# Performance of Polyvinyl Alcohol and Polypropylene Fibers under Simulated Cementitious Composites Pore Solution

Authors: A. R. Krishnaraja; P. Kulanthaivel; P. Ramshankar; Vincent Herald Wilson; Ponnusamy Palanisamy; S. Vivek; V. Sampathkumar; P. Ganeshan; M. C. Sashikkumar; K. Raja; Senthil Kumaran Selvaraj; A. John Rajan; S. Jose
Journal: Advances in Materials Science and Engineering
 (2022)

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## Abstract

The thermal properties of polymer fibers namely polyvinyl alcohol fiber (PVA) and polypropylene fiber (PP) have been taken for study to carry out this present work. Simulated pore solution (SPS) is prepared by using the combination of chemicals NaOH, KOH, and Ca(OH)2 with distilled water to study the effect of C-S-H gel formation on fibers. The fibers are dipped in the solution for 35 days. The thermal properties of raw and SPS-dipped fibers are fetched out by performing various tests such as Fourier transform infrared (FTIR) analysis, thermo gravimetric analysis (TGA), differential scanning calorimetry analysis, and scanning electron microscopy (SEM). On analysis, the thermal properties of SPS-dipped fiber have better properties when compared with raw fiber. In FTIR analysis the first broad peak of both raw and SPS-dipped fibers are observed between 3000 cm−1 to 2800 cm−1 indicating that fibers have strong bond. In TGA analysis noted that the residual mass of raw fiber (77.19%) is higher than SPS-dipped fiber (52.33%) due to the formation of C-S-H gel formation. DSC analysis showed both endothermic and exothermic reaction under N2 atmosphere.


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## Body

## 1. Introduction

Concrete is a brittle material with a high compressive strength but a low tension and flexural strength. The concrete fails when ultimate load is applied over the concrete [1–3]. Researches are being carried out with different types of fibers in order to reduce the failure and to increase the strength of concrete [4]. Each of the polymer fibers being used in the concrete for this purpose has different nature and exhibits different properties [5, 6]. Some fibers are used for reinforcing whereas some fibers are used for controlling cracks [7, 8]. In order to reduce the cracks in concrete, a special type of concrete known as engineered cementitious composites (ECC) is used in the tensile zone of concrete [9–11]. ECC, which is based on micromechanical design [12], has a good tensile strain hardening capacity of 3 to 7% with fiber volume fraction of 2% or lesser [13]. The polymer fibers used in ECC are polyvinyl alcohol (PVA) fiber and polypropylene (PP) fiber. PVA fiber has a high structural strength and can also be used to control shrinkage [14] whereas PP fiber can stretch to the greatest extent possible to provide tensile stress resistance [15]. Before using the fibers in the concrete, formation of C-S-H gel is to be studied because it is responsible for most of the engineering properties of the concrete [16]. Selection of suitable fibers to develop the novel ECC mix is one of the important factor, which defines the performance of the developed ECC materials under different loading conditions. Moreover, adhesion between fiber and cement matrix should be appropriate to maintain multiple crack, strain hardening behavior, toughness, ductility, and tensile strength of the developed within the frontier given by Victor Li [17]. In this investigation, main scope is to study the performance of fibers under simulated C-S-H gel formation in the form simulated pore solution under laboratory conditions. Moreover, short random and micro fibers should be used for development of ECC [18]; hence, it is most important to study the degradation fibers. Two fibers PVA and PP available in India are taken in to this study. The present study focuses on the study of degradation and thermal properties of PVA fiber and PP fiber and analyses the behavior of the fibers by using various tests like Fourier transform infrared (FTIR) analysis, thermogravimetric analysis (TGA), differential scanning calorimetry analysis, and scanning electron microscopy (SEM).


## 2. Materials

### 2.1. Polyvinyl Alcohol Fiber

Polyvinyl alcohol fiber (PVA) is really an excellent environmental-friendly reinforced substance with alkali and weather resistance due to its unique molecular structure, as well as a high affinity for cement. It effectively prevents crack formation and development, as well as improving concrete’s bending strength, impact strength, crack strength, permeability, impact, and seismic resistance.


### 2.2. Polypropylene Fiber

Because the macromolecule has a satirically regular atomic arrangement, polypropylene fiber (PP) can be manufactured in a crystalline form. The polypropylene film is made up of both amorphous and crystalline micro fibrils. Splits in the longitudinal direction are induced, and fibrillation is facilitated using specially designed machines [19]. It is used as a discontinuous fibrillated material for the mixing method of producing FRC, or as a continuous mat for the production of thin sheet elements. Table 1 shows the physical properties of PVA and PP fiber.Table 1
Physical properties of PVA and PP Fiber.
PropertiesPVA fiberPP fiberLength (mm)1210Diameter (μm)3937Tensile strength (MPa)1600400Elastic modulus (MPa)42.52.5Density (kg/m3)1300910Melting point (°C)225165Elongation (%)236


## 2.1. Polyvinyl Alcohol Fiber

Polyvinyl alcohol fiber (PVA) is really an excellent environmental-friendly reinforced substance with alkali and weather resistance due to its unique molecular structure, as well as a high affinity for cement. It effectively prevents crack formation and development, as well as improving concrete’s bending strength, impact strength, crack strength, permeability, impact, and seismic resistance.


## 2.2. Polypropylene Fiber

Because the macromolecule has a satirically regular atomic arrangement, polypropylene fiber (PP) can be manufactured in a crystalline form. The polypropylene film is made up of both amorphous and crystalline micro fibrils. Splits in the longitudinal direction are induced, and fibrillation is facilitated using specially designed machines [19]. It is used as a discontinuous fibrillated material for the mixing method of producing FRC, or as a continuous mat for the production of thin sheet elements. Table 1 shows the physical properties of PVA and PP fiber.Table 1
Physical properties of PVA and PP Fiber.
PropertiesPVA fiberPP fiberLength (mm)1210Diameter (μm)3937Tensile strength (MPa)1600400Elastic modulus (MPa)42.52.5Density (kg/m3)1300910Melting point (°C)225165Elongation (%)236


## 3. SPS Solution Preparation

In this investigation, the fibers are tested under simulated condition. When the fiber combines with cementing admixtures, there will be a gel formation around the fibers due to C-S-H reaction in the composites. This gel formation is simulated outside the concrete by dipping the fiber in the combination of chemicals NaOH, KOH, and Ca(OH)2 with distilled water in the ratio of 1 : 8.17 : 0.83 for 35 days. This was carried out on PVA and PP fibers. The diameter of fibers are less than 40 micro meter. Hence, C-S-H gel formation may affect the performance of the fiber. Figure 1 shows the fibers dipped in the saturated pore solution and raw fibers.Figure 1
Colour changes in the PVA and PP fiber.


## 4. Testing Methods

### 4.1. Fourier Transform Infrared (FTIR) Analysis

Fourier transform infrared (FTIR) analysis of raw and SPS-dipped fibers is conducted by using Shimadzu spectrophotometer as per ASTM E1252-98 to analyse the functional group of the fibers at molecular level in the range of 4000–500 cm−1 [17].


### 4.2. Thermogravimetric Analysis (TGA)

Thermogravimetric analysis (TGA) of raw and SPS-dipped fibers is conducted by using the thermogravimetric analyzer as per ASTM E2550-11 to measure the physical and chemical changes of fibers as a function of increasing temperature from 0oC to 500oC at a constant heating rate of 10oC/min. For every scan, 5 mg of fibers has been used [18].


### 4.3. Differential Scanning Calorimetry Analysis

Differential scanning calorimetry analysis of raw and SPS-dipped fibers is conducted by using a differential scanning calorimeter as per ASTM D3418–15 to measure the melting point of the fibers by constantly increasing the temperature [20].


### 4.4. Scanning Electron Microscopy (SEM)

Scanning electron microscopy of raw and SPS-dipped fibers is conducted by using scanning electron microscopy as per ASTM E2809–13 to obtain information about fiber surface topography and composition [21].


## 4.1. Fourier Transform Infrared (FTIR) Analysis

Fourier transform infrared (FTIR) analysis of raw and SPS-dipped fibers is conducted by using Shimadzu spectrophotometer as per ASTM E1252-98 to analyse the functional group of the fibers at molecular level in the range of 4000–500 cm−1 [17].


## 4.2. Thermogravimetric Analysis (TGA)

Thermogravimetric analysis (TGA) of raw and SPS-dipped fibers is conducted by using the thermogravimetric analyzer as per ASTM E2550-11 to measure the physical and chemical changes of fibers as a function of increasing temperature from 0oC to 500oC at a constant heating rate of 10oC/min. For every scan, 5 mg of fibers has been used [18].


## 4.3. Differential Scanning Calorimetry Analysis

Differential scanning calorimetry analysis of raw and SPS-dipped fibers is conducted by using a differential scanning calorimeter as per ASTM D3418–15 to measure the melting point of the fibers by constantly increasing the temperature [20].


## 4.4. Scanning Electron Microscopy (SEM)

Scanning electron microscopy of raw and SPS-dipped fibers is conducted by using scanning electron microscopy as per ASTM E2809–13 to obtain information about fiber surface topography and composition [21].


## 5. Results and Discussion

### 5.1. Fourier Transform Infrared Analysis (FTIR)

#### 5.1.1. Polyvinyl Alcohol Fiber

Figure2 depicts the FTIR spectra of raw and SPS-dipped PVA fiber. PVA fiber is created by polymerizing vinyl acetate to poly vinyl acetate, then hydrolyzing PVAc to PVA. The first broad peak of both raw and SPS-dipped fibers are observed between 3000 cm−1 to 2800 cm−1 indicating that fibers have strong bond. The second broad peak of both raw and SPS-dipped fibers are observed between 2400 cm−1 to 2300 cm−1 indicating that fibers have OH stretching groups. On increase in wave number, it is evident that both raw and SPS-dipped fibers behaves differently in the weaker bond zone. Both fibers behave relatively similar up to stretching of OH groups, and energy absorption of raw fiber is high compared to the SPS-dipped fiber [22].Figure 2
FTIR analysis of raw and SPS-dipped PVA fibers.


#### 5.1.2. Polypropylene Fiber

The FTIR spectra for raw and SPS-dipped PP fiber is shown in Figure3. The first broad peak of raw fibers occurs between 2900 cm−1 to 2800 cm−1 and SPS-dipped fibers are observed between 3800 cm−1 to 3750 cm−1 indicating that SPS-dipped fibers have strong bond compared to raw fiber. The second broad peak of raw fiber takes place between 2300 cm−1 to 2250 cm−1 and SPS-dipped fibers are observed between 2800 cm−1 to 2650 cm−1 indicating that fibers have C-H stretching groups at different wave numbers [22]. Both the fibers have different energy absorption in different zone. The energy absorption of SPS-dipped fiber is high compared to raw fiber.Figure 3
FTIR analysis of raw and SPS-dipped PP fibers.


### 5.2. Thermogravimetric Analysis (TGA)

#### 5.2.1. Polyvinyl Alcohol Fiber

The TGA curves of both raw and SPS-dipped PVA fibers are shown in Figure4. It is noted that both raw and SPS-dipped PVA fiber undergo degradation in two steps. The first step occurred in the range of 26oC to 28oC for raw PVA fiber and in the range of 26oC to 50oC for SPS-dipped PVA fiber and could be due to the low molecular weight cellulose in the fiber [23]. The second stage of decomposition occurred in the range of 30oC to 250oC for raw PVA fiber and in the range of 220oC to 250oC for SPS-dipped PVA fiber due to thermochemical decomposition of organic materials in the fiber. It is noted that the residual mass of raw fiber (77.19%) is higher than SPS-dipped fiber (52.33%) due to the formation of C-S-H gel formation. The curve indicates that due to the formation of gel in the fibers, the thermal stability of SPS-dipped fiber will increase.Figure 4
TGA of raw and SPS-dipped PVA fiber.


#### 5.2.2. Polypropylene Fiber

The TGA curves of both raw and SPS-dipped PP fibers are shown in Figure5. From the figure, it was noticed that the thermal degradation of raw PVA fibers has taken place within the temperature range of 26oC to 176.6oC and 26oC to 248oC temperature range for SPS-dipped PVA fiber. On analysing the weight loss curve, it was found that the first weight loss for both raw PP fiber and SPS-dipped PP fiber occurs at 26oC, which occurs due to the presence of moisture and impurities in the composites. In the raw PP fiber, the rate of weight loss is always minimum throughout the graph whereas for SPS-dipped PP fiber, the maximum rate of weight loss occurs at 26°C and also in the range of 84°C to 122°C. It is noted that there is no notable amount of degradation occurs in raw PP fibers whereas SPS-dipped PP fiber undergoes degradation in two steps [24]. The first step occurred at 26°C due to the low molecular weight cellulose in the fiber and the second stage of decomposition occurred in the range of 184°C to 224°C due to thermochemical decomposition of organic materials in the fiber. In the SPS-dipped PP fiber, there is a considerable increase in the weight of fiber from 27°C to 83°C due to the polymerization occurs within the fiber. It is noted that the residual mass of raw fiber (99.24%) is higher than SPS-dipped fiber (77.17%) due to the formation of C-S-H gel formation. The curve indicates that due to the formation of gel in the fibers, the thermal stability of SPS-dipped fiber will increase.Figure 5
TGA of raw and SPS-dipped PP fiber.


### 5.3. Differential Scanning Calorimetry (DSC) Analysis

#### 5.3.1. Polyvinyl Alcohol Fiber

The DSC curves for the both raw and SPS-dipped PVA fibers are shown in Figure6. In the differential scanning calorimetry, there will be two reactions (endothermic and exothermic) will takes place [25, 26]. If the exothermic reaction takes places, it indicates that heat is released from the fiber. Whereas if endothermic reaction takes places, it indicates that heat is absorbed by the fibers. In the raw PVA fiber, the exothermic reaction takes places in the fiber with increase in temperatures and after reaching the melting point endothermic reaction takes places and agin exothermic reaction takes place. The melting point of the raw PVA fiber is 240.6°C. In the SPS-dipped PVA fiber, endothermic reaction takes place at initial low temperature and with increase in temperature exothermic reaction takes place certain temperature and once again endothermic reaction takes place at the melting temperature. The melting temperrature of SPS-dipped PVA fiber is 228.1°C. This alternate endothermic and exothermic reaction takes place due to the chemical reaction in the fibers.Figure 6
DSC of raw and SPS-dipped PVA fiber.


#### 5.3.2. Polypropylene Fiber

The DSC curves for the both raw and SPS-dipped PP fibers are shown in Figure7. In the differential scanning calorimetry, there will be two reactions (endothermic and exothermic) will takes place. In the raw PP fiber, there is a slight oscillation between both endothermic and exothermic reaction. After reaching 150°C, endothermic reaction takes place. The heat absorption takes pace after reaching the melting point [27]. The melting point of raw PP fiber is 168.3°C. In the SPS-dipped PP fiber, endothermic reaction only takes place. No heat release occurs in SPS-dipped fiber. The melting point of SPS-dipped PP fiber is 166.4°C.Figure 7
DSC of raw and SPS-dipped PP fiber.


### 5.4. Scanning Electron Microscopy (SEM)

#### 5.4.1. Polyvinyl Alcohol Fiber

Scanning electron microscopy(SEM) analysis was carried on both raw and SPS-dipped PVA fibers and are shown in Figures 8(a) and 8(b).Figure 8
(a) SEM of raw PVA fiber. (b) SEM of SPS-dipped PVA fiber.
(a)(b)In the SEM analysis, it is found that there are no changes in the structure and internal bonding of the fibers, but there are changes in the texture and colour of the fiber. Raw PVA fibers are pure white in colour whereas SPS-dipped fibers are yellowish, and SPS-dipped fibers are smooth compared to raw fiber for physical appearance [28, 29]. From the figures, it was observed that raw PVA have additional coating in the surface which produce stiffness to the fiber. Whereas the SPS-dipped fiber has a rough surface, and C-S-H gel remove the addition coating on fiber. However, there is no reduction and disintegration in the cross section of fibers.


#### 5.4.2. Polypropylene Fiber

SEM analysis was carried on both raw and SPS-dipped PP fibers and are shown in Figures9(a) and 9(b). In the SEM analysis, it is found that there are no changes in the structure, internal bonding, and colour of the fibers but there is a change in the texture of the fiber. SPS-dipped fibers are smooth compared to raw fiber, and it is found that there is a formation of batches of slumps among the circumference fibers. This may be due to sedimentation of C-S-H gel [30]. From the figure, it was also observed the two fibers join together along the length and this is due to C-S-H gel which creates bond between the adjacent materials. Moreover, there is no reduction and disintegration in the cross-section of fibers. Among all the fibers, the PP fiber has a smooth surface texture.Figure 9
(a) SEM for raw PP fiber. (b) SEM for SPS-dipped PP fiber.
(a)(b)From the SEM analysis, it was observed that there is no reduction of cross section and disintegration of fibers. The C-S-H gel react with the fiber surface and made the surface rough and remove the top coating in the fiber. This rough surface creates the additional bond between fibers and ECC mixes. Presence of C-S-H gel in form of lumps does not create any impact because fibers are removed from simulated pore solution and allow to dry in the room temperature, gel located in the surrounding area of fibers formed as a crystal. Crystals are located in the circumference of the fibers in the form of lumps.


## 5.1. Fourier Transform Infrared Analysis (FTIR)

### 5.1.1. Polyvinyl Alcohol Fiber

Figure2 depicts the FTIR spectra of raw and SPS-dipped PVA fiber. PVA fiber is created by polymerizing vinyl acetate to poly vinyl acetate, then hydrolyzing PVAc to PVA. The first broad peak of both raw and SPS-dipped fibers are observed between 3000 cm−1 to 2800 cm−1 indicating that fibers have strong bond. The second broad peak of both raw and SPS-dipped fibers are observed between 2400 cm−1 to 2300 cm−1 indicating that fibers have OH stretching groups. On increase in wave number, it is evident that both raw and SPS-dipped fibers behaves differently in the weaker bond zone. Both fibers behave relatively similar up to stretching of OH groups, and energy absorption of raw fiber is high compared to the SPS-dipped fiber [22].Figure 2
FTIR analysis of raw and SPS-dipped PVA fibers.


### 5.1.2. Polypropylene Fiber

The FTIR spectra for raw and SPS-dipped PP fiber is shown in Figure3. The first broad peak of raw fibers occurs between 2900 cm−1 to 2800 cm−1 and SPS-dipped fibers are observed between 3800 cm−1 to 3750 cm−1 indicating that SPS-dipped fibers have strong bond compared to raw fiber. The second broad peak of raw fiber takes place between 2300 cm−1 to 2250 cm−1 and SPS-dipped fibers are observed between 2800 cm−1 to 2650 cm−1 indicating that fibers have C-H stretching groups at different wave numbers [22]. Both the fibers have different energy absorption in different zone. The energy absorption of SPS-dipped fiber is high compared to raw fiber.Figure 3
FTIR analysis of raw and SPS-dipped PP fibers.


## 5.1.1. Polyvinyl Alcohol Fiber

Figure2 depicts the FTIR spectra of raw and SPS-dipped PVA fiber. PVA fiber is created by polymerizing vinyl acetate to poly vinyl acetate, then hydrolyzing PVAc to PVA. The first broad peak of both raw and SPS-dipped fibers are observed between 3000 cm−1 to 2800 cm−1 indicating that fibers have strong bond. The second broad peak of both raw and SPS-dipped fibers are observed between 2400 cm−1 to 2300 cm−1 indicating that fibers have OH stretching groups. On increase in wave number, it is evident that both raw and SPS-dipped fibers behaves differently in the weaker bond zone. Both fibers behave relatively similar up to stretching of OH groups, and energy absorption of raw fiber is high compared to the SPS-dipped fiber [22].Figure 2
FTIR analysis of raw and SPS-dipped PVA fibers.


## 5.1.2. Polypropylene Fiber

The FTIR spectra for raw and SPS-dipped PP fiber is shown in Figure3. The first broad peak of raw fibers occurs between 2900 cm−1 to 2800 cm−1 and SPS-dipped fibers are observed between 3800 cm−1 to 3750 cm−1 indicating that SPS-dipped fibers have strong bond compared to raw fiber. The second broad peak of raw fiber takes place between 2300 cm−1 to 2250 cm−1 and SPS-dipped fibers are observed between 2800 cm−1 to 2650 cm−1 indicating that fibers have C-H stretching groups at different wave numbers [22]. Both the fibers have different energy absorption in different zone. The energy absorption of SPS-dipped fiber is high compared to raw fiber.Figure 3
FTIR analysis of raw and SPS-dipped PP fibers.


## 5.2. Thermogravimetric Analysis (TGA)

### 5.2.1. Polyvinyl Alcohol Fiber

The TGA curves of both raw and SPS-dipped PVA fibers are shown in Figure4. It is noted that both raw and SPS-dipped PVA fiber undergo degradation in two steps. The first step occurred in the range of 26oC to 28oC for raw PVA fiber and in the range of 26oC to 50oC for SPS-dipped PVA fiber and could be due to the low molecular weight cellulose in the fiber [23]. The second stage of decomposition occurred in the range of 30oC to 250oC for raw PVA fiber and in the range of 220oC to 250oC for SPS-dipped PVA fiber due to thermochemical decomposition of organic materials in the fiber. It is noted that the residual mass of raw fiber (77.19%) is higher than SPS-dipped fiber (52.33%) due to the formation of C-S-H gel formation. The curve indicates that due to the formation of gel in the fibers, the thermal stability of SPS-dipped fiber will increase.Figure 4
TGA of raw and SPS-dipped PVA fiber.


### 5.2.2. Polypropylene Fiber

The TGA curves of both raw and SPS-dipped PP fibers are shown in Figure5. From the figure, it was noticed that the thermal degradation of raw PVA fibers has taken place within the temperature range of 26oC to 176.6oC and 26oC to 248oC temperature range for SPS-dipped PVA fiber. On analysing the weight loss curve, it was found that the first weight loss for both raw PP fiber and SPS-dipped PP fiber occurs at 26oC, which occurs due to the presence of moisture and impurities in the composites. In the raw PP fiber, the rate of weight loss is always minimum throughout the graph whereas for SPS-dipped PP fiber, the maximum rate of weight loss occurs at 26°C and also in the range of 84°C to 122°C. It is noted that there is no notable amount of degradation occurs in raw PP fibers whereas SPS-dipped PP fiber undergoes degradation in two steps [24]. The first step occurred at 26°C due to the low molecular weight cellulose in the fiber and the second stage of decomposition occurred in the range of 184°C to 224°C due to thermochemical decomposition of organic materials in the fiber. In the SPS-dipped PP fiber, there is a considerable increase in the weight of fiber from 27°C to 83°C due to the polymerization occurs within the fiber. It is noted that the residual mass of raw fiber (99.24%) is higher than SPS-dipped fiber (77.17%) due to the formation of C-S-H gel formation. The curve indicates that due to the formation of gel in the fibers, the thermal stability of SPS-dipped fiber will increase.Figure 5
TGA of raw and SPS-dipped PP fiber.


## 5.2.1. Polyvinyl Alcohol Fiber

The TGA curves of both raw and SPS-dipped PVA fibers are shown in Figure4. It is noted that both raw and SPS-dipped PVA fiber undergo degradation in two steps. The first step occurred in the range of 26oC to 28oC for raw PVA fiber and in the range of 26oC to 50oC for SPS-dipped PVA fiber and could be due to the low molecular weight cellulose in the fiber [23]. The second stage of decomposition occurred in the range of 30oC to 250oC for raw PVA fiber and in the range of 220oC to 250oC for SPS-dipped PVA fiber due to thermochemical decomposition of organic materials in the fiber. It is noted that the residual mass of raw fiber (77.19%) is higher than SPS-dipped fiber (52.33%) due to the formation of C-S-H gel formation. The curve indicates that due to the formation of gel in the fibers, the thermal stability of SPS-dipped fiber will increase.Figure 4
TGA of raw and SPS-dipped PVA fiber.


## 5.2.2. Polypropylene Fiber

The TGA curves of both raw and SPS-dipped PP fibers are shown in Figure5. From the figure, it was noticed that the thermal degradation of raw PVA fibers has taken place within the temperature range of 26oC to 176.6oC and 26oC to 248oC temperature range for SPS-dipped PVA fiber. On analysing the weight loss curve, it was found that the first weight loss for both raw PP fiber and SPS-dipped PP fiber occurs at 26oC, which occurs due to the presence of moisture and impurities in the composites. In the raw PP fiber, the rate of weight loss is always minimum throughout the graph whereas for SPS-dipped PP fiber, the maximum rate of weight loss occurs at 26°C and also in the range of 84°C to 122°C. It is noted that there is no notable amount of degradation occurs in raw PP fibers whereas SPS-dipped PP fiber undergoes degradation in two steps [24]. The first step occurred at 26°C due to the low molecular weight cellulose in the fiber and the second stage of decomposition occurred in the range of 184°C to 224°C due to thermochemical decomposition of organic materials in the fiber. In the SPS-dipped PP fiber, there is a considerable increase in the weight of fiber from 27°C to 83°C due to the polymerization occurs within the fiber. It is noted that the residual mass of raw fiber (99.24%) is higher than SPS-dipped fiber (77.17%) due to the formation of C-S-H gel formation. The curve indicates that due to the formation of gel in the fibers, the thermal stability of SPS-dipped fiber will increase.Figure 5
TGA of raw and SPS-dipped PP fiber.


## 5.3. Differential Scanning Calorimetry (DSC) Analysis

### 5.3.1. Polyvinyl Alcohol Fiber

The DSC curves for the both raw and SPS-dipped PVA fibers are shown in Figure6. In the differential scanning calorimetry, there will be two reactions (endothermic and exothermic) will takes place [25, 26]. If the exothermic reaction takes places, it indicates that heat is released from the fiber. Whereas if endothermic reaction takes places, it indicates that heat is absorbed by the fibers. In the raw PVA fiber, the exothermic reaction takes places in the fiber with increase in temperatures and after reaching the melting point endothermic reaction takes places and agin exothermic reaction takes place. The melting point of the raw PVA fiber is 240.6°C. In the SPS-dipped PVA fiber, endothermic reaction takes place at initial low temperature and with increase in temperature exothermic reaction takes place certain temperature and once again endothermic reaction takes place at the melting temperature. The melting temperrature of SPS-dipped PVA fiber is 228.1°C. This alternate endothermic and exothermic reaction takes place due to the chemical reaction in the fibers.Figure 6
DSC of raw and SPS-dipped PVA fiber.


### 5.3.2. Polypropylene Fiber

The DSC curves for the both raw and SPS-dipped PP fibers are shown in Figure7. In the differential scanning calorimetry, there will be two reactions (endothermic and exothermic) will takes place. In the raw PP fiber, there is a slight oscillation between both endothermic and exothermic reaction. After reaching 150°C, endothermic reaction takes place. The heat absorption takes pace after reaching the melting point [27]. The melting point of raw PP fiber is 168.3°C. In the SPS-dipped PP fiber, endothermic reaction only takes place. No heat release occurs in SPS-dipped fiber. The melting point of SPS-dipped PP fiber is 166.4°C.Figure 7
DSC of raw and SPS-dipped PP fiber.


## 5.3.1. Polyvinyl Alcohol Fiber

The DSC curves for the both raw and SPS-dipped PVA fibers are shown in Figure6. In the differential scanning calorimetry, there will be two reactions (endothermic and exothermic) will takes place [25, 26]. If the exothermic reaction takes places, it indicates that heat is released from the fiber. Whereas if endothermic reaction takes places, it indicates that heat is absorbed by the fibers. In the raw PVA fiber, the exothermic reaction takes places in the fiber with increase in temperatures and after reaching the melting point endothermic reaction takes places and agin exothermic reaction takes place. The melting point of the raw PVA fiber is 240.6°C. In the SPS-dipped PVA fiber, endothermic reaction takes place at initial low temperature and with increase in temperature exothermic reaction takes place certain temperature and once again endothermic reaction takes place at the melting temperature. The melting temperrature of SPS-dipped PVA fiber is 228.1°C. This alternate endothermic and exothermic reaction takes place due to the chemical reaction in the fibers.Figure 6
DSC of raw and SPS-dipped PVA fiber.


## 5.3.2. Polypropylene Fiber

The DSC curves for the both raw and SPS-dipped PP fibers are shown in Figure7. In the differential scanning calorimetry, there will be two reactions (endothermic and exothermic) will takes place. In the raw PP fiber, there is a slight oscillation between both endothermic and exothermic reaction. After reaching 150°C, endothermic reaction takes place. The heat absorption takes pace after reaching the melting point [27]. The melting point of raw PP fiber is 168.3°C. In the SPS-dipped PP fiber, endothermic reaction only takes place. No heat release occurs in SPS-dipped fiber. The melting point of SPS-dipped PP fiber is 166.4°C.Figure 7
DSC of raw and SPS-dipped PP fiber.


## 5.4. Scanning Electron Microscopy (SEM)

### 5.4.1. Polyvinyl Alcohol Fiber

Scanning electron microscopy(SEM) analysis was carried on both raw and SPS-dipped PVA fibers and are shown in Figures 8(a) and 8(b).Figure 8
(a) SEM of raw PVA fiber. (b) SEM of SPS-dipped PVA fiber.
(a)(b)In the SEM analysis, it is found that there are no changes in the structure and internal bonding of the fibers, but there are changes in the texture and colour of the fiber. Raw PVA fibers are pure white in colour whereas SPS-dipped fibers are yellowish, and SPS-dipped fibers are smooth compared to raw fiber for physical appearance [28, 29]. From the figures, it was observed that raw PVA have additional coating in the surface which produce stiffness to the fiber. Whereas the SPS-dipped fiber has a rough surface, and C-S-H gel remove the addition coating on fiber. However, there is no reduction and disintegration in the cross section of fibers.


### 5.4.2. Polypropylene Fiber

SEM analysis was carried on both raw and SPS-dipped PP fibers and are shown in Figures9(a) and 9(b). In the SEM analysis, it is found that there are no changes in the structure, internal bonding, and colour of the fibers but there is a change in the texture of the fiber. SPS-dipped fibers are smooth compared to raw fiber, and it is found that there is a formation of batches of slumps among the circumference fibers. This may be due to sedimentation of C-S-H gel [30]. From the figure, it was also observed the two fibers join together along the length and this is due to C-S-H gel which creates bond between the adjacent materials. Moreover, there is no reduction and disintegration in the cross-section of fibers. Among all the fibers, the PP fiber has a smooth surface texture.Figure 9
(a) SEM for raw PP fiber. (b) SEM for SPS-dipped PP fiber.
(a)(b)From the SEM analysis, it was observed that there is no reduction of cross section and disintegration of fibers. The C-S-H gel react with the fiber surface and made the surface rough and remove the top coating in the fiber. This rough surface creates the additional bond between fibers and ECC mixes. Presence of C-S-H gel in form of lumps does not create any impact because fibers are removed from simulated pore solution and allow to dry in the room temperature, gel located in the surrounding area of fibers formed as a crystal. Crystals are located in the circumference of the fibers in the form of lumps.


## 5.4.1. Polyvinyl Alcohol Fiber

Scanning electron microscopy(SEM) analysis was carried on both raw and SPS-dipped PVA fibers and are shown in Figures 8(a) and 8(b).Figure 8
(a) SEM of raw PVA fiber. (b) SEM of SPS-dipped PVA fiber.
(a)(b)In the SEM analysis, it is found that there are no changes in the structure and internal bonding of the fibers, but there are changes in the texture and colour of the fiber. Raw PVA fibers are pure white in colour whereas SPS-dipped fibers are yellowish, and SPS-dipped fibers are smooth compared to raw fiber for physical appearance [28, 29]. From the figures, it was observed that raw PVA have additional coating in the surface which produce stiffness to the fiber. Whereas the SPS-dipped fiber has a rough surface, and C-S-H gel remove the addition coating on fiber. However, there is no reduction and disintegration in the cross section of fibers.


## 5.4.2. Polypropylene Fiber

SEM analysis was carried on both raw and SPS-dipped PP fibers and are shown in Figures9(a) and 9(b). In the SEM analysis, it is found that there are no changes in the structure, internal bonding, and colour of the fibers but there is a change in the texture of the fiber. SPS-dipped fibers are smooth compared to raw fiber, and it is found that there is a formation of batches of slumps among the circumference fibers. This may be due to sedimentation of C-S-H gel [30]. From the figure, it was also observed the two fibers join together along the length and this is due to C-S-H gel which creates bond between the adjacent materials. Moreover, there is no reduction and disintegration in the cross-section of fibers. Among all the fibers, the PP fiber has a smooth surface texture.Figure 9
(a) SEM for raw PP fiber. (b) SEM for SPS-dipped PP fiber.
(a)(b)From the SEM analysis, it was observed that there is no reduction of cross section and disintegration of fibers. The C-S-H gel react with the fiber surface and made the surface rough and remove the top coating in the fiber. This rough surface creates the additional bond between fibers and ECC mixes. Presence of C-S-H gel in form of lumps does not create any impact because fibers are removed from simulated pore solution and allow to dry in the room temperature, gel located in the surrounding area of fibers formed as a crystal. Crystals are located in the circumference of the fibers in the form of lumps.


## 6. Conclusion

This study has explored the characteristics of raw fibers and SPS-dipped fibers by using FTIR test, TGA test, SEM analysis, and DSC test. The observations are as follows;(i)
From the FTIR analysis, it is found that transmittance (%) of both SPS-dipped PVA and SPS-dipped PP fibers are low indicating that energy absorption is high for both SPS-dipped PVA and SPS-dipped PP fiber when compared with raw PVA and PP fibers.(ii)
From TGA analysis, it is found that both raw PVA and raw PP fiber have more residual mass indicating that the loss of weight in raw PVA and PP fibers is minimum with increase in temperature when compared with SPS-dipped PVA and SPS-dipped PP fibers.(iii)
From DSC analysis, it is found that both raw PVA fiber and SPS-dipped PVA fibers release heat energy whereas both raw PP fiber and SPS-dipped PP fiber absorbs heat energy.(iv)
From SEM analysis, it is found that there are no considerable changes in the fibers whereas all fibers have changes in smoothness. However, PVA fiber only changes from white to yellowish colour.(v)
The roughness nature of the fiber influences the bonding nature between fiber and concrete interface.(vi)
On analysing all the results, it is found that the properties of both PVA fiber and PP fiber is not affected by the formation of C-S-H gel.



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*Source: 9669803-2022-07-16.xml*