Effects of Molecular Weight of Nitrocellulose on Structureand Properties of Polyurethane/Nitrocellulose IPNs

LINA ZHANG, QI ZHOU

Department of Chemistry, Wuhan University, Wuhan 430072, China

Received 13 July 1998; revised 8 January 1999; accepted 13 January 1999

ABSTRACT: Semi-interpenetrating polymer network (semi-IPN) coatings were pre-pared by using castor oil-based polyurethane (PU) and nitrocellulose (NC) with variousviscosity-average molecular weights (Mh) from 6 3 104 to 42 3 104, and coated on aregenerated cellulose (RC) film to obtain water-resistant film. The PU/NC coatings andcoated films, which were cured at 80°C for 5 min and 2 min, respectively, wereinvestigated by infrared (IR) and ultraviolet (UV) spectroscopy, X-ray diffraction,swelling test, strength test, dynamic mechanical thermal analysis (DMTA), differentialscanning calorimetry (DSC), and thermogravimetric analysis (TGA). The results showthat the crosslink densities of the PU/NC semi-IPNs were smaller than that of pure PU,and decreased with the decrease of Mh of nitrocellulose (NC Mh), indicating NCmolecules cohered intimately with PU, and hindered the PU network formation. Thephysical and mechanical properties of the films coated with PU/NC coatings weresignificantly improved. With the increase of NC Mh, the strength and thermal stabilityof the coated films increased, but the pliability, water resistivity, and optical transmis-sion decreased slowly. The PU/NC coating with low NC Mh more readily penetrated intothe RC film, and reacted with cellulose, resulting in a strong interfacial bonding anddense surface caused by intimate blend of PU/NC in the coated films. © 1999 John Wiley& Sons, Inc. J Polym Sci B: Polym Phys 37: 1623–1631, 1999Keywords: regenerated cellulose film; nitrocellulose; semi-IPNs; molecular weight;crosslink density; mechanical properties; dynamic mechanical thermal analysis; biode-gradable polymer

INTRODUCTION

Nowadays, the polymers from renewable re-sources have attracted considerable attention inthe world because of the escalating price of petro-chemicals and high rate of depletion of naturalmineral resources.1 Cellulose, an abundant rawmaterial with low cost, has been reevaluated as afunctional material to meet the diverse needs oftoday’s society because of the unique reactivitiesand molecular characteristics.2 Nitrocellulose, a

cellulose derivative, has been long used in protec-tive and decorative lacquer coating applications.However, the coatings are not very satisfactory intheir transparency, thermal stability, low-tem-perature flexibility, and flame resistance. In orderto improve the shortcomings, a semi-interpene-trating polymer networks (IPNs) of nitrocelluloseand castor-oil based polyurethane (PU) has beenreported.3 Recently, the water-resistant filmsfrom PU/poly(methylacrylate-co-styrene),4 PU/ni-trocellulose,5 PU/chitosan,6 and PU/elaeostearin7

coatings to regenerated cellulose films were sat-isfactorily investigated in our laboratory. It wasverified that the PU prepolymers in the coatingsplay an important role in forming IPNs, semi-IPNs, or grafted IPNs, and give rise to a share

Correspondence to: L. Zhang (E-mail: lnzhang@elm.pdexpress.com)Journal of Polymer Science: Part B: Polymer Physics, Vol. 37, 1623–1631 (1999)© 1999 John Wiley & Sons, Inc. CCC 0887-6266/99/141623-09

1623

network crosslinked with cellulose and coating,which results in the strong interfacial bonding.The tensile strength, water resistivity, and opti-cal transmission of the coated films were signifi-cantly higher than those of the uncoated films. Itis worth noting that castor oil is also a renewableresource, and the biodegradability of PU foamscould be accelerated by incorporation of molas-ses.8 Hence, the development of IPNs from PUand natural products can stimulate both the uti-lization of renewable resources and synthesis ofbiodegradable materials.

The IPNs are an intimate blend of two networkpolymers with very special properties, and thecrosslink density in the polymer networks greatlyinfluences the mechanical and the damping prop-erties.9 In general, the structure and properties ofthe polymer materials is related to the molecularweight of the components. However, little atten-tion has been paid to the relation of molecularweight in IPN blends to the structure and prop-erties of the materials. In this work, semi-IPNcoatings were prepared by using a certain contentof nitrocellulose and castor-oil-based polyure-thane, and the coatings were coated on the regen-erated cellulose (RC) films. The effects of molecu-lar weight of nitrocellulose on the crosslink den-sity, crystallinity, mechanical properties, opticaltransmission, thermostability of the IPN coat-ings, and the coated films were investigated byinfrared spectroscopy (IR), ultraviolet spectros-copy (UV), X-ray diffraction (XRD), swelling test,strength test, dynamic mechanical thermal anal-ysis (DMTA), differential scanning calorimetry(DSC), and thermogravimetric analysis (TGA).

EXPERIMENTAL

Materials

A commercial cotton was used here, whose viscos-ity-average molecular weight (Mh) was deter-mined to be 5.24 3 105 by viscometry. The 6 g ofcotton was agitated vigorously in a vessel contain-ing 30 g of HNO3/H2SO4/H2O (18:62:20 by weight)to obtain nitrocellulose with desired degree of ni-tration (10.7;11.7% N). After 20;30 min, thereaction mixture was centrifuged, and the nitro-cellulose cake was quickly slurred in a large vol-ume of water. Then the products were washed bywater and dried at room temperature. By chang-ing the reaction temperature to 15, 25, 40, 50, 60,70, and 80°C, we prepared a series of nitrocellu-

lose with various molecular weights coded asNC1, NC2, NC3, NC4, NC5, NC6, and NC7.

Preparation of PU/Nitrocellulose IPNs

All the reagents except for castor oil were pur-chased from commercial resources in China, andwere of analytical grade. Castor oil, chemicallypure, was dehydrated at 100°C under 20 mmHgfor 1 h. 2,4-Tolylene diisocyanate (TDI) was redis-tilled under reduced pressure at 110°C before use.S01-17, a commercial solution, provided by WuhanDouble Tigers Coating Co. is mainly composed ofcastor oil, glycerol, and cyclohexanone as a dilut-ing agent. Castor oil-based polyurethane (PU)prepolymer (NCO : OH 5 2.0 ) was preparedsimilar to the method described by Sperling.10

The 70 wt % PU prepolymer/S01-17 (1 : 1 byweight) was mixed with 30 wt % nitrocellulose(NC), then acetic ether as a diluting agent wasadded to give PU/NC solution with 20 wt % solidcontent. The PU/NC coating solution was cast ona clean glass plate to form a film and cured at80°C for 5 min. The plate stayed at room temper-ature for a week then was used as a measure-ment. Using nitrocellulose with different molecu-lar weight, a series of films coded as PUNC1,PUNC2, PUNC3, PUNC4, PUNC5, PUNC6, andPUNC7 with approximately 50 mm thickness wasobtained. The film PU was prepared in the sameway except for a longer cure time (10 min).

Regenerated Cellulose Films Coated withPU/Nitrocellulose IPNs

Cellulose, a bagasse pulp (Mh 5 1.26 3 105, 83%a-cellulose), was purchased from Jiangman Fac-tory of Guangdong, China. The regenerated cellu-lose (RC) film was prepared by coagulating cellu-lose cuoxam solution (7% cellulose) according toour previous work.11 The PU/NC (70 : 30 byweight) coating solution was diluted by acetic togive 10% solid content, then coated on the bothsides of the RC films. The coated films were curedat 80°C for 2 min to give water-resistant films. Aseries of coated films was obtained by coating theRC film with PUNC1 ; PUNC7, and coded asRCUN1 ; RCUN7. The RC film coated with purePU was coded as RCU and the uncoated RC filmas RC0. The film thickness including ca 4mm coat-ing layer was adjusted to be 40 mm, except for IRmeasurement.

1624 ZHANG AND ZHOU

Characterization

The N content (C) in nitrocellulose was measuredby the Elemental Analyzer (CHN-O-Rapid, Hera-cus, Germany). The degree of substitution (DS) ofnitrocellulose was calculated by:

DS 5162 3 C

14 2 45 3 C (1)

The intrinsic viscosity [h] of nitrocellulose inacetone at 25°C was measured by using a Ubbel-odhe viscosimeter, and the viscosity-average mo-lecular weight (Mh) of the nitrocellulose was cal-culated according to the Mark-Houwink equationfor nitrocellulose in acetone at 25°C,12

@h# 5 0.377 3 1022M0.95 ~ml g21! (2)

The X-ray diffraction (XRD) of the samples ofPUNC1, PUNC3, and PUNC7 was carried out onX-ray diffractometer (D/MAX-1200, RigakuDenki, Japan). The X-ray diffraction patternswith Cuka radiation (l 5 1.5402Å) at 40 Kv and30 mA were recorded in the range of 2u 5 8 ; 80°.Infrared spectra (IR) of the coated films were re-corded with a Nicolet 170SX FT-IR spectrometer.

Swelling Test

The crosslink density of the samples of PUNC1 ;PUNC7 and PU was determined according to theswelling test method reported by Yoshida.13 Priorto the testing, the samples were freed from solu-ble material by extraction with acetone. Threepieces of the film sample having a weight of 0.4 geach were placed in 40 ml of dimenthyl form-amide (DMF) and allowed to stand for 1 week at25°C. After swelling, the film samples were re-moved from the DMF, and absorbed to removeexcess DMF using a filter paper, then weighed.The crosslink density was obtained by13:

yc

V0~mol/cm3! 5

2 2@y 1 xy2 1 ln~1 2 y!#

V1~2y1/3 2 y!(3)

where yc is effective molar number of crosslinkedchains, V1 is molar volume of solvent, x is poly-mer–solvent interaction parameter, y is volumefraction of polymer in swollen gel (y 5 V0/V), V0 isvolume of dry polymer (w/r), and V is volume ofswollen gel at equilibrium.

To determine x for the PU/NC-DMF system,swelling tests were carried out at 25, 29, 33, and36°C. From the temperature dependence of the y,x values were obtained as follows14:

d ln y/d ln T 5 x/2@5/6~x 2 1! 2 8y/9

2 11y2/12 2 14y3/15 2 · · ·# (4)

where T is temperature (K).The density (r) of the samples of PUNC1

; PUNC7 and PU was measured at 25, 29, 33,and 36°C by determining the weight of a volume-calibrated pycnometer filled with a mixture ofalcohol and chloroform, in which the samplesachieved flotation level. The density of the sampleequals the mixture density.

Thermal Analysis

Differential scanning calorimetry (DSC) of thesamples of PUNC1 ; PUNC7 and PU was per-formed with DSC-2C thermal analyzer (Perkin-Elmer Co., USA) under nitrogen atmosphere (30ml/min) at a rate of 10°C/min from 260 to 120°C.Thermal gravimetric analysis (TGA) of the coatedfilms and film RC0 were measured by using athermal analyzer (DT-40, Shimadzu Co.) at aheating rate of 20°C/min from room temperatureto 650°C.

Dynamic mechanical measurements of thecoated films of RCUN1, RCUN3, RCUN7, andfilm RC0 were taken on a dynamic mechanicalthermal analyzer (DMTA, Rheometric Scientific,MK-III) at a frequency of 10 Hz, temperatureranging from 2110 to 300°C at a heating rate of3°C/min. The measurement interval was about4 s and the film length was 8 mm.

Measurements of Properties

The tensile strength (sb) and the breaking elon-gation («b) of the coated films in states of dry andwet were measured on an electronic strengthtester XLD-0.1 (The Second Tensile Testing Ma-chine Manufactory of Changchun, China) accord-ing to the Chinese standard method (GB4456-84).After being immersed in the water for 1 h, thecoated films were taken out and used as wet filmsfor measurement. The water resistivity (R) of thecoated films was evaluated from sb(dry) in drystate and sb(wet) in wet state by the followingequation:

STRUCTURE AND PROPERTIES OF POLYURETHANE/NITROCELLULOSE IPNS 1625

R 5 sb~wet!/sb~dry! (5)

The strength data are related to the amount ofwater absorbed by the film; therefore, these datawere measured under the same conditions to de-crease the effect.

The percent light transmittance of the coatedfilms and film RC0 in the wavelength range of400–800 nm was measured by using a ShimadzuUV-160A Spectroscope.

RESULTS AND DISCUSSION

Effect of Molecular Weight of Nitrocellulose onCrosslink Density

The degree of substitution (DS) and the viscosityaverage molecular weight of the nitrocellulose(NC Mh) were summarized in Table I. With theincrease of the reaction temperature, the DS

value of the nitrocellulose slightly increased from1.9 to 2.1, but the NC Mh obviously decreased.

Semi-IPNs synthesized from PU prepolymerand nitrocellulose have been described.3,5 It isregarded that the nitrocellulose macromoleculespenetrate into PU networks, and give rise tosemi-IPNs in the PU/NC samples. The X-ray dif-fractogram of the samples PU and PU/NC showeda broad halo commencing from 13° to 32° in 2uwith lower magnitude, and there is no crystallineregion. This indicates that the samples of PU andPU/NC are amorphous similar to the result re-ported by Bhunia.1 Figure 1 shows IR spectra ofthe coated films of RCUN1, RCUN3, RCUN7,RCU, and the film RC0. The asymmetric stretch-ing vibrations of O–NO2 for pure nitrocellulosehave split into two new bands at 1654 and 1648cm21 in the coated films RCUN1, RCUN3, andRCUN7, indicating the presence of free and per-turbed O–NO2 group,15 which are absent in both

Table I. Molecular Weight (Mh) and Degree of Substitute (DS) of Nitrocellulose Samples

NitrocelluloseNo. NC1 NC2 NC3 NC4 NC5 NC6 NC7

DS 1.9 1.9 2.0 2.0 2.1 2.1 2.1Mh 3 1024 42.3 32.7 27.0 17.0 9.7 8.4 6.2

Figure 1. FT–IR spectra of the coated films of RCUN1, RCUN3, RCUN7, RCU, andthe film RC0 (from bottom to top).

1626 ZHANG AND ZHOU

the RC0 and RCU films. It may be concluded thatthe hydrogen bonds and interaction exist betweenthe O–NO2 of NC and N–H of PU in the PU/NCsemi-IPNs of the coated films.

The polymer–solvent interaction parameters(x) of PU/NC samples in DMF are summarizedin Table II. The mean value of 0.38 for thesamples of PUNC1 ; PUNC7 and 0.42 for PUwere chosen to estimate the crosslink density(yc/V0) of the samples. The yc/V0 values obtainedare listed in Table II. The error margin of mea-surement was 610%. The NC Mh dependence ofthe crosslink density for PU/NC samples isshown in Figure 2. The crosslink densities ofthe PU/NC samples increased with the increaseof the NC Mh until 2.7 3 105, then almost didnot change, and all were much smaller thanthat of the pure PU. As shown in Table II, thedensities of the PU/NC samples were slightlylarger than that of the PU, and decreased withincreasing the NC Mh. Interestingly, the PU/NCsamples with high NC Mh has higher crosslinkdensity but lower density, compared withPU/NC with low NC Mh. This indicates that thenitrocellulose in the PU/NC semi-IPNs plays animportant role in the hinder of PU network

formation, resulting in the enhancement of den-sity and reduction of crosslink density in thePU/NC samples. It can be explained that thenitrocellulose molecules with lower NC Mh

more readily penetrated into the PU networksand intimately blended with PU than that withhigher NC Mh. The interpretation was sup-ported by the results from IR and DMTA. Asshown in Figure 1, the intensity at 1648 cm21 ofthe hydrogen bonds between the O–NO2 of NCand N–H of PU in the coated films increasedwith the decrease of NC Mh. Moreover, the den-sity of nitrocellulose was measured to be 1.225g/ml at 25°C and did not change almost with itsmolecular weight. However, the densities ofPU/NC samples were larger slightly than bothPU and NC, showing that NC molecules coheredintimately with PU in the networks to increasemolecular content per volume. Figure 3 showstan d–temperature curves for the coated films ofRCUN1, RCUN3, RCUN7, and the film RC0obtained by DMTA. The data of the mechanicalrelaxation of the coated films and film RC0 aresummarized in Table III. There are three kindsof relaxation peaks, namely, a-relaxation at 170

Table II. Main Characteristics of the Samples PU/NC and PU

Film no. PU PUNC1 PUNC2 PUNC3 PUNC4 PUNC5 PUNC6 PUNC7

x 0.42 0.37 0.36 0.40 0.37 0.38 0.39 0.38r (g/ml) 1.24 1.26 1.26 1.25 1.27 1.31 1.30 1.28(xc/V0) 3 103

(mol/cm3)1.96 1.33 1.28 1.52 1.19 0.97 1.12 0.79

Figure 2. The NC Mh dependence of the crosslinkdensity for PUNC samples at 25°C. (. . .) represents thevalue of crosslink density for pure PU.

Figure 3. The tand – T curves for the coated films ofRCUN1 (C), RCUN3 (h), RCUN7 (‚), and film RC0 (●)by DMTA.

STRUCTURE AND PROPERTIES OF POLYURETHANE/NITROCELLULOSE IPNS 1627

; 270°C for cellulose, a- and b-relaxation at 43; 54°C for PU/NC semi-IPNs, and g-relaxationat 240 ; 250°C for PU/NC semi-IPNs, which ispossibly merged with the b-relaxation for cellu-lose. The narrow a-peak of PU/NC semi-IPNs inthe coated film RCUN7 shifted to higher tem-perature, indicating that better molecular mix-ing occurs between PU and NC. In tan d –temperature curve for the film RCUN1, thea-peak at 43°C displays distinct peak separa-tion. It is clear that the interaction between PUand NC of the film RCUN1 was weaker thanthat of the film RCUN7, so that PU networks inthe film RCUN1 were more than in the filmRCUN7.

Effect of Molecular Weight of Nitrocellulose onMechanical Properties

Figures 4 and 5 show the effects of the NC Mh onthe tensile strength (sb) and breaking elongation(«b) of the coated films RCUN1 ; RCUN7. The

strengths of the coated films in dry state in-creased with the increasing NC Mh until 27.03 104, then decreased slowly. However, thestrengths of the coated films in wet state slightlydecreased with the increasing NC Mh. This indi-cates that the strength of the coated films in drystate increased with the increase with the NC Mh,corresponding to the relations of the molecularweight and the crosslink density to strengthof the polymer. However, the strengths of thecoated films with lower NC Mh such as RCUN5; RCUN7 in wet state were higher than the filmswith larger Mh, owing to high density of thePU/NC coating layer, resulting in enhancementin water resistivity of the coated films. The effectof the NC Mh on water resistivity (R) of the coatedfilms is shown in Figure 6. The R values ofthe coated films increased with decreasing theMh NC.

As shown in Figure 5, the breaking elongation(«b) of the coated films in the dry state decreasedwith the increase of the NC Mh until 10 3 104,

Table III. Mechanical Relaxation for RC Film and the Coated Films

FilmNo.

a (Cellulose) a, b (PUNC IPNs) g

Tmax

(°C)Half-peak width

(°C)Tmax

(°C)Half-peak width

(°C)Tmax

(°C)Half-peak width

(°C)

RC0 268 53 — — 249.4 31.9RCUN1 207 62 42.9 65.3 255.5 44.1RCUN3 185 36 53.5 45.6 241.0 34.9RCUN7 170 33 54.3 38.0 246.4 24.3

Figure 4. Effects of Mh of nitrocellulose on the tensilestrength (sb) of the RC films coated with PU/NC coat-ings in dry (●) and wet (C) states.

Figure 5. Effects of Mh of nitrocellulose on the break-ing elongation («b) of RC films coated with PU/NC coat-ings in dry (●) and wet (C) states.

1628 ZHANG AND ZHOU

then decreased slowly. This is attributable to thatan increase in crosslink density leads to a de-crease in ultimate strain.16 It may be explainedthat with the increase of the crosslink density inthe coating layer of the coated films, cohesiveforces of polar groups (urethane groups and phe-nyl groups) increased, and restricted the rotationof the segments of PU and nitrocellulose, result-ing in a decrease in elongation at breaking.17 The«b values of the coated films in wet state increasedwith the increase of the NC Mh until 10 3 104,then kept constant almost. This indicates that thecoated films having higher density in wet statehave small elongation. Interestingly, when theNC Mh was lower than 10 3 104, the «b values ofthe coated films in dry and wet states were almostclose, suggesting the nitrocellulose with low Mh

plays a role in the plastification of the PUNCcoating layer, resulting in increase in the chainflexibility of the coated film in dry state.

Effect of Molecular Weight of Nitrocellulose onLight Transmittance

Figure 7 shows the effects of the NC Mh on lighttransmittance of the coated films. The error mar-gin for the measurements was 68%. When theNC Mh was lower than 17 3 104, the light trans-mittance values of the coated films almost keptconstant, and were the same as RC film (82% at400 nm and 88% at 800 nm). The good opticaltransmission of the coated films suggests thestrong interfacial bonding between the RC filmand PU/NC coating.5 Normally, the interface be-tween two materials will cause losses in optical

transmission because of the quantity of light,which is scattered and reflected at the interface.18

When the NC Mh was higher than 17 3 104, thelight transmittance of the coated films decreasedwith the increase of the NC Mh. This suggeststhat nitrocellulose molecules with higher Mh hin-dered the penetration of the PU/NC coatingacross the interface to RC film, resulting in de-crease of the interfacial bonding of the coatedfilms. From Figure 1, the intensity of COOOCstretching bands (1000 ; 1050 cm21) of the cel-lulose for the coated films was lower than that ofRC film, indicating the reaction at the interfacebetween PU/NC coating and RC film in the coatedfilm.19 The intensity of COOH in plane bendingmodes at 1202 cm21 for the films decreased inorder of RC0, RCU, RCUN7, RCUN3, andRCUN1. This implies that stronger hydrogenbonds exist between PU/NC coating and RC filmin the coated film. In addition, the a-relaxation ofcellulose for the coated films in Figure 3 shifted tolow temperature, and the shift decreased in orderof the films RCUN7, RCUN3, and RCUN1, sug-gesting a more enhancement in the interfacialinteraction of the film RCUN7 than RCUN1. Thedynamic mechanical data listed in Table III showthat the half -peak width of the coated films wassignificantly different from RC film. This impliesalso that a strong interaction exists between thePU/NC coating layer and cellulose film. Fromthese data, the interfacial bonding of the coatedfilms increased with decrease of the NC Mh in thePU/NC coatings, corresponding to the result fromthe optical property.

Figure 7. Effect of Mh of nitrocellulose on light trans-mittance of the coated films 400 nm (C) and 800 nm (●).

Figure 6. Effect of Mh of nitrocellulose on water re-sistivity (R) of the coated films.

STRUCTURE AND PROPERTIES OF POLYURETHANE/NITROCELLULOSE IPNS 1629

Effect of Molecular Weight of Nitrocellulose onThermal Properties

Figure 8 shows the effect of the NC Mh on theglass-transition temperature (Tg) of the PUNCsamples obtained by DSC. The Tg values of thePU/NC samples were obviously higher than thatof PU sample, and increased with the increase ofthe Mh. It is indicated that the pliability of thePU/NC samples decreased with the increase ofthe Mh. The effects of the NC Mh on the thermalstability of the coated films are shown in Table IVand Figure 9. The initial decomposition tempera-tures (Ti), and 10%, 50% mass loss temperature(T10%, T50%) of the coated films decreased withdecreasing the NC Mh, and were lower than thoseof RC film. However, the maximum decomposi-tion temperature (Tmax) and mass residues at644°C exhibit that the thermal stability of thecoated films was higher than RC film. It has beenreported that the enhancement in the thermalstability of the coated films is attributed to stronginterfacial bonding, which is caused by covalent

and hydrogen bonds between the PU/NC coatingand cellulose film.5

CONCLUSION

The physical and mechanical properties of theregenerated cellulose films coated with PU/NCcoating, which was synthesized from castor oil-based PU prepolymer and NC with various Mh toform semi-IPNs, were improved significantly. TheMh of nitrocellulose plays an important role in thestructure and properties of the PU/NC semi-IPNsand coated films. The crosslink densities of thePU/NC semi-IPNs were smaller than that of purePU and decreased with the decrease of the NCMh, indicating that NC molecules cohered inti-mately with PU, and hindered the PU networkformation. According to the diffusion model,20 theintimate adhesion of two macromolecules resultsfrom the interdiffusion of these molecules; there-fore, cohesive force between PU and nitrocellulosewith low Mh is larger than that with high NC Mh.Moreover, the PU/NC coating containing nitrocel-lulose with low Mh readily penetrated into the RCfilm and reacted with cellulose, resulting in astrong interfacial bonding and dense architec-ture. With increase of the NC Mh, the strengthand thermal stability of the coated films in-creased, but pliability, water resistivity, and op-tical transmission decreased. The interchain in-teraction between PU, NC, and cellulose in thecoated films with lower NC Mh, which plays a rolein enhancement of blend miscibility and plasticitydue to plastification of small molecules, wasstronger than the films with higner NC Mh.

Figure 8. Mh dependence of the glass-transition tem-perature (Tg) for the PUNC samples (E). (. . .) repre-sents the value of Tg for pure PU.

Table IV. Effects of Mh of Nitrocellulose on theThermal Properties of the Coated Films

FilmNo.

Ti

(°C)T10%

(°C)T50%

(°C)Tmax

(°C)

Residueat 644°C

(%)

RC0 246 318 343 364 10.6RCUN1 169 255 339 375 15.9RCUN3 148 237 330 371 16.7RCUN7 140 214 318 361 18.9

Figure 9. TGA curves of the films RC0 (—), RCUN1(- - - -), RCUN3 (. . .), RCUN7 (- z - z - z ).

1630 ZHANG AND ZHOU

This research was supported by the National NaturalScience Foundation of China (59773026) and Labora-tory of Cellulose and Lignocellulose Chemistry, Chi-nese Academic Sinica.

REFERENCES AND NOTES

1. Bhunia, H. P.; Jana, R. N.; Basak, A.; Lenka, S.;Nando, G. B. J Polym Sci Part A: Polym Chem Ed1998, 36, 391.

2. Miyamoto, T. Kinoshi Kenkyu Kaishi 1995, 34, 2.3. Natchimuthu, N.; Rajalingam, P.; Radhakrish-

nan, G.; Francis, D. J. J Appl Polym Sci 1990, 41,3059.

4. Zhang, L.; Liu, H.; Yan, S.; Yang, G.; Feng, H. JPolym Sci Part B: Polym Phys Ed 1997, 35,2495.

5. Zhang, L.; Zhou, Q. Ind Eng Chem Res 1997, 36,2651.

6. Gong, P.; Zhang, L. J Appl Polym Sci 1998, 68,1313.

7. Gong, P.; Zhang, L. Ind Eng Chem Res 1998, 37,2681.

8. Morohoshi, N.; Hirose, S.; Hatakeyama. H.; To-kashiki, T.; Teruya, K. Sen-1 Gakkaishi 1995,51(3), 143.

9. Hourston, D. J.; Schafer, F. U. J Appl Polym Sci1996, 62, 2025.

10. Devia, N.; Manson, J. A.; Sperling, L. H. Macromol-ecules 1979, 12, 360.

11. Zhang, L.; Yang, G.; Yan, S.; Liu, H. Chin Pat. CN1091144A (L1.C08L97/02), 1994.

12. Michie, R. J. C. Polymer 1961, 2, 446.13. Yoshida, H.; Morck, R.; Kringstad, K. P. J Appl

Polym Sci 1987, 34, 1187.14. Flory, P. J.; Rehner, J. J Chem Phys 1943, 11, 521.15. Natchimuthu, N.; Rajalingam, P.; Radhakrishnan,

G. J Appl Polym Sci 1992, 44, 981.16. Waever, K. D.; Stoffer, J. O.; Day, D. E. Polym

Comp 1995, 16, 161.17. Liaw, D.; J Appl Polym Sci 1997, 66, 1251.18. Saunders, J. H. Rubber Chen Technol 1960, 33,

1259.19. Liang, C. Y.; Marchessault, R. H. J Polym Sci 1959,

39, 269.20. Voyutskii, S. S.; Margolina, Y. L. Uspekhi Khimi

1949, 18, 449.

STRUCTURE AND PROPERTIES OF POLYURETHANE/NITROCELLULOSE IPNS 1631