Articulo Practica 3

fibre..........................................................1

Study on the interface modification of bagasse fibre and the mechanical properties of its composite with PVC

Yu-Tao Zheng b,c, De-Rong Cao a,b,*, Dong-Shan Wang b, Jiu-Ji Chen b a College of Chemistry, South China University of Technology, Guangzhou 510641, China b LCLC, Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou 510650, China

c Graduate School of the Chinese Academy of Sciences, Beijing 100039, China Received 15 April 2005; received in revised form 21 December 2005; accepted 28 January 2006

Tabla de contenidos. 1.Introduction..........................................................................................................................3 2. Experimental.......................................................................................................................3 2.1. Materials.......................................................................................................................3 2.2. Treatment of BF...........................................................................................................4 2.3. Preparation of the composites and samples.................................................................4 2.4. Mechanical properties of the composites.....................................................................4 3. Results and discussion.........................................................................................................4 3.1 Tensile strength..............................................................................................................5 3.2. Impact strength.............................................................................................................6 .............................................................................................................................................7 3.3. Elongation at break......................................................................................................8 3.4. Tensile modulus............................................................................................................9 3.5. Analysis of the SEM pho tographs of BF/PVC..........................................................10 4. Conclusions.......................................................................................................................12 Acknowledgement.................................................................................................................12 References.............................................................................................................................12

Tabla de figuras y tablas. Ilustración 1.............................................................................................................................6 Ilustración 2.............................................................................................................................7 Ilustración 3.............................................................................................................................8 Tabla 1.....................................................................................................................................4 Tabla 2.....................................................................................................................................5 Tabla 3.....................................................................................................................................6 Tabla 4.....................................................................................................................................6

1359-835X/$ - see front matter _ 2006 Published by Elsevier Ltd. 2 doi:10.1016/j.compositesa.2006.01.023 * Corresponding author. Address: LCLC, Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou 510650, China. Tel.: +86 20 85231666; fax: +86 20 85232903. E-mail address: [email protected] (D.-R. Cao).

1. Introduction In recent years, significant efforts have been directed to investigating the use of natural fibres as a reinforcement in thermoplastics. Natural fibres, such as wood fibre, wheat straw, jute fibre and bagasse fibre have several benefits: low cost, low density, high toughness, acceptable specific strength properties, enhanced energy recovery and biodegradability [1–3]. The use of natural fibres in plastic matrix includes many benefits, such as low volumetric cost, increase of heat deflection temperature, increase of stiffness of thermoplastics and improvement of ‘‘wood’’ surface appearance. So natural fibres reinforced plastic composites have achieved applications in decking, furniture components, door moldings, packing pallets and interior panels of automobiles [4–6]. However, there is poor interfacial adhesion between the hydrophobic matrix and the hydrophilic fibre. If no modification of fibre or compatibilization of the two materials is developed, the weak interfacial adhesion between fibre and matrix usually results in poor mechanical properties of the composites. Obviously, improvement of the compatibility between the two components is a key to success in the area. In order to introduce natural fibres profitably into hydrophobic thermoplastics, such as HDPE, PP and PVC, a pretreatment of the fibre surface or the incorporation of interface modifiers is generally required. In order to improve the compatibility of the wood fibre/polymer composites, a lot of chemicals and methods have been developed, such as the different treatments [7,8] of the polymer matrices (e.g. graft copolymerization or grafting fibre), coupling agents [9–11] (e.g. silanes and isocyanates) and interface compatibilizer [11–14] (e.g. maleic anhydride grafted polyolefin or elastomer). In the previous studies, the use of the organic carboxylic acids [15–17] (e.g. stearic acid, acetic anhydride, maleic anhydride and phthalic anhydride) have also drawn considerable attention, due to their effectiveness in improving adhesion between natural fibre and thermoplastic matrix. According to the principles of interface coupling, the hydrophilic carboxyl group of organic acid as the modifier is expected to react with the hydroxyl groups of natural fibre in the surface, and the hydrophobic group should react or have relatively high compatibility with the polymer matrix. The combined effects of these interactions will effectively improve the fibre dispersion and resultant adhesive coupling. In this work we focused on the effect of benzoic acid as the surface modifier on the mechanical properties of the natural fibres/reinforced plastic composites. The surface of BF was modified by benzoic acid, and then compounded with PVC resin to prepare the composite. The main objective of this study was to evaluate the effects of the content of BF, the content of benzoic acid and BF-treated temperature on the mechanical properties of BF/PVC composites by the orthogonal optimal method. The processing conditions was used according to the general procedure [18].

2. Experimental 2.1. Materials PVC (LS080S, K value 84), supplied by LG Chem.; Waste BF (100-mesh); Liquid tin stabilizer (SS218, Shanghai Plastic Auxiliary Co., China); Calcium stearate and household PE wax (H110, Shanghai Naduo Co., China); acrylic processing aid (ACR-401, Shanghai Plastic Auxiliary Co., China).

1359-835X/$ - see front matter _ 2006 Published by Elsevier Ltd. 3 doi:10.1016/j.compositesa.2006.01.023 * Corresponding author. Address: LCLC, Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou 510650, China. Tel.: +86 20 85231666; fax: +86 20 85232903. E-mail address: [email protected] (D.-R. Cao).

2.2. Treatment of BF BF (150-lm sieve) was treated with H2O2 solution under ultrasonic condition for 15 min and dried at 60 _C for 48 h. BF was then mixed at room temperature with the solution of benzoic acid in a small quantity of ethanol. After the solvent was evaporated, BF was dried in air circulating oven at 105 _C for 24 h. The treated-BF was added to the rolls, heated at different temperature (140 _C, 150 _C or 160 _C) and ground simultaneously for 4 min. The surface of fibre contacted and reacted with benzoic acid in situ during grinding.

Tabla 1

2.3. Preparation of the composites and samples BF and PVC were compounded in a two-roll mill for 7 min. The temperatures of the two rolls were at 150 _C and 170 _C, respectively. After the addition of the matrix, the fibre was added as soon as the polymer had reached a steady plastifying state which needed about 3 min. After mixing for 3–4 min, the resulting mixture was compressionmolded into panels to produce the specimens for mechanical property test. All of the samples were performed in a preheated press at 185–190 _C under a pressure of 10 MPa for 8 min, and followed by cooling to room temperature in another press equipped with refrigeration facilities. The dogbone-shaped specimens were made for tensile test (1.0 mm thick, 4.0 mm width). Rectangular specimens were cut from the pressed sheet (80 * 10 * 4 mm) for impact test. The untreated BF/PVC composite was prepared with BF (25%) and the same dosage in Table 1.

2.4. Mechanical properties of the composites The tensile properties of the composites were measured in an Universal Tensile Machine at a crosshead speed of 5 mm/min. Three tensile properties were tested: (i) the tensile strength; (ii) the tensile modulus; and (iii) the elongation at break. The unnotched Charpy impact strength was measured in a Charpy Impact Test Machine. All evaluation reported were the average values of at least five measurements.

3. Results and discussion A L9(33) three factor three-level orthogonal optimal method was chosen by Orthogonal Experiment Assistant 1359-835X/$ - see front matter _ 2006 Published by Elsevier Ltd. 4 doi:10.1016/j.compositesa.2006.01.023 * Corresponding author. Address: LCLC, Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou 510650, China. Tel.: +86 20 85231666; fax: +86 20 85232903. E-mail address: [email protected] (D.-R. Cao).

II 3.1 (Sharetop Software Studio). BF content (A), content of benzoic acid (B) and fibre-treated temperature (C) were the three key variables, whereas the mechanical properties were the variable responses. The analysis of the data was made to identify the key factors which affected the tensile and impact strength properties. Table 2 presents these factors with their normalized levels. Factor A is BF content, Factor B is the content of benzoic acid, and Factor C is the fibre-treatment temperature. Table 3 shows the corresponding experimental units and the results of the experimental matrix. The mechanical data generated by Orthogonal Experiment Assistant II 3.1 software were entered into the design matrix (Table 3) and a corresponding analysis was carried out. Table 4 shows

Tabla 2

Table 4 indicates that the content of BF (A) and content of benzoic acid (B) had more e ect than the fibre-treated temperature (C) on the tensile strength 123 of the rigid BF/PVC composites. Content of BF was the Level most significant factor.’ Fig. 1

3.1 Tensile strength shows the interaction graphs Fig. 1. Interaction graphs of tensile strength against three variables. (n) of tensile strength against the three variables, which illusBF content, (n) benzoic acid content, (.) treatment temperature. trates the changes of tensile strength with di erent factors. The tensile strength clearly increased as the content of BF composite (38 MPa). The maximum values (52 MPa) was and the content of the modifier increased. This phenomenon can be explained in terms of the strong interface interobtained with the maximum amount of fibres, and also actions of BF with PVC matrix. It also indica tes that the maximum amount of the modifier, which was conbenzoic acid had reacted with the hydroxyl groups of BF firmed by the entry 9 in Table 3 1359-835X/$ - see front matter _ 2006 Published by Elsevier Ltd. 5 doi:10.1016/j.compositesa.2006.01.023 * Corresponding author. Address: LCLC, Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou 510650, China. Tel.: +86 20 85231666; fax: +86 20 85232903. E-mail address: [email protected] (D.-R. Cao).

Tabla 3

Tabla 4

Ilustración 1

3.2. Impact strength 1359-835X/$ - see front matter _ 2006 Published by Elsevier Ltd. 6 doi:10.1016/j.compositesa.2006.01.023 * Corresponding author. Address: LCLC, Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou 510650, China. Tel.: +86 20 85231666; fax: +86 20 85232903. E-mail address: [email protected] (D.-R. Cao).

of BF in PVC matrix. The improvement of the interfacial adhesion made the fibre act as an agent of reinforcement The e ects of the three variables on the unnotched in PVC matrix. So the addition of benzoic acid brought Charpy impact property are shown in Table 4 and Fig. 2 . about an increase in tensile strength instead of decrease From Table 4 we can see that the content of BF was the comparing to the tensile strength of untreated BF/PVC Table 3

Ilustración 2

1359-835X/$ - see front matter _ 2006 Published by Elsevier Ltd. 7 doi:10.1016/j.compositesa.2006.01.023 * Corresponding author. Address: LCLC, Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou 510650, China. Tel.: +86 20 85231666; fax: +86 20 85232903. E-mail address: [email protected] (D.-R. Cao).

Ilustración 3

Results of the orthogonal optimal method 2 Composite Factors Tensile strength (MPa) Impact strength (kJ/m ) Elongation at break (%) Tensile modulus (MPa) ABC Interaction graphs of tensile modulus against three variables. (j) Level BF content, (n) benzoic acid content, (.) treatment temperature. Fig. 2. Interaction graphs of unnotched Charpy impact strength against three variables. (j) BF content, (n) benzoic acid content, (.) treatment temperature. Figs. 1 and 2 . Thus, better result (13 kJ/m ) was obtained 2 with the minimum content of fibre, as shown by entry 2 in Table 3

3.3. Elongation at break 7.5 The e ect of three variables on the elongation at break was shown in Table 4 and 1359-835X/$ - see front matter _ 2006 Published by Elsevier Ltd. 8 doi:10.1016/j.compositesa.2006.01.023 * Corresponding author. Address: LCLC, Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou 510650, China. Tel.: +86 20 85231666; fax: +86 20 85232903. E-mail address: [email protected] (D.-R. Cao).

Fig. 3 . Table 4 indicates that 7.0 the content of BF was the main factor a ecting the elongation at break. Fig. 4 shows that elongation at break 6.5 decreased, as expected, as the content of fibre increased. The decrease of elongation at break might be due to the higher brittleness introduced by blending BF with the 6.0 PVC matrix. As in the case of the benzoic acid treatment, it did enhance the elongation at break (5.8%, comparing 5.5 to the elongation at break (3.5%) of untreated BF/PVC composite), as expected, though the change was small. 5.0 The fibre-treatment temperature had a less significant 123 e ect. Level Fig. 3. Interaction graphs of elongation at break against three variables.

3.4. Tensile modulus (n) BF content, (n) benzoic acid content, (.) treatment temperature. The analysis of the e ect of the three factors on tensile main factor a ecting the impact strength. Fig. 2 shows a modulus for BF/PVC composites is shown in Table 4 linear decay on impact strength of the composites as the and Fig. 4 . The treatment of benzoic acid improved the content of BF increased. BF in the PVC matrix restricts modulus of the composite when it increased up to 5% molecular motion, imposing more resistance to deformaand then decreased. The content of BF had a strong position that could absorb impact energy, which explains the tive e ect on the tensile modulus. When there was a good 1359-835X/$ - see front matter _ 2006 Published by Elsevier Ltd. 9 doi:10.1016/j.compositesa.2006.01.023 * Corresponding author. Address: LCLC, Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou 510650, China. Tel.: +86 20 85231666; fax: +86 20 85232903. E-mail address: [email protected] (D.-R. Cao).

decrease of impact strength of the composites as the condispersion of BF in PVC matrix the tensile strength was tent of BF increased. Benzoic acid did not e ect the impact expected to increase with the addition of fibre. This was strength much as shown in Fig. 2 . For example, the impact reasonable because it demands a higher stress to su er 2 strength changed between 8.3 and 9.2 kJ/m comparing to some deformation as the fibre plays a reinforcing role. It the impact strength of untreated BF/PVC composite could be seen that as the content of BF increased the mod2 (7.5 kJ/m ) when the content of benzoic acid changed ulus increased, especially when 35% of BF was used. between 3% and 10%. The tensile strength and impact According to the analysis above, the maximum values of strength increased as fibre-treatment temperature rose modulus were obtained with the maximum content of fibre firstly (lower than 150 °C), and then decreased as temperaand lowest fibre-treatment temperature (see entry 8 in ture continued to rise (higher than 150 °C) as shown in Table 3 ).

3.5. Analysis of the SEM pho tographs of BF/PVC pellets. The samples were prepared as follows: (a) untreated composites BF (BF1); (b) BF with benzoic acid (5%) (BF2); (c) BF with benzoic acid (5%) was ground at 160 °C for 4 min The SEM micrographs of a fractured surface of the trea1359-835X/$ - see front matter _ 2006 Published by Elsevier Ltd. 10 doi:10.1016/j.compositesa.2006.01.023 * Corresponding author. Address: LCLC, Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou 510650, China. Tel.: +86 20 85231666; fax: +86 20 85232903. E-mail address: [email protected] (D.-R. Cao).

(BF3); (d) BF with benzoic acid (5%) was ground at ted BF/PVC composites and the untreated BF/PVC com150 °C for 4 min (BF4); (e) BF with benzoic acid (5%) posite are shown in Fig. 5 . The untreated BF was pulled was ground at 140 °C for 4 min (BF5). Fig. 6 shows their out of the PVC matrix with smooth and clean surfaces IR spectra. The characteristics absorption band of carbecause of the poor interfacial adhesion as shown in bonyl group of benzoic acid at 1714 cm (BF2), and the À1 Fig. 5 c. However, the treated BF with benzoic acid was peak decreased in intensity when it was ground at 140 °C pulled out of the PVC matrix with little rough surfaces for 4 min (BF5) due to the partly esterification of benzoic because the interfacial adhesion was better, as shown in acid. The absorption band of carbonyl group of benzoic Fig. 5 d. There were many empty spaces due to the formaacid at 1714 cm disappeared when it was ground at À1 tion of aggrega tes of fibers as shown in Fig. 5 a. But these 160 °C for 4 min (BF3). A new band appeared at empty spaces disappeared mostly in the treated BF/PVC 1735 cm which belongs to the ester carbonyl stretching. À1 composites as shown in Fig. 5 b. It is evident that treated It illustrated that esterification between benzoic acid and BF is more compatible with PVC rather than untreated bagasse fiber occurred in situ during grinding. BF, which can be explained that the hydrophilic carboxyl groups of benzoic acid react with the hydroxyl groups of 1359-835X/$ - see front matter _ 2006 Published by Elsevier Ltd. 11 doi:10.1016/j.compositesa.2006.01.023 * Corresponding author. Address: LCLC, Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou 510650, China. Tel.: +86 20 85231666; fax: +86 20 85232903. E-mail address: [email protected] (D.-R. Cao).

4. Conclusions natural fibre in the surfa ce, and the hydrophobic group has relatively high compatibility with the polymer matrix. The e ect of the content of the modifier (3, 5 or 10 wt% by fibre), the content of the composition (15, 25 or 3.6. Fourier transform infrared spectroscopy (FTIR) 35 wt%), and fibre-treatment temperature (140, 150 or 160 °C) were studied on the mechanical properties of BF/ The BF treated and untreated with benzoic acid were PVC composites. The following conclusions could be analyzed by FTIR (Analect, model RFX-65 A) with KBr drawn from the experimental results: Benzoic acid was an e ective adhesion promoter for BF/PVC composites. The treatment of BF with benzoic acid improved significantly dispersion of BF in PVC matrix, which could be supported by SEM micrographs of impact fractured BF/PVC composites and the fact that the addition of benzoic acid BF1 (10%) brought about an increase in tensile strength (52 MPa) of the BF/PVC composite comparing to the tenBF3 sile strength (38 MPa) of untreated BF/PVC composite. BF5

Acknowledgement BF2 Funding for this project was provided by the Chinese Academy of Sciences (KJCXZ-SW-04). BF4

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1359-835X/$ - see front matter _ 2006 Published by Elsevier Ltd. 14 doi:10.1016/j.compositesa.2006.01.023 * Corresponding author. Address: LCLC, Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou 510650, China. Tel.: +86 20 85231666; fax: +86 20 85232903. E-mail address: [email protected] (D.-R. Cao).