Retrograde Foaming

Most polymer-gas systems have a single glass transition temperature at a given gas pressure or gas concentration, which often decreases linearly with gas pressure or gas concentration in polymers. PMMA-CO2 is one of the few polymer systems that 

FIGURE 1.4 Schematic of a typical continuous extrusion foaming setup. (Reprinted with permission from Han X. et ah, Polymer Engineering and Science 2003, 43, 1261-1275. 

Chen et al. (2011) prepared PMMA-CNT nanocomposite foams by retrograde foaming and identified two additional complications that might occur. First, as will be discussed in great detail in Section 1.4.1.2, the exceptionally high nucleation rates 

FIGURE 1.6 SEM of a PMMA/5% MHABS nanocomposite foam by retrograde foaming. The average cell size is around 0.3 pm and the cell density is around is 1.86 x 10 cells/cm. (Reprinted with permission from Zeng C. et al.. Advanced Materials 2003, 15, 1743-1747. Copyright 2003, John Wiley Sons.) 

---

Retrograde foaming of PMMA nanocomposites have been studied. Zeng etal. (2003) prepared clay nanocomposite foam by retrograde foaming of PMMA-5%. MHABS nanocomposite and submicron cellular foams were prepared (Figure 1.6). 

Starch for use in papermaking has to meet specific purity requirements in residual oil, protein, bran and ash content. Industrial starches have a protein content (N X 6.25), ranging from about 0.05% for potato starch to 0.3-0.6% for com starch, depending on separation efficiency during production. Excess protein content will induce foaming in dispersions of starch and affect the quality and strength of the coated surface. Starch for use in the paper industry should not contain more than 0.4% protein. Oxidized starches tend to have the lowest protein content. Residual oil will cause retrogradation due to complex formation with amylose. 

Stabilization of protein foam in beer, whipped cream, meringues, chocolate marshmallows Prevention of starch retrogradation in bread and cakes, water binding in dough... 

The majority of lecithin is used as feed (as extraction meals dipped in hydration sludge) and only a smaller part of a better quahty product is used in the food industry, mostly in the bakery industry. Lecithin is used as a substance for improving dough properties, as it increases the amount of gas retained in the rigid dough foam and reduces the rate of amylose retrogradation. It is also used as an emulsifier in the production of mayonnaise and emulsified fats of the margarine type (it allows the creation of both o/w and w/o... 

In all patients, foam was observed in the target vessels at C-arm CT. The mean dose of polidocanol used for balloon-occluded retrograde transvenous obliteration was significantly smaller than the dose of contrast medimn used for venography. Haemoglobinuria was foimd in only one patient. Except in one instance of recanalisation, full variceal thrombosis was confirmed at contrast-enhanced CT 1 week after transvenous obliteration. In one patient, air migrated into the liver during transvenous obliteration, but it was spontaneously absorbed. 

Koizumi J, Hashimoto T, Myojin K, Itou C, KagawaT NT, Janne D Othes B. BaUoon-occluded retrograde transvenous obliteration of gastric varices use of CT-guided foam sclerotherapy to optimise technique. Am JR Am J Roentgenol 2012 199(l) 200-7. 

Chen Z., Kynard K., Zeng C., Zhang, C., and Wang B., Foaming of polymer carhon nanotube nanocomposite from the retrograde phase. SPEANTEC 2011, 69, 2678-2682. 

Handa Y. P. and Zhang Z., A new technique for measuring retrograde vitrification in polymer-gas systems and for making ultramicrocellular foams from the retrograde phase. Journal of Polymer Science Part B Polymer Physics 2000, 38, 716-725. 

Figure 3 Relative density as a function of foaming temperature at various saturation conditions and 0 day desorption. The bold circles represent the relative densities of microcellular ABS samples prepared with partial saturation in the retrograde region. The hollow circles represent the relative densities of microcellular ABS samples prepared with equilibrium saturation in the glassy region.

---