Recycled Acrylonitrile Butadiene(NBRr)/Rice Husk ...

LPTE #698685, VOL 51, ISS 12

Effects of Acetic Anhydride on the Properties of Polypropylene(PP)/Recycled Acrylonitrile Butadiene(NBRr)/Rice Husk Powder(RHP) Composites Santiagoo Ragunathan, H. Ismail, and K. Hussin QUERY SHEET This page lists questions we have about your paper. The numbers displayed at left can be found in the text of the paper for reference. In addition, please review your paper as a whole for correctness. Q1: Q2: Q3: Q4: Q5: Q6: Q7: Q8:

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Polymer-Plastics Technology and Engineering, 51: 1–8, 2012 Copyright # Taylor & Francis Group, LLC ISSN: 0360-2559 print=1525-6111 online DOI: 10.1080/03602559.2012.698685

Effects of Acetic Anhydride on the Properties of Polypropylene(PP)/Recycled Acrylonitrile Butadiene(NBRr)/Rice Husk Powder(RHP) Composites Santiagoo Ragunathan1, H. Ismail2, and K. Hussin2

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School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, Nibong Tebal, Penang, Malaysia 2 School of Environmental Engineering, Kompleks Pengajian Jejawi,Universiti Malaysia Perlis, Arau, Perlis, Malaysia

Considerable amount of studies have been carried out on utilisations natural fillers such as sago, sisal, short silk fibre, oil palm empty fruit bunch, rice husk ash, jute fibre, rubber wood powder, jute, hemp, sisal, cotton stalk, kenaf, sugarcane banana fibers and other cellulosic fibres as reinforcement materials in various waste polymeric materials[3,4]. Consequently, it has not been surprising that the use of lignocellulosic materials in the production of composites has gained significant importance in various manufacturing fields and industry[4–7]. The main disadvantage encountered during the incorporation of natural lignocellulosic materials into polymers is the lack of good interfacial adhesion between the two components, which results in poor properties of the final material[8]. The polar hydroxyl groups on the surface of the lignocellulosic materials have difficulty in forming a wellbonded interface with a non-polar matrix, as the hydrogen bonds tend to prevent the wetting of the filler surfaces. Furthermore, the incorporation of lignocellulosic materials in a synthetic polymer is often associated with agglomerationas a result of insufficient dispersion, caused by the tendency of the fillers to also form hydrogen bonds with each other. This incompatibility leads to poor mechanical properties and high water absorption, especially when the matrix is hydrophilic. Thus, in order to develop composites with good properties, it is necessary to improve the interface between the matrix and the lignocellulosic material. There are various methods for promoting interfacial adhesion in systems where lignocellulosic[9–14], silane treatment[15,16], graft co-polymerization[17], use of compatibilizers[18], plasma treatment[19], and treatment with other chemicals[20]. These methods are usually based on the use of reagents, which contain functional groups that are capable of bonding to the hydroxyl groups of the lignocellulosic material, while maintaining good compatibility with the matrix.

PP/NBRr/RHP composites were prepared by incorporation of rice husk powder at different loadings into PP/NBRr matrix with an internal mixer at 180 C for 9 min and 50 rpm rotor speed. The effects of rice husk powder filler loading and acetic anhydride treatment on properties of PP/NBRr/RHP composites were investigated for processing torque, mechanical properties, water absorption, swelling behavior, FTIR and SEM. Acetic anhydride-treated RHP caused a significant increase in mechanical properties, stabilization torque, water and oil resistance of the PP/NBRr/RHP composites. Results from FTIR and SEM observations indicate that better adhesion was observed for all acetic anhydride-treated composites. Keywords Acetic anhydride; Morphology; Polypropylene; Recycled acrylonitrile butadiene rubber; Rice husk powder; Tensile properties

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INTRODUCTION In recent years, the incorporation of lignocellulosic materials as reinforcing agents or as fillers in polymer composites has received an increased attention. The addition of fillers has a high impact upon economics for thermoplastics, while a general improvement in certain properties is also achieved. Lignocellulosic materials exhibit a number of attractive features including low density, low requirements on processing equipment, less abrasion during processing, abundance and certainly biodegradability[1,2]. The main advantage of lignocellulosic materials upon mineral fillers is their environmental friendliness. In general, polymer waste is disposed in large landfills causing serious problems on the environment, while biodegradable materials are envisaged to be an excellent alternative to tackle this problem, by reducing the waste volume. Address correspondence to H. Ismail, School of Environmental Engineering, Kompleks Pengajian Jejawi 3, Universiti Malaysia Perlis, 02600 Arau, Perlis, Malaysia. E-mail: hanafi@eng.usm.my

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Interfacial compatibilization improves the stress transfer between the two components and leads to the improvement of mechanical and physical properties of the produced 80 composites. Esterification by means of acetylation is the chemical modification procedure, which has been studied the most[9–14]. However, so far no work has been reported on acetylation of RHP using acetic anhydride chemical treatment for the purpose manufacturing PP=NBRr= 85 RHP composites. The aim of the present work is to evaluate the effect of acetic anhydride treatment on rice husk powder as filler in polymer waste primarily on recycled acrylonitrile butadiene rubber and polypropylene. Processing stabilization 90 torque, mechanical properties, water absorption, swelling behavior, FTIR and morphological studies of PP=NBRr= RHP composites were also investigated. EXPERIMENTAL Materials The materials used for the preparation of PP=NBRr= 95 RHP composites are shown in Table 1. The rice husk powQ2 der were ground in a table type pulverizing machine (Rong Tsong Precision Technology Co. Product Id: RT-34) with speed of 2850 rpm, sieved at 300–500 mm in particle size 100 and dried at 110 C for 24 h in a vacuum oven to produce rice husk powder of homogeneous fractions. Acetic Anhydride Treatment The fibers were dipped in glacial acetic acid for 30 min. The acid was drained, and the fibers were dipped in 50% 105 acetic anhydride solution and stirred for 1 h, with filler to solution ratio at 1:25. A few drops of concentrated sulfuric acid were also added as catalyze. The fibers are finally washed in distilled water for few times and then dried in the vacuum oven at 80 C for 24 h. 110

Processing/Sample Preparation Polypropylene (PP) was mixed with recycled acrylonitrile butadiene rubber (NBRr) and rice husk powder

(RHP) at various loading (0, 10, 15, 20, 30) phr. Rice husk powder was dried at 110 C for 24 h in a vacuum oven prior to mixing. A constant PP and NBRr was used at 70 phr and 30 phr, respectively. Table 2 shows the formulation of PP= NBRr=RHP composites. The composites were prepared by melt mixing using a Haake Rheomix Polydrive R 600=610 Mixer at 180 C with the rotor speed of 50 rpm. PP was charged into the mixing chamber and melted for 4 min before NBRr was added. At 6 min the RHP was added and the mixing was continued for another 3 min for a total mixing time of 9 min. PP granules and NBRr powder were dried for 24 h at 80 C under vacuum prior to melt mixing in an internal mixer. The compounded samples were compression-moulded in a Go-Tech compression moulding machine. A seven (7) min of preheating at 180 C, 2 min of compression at 1000 psi and another 2 min of cooling for sample fabrication. Moulded samples were cut into dumbbell with a Wallace die cutter S6=1=6.A according to ASTM D638. A period of 7-min preheating occurred at 180C, followed by 2 min of compression at 1000 psi and another 2 min of cooling for sample fabrication. Moulded samples were cut into dumbbell shapes with a Wallace die cutter S6=1=6.A, according to ASTM D638.

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Absorption Studies 145 The specimens were dried for 4 h in a vacuum oven at 100 C until a constant weight was attained prior to immersion in water in thermostated vessels at ambient temperature. Weight gains, after exposure, were recorded by removal of the specimen from the environment and by 150

Description

Polypropylene(PP)

Homopolymer 6331: Code 3cm=g 0.9: Density

Recycled Acrylonitrile Butadiene Rubber (NBRr) Rice Husk Powder (RHP)

Content: 33% of Acrylonitrile Density: 1.0153cm=g

Treatment agent

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Tensile Test Tensile tests were carried out according to ASTM D 638 using an Instron machine model 3366. The specimens with 1 mm thickness were cut from the molded sheets using a 140 Wallace die cutter S.A.6=1=6. Tensile modulus, tensile strength and elongation at break were measured at a cross-head speed of 5 mm=min and tests were performed at room temperature (25 3 C).

TABLE 1 Materials specification and description Material

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Cellulose 35% Hemicellulose 25% Lignin 20% Ash 17% Density :1.4702cm=g m 500-300: Size Acetic anhydride

Source Titan Pro Polymers (M) Sdn. Bhd. Johor, Malaysia Juara One Resources Sdn. Bhd. Penang, Malaysia Thye Heng Chan Enterprise Sdn. Bhd. Alfa Aesar (M) Sdn Bhd

EFFECTS OF ACETIC ANHYDRIDE ON PP=NBRr=RHP

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TABLE 2 Formulation for PP=NBRr=RHP composites PP=NBRr =RHP composites (phr) Composite Materials

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S9

PP NBRr Pure RHP Acetic anhydride-treated RHP

70 30 – –

70 30 5 –

70 30 10 –

70 30 15 –

70 30 30 –

70 30 – 5

70 30 – 10

70 30 – 15

70 30 – 30

weighing them periodically on a Stanton balance with a precision of 1 mg. The moisture content at any time t, Mt as a result of moisture absorption, was calculated by using Equation (1).

Mt ð % Þ ¼

W o Wd 100% Wo

ð1Þ

where by, Wd and W0 were, weight of dry material (i.e., the initial weight of the material prior to exposure to the environment) and weight of moist material. The percentage equilibrium moisture absorption, Mm, was calculated as an 160 average value of several consecutive measurements that showed no appreciable additional absorption. Swelling ASTM Oil No. 3 Determination of the swelling percentage in ASTM oil 165 No. 3 was carried out in accordance with ASTM D 471 test method. The test pieces of dimension 30 mm 5 mm 1 mm were weighed and immersed in ASTM oil No.3 at room temperature for 70 hours. As for toluene the test, samples were immersed for 48 hours at room temperature. 170 The swelling percentage of the samples for both ASTM oil No. 3 and toluene was calculated using Equation. (2).

Swelling ð%Þ ¼

Fractography Studies The failure mode of the fracture tensile specimens was examined using Field Emmision Scanning Electron Microscope FESEM Model ZEISS 36VP-24-54SUPRA. 185 SEM micrographs were taken at various magnifications for fracture and other observations. Prior to the SEM observations the fractured ends of the specimens were mounted on aluminium stubs and were sputter coated with a thin layer of gold to avoid electrical charging dur- 190 ing examinations. RESULTS AND DISCUSSION Processing Properties Figure 1 shows plot of stabilization torque at end of mixing 9 min for PP=NBRr=RHP composites. The stabili- 195 zation torque can be a direct measurement for evaluating the viscosity and processability of molten polymer composite systems. An increase in the torque value means an increase in the viscosity of the molten polymer composite systems, whereas processability is decreased. It can be seen 200 that stabilization torque increases gradually with the increase in filler loading. This is due to the presence of more rigid filler and interfacial interactions between filler and matrix, therefore reducing the polymer chains’ mobility[22,23]. 205

swollen weight original weight 100 original weight ð2Þ

Fourier Transform Infrared Spectroscopy Analysis FTIR spectroscopic analysis of the composites was carried out using Perkin Elmer Spectrometer 2000 FTIR. The ATR (Attenuated Total Reflectance) is applied. Scanned range was 4004000 cm1. Both untreated and acetic anhydride-treated rice husk powder filler were character180 ized by FTIR to confirm the chemical reaction between the acetic anhydride and the rice husk powder filler. 175

FIG. 1. Stabilization torque at end of mixing 9 min for PP=NBRr=RHP composites.

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At a similar filler loading, the composites with acetic anhydride-treated filler shows higher stabilization torque as compared to the composites with untreated filler which indicates more force is needed for each compounding to 210 be done. This is due to esterification process enhances interactions between filler and matrix and resulted in the increases of viscosity of the molten materials for acetic anhydride-treated RHP. We have reported a similar observation in our previous study on the PP=NBRr=RHP 215 with PPMAH(Polypropylene Maleic Anyhdride) compatibilization[24], whereby higher stabilization torque resulted for composites with good interfacial interactions between RHP and PP=NBRr matrixs. Tensile Properties Figure 2 shows plot of tensile strength versus filler loading of PP=NBRr=RHP composites. For composites with untreated filler, tensile strength decreases with the increasing of filler loading. The reduction of this property may be because of the weak interaction between filler and matrix as 225 shown in SEM micrographs later in Figure 8. However, for composites with acetic anhydride-treated filler shows higher values of tensile strength at similar filler loading. This was due to the incorporation of non-reinforcing material into the composites and the inability of RHP to 230 support stress transfer from the PP=NBRr matrices. The tensile properties of these composites depend on how RHP is well dispersed in the PP=NBRr matrices. The tensile strengths at 5 phr and 10 phr RHP remain almost the same as the tensile strength for the PP=NBRr 235 blends. However, acetic anhydride-treated PP=NBRr= RHP composites showed significant increase in tensile strength. The increases in tensile strength for 5 phr and 10 phr of RHP loading as a result of modification with acetic anhydride were observed to be about 5.5 MPa and 220

FIG. 2. Tensile strength versus filler loading of PP=NBRr=RHP composites.

4.1 Mpa, respectively, compared to the PP=NBR=RHP composites. The ester bond between the hydroxyl group from RHP and acetic anhydride may enhance the filler matrix interaction leading to good adhesion. As mechanical properties of the composite highly depend on filler dispersion and adhesion of filler in the disperse matrix phase as shown in the morphological studies latter. This again due to good stress transfer between the PP=NBRr matrix and acetic anhydride-treated RHP. The evidence of better interactions between matrix and filler can be seen from SEM micrographs shown in Figure 9. Similar findings were reported by Arbelaiz et al.[31], whereby improvement of stress transfer from the PP matrix to the flax fibre bundle for maleic anhydride treated composites. Jebrane et al.[32] in their research indicated that the acetylation of lignocelulisic material with acetic anhydride very found to be more readily to interact with lignin. Hence found to make good interaction with lignocellulosic materials beside vinyl acetate. Further addition of RHP filler exhibited a decreasing trend in the tensile strength for both series acetic anhydride-modified and -unmodified specimen. This observation was attributed to particle agglomeration due to uneven distribution of fillers at high filler loading. Besides poor ability of RHP fillers to absorb stress and distributing it the PP=NBRr matrix increasing the stress-concentration points in the composites, which caused the tensile strength failure[21,26]. Figure 3 shows the elongation at break verses RHP filler loadings of PP=NBRr=RHP composites. Addition of RHP to the PP=NBRr=RHP composites exhibited a significant decrease in elongation of both acetic anhydride-modified composites and -unmodified specimens. Elongation at break shows a decrease of 35% upon the addition of 30 phr of RHP. The decrease in Eb caused by RHP indicates the lignocellulosic fiber RHP may act as a hindrance

FIG. 3. Elongation at break versus fiber loading of PP=NBRr=RHP composites.

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for molecular mobility of the PP=NBRr matrixes. The brittle behaviour of RHP is also supported by the Young Modules results, which is discussed later. However the acetic anhydride-modified composites have indicated a 15% increase in Eb at 5 phr of RHP. This is resulted from formation of the ester bond (CO–O) and evidenced by corresponding carbonyl groups (C¼O) related to the ester functions for acetic anhydride. Good matrix and filler interactions and resulted in higher elongation at break. The presence of acetic anhydride act a linker to the RHP filler resulting in greater support and increase in stiffness. However at higher RHP content the brittle nature of RHP was exhibited with very small increment of 2% in Eb at 30 phr of RHP. This due to RHP filler dominant state in the PP=NBRr=RHP system. Figure 4 shows plot of tensile modulus versus filler loading of PP=NBRr=RHP composites. Tensile modulus increases with the increase of filler loading. This observation indicates that the incorporation of RHP filler into the matrix improves the stiffness of the composites. The addition of RHP filler into the PP=NBRr matrix reduces the chains’ mobility, consequently producing more rigid composites. At a similar filler loading, tensile modulus for composites with acetic anhydride-treated filler exhibited higher tensile modulus compared to composites with untreated filler. According to Bledzki et al.[26] an increase in tensile modulus was reported in treated natural vegetable fiber due to better interactions between matrix and filler. Olsen et al.[30] also indicated that formation of covalent bonds between OH groups of cellulose and anhydride group may be long enough to permit entanglements with the PP in the interphase. This again supported results for higher tensile modulus of PP=NBRr=RHP composited in acetic anhydride-treated RHP fillers.

FIG. 4. Tensile modulus versus filler loading of PP=NBRr=RHP composites.

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FIG. 5. Swelling percentage of PP=NBRr=RHP composites with and without acetic anhydride treatment.

Swelling Test Figure 5 shows a plot of swelling percentage of PP= NBRr=RHP composites with and without acetic anhydride treatment in ASTM oil No. 3 for 70 h. It was found that swelling percentage increased with increasing of RHP content in both acetic anhydride-treated and untreated PP= NBRr=RHP composites. This was due to the properties of natural fiber RHP which absorb oil on its surface[3,4,22,23]. However, for the similar composites composition, the treated composites exhibited lower swelling percentage due to better interaction of RHP particles in the continuous PP=NBRr matrix, which limit the penetration of oil into the treated composites matrix. This might due to the ability of acetic anhydride to form better interaction and a protective layer at the interfacial zone to consequently prevent the direct diffusion of water and oil molecules into the composites. We have reported similar observation on polypropylene-maleic-anhydride (PPMAH) compatibilization to PP=NBRr=RHP composites in our previous work[24].

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FTIR Analysis and Reaction Scheme 330 Figure 6 shows FTIR spectra comparison of untreated and acetic anhydride-treated filler in the region of 400–4000 cm1. The spectra were baseline corrected and normalized at 1160 cm_1, the major absorbance peak reflecting the C-C ring of the carbohydrate backbone of 335 cellulose. Rice husk is mostly composed of cellulose, hemicellulose, lignins and some pectins. The C–OH of the cellulose backbone (C–O secondary and C–O primary alcohols) corresponded to the 1056 cm1 and 1030 cm1 peaks, respectively. We also observed an increase of the band at 340 1260 cm1 corresponding to the ester (CO–O) group formation and a vibration band at 1740 cm1 corresponding to the carbonyl groups (C¼O) related to the ester functions for acetic anhydride-treated RHP. Silmilar findings were

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FIG. 6. FTIR spectra comparison anhydride-treated RHP filler.

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of

untreated

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acetic

observed by Bessadok et al. on Alfa fibers, modified by chemical treatments acetic anhydride[25].

Water Absorption Properties Figure 7 shows plot of water absorption of PP=NBRr= RHP composites with and without acetic anhydride treatment. Each data point represents the average of five specimens. Water uptake increased with immersion time and 355 increasing filler loading as also reported by other researchers[26,27]. However, in our previous research PP=NBRr= [28] Q8 RHP were found to exhibit 2 stage absorption behavior . The RHP in continues matrix absorb water much easier compared to the RHP particles encapsulated by NBRr. It 360 can be seen in Figure 7 that filler content had a significant effect on water absorption properties of the composites. 350

FIG. 7. Water absorption of PP=NBRr=RHP composites with and without Acetic anhydride treatment.

It indicates that, the higher the filler content, the higher the percentage of equilibrium water absorption[27]. This is due to the fact that, the increases of filler content in composite will increase the number of free OH groups of ligno- 365 cellulosic fiber. Free OH groups come in contact with water through hydrogen bonding which results in water uptake and weight gain in the composites. At a similar filler loading, it can be seen that the composites with acetic anhydridetreated filler shows a lower water uptake compared to the 370 composites with untreated filler. This result provides a clear indication that the RHP treatment with acetic anhydride enhances the filler-matrix interactions at the interface, thus decreasing the amount of equilibrium water uptake by the composites. Ismail et al.[23] reported similar findings, 375 whereby lower absorption in PP=NR=RHP is attributed to the ability of the chemical to form a protective layer at the interfacial zone to consequently prevent the direct diffusion of water molecules into silane-treated composites. SEM Micrographs Figure 8(a–b) shows SEM micrographs of fractured surface of PP=NBRr=RHP composites with 15 and 30 phr RHP loading, respectively. The SEM micrographs shows that poor adhesion of RHP to the PP=NBRr matrix is the main factor for the reduction of the tensile strength with an increasing of filler loading in the composites. The incorporation of RHP filler into the PP=NBRr matrix increases the rigidity of the material thus reduces the ductility of the composites. Figure 8(a) shows some noticeable gaps between the filler and matrix, which is the evidence of poor adhesion between the filler and matrix. Figure 8(b) shows that the RHP fillers were pulled out from the matrix, which are marked with the white circles, exhibited more detachment of RHP filler from the matrix. This is due to the poor dispersion and poor wettability of the filler by the PP=NBRr matrix. Figures 9(a–b) show SEM micrographs of fractured surface of PP=NBRr=RHP composites with acetic anhydride filler at 15 phr and 30 phr filler loadings. It can be seen in Figures 9(a–b) with 15 and 30 phr RHP loading, respectively, good filler and matrix and attachment and dispersion. The adhesion between filler and matrix were

FIG. 8. (a) SEM micrograps of PP=NBRr=RHP composite without acetic anhydride for 70=30=15 composition. (b). SEM micrograps of PP=NBRr= RHP composite without acetic anhydride for 70=30=30 composition.

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FIG. 9. (a) SEM micrograps of PP=NBRr=RHP composite with acetic anhydride treatment for 70=30=15 composition. (b). SEM micrograps of PP=NBRr=RHP composite with acetic anhydride treatment for 70=30= 30 composition.

enhanced with the usage of acetic anhydride. This explains why higher mechanical properties for PP=NBRr=RHP were exhibited for acetic anhydride-treated RHP 405 composites. These findings are supported by the ductile morphology of the treated composites (Fig. 9b). CONCLUSIONS The following conclusions can be made, based on the results presented in this work. 410

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1. The processing torque and tensile modulus and swelling in oil increases with increasing RHP filler loading in untreated composites. It is attributed to the brittle nature of RHP. 2. Acetic anhydride-treated composites exhibits higher processing stabilization torque, tensile modulus and elongation at break compared to untreated composites due to strong interfacial bonding between RHP filler and PP=NBRr matrices. 3. The acetic anhydride treatment improved the mechanical properties of PP=NBRr=RHP composites. This is due to the good adhesion between RHP filler and the PP=NBRr matrices, as shown in the SEM micrograps. 4. Acetic anhydride treatment is effective in reducing water and oil absorption in PP=NBRr=RHP=composites. This may due to the ability of acetic anhydride to form better interactions and a protective layer at the interfacial zone to consequently prevent the direct diffusion of water and oil molecules into the composites. REFERENCES

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