Green Composites from Natural Fibers

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Green Composites from Natural Fibers: Mechanical and Chemical Aging Properties V. K. Thakur

a b

b

, A. S. Singha & M. K. Thakur

c

a

School of Materials Science and Engineering , Nanyang Technological University , Singapore b

Department of Chemistry , National Institute of Technology Hamirpur , India c

Division of Chemistry , Govt. Degree College Sarkaghat, Himachal Pradesh University , Shimla , India Published online: 07 Aug 2012.

To cite this article: V. K. Thakur , A. S. Singha & M. K. Thakur (2012) Green Composites from Natural Fibers: Mechanical and Chemical Aging Properties, International Journal of Polymer Analysis and Characterization, 17:6, 401-407, DOI: 10.1080/1023666X.2012.668665 To link to this article: http://dx.doi.org/10.1080/1023666X.2012.668665

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International Journal of Polymer Anal. Charact., 17: 401–407, 2012 Copyright # Taylor & Francis Group, LLC ISSN: 1023-666X print=1563-5341 online DOI: 10.1080/1023666X.2012.668665

GREEN COMPOSITES FROM NATURAL FIBERS: MECHANICAL AND CHEMICAL AGING PROPERTIES V. K. Thakur,1,2 A. S. Singha,2 and M. K. Thakur3 1

School of Materials Science and Engineering, Nanyang Technological University, Singapore 2 Department of Chemistry, National Institute of Technology Hamirpur, India 3 Division of Chemistry, Govt. Degree College Sarkaghat, Himachal Pradesh University, Shimla, India The increasing demand for green, environmentally friendly materials has resulted in new natural fiber–based materials as replacements for nondegradable materials derived from petroleum resources that are currently being used for a number of applications. Hence, this study deals with long fiber–reinforced green polymer composites fabricated using the compression molding technique. Initially, green composites were produced with long fibers using 10, 20, 30, and 40 wt.% fiber loading. A fiber content of 30 wt.% was found to exhibit optimum mechanical properties. Physicochemical properties of the composites were also tested to check their application potential in everyday life. Keywords: Green polymer composites; Natural fibers; Mechanical, physical, and chemical aging properties

INTRODUCTION Environment-friendly, ‘‘green’’ composite materials based on natural cellulosic fibers and polymer resins are increasingly being developed for various applications as replacements for synthetic materials derived from different kinds of petroleum resources.[1–5] Unlike petroleum resources, natural polymer–based materials are found abundantly in nature and are of renewable nature.[6–11] Among different kinds of natural materials, natural cellulosic fibers possess a number of advantages over their synthetic counterparts and have been used in the past as reinforcing materials for different types of matrices.[12–17] There is a wide variety of cellulose fibers that can be used to reinforce different kinds of polymers matrices such as thermoplastics and thermosetting polymers resins. These include a variety of agro-based fibers such as stems, leaves, stalks, bast, and seed hairs, along with wood fibers.[18–24] These fibers are abundantly available throughout the world. Natural fibers, depending on the part Submitted 27 January 2012; accepted 17 February 2012. The authors wish to thank their parental institutes for providing the necessary facilities to accomplish the present research work. Correspondence: V. K. Thakur, School of Materials Science and Engineering, Nanyang Technological University, Singapore 637553. E-mail: [email protected] 401


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of the plant from which they are taken, can be classified into different types. The properties of these fibers depend on the source, age, and separating techniques of the fibers from their parental sources. The quality of the raw components is very important when manufacturing a bio-based material.[25–31] Environment friendly, green composites fabricated using natural fibers offer an attractive alternative to conventional petroleum-based plastics. Considerable research efforts have been made to develop green composites from different renewable resources. Among various types of cellulosic fibers, Grewia optiva fibers have high potential as reinforcement in polymer matrix–based composites.[16–26] In our earlier study we demonstrated that Grewia optiva fibers in particle and short fiber form exhibit promising mechanical properties.[16,26] In continuation of previous research efforts, the present research work deals with physicochemical and mechanical properties of long Grewia optiva fiber–reinforced polymer composites. The green composites prepared showed good mechanical properties and may be used for packaging or indoor paneling in the near future. METHODS Materials Grewia optiva fibers were collected from local resources of the Himalayan region and were used as reinforcing material in long fiber form after proper purification described elsewhere.[16,26] Phenol, formaldehyde solution, and sodium hydroxide of Qualigens make were used as received. Phenol-formaldehyde (PF) resin was used as a novel polymer matrix for preparing green composites. The polymer resin was synthesized by the standard method further developed in our laboratory.[26] Preparation of Green Polymer Composites Dried Grewia optiva fibers in long fiber form were mixed thoroughly with polymer resin with the help of a mechanical stirrer with different loadings (10, 20, 30, and 40%) in terms of weight. Then the mixture was poured into molds and spread evenly on the surface of the mold. Composite sheets of size 150 x 150 5.0 mm were prepared by compression molding technique as described in some of our earlier publications.[25–27] Characterization of Green Polymer Composites Mechanical properties of the green composites such as tensile, compressive, flexural, and wear resistance were tested in accordance with ASTM D 3039, ASTM D 3410, ASTM D 790, and ASTM D 3702 methods respectively. Thermogravimetric properties of conditioned green polymer composites were measured in nitrogen atmosphere on a thermal analyzer (PerkinElmer) at a heating rate of 10 C=min. Swelling studies of green composites in different solvents were carried out as per methods reported earlier.[29,31] The percent swelling was calculated from the increase in initial weight in the following manner: Percent swelling ðPs Þ ¼

Wf W i 100 Wi

GREEN COMPOSITES FROM NATURAL FIBERS

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Chemical resistance studies were carried out on the green composites using acid (HCl) and base (NaOH) of 1 N concentration.[23,34] The chemical resistance of the green composites towards acid and base in terms of percentage weight loss was evaluated in the following manner:


Percent chemical resistance ðPcr Þ ¼

Tw Waci 100 Tw

RESULTS AND DISCUSSION Phenol-formaldehyde polymer resin synthesized by the condensation of phenol with formaldehyde contains hydroxyl groups present in the resulting polymer matrix.[26] Hydroxyl groups present in the natural cellulosic fibers are the active sites for cross-linking with phenol-formaldehyde during pre-curing and curing processes. Hence, the overall mechanical properties of cellulosic Grewia optiva fiber–reinforced green composites depend upon (i) the extent of fiber-matrix bonding and (ii) the load transfer from matrix to reinforcement. Higher magnitude of bonding between the phenolic matrix and natural fibers facilitates the load transfer, resulting in higher mechanical properties. However, fiber loading beyond 30% results in decreased mechanical properties due to the agglomeration of fibers at higher loading, as reported earlier.[29–31] Tensile Strength It is evident from Figure 1(a) that green composites reinforced with natural Grewia optiva fibers showed better tensile strength than the parent polymer matrix. The tensile strength of green composites has been found to increase with Grewia optiva reinforcement. Composites with 30% loading exhibit maximum tensile strength, followed by 40%, 20%, and 10% loadings. The failure of reinforced composites at a particular loading under tensile load could be due to breaking of cellulosic fibers at the weaker point followed by further propagation under the applied load that is transferred to the remaining intact reinforcement, leading to complete rupture of the composites. Compressive Strength Like tensile strength, compressive strength of green composites has been found to increase with increase in fiber loading in the polymer matrix (Figure 1(b)). The failure of Grewia optiva fiber–reinforced composite compression occurs when the fibers exhibit sudden and dramatic buckling. The prime mode of failure in green composites with different loadings of samples under compressive load can be attributed to the buckling of columns or micro buckling, which was preceded by de-bonding and micro cracking of the matrix. Flexural Strength The flexural strength results of the green composites of Grewia optiva fibers follow the same trends as obtained in tensile strength and compressive strength tests (Figure 1(c)).


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Figure 1. Load elongation (a), deformation (b), and deflection (c) curves and wear resistance (d) of Grewia optiva fiber–reinforced green composites (color figure available online).

Wear Test It is quite evident from Figure 1(d) that phenol-formaldehyde polymer resin shows less wear resistance than composites. It can be observed from the figure that reinforcement with Grewia optiva fibers improved wear resistance significantly as compared to pristine polymer. Maximum wear resistance behavior is shown by green composites with 30% loading, followed by 40%, 20%, and 10% loading. The comparison of the mechanical properties of the green composites prepared using long fiber forms with particles and short fiber–reinforced composites shows that properties of the long fiber–reinforced composites are slightly inferior to short fiber-, followed by particle fiber–reinforced composites. This behavior can be attributed to the fact that in long fiber–reinforced composites there is an agglomeration of the fibers as they are randomly mixed with the polymer, which results in decreased mechanical properties.



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Figure 2. Swelling behavior of fiber-reinforced composites in different solvents (color figure available online).

Swelling and Chemical Resistance Behavior of Green Composites Grewia optiva–reinforced composites with different loadings demonstrate different swelling behavior in different solvents, as shown in Figure 2. The swelling behavior of the green composites in different solvents follows the trend: H2O > CH3OH > C4H9OH > CCl4. Swelling behavior has been found to increase with increase in fiber loading due to greater affinity of water for OH groups present in the biocomposites.[29,31] On the other hand, for the chemical resistance behavior, it has been observed that resistance towards chemicals decreases with the increase in percent loading (Figure 3). This may be due to the increase in fiber content in the composite, which is vulnerable to chemical attack, resulting in decreased resistance towards the chemicals.

Figure 3. Chemical resistance behavior of green composites with different fiber loadings against 1 N NaOH (a) and 1 N HCl (b) (color figure available online).

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V. K. THAKUR ET AL. Table I. TGA=DTA analysis of P-F, Grewia optiva, and long fiber–reinforced composites Sr. no.


1. 2. 3.

Sample Code

IDT ( C)

% wt. loss

FDT ( C)

% wt. loss

Final residue (%)

Exothermic endothermic peaks C(mV)

GO P-F Resin LF-Rnf PF

202 397 325

6.80 14.04 26.37

505 1188 974

84.02 49.25 57

15.97 50.70 42.45

57 [-4.0] 171 [9.0] 75 [-5]; 341 [-4]

Thermal Study of Green Composites The thermal stability of the composites was characterized using thermogravimetric (TGA) analysis. Table I shows the TG and differential thermal analysis (DTA) results of Grewia optiva fiber, polymer matrix, and the fiber-reinforced composite with 10% loading. The green composites show intermediate behavior between the fiber and the matrix, consistent with results reported earlier.[26] CONCLUSIONS Green composites were fabricated with Grewia optiva fibers using phenolic resin as polymer matrix. The fiber was assessed in long fiber form to improve the mechanical properties through increasing fiber content. The effect of fiber loading on liquid sorption and chemical resistance was also investigated. The overall results of the above experiment suggest that natural fiber reinforcement has a beneficial effect in the adhesion of the polymer resin into the green composites. REFERENCES 1. Goud, G., and R. N. Rao. 2011. The effect of alkali treatment on dielectric properties of Roystonea regia=epoxy composites. Int. J. Polym. Anal. Charact. 16(4): 239–250. 2. Singha, A. S., and V. K. Thakur. 2009. Chemical resistance, mechanical and physical properties of biofiber based polymer composites. Polym. Plast. Technol. Eng. 48(7): 736–744. 3. Sˇiroka´, B., J. Sˇiroky´, and T. Bechtold. 2011. Application of ATR-FT-IR single-fiber analysis for the identification of a foreign polymer in textile matrix. Int. J. Polym. Anal. Charact. 16(4): 259–268. 4. Singha, A. S., V. K. Thakur, I. K. Mehta, A. Shama, A. J. Khanna, R. K. Rana, and A. K. Rana. 2009. Surface modified Hibiscus sabdariffa fibers: Physico-chemical, thermal, and morphological properties evaluation. Int. J. Polym. Anal. Charact. 14(8): 695–711. 5. Thakur, V. K., A. S. Singha, and M. K. Thakur. 2012. In air graft copolymerization of ethyl acrylate onto natural cellulosic polymers. Int. J. Polym. Anal. Charact. 17(1): 48–60. 6. Lapcik, L., K. Benesova, L. Lapcik, S. de Smedt, and B. Lapcikova. 2010. Chemical modification of hyaluronic acid: Alkylation. Int. J. Polym. Anal. Charact. 15(8): 486–496. 7. Nervo, R., O. Konovalov, and M. Rinaudo. 2012. Chitosan-behenic acid monolayer interaction at the air-water interface: Characterization of the adsorbed polymer layers by X-ray reflectivity. Int. J. Polym. Anal. Charact. 17(1): 11–20. 8. Ramanaiah, K., A. V. Ratna Prasad, and K. H. Chandra Reddy. 2011. Thermal and mechanical properties of Sansevieria green fiber reinforcement. Int. J. Polym. Anal. Charact. 16(8): 602–608. 9. Singha, A. S., and V. K. Thakur. 2009. Fabrication and characterization of S. cilliare fiber reinforced polymer composites. Bull. Mater. Sci. 32(1): 49–58.



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