Biobased Polymeric Materials Prepared from Cotton Byproducts - ACS

Chapter 4

Biobased Polymeric Materials Prepared from Cotton Byproducts Downloaded by UNIV OF PITTSBURGH on October 8, 2015 | http://pubs.acs.org Publication Date (Web): August 16, 2012 | doi: 10.1021/bk-2012-1105.ch004

H. N. Cheng,*,1 Michael K. Dowd,1 and Atanu Biswas2 1Southern

Regional Research Center, USDA Agricultural Research Service, 1100 Robert E. Lee Blvd., New Orleans, LA 70124, U.S.A. 2National Center for Agricultural Resource Utilization, USDA Agricultural Research Service, 1815 N. University Street, Peoria, IL 61604, U.S.A. *E-mail: [email protected]

Cotton burr and cottonseed hull are relatively inexpensive natural renewable materials from cotton and cottonseed processing. Recently several new polymer applications have been reported involving these byproducts. These new developments are briefly reviewed in this article. In the first application, the cotton byproducts have been used directly as fillers in poly(lactic acid) and low-density polyethylene composites. The composites have been prepared by melt blending and extrusion. The addition of these low-cost fillers has slightly changed the composite’s thermal properties but significantly affected the composite’s mechanical properties. In the second application, the cotton byproducts have been partly converted into cellulose esters without prior chemical breakdown or physical separation of cellulose, lignin, protein, and other components. The process entails treating these materials with acetic anhydride and iodine, with no solvent involved except during sample workup. In the third application, these materials have been partly converted into carboxymethyl cellulose and carboxymethyl xylan. Potential uses of these materials are discussed.

Not subject to U.S. Copyright. Published 2012 by American Chemical Society In Biobased Monomers, Polymers, and Materials; Smith, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.

Downloaded by UNIV OF PITTSBURGH on October 8, 2015 | http://pubs.acs.org Publication Date (Web): August 16, 2012 | doi: 10.1021/bk-2012-1105.ch004

Introduction In the past several years there have been a lot of research activities to use natural renewable materials to develop new polymeric products and processes (1–11). One of the promising approaches is to utilize agricultural byproducts and wastes as raw materials. In this regard, the byproducts from cotton and cotton processing, such as gin trash, cotton burr, and cottonseed hull, seem attractive. Cotton burr is a byproduct of cotton harvesting and ginning and is often used as fuel for boilers or occasionally as mulch (12–15). Cottonseed hull is a byproduct of cottonseed oil extraction and is currently used as roughage in animal feed, as a garden or field mulch, or as a component of the growth media for mushroom production (12, 13). Both materials are readily available and inexpensive. Recently there have been several reports describing the use of cotton burr and cottonseed hull in polymer applications. In the first application, these materials have been ground into powder and used as fillers in polymer composites (16). In the second application, these materials have been chemically converted into cellulose acetates (17) and mixed esters (18). In the third application, these materials have been converted into cellulose and hemicellulose ethers (19). These developments are briefly reviewed in this article.

Polymer Composites For composite formation (16), powdered burr and hull were separately mixed with PLA and LDPE and extruded into ribbons. The scanning electron microscopy (SEM) photomicrographs of the fracture surfaces of PLA, LDPE, and their composites are shown in Figure 1. PLA itself had a smooth fracture surface, but the surfaces of the PLA-burr and PLA-hull composites were more irregular, reflecting the topography of the fillers. In contrast, the LDPE surface appeared somewhat wrinkled; with the fillers, the surface became rougher, with some evidence of polymer-filler separation. In general, the mechanical properties of PLA (tensile strength, elongation at breakage, and Young’s modulus) were reduced by addition of the fillers (Table 1). Maleic anhydride (MA) and peroxide are sometimes used to compatibilize polymer and filler; however, in this case, MA and Lupersol 101 peroxide (L101) caused further reduction in mechanical properties. As for thermal properties, PLA exhibited the expected glass transition (Tg) of ~57 °C, melting temperature (Tm) of ~156 °C, a broad exothermic cold crystallization peak (Tcc) starting at ~107 °C, and a low degree of crystallinity (χc), consistent with similar values reported in the literature (20–22). With filler addition, Tg was reduced, Tm was broadened and shifted to lower temperature, Tcc became larger and occurred at lower temperature, and χc increased (Table 1). Increasing the amount of filler material in the formulation, either burr or hull, tended to increase the differences, and the use of MA and L101 increased the differences even further. In view of similar effects observed for several other fillers in PLA (23–25), the broadening of the peak associated with melting may be due to the presence of different 48 In Biobased Monomers, Polymers, and Materials; Smith, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


crystallite sizes or levels of crystal perfection as a result of burr addition. The decrease in Tcc and the increase in χc suggest that filler particles are acting as nucleating sites that enhance cold crystallization (23–25). These observations imply some interactions between filler particles and PLA.

Figure 1. SEM photomicrographs at 500X of PLA by itself (1a), PLA with 20% burr (1b), PLA with 20% hull (1c); LDPE by itself (1d), LDPE with 20% burr (1e), and LDPE with 20% hull (1f). Reproduced with permission from ref. (16). Copyright 2011 Elsevier. 49 In Biobased Monomers, Polymers, and Materials; Smith, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.

50


Table 1. Mechanical and thermal properties of poly(lactic acid) (PLA) and PLA composites formed with cotton burrs and cottonseed hullsab PLA:filler:MA:L101

Thickness (mm)

TS (N/mm2)

E (%)

YM (MPa)

Tg (°C)

Tcc (°C)

Tm (°C)

ΔHcc (J/g)

ΔHm (J/g)

χc (%)

100 : 0

1.83 (0.10)

62 (2)

16 (1)

550 (19)

58.9

109

156.0

-9

10

2

90 : 10

1.64 (0.05)

39 (1)

9 (1)

529 (18)

56.3

107

154.0

-8

14

7

80 : 20

1.90 (0.10)

15 (1)

7 (1)

318 (9)

55.3

104

153.2

-12

19

9

90 : 10 : 2 : 0.5

1.85 (0.08)

24 (3)

9 (1)

362 (36)

54.0

102

153.4

-11

17

8

90 : 10 : 4 : 0.5

2.02 (0.08)

15 (0)

8 (1)

292 (23)

48.0

95

147.4, 153.5

-22

28

8

80 : 20 : 2 : 0.5

1.89 (0.05)

16 (1)

7 (1)

346 (19)

53.8

100

151.4, 154.7

-14

22

11

80 : 20 : 4 : 0.5

1.91 (0.06)

16 (1)

7 (1)

328 (12)

50.8

95

149.2, 154.2

-18

27

13

90 : 10

1.88 (0.12)

36 (3)

9 (1)

504 (46)

56.6

105

154.7

-10

13

3

80 : 20

1.76 (0.10)

29 (3)

8 (1)

506 (32)

54.6

103

152.0

-15

22

9

90 : 10 : 2 : 0.5

1.95 (0.05)

19 (1)

8 (1)

338 (14)

51.0

98

149.2, 154.5

-14

23

11

90 : 10 : 4 : 0.5

2.03 (0.05)

15 (2)

8 (2)

284 (16)

46.5

91

144.0, 152.0

-20

31

14

80 : 20 : 2 : 0.5

1.93 (0.05)

18 (3)

8 (2)

350 (6)

51.6

100

150.5, 154.9

-10

20

13

80 : 20 : 4 : 0.5

2.14 (0.05)

11 (1)

7 (1)

254 (9)

47.2

91

145.9, 152.7

-16

28

17

Burr Filler

Hull Filler

a Standard deviations are in parentheses. b Data adapted from ref. (16); TS = tensile strength, E = elongation during breakage, YM = Young’s modulus; the explanation of other acronyms is given in the text.

In Biobased Monomers, Polymers, and Materials; Smith, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.

51


Table 2. Mechanical and thermal properties of low density polyethylene (LDPE) and LDPE composites formed with cotton burrs and cottonseed hullsab LDPE:filler:MA:L101

Thickness (mm)

TS (N/mm2)

E (%)

YM (MPa)

Tm (°C)

ΔHm (J/g)

χc (%)

100 : 0

3.78 (0.11)

9 (1)

549 (128)

44 (3)

110.5

120

40

90 : 10

2.97 (0.25)

7 (0)

83 (16)

54 (5)

110.5

102

38

80 : 20

2.40 (0.09)

7 (0)

38 (8)

68 (5)

111.9

89

37

60 : 40

1.97 (0.12)

7 (0)

21 (6)

109 (22)

111.9

71

39

90 : 10 : 2 : 0.5

3.47 (0.23)

8 (0)

76 (22)

55 (5)

109.2

102

39

90 : 10 : 4 : 0.5

4.08 (0.38)

8 (0)

111 (38)

51 (3)

109.9

103

40

80 : 20 : 2 : 0.5

3.08 (0.14)

7 (0)

52 (13)

58 (5)

111.2

82

35

80 : 20 : 4 : 0.5

3.13 (0.16)

7 (1)

52 (8)

56 (3)

109.7

103

45

90 : 10

4.01 (0.08)

7 (0)

110 (23)

51 (2)

111.2

106

39

80 : 20

3.42 (0.13)

6 (0)

68 (9)

54 (7)

110.4

88

37

60 : 40

2.34 (0.14)

4 (0)

40 (5)

61 (6)

112.0

49

27

90 : 10 : 2 : 0.5

4.70 (0.18)

7 (1)

108 (32)

48 (3)

110.0

102

39

90 : 10 : 4 : 0.5

4.59 (0.13)

8 (0)

109 (9)

51 (3)

111.0

100

39

Burr Filler

Hull Filler

Continued on next page.


LDPE:filler:MA:L101

Thickness (mm)

TS (N/mm2)

E (%)

YM (MPa)

Tm (°C)

ΔHm (J/g)

χc (%)

80 : 20 : 2 : 0.5

3.98 (0.31)

7 (0)

64 (8)

55 (3)

110.2

85

37

80 : 20 : 4 : 0.5

4.24 (0.48)

6 (0)

54 (9)

53 (5)

109.9

78

34

a Standard deviations are in parentheses. b Data adapted from ref. (16); TS = tensile strength, E = elongation during breakage, YM = Young’s modulus; the explanation of other acronyms is given in the text.

52


Table 2. (Continued). Mechanical and thermal properties of low density polyethylene (LDPE) and LDPE composites formed with cotton burrs and cottonseed hullsab



The addition of cotton fillers to LDPE modestly reduced the tensile strength but more severely reduced the elongation of the composite materials (Table 2). The addition of fillers to LDPE, however, increased Young’s modulus, the effect being stronger for the addition of burr than for the addition of hull. The effects of MA and L101 were relatively minor. Addition of the fillers to LDPE had relatively small effects on the thermal properties of the composites compared with the thermal effects observed with the addition of fillers to PLA. When fillers were added to LDPE without MA and L101, Tm was almost constant. In the presence of MA and L101, Tm was reduced by at best 1 to 2 °C. Moreover, ΔHm decreased and χc decreased modestly with added filler, and these changes were more pronounced as more filler was added. The use of MA and L101 perhaps slightly increased ΔHm and χc in some composites compared with the same formulation without the added agents. The relatively small impact of fillers on the thermal properties of polyethylene has also been observed with other filler materials (26, 27). An advantage of using cotton byproducts as fillers in polymers is to decrease the cost. For PLA, the fillers perhaps can be used in applications where cost reduction is important and reduced mechanical properties are acceptable. Possible examples are biodegradable and compostable plastics, such as agricultural mulch films, compost bags, and perhaps disposable dinnerware. As for LDPE, the addition of burr or hull filler materials to LDPE increases the composite material’s Young’s modulus. Thus for applications needing a stiffer polyethylene at reduced cost, the use of these fillers might be beneficial.

Cellulose Esters Another method to increase the value of cotton byproducts is to derive chemically modified products from them. Iodine-catalyzed acetylation reaction has been reported earlier (28, 29) and used for cotton byproducts (17), e.g.,

The reaction was conducted with acetic anhydride in the presence of iodine and heat. At 80°C, product yield depended on iodine and acetic anhydride levels (Table 3, samples H1 through H5). As the yield increased, the degree of substitution (DS) tended to decrease. This was probably a result of the crystalline structure of cellulose, which would tend to resist chemical reaction. Thus, acetylation started at amorphous region, and once acetylation took place on an anhydroglucose unit, that same unit became more susceptible to further acetylation reaction, thereby leading to a larger DS. At 100°C, a notable increase 53 In Biobased Monomers, Polymers, and Materials; Smith, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


in the product yield and a relatively high DS were observed (sample H6). The higher temperature apparently allowed the hull cellulose molecules to be more accessible to acetylation reaction. At 120°C, however, cellulose hydrolysis began to become apparent, leading to products with a lower yield and a DS greater than 3.0 (sample H7). Thus, there was an optimal temperature window (at around 100°C) for the acetylation of cottonseed hulls.

Table 3. Iodine-catalyzed acetylation reaction of cottonseed hull, reacted for 20-24 hoursa No.

wt (g)

temp (°C)

yieldb wt %

DStot

DS6

DS2

DS3

hull

I2

H1

0.57

0.04

3.8

80

1

2.03

0.67

0.69

0.68

H2c

0.57

0.08

1.9

80

1

1.98

0.65

0.68

0.65

H3

0.57

0.16

3.8

80

7

1.46

0.45

0.46

0.48

H4

0.57

0.16

0.95

80

2

1.91

0.62

0.69

0.60

H5

0.57

0.32

0.95

80

6

1.69

0.56

0.58

0.55

H6c

0.57

0.32

1.9

100

34 d

2.03

0.69

0.68

0.66

H7

0.57

0.32

1.9

120

9

3.56

nd e

nd

nd

Ac2O

a Data taken with permission from ref. (17). starting hull. c Average for duplicate runs. with DS 2.03. e nd = not determined.

b

Observed weight of product versus weight of 22% of theoretical yield of cellulose acetate

d

The observed product yields from cotton burr also depended strongly on iodine and acetic anhydride levels at 80°C (Table 4, samples B1 through B4). Compared with hull samples, burr seemed to be more susceptible to acetylation (cf. the yields of samples B3 and B4 versus samples H-3 and H-5). At 100°C, burr also showed an increase in yield and DS, similar to what was observed in hull. At 120°C, cellulose hydrolysis became significant with DS exceeding 3.0 and decreasing yield. The optimal temperature for cottonseed burr acetylation was also ~100°C. Because hull or burr contains about 30% cellulose, the maximum weight yield observed (34-37%) corresponds to a conversion and recovery of a significant fraction of the cellulose in each cotton byproduct. The cellulose in cottonseed hull and burr can also be converted to higher alkyl and mixed cellulose esters using the same reaction; in particular, cellulose acetate propionate and cellulose acetate butyrate have been prepared and characterized in this way (18). There are several advantages of using cotton byproducts, 54 In Biobased Monomers, Polymers, and Materials; Smith, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.

such as lower cost and relative ease of reaction. Thus, in this process no prior chemical breakdown or physical separation of cellulose, lignin, protein, and other components is needed. Furthermore, the process entails no solvent during the reaction step, thereby potentially decreasing manufacturing hazards.

Table 4. Iodine-catalyzed acetylation reaction of cotton burr, reacted for 20-24 hoursa Downloaded by UNIV OF PITTSBURGH on October 8, 2015 | http://pubs.acs.org Publication Date (Web): August 16, 2012 | doi: 10.1021/bk-2012-1105.ch004

No.

wt (g)

temp (°C)

yieldb wt %

DStot

DS6

DS2

DS3

hull

I2

B1

0.57

0.04

3.8

80

0.4

1.87

0.34

0.30

0.23

B2

0.57

0.08

3.8

80

1

1.66

0.50

0.63

0.53

B3

0.57

0.16

3.8

80

16

1.01

0.38

0.36

0.27

B4

0.57

0.32

0.95

80

18

1.98

0.67

0.66

0.65

B5c

0.57

0.32

1.9

100

37 d

2.09

0.70

0.70

0.69

B6

0.57

0.32

1.9

120

7

3.84

nd e

nd

nd

Ac2O

a Data taken with permission from ref. (17). starting burr. c Average for duplicate runs. with DS 2.09. e nd = not determined.

b

Observed weight of product versus weight of 24% of theoretical yield of cellulose acetate

d

Polysaccharide Carboxymethyl Ethers Another way to derivatize polysaccharides is to form ether derivatives. Indeed, carboxymethyl derivatives have been made earlier from cotton byproducts (19), e.g.,

The reaction procedure employed sodium monochloroacetate as the alkylation reagent following standard protocols (30–33), and the chemistry was conducted on hull (H1 and H2) and burr (B1-B3) samples ground to different particle sizes. For comparative purposes, a purified cellulose sample (C) was also treated as a control case (Table 5). As expected, the product derived from the cellulose 55 In Biobased Monomers, Polymers, and Materials; Smith, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


control was fully water soluble. Reaction of hull (H1 and H2) and burr (B1, B2, and B3) samples yielded water soluble and insoluble fractions, indicating that some components of the samples were recalcitrant to reaction. The weight % of insoluble material from the cotton products was about the same in most of the burr and hull fractions (35-45% of the initial mass). The soluble fractions of the reacted hull and burr samples, yielded solution 13C NMR spectra similar to the spectra of reference carboxymethyl cellulose (CMC) and carboxymethyl xylan (CMX) samples (Figure 2). The spectra indicate that these cotton products consist mainly of CMC and CMX. Thus, with relatively standard procedures, roughly 30% of cotton burr and 45% of cottonseed hull can be converted into soluble carboxymethylated products. These products are readily soluble in water and form films when dried. These materials might be useful as low-cost replacements for CMC or for applications where the properties of CMX are preferred. The insoluble burr and hull products were only slightly carboxymethylated, and they can perhaps be used in conventional applications, such as a soil conditioner or fertilizer or as a source of roughage for animal feeds.

Table 5. Yields of water-soluble and water-insoluble fractions from the carboxymethylation of cotton hull and burr fractionsa No.

starting wt (g)

water soluble

water insoluble

wt (g)

obs’d wt %

wt (g)

obs’d wt %

total obs’d yieldb %

% theoretical yieldc

C

5.00

4.5

90

0

0

90

62

H1

5.00

1.8

36

2.2

44

80

68

H2

5.00

2.8

55

2.0

40

95

79

B1

4.64

1.3

28

1.7

36

64

56

B2

5.41

1.6

29

1.9

35

64

55

B3

5.00

1.7

35

2.2

45

80

69

Data taken with permission from ref. (19). Observed product weight versus weight of starting material. c Calculated on the assumption of total conversion of cellulose to CMC, sodium salt (DS 0.7), and xylan to CMX, sodium salt (DS 0.4). All hemicellulose is assumed to be xylan. All other components (lignin, lipid, protein, water, inorganics) are considered unchanged and not removed. a

b

56 In Biobased Monomers, Polymers, and Materials; Smith, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


Figure 2. 13C NMR spectra at 75 MHz in D2O: a) CMX; b CMC; c) water-soluble fraction of reacted burr sample (B1); d) water-soluble fraction of reacted hull sample (H1). Reproduced with permission from ref. (19). Copyright 2010 Elsevier.

Experimental Section Upland (fuzzy) cottonseed was initially acid delinted in order to remove cellulosic linters and to produce a clean hull material. The seed was then cracked in a Bauer mill, and the hulls were separated by air classification. Cotton burr was obtained as a substantial part of a cotton gin trash sample. Non-burr materials, such as stem pieces and dried leaves were removed by hand. From proximate analysis (19), hull was found to consist of 31% cellulose, 20% hemicellulose, 18% lignin, 2% crude fat, 5% proteins, and 11% moisture. The composition of the burr sample was 31% cellulose, 6% hemicellulose, 17% lignin, 2% crude fat, 8% proteins, and 12% water.



Filler Studies Both hull and burr samples were ground with a laboratory-scale Wiley mill to pass through the mill’s 1-mm opening bottom sieve (16). Polymer blends were formulated with 10, 20, or 40% of the milled byproduct filler. Each mixture of materials was manually blended and kept in closed double zip-locked bags for 1 day prior to extrusion. The data shown in Tables 1-2 were produced from polymer and filler particles that were conditioned in a convection oven at 50°C for 3 days to reduce moisture levels. Several samples were also formulated with maleic anhydride and Lupersol 101 peroxide to promote cross-linking and compatibility of the materials. Composite ribbons were prepared with a single-screw extruder (C. W. Brabender, South Hackensack, NJ) with four temperature zones that were set from the feed end at 150, 165, 165, and 165°C for the PLA blends, and at 110, 120, 115, 110°C for the LDPE blends. A high-shear screw was employed with a 1-in. ribbon slit die. Screw speed was set at 25 rpm. Sample was fed through a feed throat attached to an air chiller. A conveyor belt was used to take up the ribbon at the same speed as the ribbon exited the die plate. Ribbons were cut into dog-bone specimens with a MS Instrument Inc., punch press. Tensile properties were measured with an Instron Corp. (Norwood, MA) Universal Testing System Model 4201 tensile tester. Tensile strength, Young’s modulus, and elongation at breakage were measured with a cross-head speed of 10 mm/min, a gauge length of 7.62 mm, grip distance of 50 mm, and with a 1 kg load. Each sample was tested five times. Thermal profiles were determined with a PerkinElmer (Waltham, MA) Model DSC-7 calorimeter and a TAC7/DX controller. Powder samples of 2−3 mg were weighed into stainless steel DSC pans. The calorimeter was programmed to increase the temperature from -20 to 180 °C at a rate of 10 °C/min, then decrease the temperature back to -20 °C at a rate of 10 °C/min, then increase the temperature back to 180 °C, again at a rate of 10 °C/min. Data from the second heating cycle were used to determine Tg, Tcc, Tm, ΔHcc, ΔHm and χc. Further details are given in the original reference (16). Stretch-fractured samples from the tensile testing were examined with a JEOL (Peabody, MA) Model 6400V scanning electron microscope, operated with an accelerating voltage of 10 kV. Samples were coated with gold with a SPI (West Chester, PA) sputter coater. Ester Formation Burr and the hull samples were pulverized with a hammer mill until they passed through a 16-mesh screen (17). They were then stored in capped bottles at room temperature. In a typical reaction, 0.57 g of powder sample, 1.9 g of acetic anhydride, and 0.32 g of iodine were heated at 80–100°C for 20–24 h. The reaction mixture was then cooled to room temperature and treated with 2 mL of a saturated solution of sodium thiosulfate while stirring. The mixture changed 58 In Biobased Monomers, Polymers, and Materials; Smith, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


color from dark brown to colorless, indicating the transformation of iodine to iodide. The mixture was poured into 50 mL of ethanol and stirred for 30 min. The solid, which contained cellulose acetate, was filtered and washed with water and dried in a vacuum oven at 60°C. The cellulose acetate was then dissolved in methylene chloride and filtered. The filtrate was evaporated under vacuum at room temperature. As the solvent evaporated, cellulose acetate formed a film on the sides of the flask. Ethanol was added to remove the film. The film was washed with ethanol and hot water at ca. 85°C and dried. The % yield (at 5% precision) was calculated as the weight of cellulose acetate versus the weight of starting material. For mixed esters (18), the same procedure was used except that after the reaction mixture was poured into 50 mL of ethanol and stirred for 30 min, the solid was filtered and washed successively with water at 100°C and then washed successively with water and ethanol at room temperature. The remaining solid was then dissolved in chloroform, filtered, and the chloroform removed by evaporation. The DS was determined by 1H NMR (at 5% precision). Samples were dissolved in CDCl3. Spectra were collected on a Bruker DRX400 spectrometer.

Ether Formation

Burr and hull samples were milled with a kitchen blender (19). Hull was separated into a fine powder that passed through the 20-mesh sieve (H1) and a medium-sized powder that passed through the 7-mesh sieve but was retained on the 20-mesh sieve (H2). Burr was fractioned into a fine powder that passed through the 20-mesh sieve (B1), a medium-sized powder that passed the 7-mesh sieve but was retained on the 20-mesh sieve (B2) and a coarse fraction that was retained on the top of the 7-mesh sieve (B3). The reaction procedure consisted of three steps (19). First, 5 g of ground cotton byproducts was suspended in 125mL of 80% (v/v) isopropanol/water into which 5–6 g of sodium hydroxide was dissolved. The mixture was stirred overnight at room temperature. An alkylation solution was prepared by dissolving 8–12 g of sodium monochloroacetate in 10 mL isopropanol with a minimal amount of water added to facilitate dissolution. The alkylation solution was added slowly to the cellulose/isopropanol sample over a 30-min period, after which the mixture was purged with nitrogen and maintained at 50°C for 2–3 h. The reaction was then stopped by cooling and filtered to separate the solids. The solids was suspended in 70% ethanol/water, neutralized with glacial acetic acid, washed, and refiltered three times with 70% ethanol/water to remove unreacted reagent and salt. The remaining material was then dispersed in 200mL water. For the ground cotton byproducts, this resulted in soluble and insoluble fractions. The insoluble fraction was separated by filtration, washed with additional water, and dried in a vacuum oven. The soluble material was stripped of water on a rotary evaporator. The % yield (at 5% precision) was calculated as the weight of cellulose acetate divided by the weight of starting material. In addition to the various cotton products, cellulose, xylan, lignin were also carboxymethylated, and the products were used as control materials. 59 In Biobased Monomers, Polymers, and Materials; Smith, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.

The DS of the CMC was determined by 13C NMR (at 5% precision). Samples were dissolved in D2O, and spectra were recorded on a Varian Gemini 2000 spectrometer, operating at 75 MHz for 13C.


Acknowledgments Thanks are due to Janet Berfield (NCAUR) and Catrina Ford (SRRC) for technical work, and Gordon Selling (NCAUR) and Thomas Klasson (SRRC) for encouragement. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer.


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Biobased Polymeric Materials Prepared from Cotton Byproducts - ACS

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