Research Article The In Situ Polymerization and ...downloads.hindawi.com/journals/jspec/2013/164275.pdfThe In Situ Polymerization and Characterization of PA6/LiCl Composites DandanSun,JiangLi,QinghuaPan,ChaoweiHao,andGuoqiaoLai

Hindawi Publishing CorporationJournal of SpectroscopyVolume 2013, Article ID 164275, 4 pageshttp://dx.doi.org/10.1155/2013/164275

Research ArticleThe In Situ Polymerization and Characterization ofPA6/LiCl Composites

Dandan Sun, Jiang Li, Qinghua Pan, Chaowei Hao, and Guoqiao Lai

Key Laboratory of Organosilicon Chemistry and Material Technology Ministry of Education, Hangzhou Normal University,Hangzhou 310012, China

Correspondence should be addressed to Chaowei Hao; [email protected]

Received 5 October 2013; Accepted 23 November 2013

Academic Editor: Yizhuang Xu

Copyright © 2013 Dandan Sun et al. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

PA6/LiCl composites were synthesized by in situ anionic polymerization based on the interaction between the inorganic salts andPA6. Sodium hydroxide as initiator and N-acetylcaprolactam as activator were used in the preparation of PA6/LiCl compositeswith variety of LiCl content. X-ray diffraction (XRD) and differential scanning calorimeter (DSC) testing results showed that bothof degree of crystallinity and melting temperature of the composites were decreased under the influence of LiCl. And the 𝛾 crystalphase proportion increased with increasing the LiCl content to appropriate amount.

1. Introduction

Polyamide is general thermoplastic resin with repeat amidegroups—[NHCO]—on the molecular main chain, and it iscommonly known as nylon. PA6 is a very common andimportant polymer material used in different fields rangingfrom textile and carpet production to special technicalapplications. The intramolecular polar amide group of PA6can be found in hydrogen bond, increasing the intermolec-ular forces, and exhibiting relatively high strength, goodtoughness, chemical and abrasion resistance, and so forth.Nowadays, superfine fibers have attracted more and moreattention from people for occupying the special properties,and the research on the superfine fibers is developing quickly[1]. However, the plenty of hydrogen bonding betweenchains in PA6, quickly crystal capacity, high crystallinity,and chain defects in the crystal lattice restrict the moleculararrangement and orientation, which hinders the achievementof higher DR during the PA6 spinning and the processing ofthe superfine fiber.

The studying emphasis of PA6 is always focusing on themodification in order to change the properties of polymerand be suitable for more applications [2–5]. There are manymodification methods, which in general can be divided intoblending, in situ polymerization, and copolymerization. Asfor in situ polymerization of PA6 composite, the acquired

composites are prepared by adding the modifier (polymeror inorganic particles) to the caprolactam molten monomer,then adding sodium hydroxide as initiator to open thering, and introducing N-acetylcaprolactam as activators toa high-polymerization rate [6, 7]. This paper introduced themodification of PA6 and prepared a series of PA6/lithiumchloride composite via in situ anionic polymerization. Thecharacterization of the composites was carried out by FT-IR,NMR, DSC, and X-ray analysis methods.

2. Materials and Methods

2.1. Materials. Caprolactam, AR, Aladdin Chemistry Co.,Ltd.; Sodium hydroxide, AR, Aladdin Chemistry Co., Ltd.;lithium chloride, AR, Tianjin University Chemical ReagentFactory; acetic anhydride, Shanghai Lingfeng ChemicalReagent Co., Ltd.

2.2. The Preparation of N-Acetylcaprolactam (CCL). N-Ace-tylcaprolactam can increase the electronegativity of amidobond and improve the amide carbonyl activity of caprolactamanion. Toluene was used as solvent in the preparation; theratio of acetic anhydride and caprolactam was 1.2 : 1, thenheating reflux for 2 h and extracting the unreacted aceticanhydride and the acetic acid with distilled water. The syn-thesis of CCL was shown in Scheme 1.

2 Journal of Spectroscopy

NH + rt. N CO

O

+(CH3CO)2OToluene

CH3

CH3COOH

O

Scheme 1: Synthesis of N-acetylcaprolactam.

2.3. Synthesis of LiCl/PA6 Composites. Lithium chloridewhich acted as modifier can interact with carbonyl groupin caprolactam monomer and dissolve into the monomer,which means the well dispersed of modifier in the polymercomposites. The experimental process was as follows: firstly,adding certain amount of caprolactam in a three-flask bottleand heating to 130∘C under vacuum for 30minutes to removemoisture and impurity in the system; secondly, quicklyputting certain amount of lithium chloride into the bottle,keeping up the vacuum, and heating to 135∘C at the same timeuntil lithium chloride dissolved completely; thirdly, addingcatalyzer sodiumhydroxide into themeltmixture andheatingto 140∘C; fourthly, after catalyzing for 15 minutes, addingthe activator (CCL) into the bottle fast; finally, pouringthe melt mixture into a mold preheated at 180∘C until thepolymerization finished.

3. Results and Discussion

3.1. The Characterization of N-Acetylcaprolactam (CCL). Theproducts were characterized by FT-IR andNMR, as shown inFigures 1 and 2. 1H-NMR (CDCL

3, 𝛿): 2.49 (S, 3H, –CH3),

2.73 (T, 2H, –CH2–), 3.89 (T, 2H, –CH2–); IR (cm−1, film)2933 (–CH2–), 1696 (C=O).

3.2. XRD Analysis of PA6/LiCl Composite. PA6 was a mul-ticrystal phase polymer; the crystallization behavior includ-ing crystallinity, crystal structure, size, and distribution ofspherulite had decisive influence on the physical propertiesof nylon product. As a result, controlling the appropriatecrystalline state was very important for PA6 product toobtain excellent performance. Under different crystallizationconditions, different formation of the hydrogen bond struc-ture forming is different, which led to different spherulitestructure. PA6 mainly had two stable crystal structures 𝛼 and𝛾 [8], 𝛾-form can improve the degree of deformation, and 𝛼-form has strong stability. During PA6 spinning process, 𝛾-form could improve the deformation degree and benefit toprepare the superfine denier fiber.

The XRD patterns in Figure 3 showed that the samplesof PA6 and the composites displayed characteristic peaksat scattering angles of 20.0∘ and 23.60∘ [9], correspondingto the reflections of the crystalline planes (200) and com-bined (002)/(202), respectively, which was corresponding tomonoclinic 𝛼-phase morphology. The peak position of thecomposites had a slight displacement compared with PA6,which implied that the lattice dimension of PA6 changedwiththe addition of lithium chloride. It was interesting that thecomposite had obvious diffraction peak at about 21.4∘, whichcorresponded to the 𝛾-form of PA6.

2933

1696

1436

1367

1184

1255

964

8791081

3200 3000 2800 1800 1600 1400 1200 1000 800

Wavenumbers (cm−1)

Figure 1: FT-IR spectrum of N-acetylcaprolactam.

Table 1: The XRD parameters of the PA6/LiCl composites.

Sample HKL 2𝜃/∘ 𝐴 𝐴𝛼l/𝐴𝛼2 (%) 𝐴𝛾/𝐴𝛼 (%)

0%200 20.3 620.5

48.6 6.7100 21.8 126.4002 + 202 23.5 1276.0

0.1%200 20.3 453.3

34.2 11.9100 21.6 213.0002 + 202 23.6 1327.1

0.3%200 20.2 268.1

90.0 31.2100 21.4 176.5002 + 202 23.6 297.7

0.5%200 20.3 99.0

30.7 40.6100 21.6 171.1002 + 202 23.7 322.2

1.0%200 20.4 581.8

70.9 12.2100 21.8 171.2002 + 202 23.8 820.7

As can be seen from Table 1, compared with pure PA6,both the two diffraction angles in PA6/LiCl compositesbecame larger, which could be due to the destruction effect oflithium chloride molecule on the hydrogen bonding betweenthe PA6 chains. Comparing the proportion of 𝛼-form of PA6and the composites, we could find that the content of 𝛼-form reduced with increasing content of lithium chloride.Variation trend of the 𝛾-crystal form also can be seen fromFigure 3. With increasing content of lithium chloride, theintensity of 𝛾-form crystal diffraction peak increased first andthen decreased, which illustrated that the proportion of PA6𝛾-form crystal phase increased with lithium chloride contentincreasing in a certain range.

3.3. DSC Analysis of PA6/LiCl Composite. Figure 4 showedthe heating curves after erasing thermal history of nylonand composites. In the process of constant heating rate, themelting temperature linear declined with the increasement

Journal of Spectroscopy 3

0200400600800100012001400160018002000220024002600280030003200340036003800

3.23

1.54

1.00

1.00

1.67

1.71

1.75

1.76

1.78

2.492.71

2.72

2.73

3.88

3.89

3.90

−200

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0

3.1

3.2

3.3

3.4

3.5

3.6

3.7

3.8

3.9

4.0

4.1

OO

H2C

CH2

CH2

CH2CH2

NC

C CH3

N-Acetylcaprolactam

f1 (ppm)

Figure 2: 1H-NMR spectrum of N-acetylcaprolactam.

Intensity

123

54

6

0 5 10 15 20 25 30 35 402𝜃 (∘)

Figure 3: Wide angle X-ray diffraction patterns of LiCl/PA6 com-posites with different LiCl content: (1) 0.0%; (2) 0.1%; (3) 0.3%; (4)0.5%; (5) 1.0%; (6) 2.0%.

of lithium chloride content. When the content reached 2%,the melting temperature declined to nearly 20∘C comparedwith that of PA6. Both the pure PA6 and the PA6/LiClcomposites had multiple melting peaks, which may be dueto the different degree of crystallinity and crystal perfection.Higher temperature crystallization peak corresponded to aperfect crystal melting, while the low temperature peak wasthe low degree of crystal perfection [10, 11]. With the addition

1

2

3

4

5

6

Endo

180 190 200 210 220 230 240T (∘C)

Figure 4: The second heating process of the PA6/LiCl compositeswith different LiCl content: (1) 0.0%; (2) 0.1%; (3) 0.3%; (4) 0.5%; (5)1.0%; (6) 2.0%.

of lithium chloride, lithium ion could form six memberedring-structure via complexing interactionwith PA6molecule,which reducedmolecular chainmigration rate and the degreeof crystal perfection.

4. Conclusions

We prepared the PA6/LiCl composites via in situ anionicpolymerization. IR and NMR result confirmed the successful

4 Journal of Spectroscopy

synthesis of N-acetylcaprolactam which acted as activator.DSC and X-ray results showed that the 𝛾-crystal phaseproportion in composites increased with increasing theLiCl content to appropriate amount. While 𝛾-form couldimprove the degree of deformation, which implied that thepreparation of superfine fiber for PA6 became easily duringthe spinning.

Acknowledgments

Thisworkwas financially supported by theMajor Science andTechnology Projects of Science and Technology Departmentof Zhejiang Province (Contract Grant no. 2010C11043) andfunded by National High Technology Research and Develop-ment Program 863 (2010AA03A406).

References

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[7] Z. Xu and C. Gao, “In situ polymerization approach tographene-reinforced nylon-6 composites,”Macromolecules, vol.43, no. 16, pp. 6716–6723, 2010.

[8] H. Arimoto, M. Ishibashi, M. Hirai et al., “Crystal structure ofthe 𝛾 form of nylon6,” Journal of Polymer Science, vol. 3, no. 1,pp. 317–326, 1965.

[9] M. I. Kohan, Nylon Plastics Handbook, Hanser, New York, NY,USA, 1995.

[10] S. Yue, W. Gong, N. Qi, B. Wang, W. Zhou, and Y. Zhu,“Effect of the dispersion of organic rectorite on the nonisother-mal crystallization kinetics and melting behaviors of nylon 6nanocomposites,” Journal of Applied Polymer Science, vol. 110,no. 5, pp. 3149–3155, 2008.

[11] L. Cui, Q. Fu, C.-J. Chang, and J.-T. Yeh, “The effect of poly(vinylalcohol) hydrolysis on the properties of its blends with nylon 6,”Polymer Engineering and Science, vol. 49, no. 8, pp. 1553–1561,2009.

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Research Article The In Situ Polymerization and ...downloads.hindawi.com/journals/jspec/2013/164275.pdfThe In Situ Polymerization and Characterization of PA6/LiCl Composites DandanSun,JiangLi,QinghuaPan,ChaoweiHao,andGuoqiaoLai