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Mechanisms of nanoclay-enhanced plastic foaming processes: effects of nanoclay intercalation and exfoliation

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Abstract

The foaming behaviors of high-density polypropylene–nanoclay composites with intercalated and exfoliated nanoclay particles blown with carbon dioxide were examined via in situ observation of the foaming processes in a high-temperature/high-pressure view-cell. The intercalated nanoclay particles were 300–600 nm in length and 50–200 nm in thickness, while the exfoliated nanoclay particles were 100–200 nm in length and 1 nm in thickness. Contrary to common belief, it was discovered that intercalated nanoclay yielded higher cell density than exfoliated nanoclay despite its lower particle density. This was attributed to the higher tensile stresses generated around the larger and stiffer intercalated nanoclay particles, which led to increase in supersaturation level for cell nucleation. Also, the coupling agent used to exfoliate nanoclay would increase the affinity between polymer and surface of nanoclay particles. Consequently, the critical work needed for cell nucleation would be increased; pre-existing microvoids, which could act as seeds for cell nucleation, were also less likely to exist. Meanwhile, exfoliated nanoclay had better cell stabilization ability to prevent cell coalescence and cell coarsening. This investigation clarifies the roles of nanoclay in plastic foaming processes and provides guidance for the advancement of polymer nanocomposite foaming technology.

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References

  • Albalak RJ, Tadmor Z, Talmon Y (1990) Polymer melt devolatilization mechanisms. AlChE J 36(9):1313–1320

    Article  CAS  Google Scholar 

  • Apfel RE (1971) Vapor nucleation at a liquid–liquid interface. J Chem Phys 54:62–63

    Article  CAS  Google Scholar 

  • Blander M, Katz JL (1975) Bubble nucleation in liquids. AlChE J 21(5):833–848

    Article  CAS  Google Scholar 

  • Cole R (1974) Boiling nucleation. Adv Heat Transfer 10:85–166

    Article  CAS  Google Scholar 

  • Colton JS, Suh NP (1987a) Nucleation of microcellular thermoplastic foam with additives: part I: theoretical considerations. Polym Eng Sci 27(7):485–492

    Article  CAS  Google Scholar 

  • Colton JS, Suh NP (1987b) Nucleation of microcellular thermoplastic foam with additives: part II: experimental results and discussion. Polym Eng Sci 27(7):493–499

    Article  CAS  Google Scholar 

  • Fisher JC (1948) The fracture of liquids. J Appl Phys 19(11):1062–1067

    Article  Google Scholar 

  • Fletcher NH (1958) Size effect in heterogeneous nucleation. J Chem Phys 29(3):572–576

    Article  CAS  Google Scholar 

  • Forest TW, Ward CA (1976) Effect of a dissolved gas on the homogeneous nucleation pressure of a liquid. J Chem Phys 66(6):2322–2330

    Article  Google Scholar 

  • Forest TW, Ward CA (1978) Homogeneous nucleation of bubbles in solutions at pressures above the vapor pressure of the pure liquid. J Chem Phys 69(5):2221–2230

    Article  CAS  Google Scholar 

  • Giannelis EP (1996) Polymer layered silicate nanocomposites. Adv Mater 8(1):29–35

    Article  CAS  Google Scholar 

  • Gibbs JW (1961) The Scientific Papers of J. Willard Gibbs, vol 1. Dover Publications Inc., New York

    Google Scholar 

  • Harvey EN, Barnes DK, McElroy WD, Whiteley AH, Pease DC, Cooper KW (1944) Bubble formation in animals. I. Physical factors. J Cell Comp Physiol 24(1):1–22

    Article  CAS  Google Scholar 

  • Jarvis TJ, Donohue MD, Katz JL (1975) Bubble nucleation mechanisms of liquid droplets superheated in other liquids. J Colloid Interface Sci 50(2):359–368

    Article  CAS  Google Scholar 

  • Katz JL, Blander M (1973) Condensation and boiling: corrections to homogeneous nucleation theory for nonideal gases. J Colloid Interface Sci 42(3):496–502

    Article  CAS  Google Scholar 

  • Kim Y, Park CB, Chen P, Thompson RB (2011) Origins of the failure of classical nucleation theory for nanocellular polymer foams. Soft Matter 7(16):7351–7358

    Article  CAS  Google Scholar 

  • Lee YH, Park CB, Sain M, Kontopoulou M, Zheng W (2007a) Effects of clay dispersion and content on the rheological, mechanical properties, and flame retardance of HDPE/clay nanocomposites. J Appl Polym Sci 105(4):1993–1999

    Article  CAS  Google Scholar 

  • Lee YH, Wang KH, Park CB, Sain M (2007b) Effects of clay dispersion on the foam morphology of LDPE/clay nanocomposites. J Appl Polym Sci 103(4):2129–2134

    Article  CAS  Google Scholar 

  • Leung SN, Park CB, Li H (2006) Numerical simulation of polymeric foaming processes using modified nucleation theory. Plast Rubber Compos Macromol Eng 35(3):93–100

    Article  CAS  Google Scholar 

  • Leung SN, Wong A, Wang C, Park CB (2012) Mechanism of extensional stress-induced cell formation in polymeric foaming processes with the presence of nucleating agents. J Supercrit Fluids 63:187–198

    Article  CAS  Google Scholar 

  • Levy S (1981) Advances in plastics technology. Van Nostrand Reinhold, New York

    Google Scholar 

  • Lubetkin SD (2003) Why is it much easier to nucleate gas bubbles than theory predicts. Langmuir 19(7):2575–2587

    Article  CAS  Google Scholar 

  • Matuana LM, Park CB, Balatinecz JJ (1997) Processing and cell morphology relationships for microcellular foamed PVC/wood-fiber composites. Polym Eng Sci 37(7):1137–1147

    Article  CAS  Google Scholar 

  • Okamoto M, Nam PH, Maiti P, Kotaka T, Nakayama T, Takada M, Ohshima M, Usuki A, Hasegawa N, Okamoto H (2001) Biaxial flow-induced alignment of silicate layers in polypropylene/clay nanocomposite foam. Nano Lett 1(9):503–505

    Article  CAS  Google Scholar 

  • Seeler KA, Kumar V (1993) Tension–tension fatigue of microcellular polycarbonate: initial results. J Reinf Plast Compos 12(3):359–376

    Article  CAS  Google Scholar 

  • Shimbo M, Baldwin DF, Suh NP (1992) Viscoelastic behavior of microcellular plastics. In: American Chemical Society Division of Polymeric Materials—Science and Engineering, vol 67. ACS, Washington, DC, pp 512–513

  • Shimbo M, Higashitani I, Miyano Y (2007) Mechanism of strength improvement of foamed plastics having fine cell. J Cell Plast 43(2):157–167

    Article  CAS  Google Scholar 

  • Suh KW, Park CP, Maurer MJ, Tusim MH, De Genova R, Broos R, Sophiea DP (2000) Lightweight cellular plastics. Adv Mater 12(23):1779–1789

    Article  CAS  Google Scholar 

  • Taki K, Yanagimoto T, Funami E, Okamoto M, Ohshima M (2004) Visual observation of CO2 foaming of polypropylene-clay nanocomposites. Polym Eng Sci 44(6):1004–1011

    Article  CAS  Google Scholar 

  • Tanoue S, Utracki LA, Garcia-Rejon A, Tatibouët J, Cole KC, Kamal MR (2004) Melt compounding of different grades of polystyrene with organoclay. Part 1: compounding and characterization. Polym Eng Sci 44(6):1046–1060

    Article  CAS  Google Scholar 

  • Ton-That MT, Perrin-Sarazin F, Cole KC, Bureau MN, Denault J (2004) Polyolefin nanocomposites: formulation and development. Polym Eng Sci 44(7):1212–1219

    Article  CAS  Google Scholar 

  • Tucker AS, Ward CA (1975) Critical state of bubbles in liquid–gas solutions. J Appl Phys 46(11):4801–4808

    Article  Google Scholar 

  • Usuki A, Kojima Y, Kawasumi M, Okada A, Fukushima Y, Kurauchi T, Kamigaito O (1993) Synthesis of nylon 6-clay hybrid. J Mater Res 8(5):1179–1184

    Article  CAS  Google Scholar 

  • Wang C, Leung SN, Bussmann M, Zhai WT, Park CB (2010) Numerical investigation of nucleating-agent-enhanced heterogeneous nucleation. Ind Eng Chem Res 49(24):12783–12792

    Article  CAS  Google Scholar 

  • Ward CA, Levart E (1984) Conditions for stability of bubble nuclei in solid surfaces contacting a liquid–gas solution. J Appl Phys 56(2):491–500

    Article  CAS  Google Scholar 

  • Ward CA, Tucker AS (1975) Thermodynamic theory of diffusion-controlled bubble growth or dissolution and experimental examination of the predictions. J Appl Phys 46(1):233–238

    Article  CAS  Google Scholar 

  • Ward CA, Balakrishnan A, Hooper FC (1970) On the thermodynamics of nucleation in weak gas–liquid solutions. J Basic Eng Trans 92(4):695–704

    Article  CAS  Google Scholar 

  • Ward CA, Johnson WR, Venter RD, Ho S, Forest TW, Fraser WD (1983) Heterogeneous bubble nucleation and conditions for growth in a liquid–gas system of constant mass and volume. J Appl Phys 54(4):1833–1843

    Article  Google Scholar 

  • Wilt PM (1986) Nucleation rates and bubble stability in water-carbon dioxide solutions. J Colloid Interface Sci 112(2):530–538

    Article  CAS  Google Scholar 

  • Wong A, Park CB (2012) The effects of extensional stresses on the foamability of polystyrene-talc composites blown with carbon dioxide. Chem Eng Sci 75(1):49–62

    CAS  Google Scholar 

  • Wong A, Leung SN, Li GYG, Park CB (2007) Role of processing temperature in polystyrene and polycarbonate foaming with carbon dioxide. Ind Eng Chem Res 46(22):7107–7116

    Article  CAS  Google Scholar 

  • Wong A, Chu RKM, Leung SN, Park CB, Zong JH (2011) A batch foaming visualization system with extensional stress-inducing ability. Chem Eng Sci 66(1):55–63

    Article  CAS  Google Scholar 

  • Wong A, Guo Y, Park CB, Zhou NQ (2012) Isothermal crystallization-induced foaming of polypropylene under high pressure carbon dioxide. In: 70th annual technical conference of the society of plastics engineers, Orlando, FL. pp 2443–2449

  • Xu X, Park CB, Xu D, Pop-Iliev R (2003) Effects of die geometry on cell nucleation of PS foams blown with CO2. Polym Eng Sci 43(7):1378–1390

    Article  CAS  Google Scholar 

  • Yang H–H, Han CD (1984) Effect of nucleating agents on the foam extrusion characteristics. J Appl Polym Sci 29:4465–4470

    Article  CAS  Google Scholar 

  • Zheng WG, Lee YH, Park CB (2010) Use of nanoparticles for improving the foaming behaviors of linear PP. J Appl Polym Sci 117(5):2972–2979

    CAS  Google Scholar 

Download references

Acknowledgments

The authors of this paper are grateful to the Consortium of Cellular and Micro-Cellular Plastics (CCMCP) and Natural Sciences and Engineering Council of Canada (NSERC) for their financial support of this study.

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Correspondence to Chul B. Park.

Appendix: classical nucleation theory

Appendix: classical nucleation theory

The CNT and the concept of R cr was first developed by Gibbs (1961). Over the years, various researchers have built on this theory to examine the necessary conditions and free energy barrier for homogeneous nucleation (Blander and Katz 1975; Ward et al. 1970; Forest and Ward 1976, 1978; Tucker and Ward 1975; Katz and Blander 1973) as well as heterogeneous nucleation with different surface geometries (Ward et al. 1983; Ward and Levart 1984; Cole 1974; Wilt 1986; Fisher 1948; Fletcher 1958; Apfel 1971; Jarvis et al. 1975).

Homogeneous nucleation

According to the CNT, the free energy change (ΔF hom) from a metastable liquid–gas solution to the homogeneous formation of a gas bubble within the liquid can be given as (Tucker and Ward 1975; Ward et al. 1970):

$$ \Updelta F_{\hom } = - \left( {P_{\text{bub}} - P_{\text{local}} } \right)V_{\text{g}} + \gamma_{ \lg } A_{ \lg } $$
(A1)

where P bub is the pressure inside the bubble; P local is the system pressure surrounding the bubble; V g is the bubble volume; γ lg is the surface tension of the bubble–liquid interface; and A lg is the bubble surface area. The first term on the left hand side (i.e., −(P bub − P local)V g) is the work done by the expansion of gas volume inside the bubble, and the second term (i.e., γ lg A lg) is the work required to create the liquid–gas interface that constitutes the bubble. Assuming that the bubble is spherical in shape, Eq. A1 can be rearranged as:

$$ \Updelta F_{ \hom } = - \frac{{4\pi R_{\text{bub}}^{3} }}{3}\left( {P_{\text{bub}} - P_{\text{local}} } \right) + \gamma_{lg} \left( {4\pi R_{\text{bub}}^{2} } \right) $$
(A2)

where R bub is the radius of the bubble. Based on Eq. A2, a ΔF hom versus R bub plot can be generated (see Fig. 1), which exhibits a maximum ΔF hom value. The maximum ΔF hom represents the free energy barrier for homogeneous nucleation (W hom), and the R bub at which ΔF hom is at the maximum is the R cr. Since a system tends to seek a low energy configuration, a bubble smaller than R cr tends to collapse, and a bubble larger than R cr tends to grow spontaneously. By taking the derivative of ΔF hom with respect to R bub and equating it to zero, the R cr could be determined as (Tucker and Ward 1975; Ward et al. 1970):

$$ R_{\text{cr}} = \frac{{2\gamma_{ \lg } }}{{P_{\text{bub,cr}} - P_{\text{local}} }} $$
(A3)

where P bub,cr is the pressure inside a critical bubble. By substituting Eq. A3 into A2, the free energy barrier for homogeneous nucleation (W hom) can be determined to be (Tucker and Ward 1975; Ward et al. 1970):

$$ W_{\hom } = \frac{{16\pi \gamma_{\lg }^{3} }}{{3\left( {P_{\text{bub,cr}} - P_{\text{local}} } \right)^{2} }} $$
(A4)

Equation A4 indicates that W hom is strongly dependent on γ lg and the degree of supersaturation, which is defined to be (P bub,cr − P local). A lower γ lg and a higher degree of supersaturation would cause R cr and W hom to decrease, which lead to a higher tendency for bubble nucleation.

Heterogeneous nucleation

The derivation of R cr and the free energy barrier for heterogeneous nucleation (W het) could be formulated in a similar fashion. To be specific, the free energy change (ΔF het) from a metastable liquid–gas solution to the heterogeneous formation of a gas bubble within the liquid on a liquid/solid interface can be given as (Ward et al. 1983; Ward and Levart 1984; Cole 1974; Wilt 1986; Fisher 1948; Fletcher 1958; Apfel 1971; Jarvis et al. 1975):

$$ \Updelta F_{\text{het}} = - \left( {P_{\text{bub}} - P_{\text{local}} } \right)V_{\text{g}} + \left( {\gamma_{\text{sg}} - \gamma_{\text{sl}} } \right)A_{\text{sg}} + \gamma_{ \lg } A_{ \lg } $$
(A5)

where γ sg and γ sl are the surface tension along the solid–gas interface and solid–liquid interface; and A sg and A lg is the surface area along the solid–gas and liquid–gas interface. Similar to the case of homogeneous nucleation, the first term on the left hand side (i.e., −(P bub − P local)V g) is the work done by the expansion of gas volume inside the bubble. The second term is the energy required to replace the solid–liquid interface (e.g., nucleating agent–polymer interface) with a solid–gas interface (e.g., nucleating agent–bubble interface). The third term (i.e., γ lg A lg) is the work required to create the liquid–gas interface that constitutes the bubble. Using the Young’s equation, which relates the interfacial energies and the contact angle (θ c) between the liquid and gas phase (measured in the liquid phase) (Ward and Tucker 1975):

$$ \gamma_{\text{sg}} - \gamma_{\text{sl}} = \gamma_{ \lg } \cos \theta_{\text{c}} $$
(A6)

and the expressions for V g, A sg, and A lg (which is specific to the surface geometry of the nucleating site), Eq. 11 can be simplified to:

$$ \Updelta F_{\text{het}} = - \frac{{4\pi R_{\text{bub}}^{3} }}{3}\left( {P_{\text{bub}} - P_{\text{local}} } \right)F + 4\pi R_{\text{bub}}^{2} \gamma_{ \lg } F $$
(A7)

where F is a geometric factor that equals to the ratio of the volume of a heterogeneously nucleated bubble to that of a spherical bubble having the same radius of curvature. By taking the derivative of ΔF het with respect to R bub and equating the resulting equation to zero, it can be shown that the expression for R cr is the same as the homogeneous nucleation case (Eq. A3). The expression for W het can then be determined by substituting Eq. A3 into A7; which, after simplification, differs slightly from W hom, as follows (Fisher 1948):

$$ W_{\text{het}} = \frac{{16\pi \gamma_{\lg }^{3} F}}{{3\left( {P_{\text{bub,cr}} - P_{\text{local}} } \right)^{2} }} = W_{\hom } F $$
(A8)

Since F ≤ 1 in most scenarios, W het is lower than W hom in most cases. Therefore, nucleation is more likely to occur heterogeneously on nucleating agents or impurities as supposed to homogeneously within the bulk phase of a polymer–gas solution.

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Wong, A., Wijnands, S.F.L., Kuboki, T. et al. Mechanisms of nanoclay-enhanced plastic foaming processes: effects of nanoclay intercalation and exfoliation. J Nanopart Res 15, 1815 (2013). https://doi.org/10.1007/s11051-013-1815-y

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