specimen fracture surface of PP/FMX composite ( ϕ f = 35wt.% ).

Fig. 14 SEM photograph of specimen fracture surface of PP/FMX composite ( ϕ f = 45wt.% ).

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3

30 4 5

25

2 6

1

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20

1--PP 2--ϕf = 5wt.%

15

3--ϕf = 15wt.%

10

4--ϕf = 30wt.% 5--ϕf = 45wt.%

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Tensile stress (MPa)

35

5 0

0

20

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6--ϕf = 60wt.%

40

60

80

100

25

30

Tensile strain (%) Fig. 1

40

3

30

4 5

25

EP

6

20 15

1

1--PP 2--ϕf = 5wt.% 3--ϕf = 15wt.%

AC C

Tensile stress (MPa)

TE D

2

35

10

4--ϕf = 30wt.%

5

6--ϕf = 60wt.%

0

0

5--ϕf = 45wt.%

5

10

15

20

Tensile strain (%) Fig. 2

ACCEPTED MANUSCRIPT 40

3

30

3--ϕf = 15wt.%

4 5

4--ϕf = 30wt.%

25 6

5--ϕf = 45wt.%

RI PT

1

6--ϕf = 60wt.%

20 15 10

SC

Tensile stress (MPa)

1--PP 2--ϕf = 5wt.%

2

35

0

0

2

4

6

M AN U

5 8

10

12

14

16

18

20

Tensile strain (%) Fig. 3

7

TE D

10mm/min 50mm/min 100mm/min

4 3

EP

5

AC C

Young's modulus (GPa)

6

2 1 0

0

10

20

30

40

50

Filler weight fraction (wt.%) Fig. 4

60

70

ACCEPTED MANUSCRIPT

30 25

15

RI PT

20

10 5 0

0

10

20

30

40

SC

10mm/min 50mm/min 100mm/min

50

M AN U

Tensile yield strength (MPa)

35

60

70

Filler weight fraction (wt.%) Fig. 5

TE D

30

20 15

EP

25

10mm/min 50mm/min 100mm/min

AC C

Tensile fracture strength (MPa)

35

10 5 0

0

10

20

30

40

50

Filler weight fraction (wt.%) Fig.6

60

70

ACCEPTED MANUSCRIPT

18

10mm/min 50mm/min 100mm/min

16 14

RI PT

12 10 8

SC

6 4 2 0

0

10

20

M AN U

Tensile elongation at break (%)

20

30

40

50

60

70

Filler weight fraction (wt.%) Fig. 7

70

4

TE D

5

50 6

3

1

EP

40

2

30

1-- PP 2-- ϕf = 5wt.% 3-- ϕf = 15wt.%

AC C

Flexural stress (MPa)

60

20

4-- ϕf = 30wt.% 5-- ϕf = 45wt.%

10 0

0

1

6-- ϕf = 60wt.%

2

3

4

5

6

7

Flexural strain (%) Fig. 8

8

9

10

ACCEPTED MANUSCRIPT 4500

3500 3000

RI PT

2500 2000 1500 1000 500 0

10

20

30

40

50

M AN U

0

SC

Flexural modulus (MPa)

4000

60

70

Filler weight fraction (wt.%) Fig. 9

62

TE D

58 56

EP

54 52

AC C

Flexural strength (MPa)

60

50 48 46

0

10

20

30

40

50

Filler weight fraction (wt.%) Fig. 10

60

70

ACCEPTED MANUSCRIPT

25

RI PT

20 Equation (3)

15

SC

10 5 0

0

M AN U

Tensile yield strength (MPa)

30

10

20

30

40

50

60

Filler volume fraction (%) Fig. 11

TE D

Equation (8)

EP

15

10

AC C

Young's modulus (GPa)

20

5

0

0

10

Equation (7)

20

30

40

Filler volume fraction (%) Fig. 12

50

60

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

Fig. 13

Fig. 14