Description:Field of the Invention:
In polymer matrix composites, a variety of natural cellulose fibrous materials have recently been discovered to be an effective replacement for man-made synthetic fibres like carbon, glass, and aramid because they are not biodegradable and need more energy to manufacture. Due to their light weight, higher specific characteristics, renewability, biodegradability, and non-toxicity, natural cellulose fibres are thereby attracting the attention of manufacturers (in the automotive and construction industries), material engineers, scientists, and researchers. Numerous researchers have conducted in-depth studies on the creation and characteristics of polymer composites filled with different types of natural cellulose fibres. Better polymer composites were created as a result of increased demand for novel fibre materials with improved qualities for usage in a variety of applications, including automotive, electronics, and structural. Superior reinforcing agents can provide better physical and mechanical qualities for polymer composites.
Calotropis gigantea (CG), a member of the Asclepiadaceae family, is a traditional medicinal plant with special qualities that produces a strong fibre (Bowstring of India) excellent for ropes, carpets, fishing nets, and sewing thread. It is one of the many plants that provide natural cellulose fibres. These plants have been preserved as genetic resources and utilised as food, fibre, and fodder since ancient times. The CG plants thrive without any cultivation techniques in any type of soil and environment. They have many diverse parts, including stems, roots, leaves, flowers, fruit, seeds, and the silky hairs of seeds, all of which have the enormous potential to treat a wide range of illnesses and problems in both humans and animals. The entire plant is used to produce biogas and to replace petroleum-based products. It has enormous potential. The entire plant is used to produce biogas and to replace petroleum-based products. It is a plant resource with a lot of promise for producing silky hair and fibre from its seeds and bark, respectively. The viability of bark and seed fibres, two types of CGFs, as a promising substitute raw fibre material for fiber-reinforced composite was assessed. CGFs share a similar structural makeup with other stem fibres as those found in banana and roselle. The chemical composition is similar to that of banana and roselle fibres. The mechanical characteristics of CGF-reinforced polymer composites have received less attention.
A new set of polymer composites made of CGFs and Phenol Formaldehyde (PF) resin were created in the current study utilising a hand lay-up process, and they were then evaluated for their mechanical characteristics such as tensile, flexural, and impact. In order to discover the crucial fibre length and ideal fibre loading to achieve the highest mechanical properties, composites were made using five different fibre loadings and three different fibre lengths. The experimental and theoretically anticipated values for tensile properties were compared.

Background of the invention:
Manual extraction of the CGFs from the plant stem resulted in three lengths of 3, 9, and 15 mm, which were then chopped for use as reinforcement agents in phenol formaldehyde resin matrix. The cross-linking agent (divinylbenzene) and acidic catalyst were used with the resole type Phenol Formaldehyde (PF) liquid resin as a polymer matrix. It has a density of 1.3 g/cm3 and a specific gravity of 1.14. (hydrochloric acid).
Summary of the Invention:
Fiber-reinforced phenol formaldehyde from Calotropis gigantea A mould of 150x150x3mm was used to manually set out composite plates (Athijayamani et al., 2015). Based on five different fibre loadings (10, 20, 30, 40, and 50 vol percent) and three different fibre lengths, the tensile, flexural, and impact mechanical characteristics of the CGF/PF composites were examined (3, 9, and 15 mm). The maximum level of mechanical characteristics in this composite led to the identification of the crucial fibre length and fibre loading. The outcomes showed that the PF composite's mechanical properties are being enhanced by the inclusion of CGFs. In 20% of situations, the properties of composite materials match those of a neat resin sample. The critical fibre loading and length for achieving the best mechanical properties were found to be 9 mm and 40 vol%, respectively. When experimental and theoretical tensile property values were examined, they were found to be in good agreement.
Detailed Description of the Invention:
Figure 1: -Digital image of fabricated CGF/PF composite specimens.
Figure 2: -Schematic diagram of the producers of the used equipments for the investigations:
(a)Tensile Test, (b) Flexural (three point bending) Test and (c) Impact Test.
Figure 3:- Variations of mechanical properties: (a) Tensile properties, (b) Flexural properties,
and (c) Impact strength of the CGF/PF composite prepared with the fiber length of 3mm
for various fiber loadings.
Figure 4:-Variations of mechanical properties: (a) Tensile properties, (b) Flexural properties, and
(c) Impact strength of the CGF/PF composite prepared with the fiber length of 9 mm for
various fiber loadings.
Table.1:- Average mechanical properties of CGF/PF composite prepared with the fiber length of 15
mm along with standard deviation.
Figure 5:-Comparison of experimental tensile modulus and strength values with theoretically
predicted result values at different fiber loading: (a) tensile strength and (b) tensile
modulus.

FABRICATION OF COMPOSITES
A mould of 150x150x3mm was used to manually set out composite plates (Athijayamani et al., 2015). To make sure that the cured composite plates could be removed easily from the mould, poly vinyl alcohol was first used as a releasing agent on the inside of the mould. The PF resin is then added to the calculated amount of fibres, and the mixture is agitated mechanically for 30 minutes. After that, the fibres and PF resin mixture are mixed with the cross-linking agent (divinylbenzene) and acidic catalyst (hydrochloric acid) in a ratio of 2:1.5:100, and again stirred by a mechanical stirrer for 15 min. Using a lab hot press, the liquid is put into the mould and compressed. The composite plate-containing mould box was then given 24 hours to cure at ambient temperature and atmospheric pressure. The digital image of the manufactured CGF/PF composite specimens is shown in Figure (1).
Mechanical properties of composites having the fiber length of 3 mm
Tensile Properties
According to five different fibre loadings, the variations in the average tensile characteristics of the CGF/PF composite with 3mm fibre length were measured and are shown in Figs. 3(a)–3(c). It is evident from Fig. 3a that the tensile strength of composite increases as fibre loading increases. At 40 vol % of the CGF, the composite shows the maximum tensile strength of 35.26 MPa which is 22.76% higher than the neat resin sample. This is may be due to the better interfacial bonding between the fibers and the matrix and also due to the proper load sharing between them. The further addition of the CGFs (50 vol%) decreases the tensile strength of composite. This is due to the poor wettability between the fibers and the matrix, i.e., brittleness of composite increases. Moreover, it can be identified that the percentage increments from the one fiber loading to the other fiber loading i.e., from 20 to 30 vol% and 30 to 40 vol%, is small. The probable reason is that the end points of fibers are more due to the short length of the fibers. It means that there is an insufficient fiber length to transmit the applied load.
Figure 3(a) also shows the tensile modulus of the CGF/PF composite plotted against the percentage of fiber loading. It shows that composite reaches the tensile modulus of the neat resin sample at 20 vol%. The tensile modulus was also increased up to 40 vol% and then dropped like tensile strength. An improvement of 6.39% was obtained at the tensile modulus of 40 vol% composite, when compared with the neat resin sample.
Flexural properties
Figure 3(b) shows the variations of the flexural properties, flexural strength and modulus, of CGF/PF composites containing various loadings of the CGFs. The values of flexural strength increased upon increasing the loading of the CGFs in the composites. The maximum flexural strength was obtained in 40 vol%. At 50 vol%, the sufficient cross-linking density cannot be attained due to the higher percentage of fiber loading, whereas at 40 vol% composite, the sufficient cross-linking density can attain due to the required percentage of fiber loadings. The percentage of increment from one fiber loading to the other fiber loading is also small like in tensile strength. It is may be due to the insufficient fiber length in the composites.
The variations of flexural modulus of composite are also shown in Fig. 3(b). The flexural modulus values of composite increased with the addition of the CGFs. Here also, the flexural modulus values are increased up to 40 vol% and then dropped. It is due to the better bonding between the fiber and the matrix at 40 vol% composite.
Impact strength
The results of the impact tests for the CGF/PF composites at various fiber loadings are given in Fig. 3(c). It can be observed that the maximum impact strength was attained at 40 vol% of the CGFs, which is 7.02% higher than the neat resin sample. The value of impact strength was decreased at 50 vol% of the CGFs. It is may be due to the poor wettability between the fibers and the matrix.
MECHANICAL PROPERTIES OF COMPOSITES HAVING THE FIBER LENGTH OF 9 mm
Tensile Properties
Figure 4(a) shows the measured tensile properties of the CGF/PF composite according to the different fiber loading. The tensile strength of the neat resin sample was reached by the composite with the fiber loading of 20 vol%. The tensile strength of composite increased continuously from 20 vol% to 40 vol% and then decreased at 50 vol%. The wettability at the 50 vol% composite is comparatively lower than the composite having the fiber loading of 40 vol% which is due to the weaker composite specimens. It means that at 40 vol% composite, the matrix wets the fibers in a sufficient manner, whereas at 50 vol% composite, the matrix is insufficient to the effective wettability of the fibers. Moreover, 40 vol% composite at the fiber length of 3 mm shows the low tensile strength compared to the 40 vol% composite at the fiber length of 9 mm. The probable reason is that the applied load is properly transmitted to the fibers through the matrix, i.e., proper load sharing between the fibers and the matrix.
The tensile modulus of composite for different fiber loadings is also illustrated in Figure 4(b). The tensile modulus was increased with the increasing of loading of the CGFs. The maximum tensile modulus of 1231.9 MPa was observed at 40 vol%. The tensile modulus values of composite with the fiber length of 3 mm and the fiber loading of 40 vol% were also high compared to the 40 vol% composite at 9 mm.
Flexural Properties
The results of the flexural test carried out on the CGF/PF composites according to the different fiber loading were shown in Figure 4(b).The flexural strength of composite decreased after addition of the CGFs from 40 vol% to 50 vol%. This is due to the incompatibility between the fibers and the matrix due to the poor wetting of fibers by the matrix, which leads to the reduction in the composite strength. Here also, the flexural strengths of composite prepared with the fiber length of 3 mm are lower than the composite prepared with the fiber length of 9 mm. The proper load sharing with the sufficient fiber length is responsible for this higher range of flexural strength.
The flexural modulus values obtained after three point bending flexural tests were also shown in Figure 4(b). The flexural modulus values also increased from 20 vol% to 40 vol% and then dropped. This is may be due to the fiber-to-fiber interaction by the insufficiency of the resin matrix to wet the fibers. It increases the brittleness of the composite which leads to the sudden failure of the composite specimen. It means that there is an insufficient resin matrix for load sharing.
Impact Strength
Figure 4(c) presented the impact strength results of the CGF/PF composites for the different fiber loading. The 40 vol% composite showed the highest impact strength (1.27 KJ/m2). The impact strength values of composite having the fiber length of 9 mm are superior compared to the composite prepared with the fiber length of 3 mm.
MECHANICAL PROPERTIES OF COMPOSITES HAVING THE FIBER LENGTH OF 15 mm.
Table 1 lists the mechanical properties, including tensile, flexural and impact, of the CGF/PF composite containing the different loading of the CGFs. From the Table 5, it is inferred that the tensile strength is higher at the fiber loading of 30 vol% than at 40 and 50 vol%. The probable reason is that the higher fiber length with the highest fiber loading creates the improper fiber wetting by the matrix due to the increased fiber entanglement. Moreover, there is a possibility of formation of the fiber or the matrix- rich areas within the composite specimens due to the higher fiber length. Due to this, the strength of the composite prepared with longer fiber length and the higher fiber loading was reduced (Ku et al. (2011)).
The tensile modulus of the CGF/PF composite for the various fiber loadings is also given in Table 5. The tensile modulus of composite reached the neat resin sample at 20 vol%. Composite attains the maximum value of tensile modulus at 30 vol% and then the tensile modulus values decreased. The tensile strength and modulus value of 40 vol% composite with the fiber length of 9 mm were higher than the 30 vol% composite with the fiber length of 15 mm.
The flexural properties of the CGF/PF composite after three point flexural tests for varying fiber loading are illustrated in Table 5. It can be seen that the flexural properties are also increased up to 30 vol% and then dropped at 40 and 50 vol%. This is also the reason of longer fiber length with the highest fiber loading, which results in formation of fiber bending at a particular location within the composite. The flexural properties of 30 vol% were also lower than the 40 vol% composite with 3 mm fiber length and the 40 vol% composite with 9 mm fiber length.
The impact strength of composite was increased with the increase of fiber loading up to 40 vol% and then dropped at 50 vol%, as given in Table 5. The maximum impact strength was obtained in 40 vol%. 50 vol% composite shows the impact strength of 1.18 KJ/m2, which is 1.69% lower than the 40 vol% composite. It is due to the better interfacial bonding between the fiber and the matrix and the better cross-linked systems. Due to the better cross-linked system, failure occurs in brittle nature, which depends on both crack initiation and crack propagation within the composite specimens during the test. The impact strength of 40 vol% composite with the fiber length of 9 mm was maximum than the 40 vol% composite prepared with the 15 mm fiber length. This is may be due to the fiber entanglement by longer fiber length within the composite.
THEORETICAL MODELING OF TENSILE PROPERTIES
Figures 5(a) and 5(b) compare the theoretically predicted tensile modulus and strength values by various theoretical models with the experimental values at different fiber loading respectively. From Figure 5(a), it is clearly observed that the tensile strength values predicted by the Hirsch’s model are very close to the experimental tensile strength values. In both the equations of Hirsch’s model, the value of constant parameter is 0.51 to obtain the good agreement between the predicted and experimental tensile strength and modulus values. MBB and Series models predict the tensile strength values, which are lower than the experimental tensile strength values. The values of k1and k2 in the MBB equations were found to be 1 and 0.45 to obtain a good agreement with experimental values. It is already observed experimentally that the tensile strength values of composite prepared with the 9 mm of fiber length are increased up to 40 vol% and then decreased in 50 vol%. When comparing the predicted strength values with the experimental strength values at higher fiber loading, it can be identified that there is a large deviation, which may be due the structural defects occurred during the preparation of composite specimens. These structural defects may occur due to the formation of fiber agglomeration by higher fiber loading during processing. The Hirsch’s model is predicting the tensile strength values above the experimental values, whereas the Series and MBB models are predicting the tensile strength values below the experimental values.
Figure 5(b) shows the comparison of the predicted and experimental tensile modulus for different fiber loadings. Here also, the Hirsch’s model predicts the tensile modulus of the composite which is very close to the experimental tensile modulus values compared to the other two models. It predicts the tensile modulus values above the experimental values. The Series and MBB models predict the tensile modulus values below the experimental values.
, C , Claims:We claim that
1. The investigation and comparison of the impact of fibre length and loading on the mechanical characteristics of the randomly oriented CGF/PF composite. The tensile and flexural property values as well as impact strength values rose with an increase in fibre loading at all fibre length composites.
2. The greatest mechanical characteristics of composites with fibre lengths of 3 and 9 mm were attained at a CGF content of 40%. However, for composites with fibre lengths of 15 mm, the maximum level of tensile and flexural characteristics was attained at 30 vol%, while the maximum value of impact strength was reached at 40 vol%. The composites with fibre lengths of 9 mm provide the highest level of mechanical qualities when comparing the mechanical properties in all circumstances.
3. As a result, it can be determined that the optimal fibre loading and critical fibre length for this combination to provide the best mechanical properties are 40 vol% and 9 mm of the CGF.
4. When the experimental and theoretically anticipated values for tensile properties were examined, it was discovered that there was a good agreement between the two. Finally, it can be said that the CGFs' integration enhanced the PF composites' mechanical qualities. Therefore, it was demonstrated that CGFs are a good candidate for reinforcement in the phenol formaldehyde resin matrix.
5. According to studies on randomly oriented CGF/PF composites, the ideal fibre loading and critical fibre length are 40 vol% and 9 mm of CGF, respectively, to achieve the best mechanical performance.