Study the Ideal Proportions of Matrix, Reinforcing Materials and Additives to Obtain a Composite Material with High Tensile Strength

Over the past decades, materials known as composites have emerged; they are a combination of two or more materials characterized by their unique properties of light weight and high resistance, which qualify them for use as fabrication materials in various fields. These include space, transportation, defense, artificial organs industry, shipbuilding, automotive, among others.

The use of polymer-reinforced polymer-based composite materials has been adopted in most industrial products. Many researches have been devoted to the determination of the ideal ratios for glass fiber addition as a reinforcement to a polymeric-based composite to achieve the best mechanical properties – including tensile strength. Shash [1] studied some of the mechanical properties of a composite material based on unsaturated polyester reinforced with random glass fiber. Sadek Atta et al. [2] investigated the impact of adding different fibers to polyester-based composites on adhesion wear properties. Jubouri et al. [3] investigated the impact of fiber reinforcement on the thermal and mechanical properties of a composite material. Some studies have suggested that polymer-based composites can be strengthened with sawdust alone because of their low cost and availability [4, 5]. Indeed, several studies have emerged on the use of fiber and sawdust as reinforcement materials for composites [6, 7]. In 2001 studies were conducted on the surface of wood fibers using plasma to enhance fibers-matrix adhesion. The results obtained showed increased tensile strength compared to specimens with untreated fibers [6]. In 2002, a chemical treatment was performed on the surface of wood dust and wood fibers using Maleic Anhydride Grafted Polypropylene (MAPP) and the results showed improved tensile and flexural strengths in composites materials based on polypropylene reinforced with treated wood flour particles in comparison to untreated ones [8].

The current research aims to determine the effect of a 01%wt ,05%wt, 10%wt addition of sawdust to a composite based on unsaturated polyester reinforced with glass fiber at different weight ratios, and this by comparing it to the same composite but without sawdust addition 00%wt. For this purpose, tensile tests were conducted and results were compared.

1.1 Composite material

A compound material formed by adding one or more constituent materials, considered a reinforcing material, to a basic material called resin, as these materials do not melt and do not fuse together, but rather join together to form a new material that has distinctive properties. The polymeric basis - the subject of this research, the first method is the closed mold, which contains several techniques for the production of the composite material, such as: - compression molding - injection molding - transfer molding - .... As for the second method, the open mold method, which includes several techniques, including: spray up method - Tape lay up – filament wending – autoclave curing and the most important of which is hand lay up or what is known as manual stacking - used in this research - where the mold is painted with a non-stick material, then a thin layer of polymeric substrate is placed and the reinforcing material is dipped in it, then The rest of the base material is added using a brush or a roller on the surface of the mold, its most important applications: in the production of truck bodies and some machines - fishing boats and boats, some structures and parts, tanks and water containers and touch search...etc. It can also be a mixture of two or more primary materials on a microscopic scale to obtain a third material which possesses properties better than the primary materials in terms of weight, thermal conductivity, thermal insulation, acoustic insulation, fatigue resistance, temperature related behavior, aesthetics, weight, corrosion resistance, wear resistance, hardness and hardness...etc. However, it should be noted that not all of these characteristics improve at the same time and some characteristics may conflict with others.

In order to manufacture a composite material, at least two substances must be available: 

The base material; also known as resin [9], which falls into three types:

•Metallic material characterized by significant weight and high hardness.

•Ceramic material characterized by light weight and low impact resistance.

•polymeric material, which can either be recycled such as thermoplastic materials like Polypropylene or non-recyclable and which are known as unsaturated polyester thermoset polymers.

1.2 Reinforcing material

This material is added to the resin in order to obtain mechanical and physical properties that the resin does not possess [10], and this by employing synthetic or natural fibers as reinforcements [11]. These include: Carbon fibers, glass fiber, which is the subject of our study, fine particulates (>1mm) or dispersed particulates (<1mm).

1.3 Sawdust

It is a by-product of the wood industry and is often used in the production of fertilizers. it is characterized by its extreme lightness and irregular form (Figure 1).

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Figure 1. Sawdust

-SEM micrographs of sawdust:

It appears in Figure 2. Scanning electron microscopic images of sawdust before preparing the composite material in an irregular shape. It was noticed that there was a fiber-like layer on top of the sawdust particles, which is of a high carbon nature, meaning it contains a high percentage of carbon that helps to adhere to the base material - the unsaturated polyester used in this research.

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Figure 2. SEM micrographs of sawdust

We divided the materials used in the sampling process into two sets.

3.1 Set 1: in this set of specimens, we used:

3.1.1 A mold made of glass material

A resin made of unsaturated polyester to which a hardener was added to stimulate and speed up reaction, Polyester is characterized by its durability and flexibility, and this toughness and flexibility varies with the amount of tension after spinning. Polyester fibers absorb moisture under normal conditions by 0.5% moisture absorbed at normal temperatures, and the saturation degree does not exceed 0.8% and does not swell in water except by a small percentage.

The polyester material withstands heating for a long period without significant disintegration, as the melting point of polyester is 249 degrees Celsius, which is the highest melting point for chemical fibers [12].

Saturated polyester was selected for its various properties and features, including being easy to manufacture, cost effective, heat resistant, resistant to electrical insulation, possessing high chemical resistance, good resistance to harsh environmental conditions, ... etc. It is also widely used in the manufacture of naval structures, steamers, boats and in various other industrial applications.

Unsaturated polyester resin is the most commonly used. it consists of a (polyhydric alcohol) together with (multiple acid alcohol), which bind together with addition of a catalyst under appropriate temperature.  

- The mechanical properties of the unsaturated polyester used in this research:

- Density .................... 1200 Kg/m³    

- Tensile strength....... 42 MPA

- Elasticity modulus.... 2.8 GPA

- Elongation ............... 3.2%

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Figure 3. Reinforcement material "Glass fiber"

3.1.2 Hardener- catalyst

It is a substance usually added to the resin i.e., unsaturated polyester, in a ratio of 2.3% in order to reach a complete curing of the saturated polyester as well as to speed up the reaction. It is worth mentioning that it is not recommended to use a hardener by more than 3% to speed up the curing of the mixture since this will cause cracks in the material.

Reinforcement material "glass fiber" of E-type was used. These were random glass fiber MAT with a density of 300gr/m² (Figure 3).

3.1.3 Properties of the reinforcing material: Glass fiber used in the research

Low weight - highly resistant to breakage but can break when folded - subject to wear and tear if exposed to friction - cost effective - low thermal conductivity and good electric insulation.

We used MAT type E glass fiber (300 gr/m²).

As for its mechanical properties, these include:

- Density .......... 2500 Kg/m³    

- Tensile strength....... 2400 MPA

- Elasticity modulus....... 85 GPA

- Elongation .............. 0.01 %

3.2 SET II

We used:

A mold was made of thick glass material (Figure 4).

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Figure 4. Glass mold

A resin made of unsaturated polyester, to which a hardener was added. The latter is a catalyst material used to speed up reaction.

Sawdust at a rate of 01%, was used directly. The moisture factor is neglected in our study due to the preparation procedure.

The additive material (sawdust) was prepared according to the following steps:

The sawdust was oven-dried at 100℃ for 24h to remove the moisture.

Then it was ground using an electric mill.

Next, it was sieved using a 2mm mesh sieve.       

3.3 Specimens'preparation

The specimens were prepared at the laboratory of the University of 20th August Skikda (Algeria) at a room temperature of 25℃, As the procedures and the specific step for preparing the samples we address in axis.

Two sets of specimens were prepared, the physical properties of samples are any properties that you can perceive or observe without changing the chemical identity of the sample. Any property that you can see, smell, touch, hear, detect and measure without having to perform a chemical reaction. Matter, colour, shape, sound, density, temperature, boiling point and viscosity, and because physical properties include such a set of properties, they are classified into extensive properties, as they depend on the amount of matter in the sample such as volume and mass, and intensive properties that do not depend on quantity Matter and its size in the body, but related to the boiling point and the state of matter and density.

3.3.1 Set I

These specimens were made of a composite material which consisted of unsaturated polyester (300gr/m²) of type E glass fiber randomly oriented at different weight ratios: 00%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%,90%, 100%.

3.3.2 Set II

These specimens were made of a composite material, which consisted of unsaturated polyester containing type E glass fiber (300gr/m²) randomly oriented at different weight ratios: 00%, 10%, 20%, 30%, 40%,50%, 60%, 70%, 80%,90%, 100%, to which sawdust was added (1%wt).

Preparation and mass weighing of the first set of specimens (unsaturated polyester resin/reinforcement: 

This process was performed using an electronic balance. Unsaturated polyester resin used in this research had a density of 1.2g/cm³ for a specimen dimension of 20cm length x2cm width x2mm thickness. The resulting specimens, 9.6g of total net weight each, were taken as reference for varying the mass of the unsaturated polyester resin with glass fiber ratios of 00%, 10%, 20%, 30%,40%,50%, 60%, 70%, 80%,90%, 100%. The results for the first set are shown in Table 1 and Table 2.

We use the following coding throughout this article:

Mass ratios of unsaturated polyester resin: po.

Mass of Glass fiber: gf.

Mass of sawdust: sd.

Preparation and mass weighing of the second set of specimens po/gf / sd. 

Table 1. State coding table Mass ratios of unsaturated polyester resin/ Mass of Glass fiber

Table 2. Mass ratios of unsaturated polyester resin % / glass fiber reinforcement %

These specimens were prepared and weighed in respect to: mass of the unsaturated polyester resin, mass of glass fiber and mass of sawdust, With an allowable error range of 10 mg g - 10 mg g accuracy for all samples.

This was performed by using an electronic balance (Figure 5).

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Figure 5. Electronic balance

Table 3. State coding table Mass ratios of unsaturated polyester resin/ Mass of Glass fiber + 01% Mass of sawdust

Table 4. Weight ratios of unsaturated polyester resin material and glass fiber reinforcement + 01 %wt added sawdust

Table 5. State coding table Mass ratios of unsaturated polyester resin/ Mass of Glass fiber + 05% Mass of sawdust

We weighed the mass of unsaturated polyester resin used in this research with a density of 1.2 g/cm³ in 20 cm length x 2cm width x 2 mm thickness specimens. The result was: 9.60 g of total net weight for each specimen. This is considered as the reference for varying the proportions of the mass of unsaturated polyester material and the mass ratios of glass fiber material in proportions of: 00%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, while the weight ratios of the unsaturated polyester resin were as follow: 00%, 09%, 19%, 29%, 39%, 49%, 59%, 69%, 79%, 89%, 99%, +01% of sawdust. The results for the second set are shown in Table 3 and Table 4.

The same as the previous steps with the addition 05% of sawdust from Table 5 and Table 6.

And add 10% of sawdust from Table 7 and Table 8.

Table 6. Weight ratios of unsaturated polyester resin material and glass fiber reinforcement + 05 %wt added sawdust

Table 7. State coding table Mass ratios of unsaturated polyester resin/ Mass of Glass fiber + 10 % Mass of sawdust

Table 8. Weight ratios of unsaturated polyester resin material and glass fiber reinforcement + 10 %wt added sawdust

3.4 Method

The specimens of the first set were made of a composite material which consists of unsaturated polyester reinforced with randomly oriented glass fiber of type E (300gr/m²) in weight ratios of 00%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% according to the following method:

3.4.1 First set: Po / gf /sd 00

A thin layer of Vaseline was spread on the surface of the mold to allow easy removal of the composite. 2%wt of a hardener was added to the unsaturated polyester and the mixture was thoroughly mixed. Next, a first amount of the mixture was poured into the mold and spread using a brush to ensure an even distribution. Then, random glass fiber was cut to the dimensions of the mold and spread on the mixture. Finally, the remaining mixture was poured onto the layer of glass fiber and rolled using a metal roller (Figure 6) to ensure even distribution and removal of air bubbles, The dimensions of the metal cylinder shown in Figure 6 are about 2 cm. The length of the metal cylinder is 01 cm in diameter.

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Figure 6. Metal roller

3.4.2 The second set: Po / gf /sd 01

The same steps followed for the preparation of the first set of specimens were performed; the only difference being the addition of sawdust (01%wt). After addition of the remaining mixture of unsaturated polyester with glass fiber using a metal roller to ensure regular distribution. It should be noted that the process of pouring the mixture and preparing the specimens should be performed quickly to prevent a hardening of the mixture before the completion of the preparation. Ten (10) specimens of composite material reinforced with glass fibers (300g/m²) were obtained.

In the last stage, the specimens were left at moderate temperature for 48 hours until they dried and cured before tensile tests could be performed (Figure 7), The temperature is 25 degrees Celsius, which is the laboratory temperature.

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Figure 7. Composite material specimens

3.4.3 The third set: Po / gf /sd 05

The same steps followed for the preparation of the first set of specimens were performed; the only difference being the addition of sawdust (05%wt)

3.4.4 The fourth set: Po / gf /sd 10

The same steps followed for the preparation of the first set of specimens were performed; the only difference being the addition of sawdust (10%wt).

- SEM micrographs of composites: Figure 8: SEM micrographs of composites: po 70 / gf 20/ sd10 and po 69 / gf 30 /sd01.

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Figure 8. SEM micrographs of composites: Po/ gf /sd

5.1 Tensile results for the first set Po / gf /sd 00

The tensile test was performed on the specimens of the first set consisting of a composite material consisting of unsaturated polyester reinforced by glass fiber (300 gr/m²) at different weight ratios, and the results of the resistance to stress R m expressed in MPA according to the Table 9.

Table 9. Results of the tensile for the first set

5.2 Results of the tensile tests for the second set: Po / gf /sd 01

The tensile tests were carried out on the second set of specimens comprising unsaturated polyester based composite reinforced with glass fiber (300g/m²) at different weight ratios to which 01%wt of sawdust was added. The results are shown in Table 10.

5.3 Results of the tensile tests for the third set: set: Po / gf /sd 05

The tensile tests were carried out on the third set of specimens comprising unsaturated polyester based composite reinforced with glass fiber (300g/m²) at different weight ratios to which 05%wt of sawdust was added. The results are shown in Table 11.

Table 10. Tensile strength results for a composite material based on unsaturated polyester reinforced by glass fiber + 1% sawdust

Table 11. Tensile strength results for a composite material based on unsaturated polyester reinforced by glass fiber + 05% sawdust

5.4 Results of the tensile tests for the fourth set: Po / gf /sd 10

The tensile tests were carried out on the fourth set of specimens comprising unsaturated polyester based composite reinforced with glass fiber (300g/m²) at different weight ratios to which 10%wt of sawdust was added. The results are shown in Table 12.

Table 12. Tensile strength results for a composite material based on unsaturated polyester reinforced by glass fiber + 10% sawdust

5.5 Graphs

Vernier Graphical Analysis Pro (Vernier, USA) was used to process the results of the tensile tests, During the experiment both the sample section and its effective length are usually measured, from which the stress and elongation are determined. In technical applications, the initial section is measured for ease and initial length, and the elongation values are recorded.

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Figure 10. Tensile test results and proportions of fiberglass

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Figure 11. Average tensile results of po% / gf% / sd%

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Figure 12. Tensile test results po%/ gf%/ sd% by po%

The tensile strength is equal to the maximum tensile the specimen can withstand and is set for its dependence on the specimen section. After exceeding the tensile strength points, the material is said to have failed or failed, as it is not possible to avoid breaking one of the parts of the machine after exceeding the tensile strength point. In this study, we take the tensile strength values for all samples and enter the data for tensile experiments, and the following curves were obtained Figure 10, Figure 11 Figure 12.

5.6 Discussion and analysis

We can notice from graph 1 and through the tensile strength results curve for the four groups po% / gf% / sd% with respect to the change in the proportions of the reinforcement material - glass fibers to unsaturated polyester -, where we notice (Figure 10). It increases significantly with the addition of 10% weight and continues to increase until 30% addition as it reaches its maximum. After this value and starting at 40%, it begins to decrease gradually and slowly, eventually reaching the minimum tensile strength of 60% of the reinforcement. After this value and up to 90% of the reinforcement, it is difficult to obtain the results of tensile experiments due to the fragility of the samples of the composite material and the impossibility of its realization in some cases. This can be explained by the fact that the amount of unsaturated polyester resin is not sufficient to guarantee the bonding of the reinforcement material.

* which leads to weakening the material and reducing its tensile strength up to 60% of the reinforcement, and from this ratio to 90%, it is impossible to embody these samples.

When interpreting the curves of the four groups po% / gf% / sd% for the ratios of the support or reinforcing material - fiberglass -, the most important points were as follows:

• The tensile strength of the second group po/ gf /sd 01 is better than that of the first group po/ gf /sd 00 for the proportions of 00%, 10%, 20%, 30%.

• The tensile strength of the third group po/ gf /sd 05 is better than that of the second and first group for the proportions of 00%, 10%, 20%, 30%.

• The tensile strength of the fourth group po/ gf /sd 10 is better than that of the third, second and first group for the proportions of 00%, 10%, 20%, 30%.

• The tensile strength of the first group is better than that of the second, third and fourth groups with percentages of 40%, 50%, 60%.

• The tensile strength of the second group is better than that of the third and fourth groups with percentages of 40%, 50%, 60%.

• The tensile strength of the third group po/ gf /sd 05 is better than that of the fourth group po/ gf /sd 10 for 40%, 50%, 60%.

One can clearly see that the additive (sawdust material) in the second group po100/ gf 00 /sd 01 and the third group po100/ gf 00 /sd 05 and the fourth group po100/ gf 00 /sd 10 at the proportions 00% - 10% - 20% - 30% of the glass fibers played the role of reinforcement, where we notice that the value of the tensile strength is in an upward trend with the increase in the percentage of sawdust during this area 00% - 30% of the reinforcing material.

• We notice a significant decrease in the tensile strength results for the four groups beyond the maximum value at 30%. However, the samples of the second group show a faster decline compared to the samples of the first group, the third group shows a faster decline compared to the samples of the second and first group, and the fourth group also shows a faster decline compared to the samples of the third, second and first group.

• Peak field: It can be seen that the maximum value of the tensile strength of the four groups po % / fb / sd % is confined to the peak field between 20% - 30% of the ratios of the reinforcement material or the reinforcing material.

Peak points: are the maximum values, and by interpreting the results and curve, we find that the value of the peak point of the tensile strength for each of the composite materials of the first group (po 70 /gf 30/sd 00) is about (MPA 66,92), while the composite material for the second group (po 69 / gf 30 / sd01) consisting of 69% unsaturated polyester and reinforced with 30% glass fibers added to it 01% of sawdust, where we recorded the value of the peak point of tensile strength of about (MPA 68,28), where it had the best value compared to the rest of the results of the composite material with other ratios and for the rest of the groups, then followed by a close ratio of the composite material of the third group (po 75 / gf 20 / sd 05) consisting of 75% unsaturated polyester and reinforced with 20% glass fibers added to it 05% of sawdust with a value of the peak tensile strength point of about (MPA 68,02). As for the composite material of the fourth group (po 70 / fb20 / sd 10), we recorded the value of the peak point of the tensile strength by about (MPA 66.09), where we notice the convergence between the values of the peak points of the four groups (Figure 11).

• Peak range: It can be seen that the maximum value of the tensile strength of the four groups po% / gf% / sd is confined to the peak range between 01% -10% of the proportions of the additive.

- Figure 12: In the third curve, the percentage change of the base material “unsaturated polyester” is curved in relation to the obtained tensile strength values, where we note that the tensile strength values are monitored starting from 35% of the base material “unsaturated polyester” for the composite material polyester / glass fibers. po/ gf /sd 00.

And starting from 40% of the base material "unsaturated polyester" for the composite material polyester / glass fibers / sawdust % po100 / gf 00 / sd. The four groups take an ascending curve until the “peak range” is between 65% to 75% of unsaturated polyester, it can be explained that the amount of unsaturated polyester resin is sufficient to ensure the bonding of the reinforcement material - glass fibers - and the additive - sawdust -, then we notice a decline The values for the four groups are up to 100% unsaturated polyester.

Where it is clearly noticed during the phase of decline from 75% to 100% of the percentage of the base material "unsaturated polyester" that the tensile strength values for the first group po/ gf / sd 00 are better than the results of the second group po/ gf / sd 01 to which 01% of sawdust is added. Wood, which in turn is better than the results of the third group po/ gf /sd05 added to it 05% of sawdust, which in turn is better than the results of the fourth group po/ gf /sd10 added to it 10% of sawdust, where it can be explained, the amount of unsaturated polyester resin is not enough to ensure the bonding of the reinforcement material - glass fibers - and the additive - sawdust, as the latter has become an additional burden to the reinforcement material that weakens the bond guarantee.

• Peak field: It can be seen that the maximum value of the tensile strength of the four groups po / gf %/sd % is confined to the peak field between 65% - 75% of the matrix or matrix ratios.