GDR AMC2-22 octobre 2013

Transcrição

1 Coagulation acide du latex d Hevea brasiliensis : Agrégation et gélification de particules colloïdales GDR AMC2-22 octobre 2013 Coagulation acide du latex d Hevea brasiliensis : Agrégation et gélification de particules colloïdales Guilherme DE OLIVEIRA REIS Frédéric BONFILS a, Paul MENUT a, Laurent VAYSSE a, Yacine HEMAR b et Christian SANCHEZ a a : UMR IATE; Montpellier, France b : School of Chemical Sciences; University of Auckland; New Zealand

2 Introduction Context of Natural Rubber 10 M Tons/year 30 million people Unique properties Socio-economic and environmental issues Reduce the variability of the quality of natural rubber Goal Identify and characterize the structuration of the natural rubber 2

3 Latex to Natural Rubber Suspension Colloidal Gel Rubber Network 3

4 Latex study d ~ 1 µm d ph i ~ 3.2 Polyisoprene Proteins Phospholipids Commercial Natural Rubber Latex ϕv = 0.6 Dialyzed : TRIS-HCl buffer (ph = 8.5, I = 7 mm) 4

5 Results Aggregation (Фv, size, ph, ) Colloidal gel (Rheology, Фv,) 5

6 Aggregation : during acidification Acidification : addition of Glucono- -lactone (GdL) Glucono- -lactone (GdL) H2O Gluconic Acid 6

7 Aggregation : during acidification Turbidity DWS Granulo-polarimetry SLS ~ ~ ~ ~ Фv 7

8 Aggregation : during acidification <1 hours SLS 8

9 Aggregation : long times <1 hours SLS 7 days 9

10 Aggregation : long times <1 hours SLS 7 days 14 days 35 days 10

11 Aggregation : long times <1 hours SLS 7 days 14 days 35 days 11

12 Phase diagram <1 hours 7 days 14 days 35 days 12

13 Phase diagram <1 hours 7 days 14 days 35 days 13

14 Gelation 14

15 Rheological properties of gel G,G = f(time) G,G = f(ω) G,G = f(γ,σ) Gel formation Mechanical properties 15

16 G,G = f (time) G 0 = f (Фv) Conditions : 20 C, 4H, 1Hz, 0.5% Strain G (close), G (open) Ф v = 0.4, Ф v = 0.18, Ф v = 0.1, Ф v = 0.05, Ф v =

17 G 0 = f (Фv) G 0 α Фv 3.35 ph 8.5 (t=0) ph 10.5 (t=0) 17

18 Limit strain of linearity 5% ph 8.5 (t=0) ph 10.5 (t=0) Hagiwara et al. Food Hydrocolloids, 1998, 12, γ 0 α Фv Shih and al. Physical Review A, 1990, 42,

19 Fractal dimension Wu and Morbidelli model Wu and Morbidelli. Langmuir , G 0 α Фv A et γ 0 α Фv B A = 3.35, B = -1.77, d = 3, α = 0 (strong link regime) x (backbone fractal dimension) = 1.1 to 1.3 Df = 1.8 Diffusion Limited Cluster Aggregation (DLCA) 19

20 Non linear regime Strain Hardening G max G 0 T.C. Gisler, R.C. Ball, D.A. Weitz, Phys. Rev. Lett. 82 (1999) 1 Pouzot and al, JCIS. 293 (2006), pp Conditions : 20 C, 1Hz, 0.02 to 3500 Pa 20

21 Strain Hardening G o G max Ф v = 0.5, Ф v = 0.4, Ф v = 0.18, Ф v = 0.1, Ф v = 0.08, Ф v = 0.05, Ф v =

22 Strain Hardening Φv =

23 Strain Hardening Φv =

24 Strain Hardening Φv =

25 Strain Hardening Φv = 0.25 Irreversibility Hardening of the plateau 25

26 Strain Hardening Φv = 0.25 Irreversibility Hardening of the plateau 26

27 Strain Hardening Φv = 0.25 Irreversibility Hardening of the plateau 27

28 Strain Hardening Φv = 0.25 Irreversibility Hardening of the plateau 28

29 Strain Hardening Фv Interaction density?? No strain hardening

30 Conclusion Aggregation : phase diagram (ph, Φv, temps) Colloidal Gel : Df = 1.8, DLCA and Strong link regime Strain hardening (Φv, irreversibility) Softening? 30

31 Thank you for your attention Coagulation acide du latex d Hevea brasiliensis : Agrégation et gélification de particules colloïdales Guilherme DE OLIVEIRA REIS UMR IATE