waste powder composites

Polymer Testing 24 (2005) 739–745 www.elsevier.com/locate/polytest

Material Characterisation

UV surface modification of waste tire powder: Characterization and its influence on the properties of polypropylene/waste powder composites A.M. Shanmugharaja, Jin Kuk Kimb, Sung Hun Ryua,* a

College of Environment and Applied Chemistry, Kyung Hee University, Yongin, Kyunggi-Do, South Korea b Department of Polymer Science and Engineering, Gyeongsang National University, Jinju, South Korea Received 9 March 2005; accepted 21 April 2005

Abstract Waste tire powder was subjected to ultraviolet radiation (UV) in the presence of allylamine and radiation sensitizer benzophenone. Fourier Transform Infrared spectral studies revealed the presence of allylamine amine on the surface of the rubber powder. The higher value of nitrogen to carbon X-ray counts obtained from energy dispersive X-ray analysis also demonstrates the presence of amine on the powder surface. Surface energy measurements were done by a dynamic wicking method. Improvement in tensile strength and elongation at break were observed for the PP/modified rubber powder and is attributed to the chemical interaction between the surface of the modified rubber powder and maleic anhydride grafted PP. q 2005 Elsevier Ltd. All rights reserved. Keywords: Waste tire powder; UV surface modification; Polypropylene

1. Introduction Scrap tires, being a form of post-consumer waste, have been subjected to incineration or landfill. However, these methods result in severe environmental problems such as air pollution. Reuse or recycling of these scrap tires becomes an important social subject and recycling of waste rubber powder by means of blending with polymeric material has become an important topic in recent years. The technical and commercial feasibility of using waste rubber powder as a filler have been demonstrated in many applications, such as roofing and shoe soles. It is a cost-effective way to produce a material that can be processed like plastic and also retains some of the elasticity of rubber. Many efforts have been made in recent years to increase the quality of plastic/waste rubber powder composites.

* Corresponding author. Tel.: C82 31 201 2534; fax: C82 31 201 1946. E-mail address: [email protected] (S.H. Ryu).

0142-9418/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymertesting.2005.04.006

Recently, surface-modification techniques have been adopted for recycling of scrap rubber powder [1]. McInnis et al. [2] modified the ground rubber powder by a gas–solid reaction with chlorine containing gas. The role of surface modified rubber powders in the toughening of the epoxy polymers has been studied by Bagheri et al. [3]. The influence of various irradiation techniques on the effective reuse of the waste rubber has been extensively studied by various researchers [4,5]. Ultraviolet energy (UV) has been extensively applied to modify the surface properties using monomers and photosensitizer. Lee and Ryu [6] and Yu and Ryu [7] used acrylamide and glycidyl methacrylate as a monomer to modify the surface characteristics of vulcanized styrene butadiene rubber (SBR) using UV. They found that photografting reaction with a monomer is an efficient way to modify the surface characteristics of vulcanized SBR, which is one of the major components of tires. In this paper, the waste tire powder was subjected to UV surface grafting in the presence of allylamine. The grafted surface has been characterized by Fourier Transform Infrared spectra (FT-IR), scanning electron microscopy

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(SEM), thermogravimetric analysis (TGA) and contact angle measurements to understand the surface modification due to allylamine grafting. The modified rubber powder was then incorporated in the polypropylene matrix and its role on the properties of the blend has been investigated.

Table 2 Compositions of the polypropylene/waste rubber composites Sample designation

PP

MA-PP

Unmodified rubber powder (PA0/0)

Modified rubber powder (PA1.25/30)

2. Experimental

P PPA0/0/10 PPA0/0/20 PPA0/0/30 PPA1.25/30/10 PPA1.25/30/20 PPA1.25/30/30

100 100 100 100 100 100 100

– 5 10 15 5 10 15

– 10 20 30 – – –

– – – – 10 20 30

2.1. Materials Waste rubber powder was obtained from the Dong-A Co. Allylamine and acetone was purchased from Kanto Chemical Co., Inc., Japan and Duksan Chemical Co. Ltd, Korea, respectively. Polypropylene, maleic anhydride grafted polypropylene (MA-PP) (Polybonde 3200) and benzophenone were obtained from Samsung Chemicals, Korea, Uniroyal Chemical Company, USA and Lancaster Synthesis, England, respectively.

The composition of polypropylene/waste rubber composites are shown in Table 2. 3. Characterization

2.2. UV photografting of rubber powder

3.1. Fourier transform infrared (FT-IR) spectroscopy

Allylamine solution (1.25 mol) was prepared by dissolving the allylamine in 1000 mL of acetone and 0.125 mol of benzophenone was added to the allylamine solution. Rubber powder was immersed in the allylamine solution for 3 h followed by 3 h drying at ambient temperature. The allylamine treated rubber powder was then subjected to UV radiation using a 400-W medium-pressure mercury lamp for 30 min.

About 0.01 g of unmodified or allylamine modified rubber powder was mixed with 1 g of potassium bromide (KBr) and pelletized using a hydraulic press at a pressure of 10 kPa. Samples were subjected to IR characterization in the range of 4000–400 cmK1 using a Perkin–Elmer 2000 spectrophotometer. The spectra were obtained at a resolution of 4.0 cmK1 in the transmission mode. FT-IR spectra of polypropylene-waste rubber composites were taken in the range of 4000–650 cmK1 in the attenuated total reflectance mode (FTIR-ATR) using a zinc selenide crystal.

2.3. Preparation of polypropylene/waste rubber composites A blend of PP and MA-PP was melted for 2 min at 200 8C, followed by the addition of the calculated amount of waste rubber powder in a Brabender Plasticorder at a speed of 50 rpm, and the mixing was continued for 5 min. It is then dumped and pressed at 200 8C for 2 min using a Carver press to prepare 0.15 mm thick sheet. 2.4. Sample designation Rubber powders are designated as PAb/c, where P represents the rubber powder, A represents the allylamine solution and suffixes b and c represent allylamine concentration and UV radiation time, respectively. Sample designations of rubber powders are represented in Table 1. Table 1 Sample designation of rubber powders Sample designation

Rubber powder content (g)

Allylamine content (mol)

UV radiation time (min)

PA0/0 PA1.25/30

100 100

0 1.25

0 30

0.125 mol of benzophenone is used as sensitizer for all cases.

3.2. Scanning electron microscopy/energy dispersive X-ray (SEM/EDX) analysis Scanning electron microscopy studies of unmodified and modified rubber powders were done using a Stereoscan 440 (Leica, Cambridge). Samples were coated with gold. The relative amounts of carbon and nitrogen X-ray counts were measured using the energy dispersive X-ray analyzer facility of the microscope. SEM photographs of the unmodified and modified rubber powders have been taken under a magnification of 100! and the tensile fractured samples have been taken under a magnification of 1000!. 3.3. Surface energy measurements by wicking method The surface energies of unmodified and modified rubber powders were calculated by the measurement of contact angle using a dynamic wicking method. The rubber powders (2 g) were tapped 200 times and packed in a graduated capillary tube (5 mm inner diameter, 50 mm long). The tube was placed vertically and in contact with liquid (water or ethylene glycol) in a beaker. Then liquid penetrates into the empty spaces of the powder column by capillary action. The

w gL q rL t he C

weight of penetrating liquid surface tension of the liquid used contact angle of the liquid in the carbon black powder density of the liquid equilibrium time viscosity of the liquid constant depends on the effective radius of the packed column in the capillary tube

The effective pore radius of the packed column was determined using Eq. (1) with toluene as the spreading liquid. The surface energy of the rubber powders was calculated by measuring the contact angle with water and ethylene glycol using the following equation [10] cos q Z K1 C

2ðgds gdl Þ1=2 2ðgps gpl Þ1=2 C gL gL

(2)

where gds dispersive component of the free energy of the solid surface gdl dispersive component of the free energy of the liquid surface gps polar component of the free energy of the solid surface gpl polar component of the free energy of the liquid surface gL surface tension of the liquid The values of gdl and gpl for water and ethylene glycol were taken from the literature [11]. 3.4. Mechanical properties Dumbbell tensile specimens (115!25!0.8 mm) with dimensions of 40!6!0.8 mm in the narrow region were punched out from the molded sheets. The test is carried out based on ISO 527-1 method in a universal testing machine (Dong Kyung UTM, Korea) at a crosshead speed of 50 mm/min. The average value of three tests is reported. 4. Results and discussion Fig. 1 shows the FT-IR spectra of the unmodified and allylamine modified rubber powder (PA0/0 and PA1.25/30) and the peak assignments are included in Table 1. The peak at 3650 cmK1 corresponds to the –OH stretching in the phenolic groups present in the carbon black. The peak at 3111 cmK1 is due to the –CH stretching vibration of ring

1551

1738 1695

(b) 3720

3500

1520

1600

997

(a) 3620

1405 1318 1228

(a)

680

1519

1705

1610

where

(b)

1610

(1)

1614

3306

3632

3111

w CgL cos Z t 2he

qr2L

741

(a)

3012 2876

2

Absorbance (arbitrary unit)

height of the penetrated liquid was calculated by taking the weight of the penetrated liquid at regular time intervals. The contact angle of the powder sample was calculated using the Washburn equation [8,9]

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888

(b)

3000

2000

1000 -1

Wave number (cm )

Fig. 1. FT-IR spectra of unmodified (a) and allylamine modified (b) rubber powder.

hydrogens present in the styrene group. The peak at 2876 cmK1 corresponds to –CH symmetric stretching of pCH2 groups. The presence of unsaturation sites of the isoprene units has been confirmed from the peak at 1610 cmK1, which is due to the pCaCo groups. The presence of carbon black in the rubber is confirmed from the IR peaks at 1705 and 1520 cmK1 that may be due to the pCaO stretching and pCaCo stretching present in the lactone ring of the carbon black. The peaks at 1318 and 680 cmK1 represent –C-C– stretching in –C-CH3 group and ring deformation vibration of styrene [12]. These peak assignments confirm that the rubber powder used for this study is a blend of natural rubber/styrene butadiene rubber. The FT-IR spectra of modified rubber powder in the specific regions are also included in Fig. 1. The new peak at 3306 cmK1 for the modified rubber powder (PA1.25/30) corresponds to –NH stretching and confirms the presence of the allylamine on the rubber powder. The increase of peak intensity at 1614 cmK1 (PA1.25/30) is due to the pCaCo stretching as well as in-plane deformation of –NH2 group and it also confirms the presence of allylamine on the surface of the rubber powder. The chemical interaction of the allylamine with the rubber powder also has been confirmed from the shifting of the peak from 1705 cmK1 (PA0/0) to 1695 cmK1 (PA1.25/30) that corresponds to the pCaO stretching of amide group [12]. The peak at 1551 cmK1, which corresponds to the –NH bending vibration and –CN stretching, further supports the above explanations. Based on these observations, a plausible mechanism of interaction between the allylamine and waste rubber powder is proposed in Fig. 2. Fig. 3 shows the SEM photographs of the unmodified (PA0/0) and modified rubber powder (PA1.25/30). Unmodified rubber powders show highly irregular aggregated structure with size in the range of 2–200 mm. The highly aggregated structure of unmodified rubber powders arises from the interaction of the free radical sites formed during

742

A.M. Shanmugharaj et al. / Polymer Testing 24 (2005) 739–745 CH2

+

CH2

CH2

UV/30 min

CH

Benzophenone CH

CH

CH

NH2

NH2

NH2 CH

CH2 n

CH2

O + NH2

UV/30 min

NH

CH

Benzophenone CH

CH

OH

CH2

CH2

NH

CH2

CH

n NH

CH2

Fig. 2. Proposed reaction mechanism of allyamine grafting on the rubber powder surface.

the grinding of the waste tire. However, modified rubber powder produces aggregates in the size range of 2–100 mm. The reduction in the aggregate size of the modified rubber powders is due to the presence of allylamine on the surface of the rubber particles which reduces the interaction of powder and thereby restricts the aggregation. The extent of modification has been characterized using EDX analysis of the unmodified and modified rubber powders. The nitrogen and carbon X-ray counts were detected at various depths of the rubber powder using the X-ray mapping obtained from EDX analysis. The ratio of the nitrogen to carbon X-ray counts can give information about the extent

of the modification and the results are reported in Fig. 4. The ratio of the nitrogen to carbon X-ray counts (NKa/CKa) increases up to ca. 300% (PA1.25/30) at a depth level of 20 mm. Fig. 5(a) and (b) shows the amount of penetrated water and ethylene glycol at various time intervals for the unmodified and modified rubber powder. The amount of water increases initially due to capillary action and becomes constant at a particular time for unmodified and modified rubber powder. The initial rate of water penetration is almost the same for unmodified (PA0/0) and modified rubber powder (PA1.25/30), while equilibrium weight is higher for

Fig. 3. SEM photographs of unmodified (a) and modified (b) rubber powder.

A.M. Shanmugharaj et al. / Polymer Testing 24 (2005) 739–745

743 PPA 0/0

WRA0/0 WRA1.25/0 WRA1.25/30

0.2

PPA 1.25/30

10 Tensile strength (MPa )

X-ray counts (NK /CK )

0.3

0.1

8 6 4 2

0.0 0

20

40 60 Depth ( m)

80

10 wt %

weight of water penetration (X 10-3)g

PA1.25/30 (Fig. 5a). On the contrary, ethylene glycol penetration in modified rubber powder (PA1.25/30) is less than that of unmodified rubber powder (PA0/0) (Fig. 5b). The contact angle between the solvents (water and ethylene glycol) and the rubber powder surface was calculated using equilibrium time and the Washburn equation [8,9]. The dispersive component, polar component and the total surface energy of the unmodified and modified rubber powders were determined by the Goodrich Girifalco equation [10]. On subjecting to allylamine modification, 15 12

PA 0/0 PA 1.25/30

9 6 3

0 0

10

20

30

40

50

60

0.015

0.010

0.005

0.000 10

70 wt %

the dispersive component of the rubber powders decreases from 0.74 (PA0/0) to 0.20 mJ/m2 (PA1.25/30), whereas the polar component increases from 22.9 to 27.2 mJ/m2 for the modified system. These results are attributed to the allylamine grafting on the surface and this is also confirmed by EDX and FT-IR data. Fig. 6 shows the variation of tensile strength of polypropylene loaded with unmodified waste rubber composites (PPA0/0) and allylamine modified waste rubber composites (PPA1.25/30). For PP-rubber composites, 50 wt% of commercial maleic anhydride grafted polypropylene (MA-PP) (Polybonde 3009) was added as the compatibilizer based on the amount of the rubber powder. On loading waste rubber powder, tensile strength of the composite decreases with increasing rubber powder content. It is observed that tensile strength of PPA1.25/30 is 10–20% higher than that of PPA0/0 up to 40 wt% rubber content and then it tends to show similar values at 70 wt% rubber content. Elongation at break shows similar behavior. The difference of elongation at break between two composites decreases with increasing rubber content (Fig. 7). These

15

20

Time (min) Fig. 5. Amount of penetrated water (a) and ethylene glycol (b) in packed powder as a function of time.

Elongation at break (%)

Weight of ethylene glycol penetration (g)

PA 0/0 PA 1.25/30

5

40 wt %

50

0.020

0

30 wt %

Fig. 6. Tensile strength of PP/MA-PP/rubber powder composite as a function of rubber powder content.

Time (min) (b)

20 wt %

Rubber powder loading

Fig. 4. EDX analysis of powders.

(a)

0

100

PPA 0/0 PPA 1.25/30

40 30 20 10 0 10 wt %

20 wt %

30 wt %

40 wt %

70 wt %

Rubber powder loading

Fig. 7. Elongation at break of PP/MA-PP/rubber powder composite as a function of rubber powder content.

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744

1667

1303

PPA1.25/30

1255

1712

P

1276

Intensity (arbitrary unit)

1696 1771

1707

PPA0/0

1635

PPA 0/0

1772

PPA 1.25/30

Intensity (arbitrary unit)

1851 1861

Intensity (arbitrary unit)

1329

1219

PPA1.25/30 PPA0/0

P

P 1800 1700

1860 1830

1600

1320

-1

-1

Wave number (cm )

Wave number (cm )

1260

1200 -1

Wave number (cm )

Fig. 8. FT-IR ATR spectra of PP, PPA0/0, PPA1.25/30 at specific regions.

phenomena can be explained by (1) effect of aggregated rubber and (2) the reaction between rubber surface and polypropylene. The aggregated rubber powder acts like a stress weakening point leading to the rupture under tension, which will lower the tensile stress and elongation. It is found in Fig. 3 that the size of aggregated modified powder is much less than that of the unmodified one and results in improved tensile properties. Allylamines on

PP. Along with the peak at 1851 cmK1, a new peak at 1861 cmK1 appears for PP/modified waste rubber blend (PPA1.25/30) indicating the surface interaction between the MA-PP and allylamine of the powder surface. This is further confirmed from the appearance of the new peak at 1667 cmK1 for PPA1.25/30, which represents the –CaO stretching in the amide group. This is also supported by the peak at 1276 cmK1 that is due to the –C–N stretching

O

O Processed at

O

+

H2N

CH2

the surface of modified rubber powder can react with maleic anhydride of MA-PP which is used as a reactive compatibilizer and this reaction is confirmed from the FT-IR analysis of the PP/waste rubber composites. Fig. 8 shows the FT-IR spectrum of PP/powder composites in some specific regions. For PP/waste rubber composites, the peak at 1851 cmK1, pCaO group, is due to the anhydride group present in the maleic anhydride of MA-

CH2 2000 C

2000 C

O

O HN

N

CH2

OH

O

O

between the blends. The possible reaction is as follows: The possible chemical interaction between the allylamine modified rubber powder and the maleic anhydride polypropylene (MA-PP) leads to improve compatibility and also dispersion of the waste rubber powder in the polypropylene matrix and thereby improves the tensile properties of the modified rubber composite, especially elongation at break. This is further supported by the

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745

Fig. 9. SEM photographs of tensile fractured surface of PPA0/0 (a) and PPA1.25/30 (b).

scanning electron photographs of the fractured PP/waste rubber composites. Fig. 9(a) and (b) shows the fracture surface of the 30 wt% unmodified and the allylamine modified waste rubber filled PP composites, respectively. The presence of rubber powder is observed for modified rubber composite (Fig. 9b), while it is absent for unmodified rubber composite.

5. Conclusions Photografting surface modification of rubber powder was done using UV radiation in the presence of allylamine monomer and benzophenone as the photoinitiator. The presence of allylamine has been confirmed from the increase in peak intensity at 3303 cmK1 that corresponds to NH stretching of amine. The presence of allylamine on the surface of the rubber powder has also been confirmed from EDX analysis. The reduction in the size of aggregates of modified rubber powders is attributed to the allylamine on the surface. The improved mechanical properties are obtained for PP/MA-PP/modified waste rubber composites and that is attributed to the increased compatibility through chemical reaction between the maleic anhydride grafted PP with the modified rubber powder. The chemical interaction of the allylamine of rubber powder and MA-PP is confirmed from FT-IR ATR and SEM photographs of fractured PP/rubber powder composites.

Acknowledgements The authors are thankful to the Industrial Waste Recycling R&D Center, KOREA, for providing fund to carry out research.

References [1] B.D. Bauman, High valued engineering materials from scrap rubber, Rubber World 5 (1995) 30. [2] E.L. McInnis, B.D. Bauman, A. Williams, US Patent (1996) 5 506 283. [3] R. Bagheri, M.A. Williams, R.A. Pearson, Use of surface modified recycled rubber for toughening of epoxy polymers, Polym. Eng. Sci. 37 (2) (1997) 245. [4] G. Adam, A. Sebenik, U. Osredkar, Z. Veksli, F. Ranogajec, Grafting of waste rubber, Rubber Chem. Technol. 63 (5) (1990) 660. [5] Peter Carstensen, Free radicals in diene polymers induced by ultraviolet radiation 1. An ESR study of cis-polyisoprene, Rubber Chem. Technol. 45 (4) (1972) 918. [6] K.I. Lee, S.H. Ryu, Ultraviolet Photografting reaction of acrylamide onto styrene–butadiene rubber, Elastomer 33 (4) (1998) 363. [7] J.J. Yu, S.H. Ryu, Ultraviolet-initiated photografting of glycidyl methacrylate onto styrene–butadiene rubber, J. Appl. Polym. Sci. 73 (9) (1999) 1733. [8] K. Inagaki, S. Tasaka, H. Abe, Surface modification of polyethylene powder using plasma reactor with fluidized bed, J. Appl. Polym. Sci. 46 (4) (1992) 595. [9] C.J. Vanoss, R.F. Giese, Z. Li, K. Murphy, J. Norris, M.K. Chaudhury, et al., Determination of contact angles and pore sizes of porous media by column and thin layer wicking, J. Adhesion Sci. Tech. 6 (4) (1992) 413. [10] F.M. Fowkes, in: R.L. Patrick (Ed.), Treatise on Adhesion and Adhesives, Marcel Dekker, New York, 1967. [11] L. Lapcik, L. Lichovnik, A. Machackova, B. Lapcikova, P. Tomecek, S. Fekete, et al., Wetting of Si and SiO2 thin layer, Silicon (2002) 46. [12] http://www.knowitall.com/handbook/ir/default_ir.html (Accessed on 23/09/2004).