Kinetic and thermodynamic study of composite with jute fiber as reinforcement

. In the present work, engineered by compression molding process via a hydraulic press, the A and B composite samples were carried out with 5% and 10% ratio respectively of Ricinodendron heudelotii oil-based alkyd resin in bio-based matrix made of unsaturated polyester using jute fibers as reinforcement material. The samples’ thermal decomposition was performed through thermogravimetry (TG) and derivative thermogravimetry (DTG) analyses. Both composite samples exhibit two stages of decomposition, where the main occurs at 200 - 550°C. Aiming to study and being able to model the thermal degradation of the elaborated composites, finding the kinetic triplets appears the best option to describe the kinetic process undergo by the composites in order to evaluate the performance application of the composites. Two non-isothermal techniques, Flynn-Wall-Ozawa (FWO) and Kissinger have been used to assess the activation energy-Ea, and it is found that the apparent activation energy varies with the degree of conversion indicating that both composites decompose with a multiple step mechanism process. The appropriate reaction model for the second stage of decomposition was best suited with Johnson-Mel-Avrami (n<1) model and has been established, allowing us to model thermal degradation behavior of our elaborated composite material and set predictions. The estimated Arrhenius factor values were respectively about A and B composites, 4.12.10 15 min -1 and 10.42.10 15 min -1 , allowing us to set the final equation characterizing the degradation process for the second and main decomposition stage. Finally, as a result of comparison between A and B composites, A appears to be the more thermally stable due to its lower values of Arrhenius pre-exponential factor over the main stage of decomposition and higher calculated the activation energy values.


Introduction
Research into the creation of novel green bio-based and biodegradable materials from natural resources for various engineering applications has been stimulated by a growing concern for environmental preservation.In fact, the availability, affordability, and numerous other benefits of natural resources make them attractive for their use in the engineering of these novel types of materials (La Mantia & Morreale, 2011;Mugdha Bhat et al., 2021;Scatolino et al., 2017).As an alternative to customary plastic made from petroleum, a lot of conducted studies were done on the utilization of natural lignocellulosic fibers (NLF) to create more valuable materials in a sustainable and ecologically acceptable manner that may be used in a variety of industrial applications.The possible use of lignocellulosic materials as sources of reinforcing fillers for thermoplastic and thermosetting biopolymers has also been investigated by number of researchers (Kakati et al., 2019;Kuranchie et al., 2021;R. H. M. Reis et al., 2020;R. S. Reis et al., 2020).One key strategy aiming to avoid the complexity of recycling is the use of naturally disintegrating materials after usage.In order to enhance composite materials properties, researchers have since developed the incorporation of natural fibers (NF) for instance hemp (Khoathane et al., 2008;Oza et al., 2014), flax (Zafeiropoulos et al., 2002), sisal (Khoathane et al., 2008), coconut (Rosa et al., 2009), kenaf (Hamidon et al., 2019), pineapple leaf (Kakati, 2019), and more in their elaboration (Arrakhiz et al., 2013;Sahin et al., 2017;Scatolino et al., 2017).Although these materials are in demand in many sectors, such as automobile, sport, aviation, building…, where materials must be preserved over the time, exposed to light or sunlight, heat and humidity.The significance of NF composites lies in their sustainability, renewability and potential to reduce environmental impact compared to the traditional synthetic fiber composites ( Butler, S. (2018); Barsoum, 2019;Keller, 2003;Kuranchie et al., 2021;La Mantia & Morreale, 2011;Raju & Kumarappa, 2012; R. H. M. Reis et al., 2020;R. S. Reis et al., 2020;Yakout & Elbestawi, 2017).However, it's important to note that they are subjected to limitations in terms of moisture absorption, dimensional stability, mechanical properties.The poor adhesion fiber/matrix compatibility mainly come from the hydrophilic property of the fiber and the hydrophobicity of the used matrix (Tserki et al., 2005;Zafeiropoulos et al., 2002), moreover, the undesired compounds of the fibers including hemicellulose and lignin.The use of untreated fibers may lead to composite materials with low properties due to the NF drawbacks.It would be important to carry out more in-depth studies in order to optimize their use and properties related to the different conditions.
Among all existing natural fibers today, jute looks to be one of the NF employed more frequently as reinforcement in green composites, and presently, bast fibers with the highest global output volume (Singh et al., 2018;Thiruchitrambalam et al., 2010).Jute chemical composition is in the range of 45-73.2%cellulose, 12-24% hemicellulose, 5-25% lignin, and properties including tensile strength (300-800Mpa), Young's modulus (2.5-55Gpa), elongation at break (1-4%) and density (1.3-1.46g/cm3)according to the review of the study of Singh et al., 2018, allowing good specifications to be used to strengthen composite materials.In fact, using jute fibers in order to create composite materials result in materials that have good thermal properties (Rangappa, 2021), mechanical properties (Nenonene, 2014; R. H. M. Reis et al., 2020), rheology properties (Elisabeth et al., 2018), and optical properties (N'Gatta et al., 2022), which are suitable for application in various domains.Despite the fact that jute fiber can deteriorate due to several factors including moisture and water damage, microbial attack, chemical degradation or under exposure to UV radiation, exploring the ways of proper handling techniques or fiber treatments will enhance the fiber properties and help reducing drawbacks on the use of jute fiber as reinforcement in composite materials elaboration.
Research on the use of jute fiber in composite materials application has been carried out up to now, and have shown good results depending on the application domain with the various treatments applied onto the fibers.The kinetic and thermodynamic investigation of the degradation of composite materials utilizing jute fiber as reinforcement, source of renewable material, however, has not yet been published.Moreover, extending the range of applications for renewable green composites requires an understanding of the kinetic mechanism and model as well as the thermal stability and deterioration processes.This work studied the kinetic analysis of the thermal degradation of green composites that were developed using jute fibers as reinforcement combine with a bio-based matrix, in order to create a completely biodegradable and environmentally friendly composite materials.

Bio-based matrix synthesis
Blends of bio-based unsaturated matrix resin were made in two sets, A and B. The first batch of blend A contains 5% i.e., 5 g RH oil-based alkyd resin in 100 g of SFR.While the second set B consists of 10% meaning 10 g of RH oil-based alkyd resin fraction in 100 g of SFR.For the preparation of the bio-based matrix blends, the RH oil-based alkyd and soy four resin were blended in a cone-shaped flask at room temperature for 2 hours at a high-speed agitator of 10,000 rpm.

Elaboration of jute fiber reinforced material with the bio-based unsaturated resin matrix
Using a PEECO PVT LTD Kolkata hydraulic press associated and by compression molding process, we managed to manufacture the A and B composite based on the prepared matrix, respectively.Non-woven and woven mats made with jute fibers were cut in 30cm×7cm dimension, and impregnated in the resin matrix.The excess resin was pressed out, and the impregnated jute mats were then allowed to dry for 24h at room temperature.Two 30cm×30cm×0.5cmsteel plates were used for the composite's elaboration.Thin plastic layer of paper was inserted between the mats and the plates in order to obtain a good composite surface, then the dried carpets were placed alternately layer after layer (Figure 1) a total of 10 carpets of non-woven sheets and 9 woven sheets.Following that, the molds were hot-cured by compression in the hydraulic press for 15 minutes at 110°C and 200Kg/cm 2 .After curing, the composite samples were taken out of the molds and desiccated to avoid moisture absorption.

TGA & DSC measurements
The thermal degradation and stability of the elaborated composite materials were determined using a DSC-TGA module instrument, TA STD series Q600 under an inert atmosphere (nitrogen gas) at 4 distinct thermal rates, 20, 15, 10 et 5°C/min.A mass of 6mg of crushed sample were taken in an alumina crucible, and subjected to a temperature program varying from 25°C to 600°C while performing the experiment.The nitrogen gas flow was 100 mL/min, and the analysis performed at North-East Institute of Science and Technology, Jorhat, India.

Thermal degradation theory
Investigation on the deterioration of polymeric materials is extremely beneficial in thermal degradation steps understanding, kinetic models and mechanisms, thermal steadiness and cycling.Kinetic analysis is critical because it gives information that can be utilized to optimize and/or improve process parameters, also to provide information on the mathematical modeling simplification (Khachani et al., 2014).The apparent activation energy (  ), frequency or Arrhenius pre-exponential factor (), and the order of reaction () are the variables kinetic analysis.With the aim of examining the kinetics of the thermal deterioration processes and identify the characteristic variables such as () and () functions, the TG analysis approach has been widely employed (Assanvo et al., 2015;Khachani et al., 2014).
The temperature T and the degree of conversion α are two metrics widely used to display the reaction rate in a process as the recognized equation ( 1 The rate or decomposition constant, (), which is frequently parameterized by the Arrhenius equation ( 2), expresses the process rate's temperature dependence, and the heating rate , which can be defined by equation (3): where  is the pre-exponential factor ( −1 ),   the activation energy (. −1 ),  the universal gas constant (8.314 . −1 . −1 ), and () the unconditional temperature.The reliance on the degree of conversion is shown by the reaction model function, (), that may be connected to the testing data.For data derived at steady heating rate,  and () are switched in equation ( 1) to get the equation ( 4): It is feasible to evaluate () with a basic model function for simple reactions.For complex reactions () functions are sophisticated and usually undetermined; in this situation, the process of simple reaction guides to considerable discrepancies in kinetics data.It exists an integral kinetic method (advanced isoconversional method) developed by Vyazovkin et al., (2011).De facto, the relative involvement of each single-step process to the global reaction rate is what causes the change in activation energy with.
In the current work, two techniques were employed to evaluate the activation energy for the disintegration of our composite materials at various heating speeds: Kissinger and Flynn-Wall-Ozawa (FWO) techniques.
No matter how complex the process is, renowned for providing an unbeatably simple way of determining the activation energy and for drastically oversimplifying the kinetics of the phenomena it considers., the Kissinger technique (Vyazovkin, 2020) is a differential method that produce a single value for the activation energy.The activation energy, , is calculated using the Kissinger equation in its most straightforward form: where   is the temperature associated with the location of the rate peak maximum.The integral version of the Kissinger equation is more illuminating through equation ( 6) that derives from equation ( 5).
( ) According to both equations ( 5) and ( 6 The activation energy and pre-exponential factor are calculated using the FWO method, an isoconversional method.Furthermore, that method required the samples to be heated at various temperature heating rate, minimum three different temperature programs.Using its final method equation ( 7), the slope of the plot line derived from various heating temperature rates can be used to solve for the activation energy.For each degree of conversion, this approach offers a different activation energy and pre-exponential factor value.

( ) ( )
The real (), which must be invariant for all heating rates, is not necessary to use the isoconversional technique.Malek's approach, which suggests that the () function are related to () and (), can be used to investigate the invariance and is principally achieved by a straightforward TG data translation.Equations ( 8) and ( 9) represent these functions under nonisothermal conditions: An overview of the of the mathematical characteristics of the () and () functions for typical kinetic models is given in the table of the fundamental kinetic models (see Table in annex) and attributes of these functions (Assanvo et al., 2015).Following by the identification of the reaction model, find the pre-exponential factor A to obtain the three key kinetic parameters,   , () and , follow the identification of the reaction model.From the Malek theory (MaÂlek, 2000), (Janković et al., 2008;Khachani et al., 2014), we derive  by the equation 10: Where  ′ (  ) is the derivative of the () function from   , and   ,   signify the maximum peak on the DTG curve.

Results and Discussions
The ICTAC Kinetic Committee's reliable isoconversional (model-free) method, which involves several temperature programs (Assanvo et al., 2015;Janković et al., 2008;Vyazovkin et al., 2011) were used to perform kinetic computations through thermal analysis data of A and B composites.Different constant heating rates were used during the trials, including 20, 15, 10 and 5°C/min.Figure 2 shows, the temperature at the four heating rates against the thermal analysis data (TGA and DTG) of A and B composites.
The TG curves in Figure 2 (a) and (c) show A and B composite samples decomposition with more than 20% residue formation.More precisely in the range gap of 25-30% and 20-25% for A and B composites respectively.At this condition, we can deduce that A contains more inorganic compounds than B composite (Tajvidi & Takemura, 2010).For both composites TG analysis at all various heating rates, a slight weight loss is observed below 100 o C which is attributed to the evaporation of absorbed moisture.All formulation exhibits significant weight losses at any temperature as compare to the different heating rate processed where tiny differences are observed at each heating rate.The derivative curves in Figure 2 (b) and (d) reveal the same trend for all composite materials, which also shows that the maximum decomposition temperature rises as the heating rates rise.In addition, they also show two distinct stages of degeneration.The first stage of degradation happens in the range of 25-125°C and may be assigned to the gradual release of remaining water from the composites and the depolymerization process.The main degradation (second stage) occurs over a broader temperature range of 225-375 °C with mass loss of 9.01-60% at a relatively high temperature with maximum temperature at approximatively 333 °C.This high temperature decomposition is attributed to the decomposition of lignocellulosic fibers by the decomposition of hemicelluloses which are the least thermally stable lignocellulosic components, cleavage of glycosidic linkage of cellulose as well as the disintegration of the crosslinking lattice formed between the matrix and the fibers (Monteiro et al., 2012;Darus et al., 2020).
Utilizing the Kissinger (differential) and FWO (integral) approaches, the activation energy values calculated and reported in, Table 1 were in good agreement, demonstrating good convergence between the two methods.Figure 3 depicts the linear plot of the Kissinger technique for the composites A and B for the main stage of decomposition.
The isoconversional Flynn-Wall-Ozawa method lines for both composites and decomposition stages are shown in Figure 4. Figure 4(a) and (c) show that the isoconversional plot for the first stage of decomposition, and it is clearly shown that, the fitted lines are non-parallel indicating a complex degradation mechanism.On the other hand, case of the second decomposition stage as shown in Figure 4 parallel.The investigation on the relationship between the activation energy and the degree of conversion (α) is a useful tool to know the degradation mechanism of the main stage.According to the solution of equation ( 6) and ( 7) and the table 1, the activation energy, which is the minimal amount of energy needed to start our composites' degradation reaction process (Hadiyanto et al., 2018), and in fact also related to the reactional material stability.Results show that the energy activation values increase as the degree of conversion increases.The activation energy's relationship to the degree of conversion suggests that the thermal disintegration of composites A and B is the result of a complex reaction process.This degradation mechanism clue  | 6 ISSN: 2252-4940/© 2024.The Author(s).Published by CBIORE can be attributed to crosslinking complex reaction associated with vitrification and debonding of the cellulosic-matrix link prior decomposition.The activation energy of the composite A is higher than of the composite B (Table 1) indicating that as the percentage of resin modifier increases, this could lead increasingly low   values resulting to a less and less stable composite material.These findings also imply that the inclusion of resin modifier can reduce the adherence of the fiber matrix.This information is crucial since A composite is probably more thermally stable than B.
The method put worth by Malek (MaÂlek, 2000) and the recommendations given by the ICTAC Kinetic Committee (Vyazovkin et al., 2011) were both used to determine which kinetic model for non-isothermal deterioration of the two composites better fit the experimental results.The normalized graphs of () and () functions are shown in Figure 5, and the curves show no significant with the given β values. , values obtained from the curves are 0.660 and 0.632 respectively for the composites A and B. () function presents a concave behavior for both composites and exhibit a maximum  , corresponding the model describes Johnson-Mel-Avrami (JMA).According to Svoboda & Málek, (2011), the value of  are calculated using  , .
Calculated  values are  = 0.48 and  = 0.5 respectively for A and B composites.In the α-range of 0.2 to 0.7, the kinetic reaction models for A and B composites degradation are established as follow: • Composite A: For JMA model; randomization (random distribution) is implemented by (1 − 1/) = 1, (1 − 1/) > 1 or an orderly distribution, and finally (1 − 1/) < 1 for a bundled distribution, then the composites degrade in a grouped way regarding their  calculated values.
After being calculated, the  ′ (  ) and Arrhenius factor  are recorded in Table 2 for A and B composites respectively, and their mean Arrhenius pre-exponential factor value were shown to be: • Composite A:  = 4.12 * 10 15  −1 ; • Composite B:  = 10.42 * 10 15  −1 .
As a result, from all above, the kinetic triplets   ,  and () are well known.For the second and main degradation step, the final equation characterizing the degradation of A and B composites is established by: After deduction regarding the analyses made above, the reaction model found to be ideal for the description of the decomposition of both composites is that of JMA with a value of  less than 1 describing a bundled distribution.Based on the different TGA and DTG curves observed and after analysis, composites A and B exhibit the same trend of thermal degradation process, with two decomposition steps showing that both composites describe the same thermal behavior.The frequency factor, or Arrhenius factor value, which describes how frequently two molecules collide, appears to be lower for This suggest that the A composite may be more stable than the B composite.In the second and main stage of decomposition, composite A has the highest calculated activation energy values using Kissinger and FWO.The type and percentage of matrix, as well as the reinforcement loadings, influence material properties such as mechanical properties, thermal stability, rheology properties, and others (Shan et al., 2016).In this study, the more the matrix percentage used in composite elaboration increases, the more the activation energy value decreases and this could be explained by less adhesion of the matrix to the fiber due to the excess of matrix 10% used.In accordance with the studies of Oza et al., (2014) and Rowe et al., (2016) driven about the stability of composite materials, increased bond energy produces higher activation energy with enhances thermal stability.A better knowledge of the thermal deterioration behavior of composites as a result of composite processing can be achieved with the use of the activation energy data.Therefore, from the all above, we can deduce that composite A is more thermally stable than B.

Conclusion
Elaborated by compression molding process, the composite materials A and B based on jute fiber undergo two major steps during the degradation process where is being processed at very higher temperatures over the range between 200°C to 550°C shows that the elaborated composites are thermally stable.The apparent activation energy of thermal deterioration was estimated using two-non isothermal methods built on the FWO and Kis singer equations.The findings show that the amount of conversion determines how much this energy is involved, and that the thermal decomposition process disintegrates composites into a number of degradation reaction steps.The JMA model ( < 1) was discovered by using the Malek technique to be the ideal decomposition reaction model for the A and B composites and could be established as: • Composite A:  The calculated values of the pre-exponential factors were respectively for A and B composite materials, 4.12 * 10 15  −1 10.42 * 10 15  −1 ; allowing us find out the final equation characterizing the process, then to model the kinetic study and to follow the degradation process of the elaborated composites.By the results analysis, our elaborated composites are both thermally stable, thereafter recapitulative analysis of the parameters, composite A is found to be more thermally stable than composite B. In addition, regarding the big gap between the calculated values of the Arrhenius factor, the possibility of investigating various ratio of blended resin or the effect of fiber treatment into the elaboration of such composite materials have to be taken into account for further studies.

Fig. 1
Fig. 1 Jute fiber layer disposition structure for the material elaboration ), the Kissinger plot's incline of  (    2 ) can be utilized to figure out the activation energy.

Fig. 4
Fig. 4 Iso-conversion plot using the F-W-O method with varied degrees of conversions of composite A first (a) and second stage (b); and composite B first (c) and second stage (d).

Table 1
Activation energies for different stages of decomposition for A and B composites