Morphology and Properties of Thermoplastic Sugar Beet Pulp and

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Morphology and Properties of Thermoplastic Sugar Beet Pulp and Poly(butylene adipate-co-terepthalate) Blends Bo Liu, Sachin Bhaladhare, Peng Zhan, Long Jiang, and Jinwen Zhang* Materials Science and Engineering Program & Composite Materials and Engineering Center, Washington State University, Pullman, Washington 99164, United States

Linshu Liu and Arland T. Hotchkiss Eastern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, 600 East Mermaid Lane, Wyndmoor, Pennsylvania 19038, United States ABSTRACT: In this work, sugar beet pulp (SBP), the residue remaining after sugar extraction, was first turned into a thermoplasticlike compound by extrusion in the presence of water and glycerol. The resulting thermoplastic SBP (TSBP) was then blended with poly(butylene adipate-co-terepthalate) (PBAT) and extruded into sheets in a single process. The effects of polymeric diphenyl methane diisocyanate (pMDI) as compatibilizer and TSBP content on rheological properties, phase morphology, mechanical properties, and water absorption of the extruded sheets were studied. In comparison, dried SBP powder was also blended with PBAT by extrusion. It was found that when SBP was used as a plastic in compounding, it yielded blends with much finer dispersion of the SBP phase than when SBP was used as a filler in compounding. The dispersion of SBP in the blends was greatly improved with the addition of pMDI. The PBAT/SBP blends with fine phase morphology showed enhanced mechanical properties and moisture resistance.

’ INTRODUCTION Sugar beet pulp (SBP) is the residue of sugar extraction from beets. It contains ca. 70
80% polysaccharides (cellulose, hemicellulose, pectin) as well as lignin, protein, and residual sugar. The United States yields 2 million tons of SBP annually from sugar extraction.1 Usually SBP is either used as animal feed or disposed as solid waste. In recent years, SBP has received increasing interest for value-added applications. Its cellulose component was carboxymethylated and the modified cellulose was attempted for use in adhesive and paper products;2,3 pectin4
6 and alkaline soluble polysaccharides were extracted from SBP and studied for food applications;7 and cellulose microfibrils separated from SBP were used as reinforcing fillers for polymer composites.8
10 On the other hand, direct use of SBP for plastics has also been studied. Because SBP contains a significant amount of pectin which is water-soluble, SBP can be turned into thermoplastic-like materials (TSBP) using a method similar to extrusion cooking. In the preparation of thermoplastic SBP by twin-screw extrusion, Rouilly et al. demonstrated that water content in SBP and specific mechanical energy input (regulated by varying kneading disks and reversed elements of screw) had great influences on destruction of cell wall structure and pectin release.11 A mixture of the above extruded SBP, glycerol, and cross-linker was then extruded using a single-screw extruder to produce films.12 In our recent study,13 we accomplished the destruction of the cell walls, gelation of pectin, and plasticization of the SBP plastics in one step using an ordinary twin-screw compounding extruder. The resulting compounds exhibited that the fibrous cellulose uniformly dispersed and formed a network structure in the matrix which comprised pectin, protein, and/or r 2011 American Chemical Society

hemicellulose. Our results showed that water played a critical role for preparation of processing. However, the neat TSBP thus prepared were of low strength due to the large amount of water in the samples and the plastics made of neat TSBP showed poor water resistance. Our study showed that the tensile strength was 10 MPa for the sample equilibrated at 0% RH but decreased to 0.7 MPa for the sample equilibrated at 93% RH. Blending with hydrophobic thermoplastic polymers is the most commonly used method to improve the water resistance of natural polymers. Blending of SBP and poly(lactid acid) (PLA) has been reported in several studies.14
17 We previously demonstrated that use of an isocyanate type coupling agent in the PLA/SBP composites greatly improved wetting and penetration of SBP by PLA and hence enhanced the strength of the PLA/SBP (70/30 w/w) composites to the level comparable to that of neat PLA.14 However, such PLA/SBP composites were very rigid and exhibited low impact toughness. Poly(butylene adipate-co-terepthalate) (PBAT) is a biodegradable aliphatic-aromatic copolyester. The high flexibility and ductility of PBAT make it suitable for food packaging and agriculture films. However, the cost of PBAT is relatively high and its stiffness is low, limiting its use in broad applications. Blending PBAT with the inexpensive SBP is a means to balance the cost and the properties of PBAT without altering the integral biodegradability. In the above-mentioned SBP composites, SBP was only used as filler. We have demonstrated Received: August 11, 2011 Accepted: November 8, 2011 Revised: November 5, 2011 Published: November 08, 2011 13859

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that for a melt processable natural polymer, e.g., soy protein (SP), the morphology and properties of its blends with other thermoplastic polymers strongly depends on its role in the mixing process. When SP behaved like a plastic component rather than a filler in mixing, morphology of the resulting blends was greatly regulated and so were the mechanical properties.18
25 Compared to mixing SP as a filler during compounding, blending SP as a plastic component with both PLA and PBAT respectively resulted in blends showing significantly higher tensile strength and modulus. Because SBP is also melt-processable, it is interesting to know if the plasticized SBP will behave differently from SBP filler and its effects on the properties of the resulting blends. In this work, SBP was blended with PBAT using a twin-screw extruder. The effects of SBP as filler and as a plastic in compounding on the properties of the resulting blends were compared. Water and glycerol were used as plasticizers to plasticize SBP during the preparation of TSBP. Polymeric diphenyl methane diisocyanate (pMDI) was used as a compatibilizer. The rheology, morphology, mechanical properties, and water resistance of the blends were investigated. The objective of this study was to improve melt processability, mechanical properties, and water resistance of SBP plastics.

haul-off system (Thermo Fisher Scientific, England). The thickness and the width of the extruded sheets were 2 mm and 40 mm, separately. The blend of PBAT/dried-SBP powder (50/50 w/w) without pMDI was also prepared and used as a control. Scanning Electron Microscopy (SEM). The phase structure of SBP and morphology of the blends was examined by SEM (FEI Quanta 200 F). To better observe the shape and the size of SBP particles in the blends, the surfaces of the extruded SBP/ PBAT blend sheets were etched in chloroform to remove the PBAT phase. The neat SBP power was also examined for comparison. All samples were sputter-coated with gold prior to examination. Rheological Test. After compounding and drying at 80 °C for 12 h, melt viscosity of the SBP/PBAT blends was assessed using a Rheometric Scientific Advanced Capillary Rheometer (Acer 2000). The diameter of the die was 2 mm, and the length was 30 mm. Samples were tested at 130, 140, and 150 °C. The sample was heated for 10 min in the barrel at the test temperature prior to test start, and the change of viscosity versus shear rate ranging from 25 to 500 s
1 was measured. Equation 1 was used to evaluate the rheological parameters.

’ MATERIALS PBAT (Ecoflex F BX 7011) was obtained from BASF (Florham Park, NJ), having a density of 1.26 g/cm3, a weight average molecular weight of 145 kg/mol, a polydispersity of 2.40 (GPC analysis), a glass transition temperature of
17 °C (DMA), and a melting point of 115 °C (DSC). SBP (Fibrex 575, < 32 μm particle size) was obtained from Nordic Sugar Company, Denmark, comprising approximately 73% dietary fiber (18% cellulose, 29% hemicellulose, 22% pectin, and 4% lignin), 9% protein, 4% minerals, 5.5% sugar, and 0.5% fat. The SBP as received contained ∼6% moisture. pMDI (Mondur 541) containing 31.73 wt % NCO was obtained from Bayer Material Science LLC (Pittsburgh, PA), having a viscosity of 186 cPs. All materials and chemicals were used as received. Preparation of TSBP. Prior to extrusion compounding, SBP was first formulated to contain (per 100 parts of dry SBP) water (20 parts) and glycerol (20 parts). The ingredients were mixed using a kitchen mixer, stored in sealed plastic bags, and then equilibrated at room temperature for at least 8 h. This formulated SBP was then extruded to obtain TSBP using a corotating twinscrew extruder (Leistritz ZSE-18) equipped with a volumetric feeder and a strand die. The diameter of the screw was 18 mm with a length-to-diameter ratio (L/D) of 40. The extruder had a feeding throat zone cooled by running tap water, seven individual heating zones, and an adapter/die section. The zone temperatures were set from 80 °C (feeding zone) to 90 °C (die) and the screw speed was 100 rpm for the preparation of TSBP. The compound was openly discharged without using a die, collected in a plastic bag and sealed for the subsequent sheet extrusion. Preparation of PBAT/TSBP Blend Sheets. Blending of TSBP and PBAT and sheet extrusion was performed in one process using the same extruder as the above one for the preparation of TSBP. The zone temperatures were set at 120, 130, 130, 130, 130, 130, 130, 130, 130 °C from the first heating zone to die for the blend compounding and the screw speed was 100 rpm. The moisture was vented at the sixth heating zone of the barrel. The extruded sheets were cool to 45 °C on a floor-standing 2-roll

where τa is the apparent shear stress at the capillary wall, γ_ a is the apparent shear rate, K is the consistency, and m is powerlaw index. Activation energy was calculated using Arrhenius
Frenkel
Eyring equation.   Ea ð2Þ ηa ¼ B exp RT

:m
1 τa ηa ¼ : ¼ Kγa γa

ð1Þ

where ηa is viscosity at a particular shear rate, B is a constant, R is universal gas constant, T is absolute temperature, and Ea is melt flow activation energy. Tensile Test. The specimens for tensile test were prepared according to an ASTM standard (ASTM D638, type III) from the extruded sheets using a sample cutter. Tensile testing was conducted on a screw-driven universal testing machine (Instron 4466) equipped with a 10 kN electronic load cell and mechanical grips. All tests were performed at a crosshead speed of 50 mm/min and the strain was measured using a 25-mm extensometer (MTS 634.12  10
24). The procedure was carried out according to the ASTM standard, and six replicates were tested for each sample to get the average value. All specimens were conditioned for 6 days at 23 °C and 50% RH. The thickness of the specimen was measured prior to testing. Dynamic Mechanical Analysis (DMA). Dynamic mechanical properties of SBP/PBAT composites were studied using a dynamic mechanical analyzer (TA Q800). The specimens with dimensions of 30  12  2 mm3 were cut from the extruded sheets and tested using a single-cantilever fixture at a frequency of 1 Hz. All tests were conducted at a strain of 0.03% and a 2 °C 3 min
1 temperature ramp from
50 to 70 °C. Water Absorption Test. Water absorption of the sheet was examined following ASTM D570-98. All samples were first dried at 50 °C for 24 h and then cooled to room temperature in a desiccator. The dried samples were immersed in distilled water at room temperature for specific intervals, removed from the water, wiped with tissue paper to remove surface water, and then 13860

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Table 1. Rheology Parameters of Neat PBAT and PBAT/ TSBP Blends

Figure 1. Dependence of apparent viscosity of neat PBAT and PBAT/ TSBP blends on shear rate. Temperature = 150 °C. (1) Neat PBAT; (2)
(5) blends with the PBAT/TSBP/pMDI ratios 80/20/2 (2); 65/35/2 (3); 50/50/0 (4); 50/50/2 (5).

weighed. Six replicates were tested for each sample. Water absorption was calculated on a dry sample weight basis.

’ RESULTS AND DISCUSSION Rheological Properties. Figure 1 shows that the increase in pMDI and TSBP content resulted in significant increase in viscosity of PBAT/TSBP blends. The apparent viscosity of the blends at shear rate 251 s
1 is listed in Table 1. It should be pointed out that most of the moisture in the blends was evaporated during the extrusion process and subsequent oven drying. The loss of moisture led TSBP to behave like a solid filler in the subsequent sheet processing. The addition of pMDI as a compatibilizer in PBAT/TSBP blends led the apparent viscosity to increase from 1541 (PBAT/TSBP/pMDI 50/50/0) to 1773 Pa 3 s (PBAT/TSBP/pMDI 50/50/2) at 251 s
1. The viscosity increase for the blend with pMDI was due to the increased restriction to flow after compatibilization between PBAT and TSBP phases. The apparent viscosity at shear rate of 251 s
1 increased from 601 to 966 Pa 3 s when the TSBP content increased from 0 phr (neat PBAT) to 20 phr (PBAT/TSBP/pMDI 80/20/2). Further increasing TSBP content to 35 phr (PBAT/TSBP/ pMDI 35/65/2) and 50 phr (PBAT/TSBP/pMDI 50/50/2), the apparent viscosity increased to 1259 and 1773 Pa 3 s at 251 s
1, respectively. Figure 1 shows the changes of melt viscosity versus shear rate for the neat PBAT and the PBAT/TSBP blends. The melt viscosity of the blends was much higher than that of the neat PBAT and increased with increasing TSBP content. In fact, the moisture content in the TSBP phase was mostly evaporated after compounding and the subsequent drying. Therefore, SBP was more like a filler in the final blends though it still contained 20% glycerol on the basis of its own mass. On the other hand, both the neat PBAT and the blends exhibited a typical shear-thinning behavior, i.e., the melt viscosity decreased continuously with shear rate in the test range. The changes of viscosity in Figure 1 could be described by the powder law equation (eq 1) and the results are summarized in Table 1. Decrease of the power-law index with TSBP content as shown in Table 1 indicated higher

sample PBAT/

apparent

TSBP/

viscosity at

pMDI

251 s
1 (Pa 3 s)

neat PBAT 80/20/2

activation consistency power-law

energy

K (Pa 3 s)

index m

Ea(kJ/mol)

601

6606

0.5664

50.3

966

23861

0.4199

28.0

65/35/2

1259

37123

0.3885

34.6

50/50/0

1541

78590

0.2855

28.6

50/50/2

1773

84204

0.3014

37.0

shear sensitivity of the melt. The viscosity of PBAT and PBAT/ TSBP blends fitted the power law very well (R2 close to 1). The addition of pMDI increased K greatly, but did not influence m too much. The consistency index, K, ranged from 6606 to 84204 Pa 3 s for the blends with different TSBP content. The power-law index, m, for all formulations with different TSBP content was between 0.3014 and 0.5664. The consistency index increased with increasing TSBP content, indicating the increase of PBAT/ TSBP viscosity. The results showed that both SBP content and the presence of pMDI influenced the viscosity significantly. The activation energy (Ea) of melt flow for a material indicates the dependence of viscosity on temperature change. For a melt with a lower Ea, its viscosity is less temperature dependent. The Ea values (Table 1) for different melts were calculated according to eq 2, using the viscosity at the shear rate of 251 s
1. The Ea values of PBAT/TSBP blends were substantially lower than that of neat PBAT. This result indicated that the processing energy barrier was lowered with addition of SBP. As TSBP content increased, Ea increased slightly. This might be due to the formation of percolated TSBP structure. The addition of pMDI also led to a slight increase in Ea. Morphology. The dried SBP behaved like a rigid filler in the compounding process, while TSBP which still contained significant amount of water was able to flow and deform like a polymer melt during compounding with PBAT. To better discern the morphology of the blends, the PBAT phase was extracted with chloroform. Figure 2a and b show that the unprocessed SBP and the SBP isolated from the PBAT/driedSBP blend were very similar in size and shape. This result indicated that the dried SBP was rigid and largely retained its shape and size after processing. When SBP was processed as a plastic (TSBP) in mixing, it presented a completely different phase structure compared with the SBP filler in the blends. Figure 2c
f show the SBP phase in the blends when SBP was used as plastic with pMDI varying from 0 to 3 phr. In all PBAT/ TSBP blends, TSBP appeared as elongated threads. However, the size and fineness of the TSBP phase differed greatly with the addition and content of pMDI. Even without pMDI added, TSBP was transformed into fairly fine threads (Figure 2c). The addition of pMDI greatly improved the dispersion of TSBP in the PBAT matrix as the SBP threads became even finer (Figure 2d). The fineness of the SBP threads appeared to increase with pMDI content (Figure 2e and f). This result indicated that pMDI as a compatibilizer effectively increased the dispersion of SBP in the blends. The thread is a metastable state in the evolution of phase structure of blends, and it tends to break and form droplets with further mixing.26
28 Because the viscosity of the TSBP was very high in this study, however, the breakup of the threads would require a long time to take place, which exceeded the residence 13861

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Figure 3. SEM micrographs of different PBAT/TSBP/blends. PBAT/ TSBP/pMDI ratio: (a) 80/20/2; (b) 65/35/2; (c) 50/50/2; (d) 35/65/2. The blend surfaces were etched using CHCl3 to remove some PBAT.

Figure 2. Effects of pMDI on phase structures of the PBAT/TSBP (50/50) blends. (a) Unprocessed SBP powder; (b) SBP particles isolated from the PBAT/dried-SBP blend after extraction of PBAT by CHCl3; (c
f) blends with 0 phr (c); 1 phr (d); 2 phr (e); 3 phr (f) pMDI. For (c
f), the blend surfaces were etched using CHCl3 to remove some PBAT.

time in the extruder. Therefore, TSBP presented in the elongated thread form. Similar phenomenon was also widely noted in the blends prepared by processing SP as plastic in mixing with PLA and PBAT.18
21,23,24 Figure 3 shows the effect of TSBP content on the morphology of the TSBP phase. Figure 3a shows the stretched TSBP phase in the PBAT/SBP/pMDI (80/20/2) blend. The TSBP phase was the dispersed particles in the blend, so the extraction of PBAT led TSBP phase became a powder-like mass. When the TSBP content varied from 20 to 65 phr, the SBP phase appeared from dispersed phase structure to interconnected phase structure. The morphology of SBP in the blend was retained after the extraction of PBAT as shown in Figure 3b
d. The formation of interconnected phase structure improved the mechanical properties of the blends. Mechanical Properties. Figure 4 shows the stress
strain curves of PBAT/TSBP (50/50 w/w) blends with different contents of pMDI. Without pMDI, the blend exhibited low strength (∼8.4 MPa), modulus (∼308 MPa), and strain at break (∼14%). These properties increased significantly with addition of only 1 phr pMDI and increased further with more pMDI addition. The effects of pMDI on mechanical properties of PBAT/SBP sheets are summarized in Table 2. PBAT exhibited a yield strength of ∼7.8 MPa, strain at break >800%, and

Figure 4. Effects of pMDI content on tensile behaviors of the PBAT/ TSBP/ (50/50) blends. pMDI content: (a) 0 phr; (b) 1 phr; (c) 2 phr; (d) 3 phr.

modulus of 145 MPa, respectively. For the blend containing 50% dried SBP in PBAT, tensile strength and strain at break decreased to 4.1 MPa and 43%, respectively, whereas tensile modulus increased to 516 MPa. During the tensile test, the dried SBP in PBAT behaved as a stress concentrator and thus led to early failure of the material. Consequently, this blend showed the decreased tensile strength. When TSBP was used for blending, e.g., the PBAT/TSBP/pMDI (50/50/0) blend, tensile strength improved significantly due to the elongated thread shape and fine dispersion of the particles, as shown in Figure 2, whereas tensile modulus decreased due to the presence of the glycerol remaining in TSBP. The strain at break for the PBAT/TSBP blends was lower than that of the PBAT/dried-SBP blend. The elongated TSBP particles appeared to be more effective in reinforcing PBAT that the round dried SBP particles. Similar results were also found in our studies on SP/PBAT blends,18,19 in which water and glycerol as plasticizers also enabled SP to undergo significant deformation during compounding and subsequently affected the mechanical properties of SP blends. The addition of pMDI in the blend increased the tensile strength. With 1 phr pMDI, the 13862

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Table 2. Tensile Properties of PBAT/TSBP Sheets with Varying Content of pMDI

a

blend PBAT/SBP/pMDI

pMDI (phr)

strength (MPa)

strain at break (%)

modulus (MPa)

PBAT

0

7.8 ( 0.2a

dried SBP

50/50/0

>800

145 ( 27

0

4.5 ( 0.4

43 ( 13

TSBP

516 ( 33

50/50/0

0

8.4 ( 0.4

14 ( 4

308 ( 37

50/50/1

1

12.8 ( 0.4

18 ( 5

389 ( 68

50/50/2

2

15.5 ( 0.3

22 ( 3

450 ( 48

50/50/3

3

17.1 ( 0.8

24 ( 3

519 ( 57

Yield strength of PBAT.

Figure 5. Tensile behaviors of the PBAT/TSBP blends with different SBP contents. PBAT/TSBP/pMDI ratio (a) 35/65/2; (b) 50/50/2; (c) 65/35/2; (d) 80/20/2 with a strain at break of 305%.

Table 3. Effects of SBP Content on Tensile Properties of Extruded PBAT/TSBP Sheets blend PBAT/ TSBP/pMDI

SBP (phr)

strength

strain at

modulus

(MPa)

break (%)

(MPa)

80/20/2

20

13.2 ( 0.6

305 ( 27

186 ( 13

65/35/2

35

15.1 ( 0.7

51 ( 7

300 ( 41

50/50/2 35/65/2

50 65

15.5 ( 0.3 13.6 ( 0.6

22 ( 3 8(2

450 ( 48 560 ( 39

tensile strength increased significantly from 8.4 to 12.8 MPa. Further increase in pMDI content to 3 phr increased the tensile strength to 17.1 MPa. At the same time, the strain at break and the modulus were also improved. This indicated that pMDI acted as a good interfacial modifier between PBAT and SBP. Isocyanate is very reactive and can react with many other functional groups such as hydroxyl, amino, and carboxyl groups. Therefore pMDI is likely to bridge the two components by reacting with the hydroxyl and other functional groups in SBP and the end hydroxyl groups of PBAT. Figure 5 shows stress
strain curves of PBAT/TSBP blends with different contents of SBP. The changes of tensile properties with SBP content are summarized in Table 3. At 20 phr SBP, the PBAT/TSBP blend exhibited low modulus and high strain at break. As the SBP content increased, modulus of the PBAT/ TSBP blends increased gradually while strain at break decreased. The tensile strength varied from 13.2 to 15.5 MPa when the SBP content changed from 20 to 50 phr. At 65 phr SBP, the tensile strength decreased a little. However, the strain at break changed dramatically due to the change of SBP content, especially from 20 to 35 phr. This was due to the formation of interconnected SBP phase structure that made the blends more rigid.

Figure 6. Storage modulus (a) and tanδ (b) of PBAT and PBAT/SBP (50/50 w/w) blends.

Dynamic Mechanical Properties. Figure 6 shows the storage modulus (E0 ) and tanδ of neat PBAT and its blends. The E0 of all samples precipitated when the glass transition temperature (Tg) of PBAT (ca.
17 °C) was reached. Another E0 drop was around 50 °C, which is the second Tg of PBAT.18,19 The two Tgs of PBAT corresponded to the two portions of PBAT: the flexible aliphatic domain and the rigid aromatic domain. The change of E0 of TSBP with temperature ranging from
40 to 60 °C was much more moderate (Figure 6a) compared with that of PBAT. E0 decreased with increasing temperature, and no obvious plateau was noted on the E0 curve in the test temperature range for TSBP. Compared with neat PBAT, the blends exhibited increased E0 due to the higher rigidity of SBP (higher E0 ), as shown in Figure 6a. E0 of PBAT/ TSBP was higher than that of PBAT/dried-SBP in the whole test range. This was attributed to the elongated SBP particles and the interconnected phase structure of SBP in the blends. 13863

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the preparation of blend by extrusion compounding. Compared with the blend prepared by mixing SBP as a filler during compounding, the PBAT/TSBP blends exhibited higher mechanical properties. pMDI as an interfacial modifier improved the interfacial adhesion and the dispersion of the SBP phase in the blends and thus resulted in enhanced tensile strength. The properties of the blends with different contents of TSBP were compared. The results showed that higher TSBP contents resulted in higher tensile modulus and lower strain at break, whereas tensile strength did not change dramatically. Compared with neat SBP plastics, the PBAT/TSBP blends displayed excellent water resistance and the addition of pMDI further reduced the water absorption. Figure 7. Water absorptions of PBAT and its SBP blends. (1) Neat PBAT; blends with the PBAT/TSBP/pMDI ratio (2) 80/20/2; (3) 65/35/2; (4) 50/50/0; (5) 50/50/2; and (6) 35/65/2.

Figure 6b shows the tanδ damping curves of neat PBAT and its blends. PBAT showed the highest peak around
17 °C and a small peak around 50 °C. TSBP displayed a major transition spanning a broad range of temperature around 20 °C. This major transition was believed to be the α-transition of pectin. The characteristic broadness of the α-transition might be a reflection of the multicomponent complexity of the SBP material. The heights of tanδ peaks of the blends were lower than that of neat PBAT. This was due to the percentage reduction of PBAT and the formation of interconnected phase structure of SBP in the samples. Similar results were noted in PBAT/SP blends.18 Due to the increase of tanδ while increasing temperature for TSBP, the heights of tanδ for all blends were higher than that of neat PBAT after 25 °C. Water Absorption. Figure 7 shows water absorption of PBAT/TSBP blends. PBAT is hydrophobic and its water absorption is negligible. SBP is highly hydrophilic; especially its major component, pectin, is a water-soluble polymer. Therefore, neat TSBP sample picked up water quickly in the immersion test and disintegrated afterward. All blends exhibited reduced water absorptions. Within the test range, blend PBAT/TSBP/pMDI 80/20/2 showed the lowest water absorption, whereas blend PBAT/TSBP/pMDI 35/65/2 showed the highest value among the blends. By comparing sample 50/50/0 with sample 50/50/2 at the early stage, it was noted that water absorption of the blends decreased with addition of pMDI. The reactive compatibilization between SBP and PBAT bridged by pMDI greatly improved the wetting of the hydrophilic SBP particles by the hydrophobic PBAT matrix, therefore decreasing the water absorption of the blends. After 10 h of water immersion, water absorptions for samples PBAT/TSBP/pMDI 50/50/0 and 35/65/2 reached the maxima and then started to decrease due to the loss of some water-soluble matter in SBP. Other compatibilized samples containing lower SBP content showed a reduced water absorption rate. For the samples with 35 and 20 phr TSBP, the maximum water absorption was reached after 4 weeks of water immersion.

’ CONCLUSIONS SBP could be effectively plasticized by water and glycerol and turned into thermoplastic-like materials. pMDI was an effective compatibilizer for PBAT/TSBP blends and led to the formation of fine phase morphology of the blends. Interconnected phase structure was formed when SBP was used as a plastic component in

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]. Tel.: 509-335-8723.

’ ACKNOWLEDGMENT We are grateful for financial support from the Agricultural Research Service of the United States Department of Agriculture, Specific Cooperative Agreement 58-1935-9-965. ’ REFERENCES (1) Hotchkiss, A.; Fishman, M.; Liu, L. S. The role of sugar beet pulp polysaccharides in the sustainability of the sugar beet industry. In Eggleston G., Ed.; ACS Symposium Series Volume 1058; American Chemical Society: Washington, DC, 2010; Chapter 17, p 283. (2) Fishman, M. L.; Chau, H. K.; Coffin, D. R.; Cooke, P. H.; Qi, P.; Yadav, M. P.; Hotchkiss, A. T. Physico-chemical characterization of a cellulosic fraction from sugar beet pulp. Cellulose 2011, 18, 787. (3) Vaccari, G.; Nicolucci, C.; Mantovani, G.; Monegato, A. Process for manufacturing paper from sugar-beet pulp and paper thus obtained. EP Patent 0,644,293, 1998. (4) Buchholt, H. C.; Christensen, T. M. I. E.; Fallesen, B.; Ralet, M. C.; Thibault, J. F. Preparation and properties of enzymatically and chemically modified sugar beet pectins. Carbohydr. Polym. 2004, 58, 149. (5) Kuuva, T.; Lantto, R.; Reinikainen, T.; Buchert, J.; Autio, K. Rheological properties of laccase-induced sugar beet pectin gels. Food Hydrocoll. 2003, 17, 679. (6) Norsker, M.; Jensen, M.; Adler-Nissen, J. Enzymatic gelation of sugar beet pectin in food products. Food Hydrocoll. 2000, 14, 237. (7) Fishman, M. L.; Chau, H. K.; Cooke, P. H.; Yadav, M. P.; Hotchkiss, A. T. Physico-chemical characterization of alkaline soluble polysaccharides from sugar beet pulp. Food Hydrocoll. 2009, 23, 1554. (8) Dufresne, A.; Cavaille, J. Y.; Vignon, M. R. Mechanical behavior of sheets prepared from sugar beet cellulose microfibrils. J. Appl. Polym. Sci. 1997, 64, 1185. (9) Leitner, J.; Hinterstoisser, B.; Wastyn, M.; Keckes, J.; Gindl, W. Sugar beet cellulose nanofibril-reinforced composites. Cellulose 2007, 14, 419. (10) Samir, M. A. S. A.; Alloin, F.; Paillet, M.; Dufresne, A. Tangling effect in fibrillated cellulose reinforced nanocomposites. Macromolecules 2004, 37, 4313. (11) Rouilly, A.; Jorda, J.; Rigal, L. Thermo-mechanical processing of sugar beet pulp. I. Twin-screw extrusion process. Carbohydr. Polym. 2006, 66, 81. (12) Rouilly, A.; Geneau-Sbarta, C.; Rigal, L. Thermo-mechanical processing of sugar beet pulp. III. Study of extruded films improvement with various plasticizers and cross-linkers. Bioresour. Technol. 2009, 100, 3076. (13) Liu, B.; Zhang, J.; Liu, L.; Hotchkiss, A. T. Preparation and properties of water and glycerol-plasticized sugar beet pulp plastics. J. Polym. Environ. 2011, 19, 559. 13864

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Industrial & Engineering Chemistry Research

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dx.doi.org/10.1021/ie2017948 |Ind. Eng. Chem. Res. 2011, 50, 13859–13865