Thermal/Mechanical Properties of Wood-PVC Composites Effect of Maleation

Transcription

1 Thermal/Mechanical Properties of Wood-PVC Composites Effect of Maleation J.Z. Lu, I. I. Negulescu,, and Q. Wu Louisiana State University Baton Rouge, LA

2 Introduction Maleation in wood-polymer composites helps create chemical bridges at the interface. Improving compatibility between polar wood and non-polar polymer Helping transfer stresses at the interface Improving interfacial adhesion strength

3 Maleation influences mechanical and thermal properties of resultant composites. Heat flow, heat capacity, and enthalpy Glass transition Moduli and bonding strength

4 Objectives To investigate thermal/mechanical characteristics of maleated wood- PVC composites. To study the relationship between measured properties and coupling agent performance in resultant composites.

5 Background Thermal/Mechanical Analysis Techniques

6 Temperature-molecular Mass Diagram Semi-polymers (e.g., PVC and Lignin) Thermal decomposition Diffusion transition zone Temperature Viscous liquid Leathery Rubbery T m T g Rigid (Semi-)crystalline Molecular mass

7 Transition Temperatures Endothermic dq dt Heating Cooling Tc T Tm Melting Exothermic Temperature Crystallization

8 Glass Transition Temperature T g a) cooling b) subsequent heating T g T g =T ga -T go T ga T ga C p B T g C B T go T go

9 Enthalpy H=KP P (area under curve) Heat flow ENDO T 1 T 2 Baseline Temperature

10 Stress-strain Relationship Under Dynamic (sinusoidal) Loading σ(t) Complex modulus: E*(ω)=E (ω)+ie (ω) E*(ω) =Peak stress/peak strain Strain Stress γ 0 0 δ/ω σ 0 2π/ω t Storage (elastic) modulus E (ω) = E*(ω) cosδ Loss modulus E (ω) = E*(ω) sinδ

11 Dynamic Stress-strain Relationship Stress σ(t) under a sinusoidal load: Strain γ(t) by a phase angle δ corresponding to the stress σ(t) (t): Dynamic modulus E*: Relationship among complex, storage, and loss moduli: σ ( t) = σ 0 sin( ωt + δ ) γ ( t) = γ 0 sin( ωt) σ ( t) E * ( ω ) = γ ( t) E *( ω) = E'( ω) + ie"( ω) Phase angle δ : tanδ = E"( ω) E'( ω)

12 Thermal/Mechanical Properties Glass transition temperature Tg - DSC and DMA Melting temperature Tm - DSC Heat flow ( (dq/dt) and enthalpy ( ( H) - DSC Bonding moduli (E' E', E",, and E*) ) and the phase angle ( (δ ) DMA Thermal stability (weight loss under heat) - TGA

13 Experimental Materials Wood Veneer - Yellow poplar (0.91 mm Thick) PVC film - Clear ( mm Thick) Maleated polypropylene (MAPP) Epolene E-43 (Mw =9,100) Epolene G-3015 (Mw =47,000) Initiator - Benzyol peroxide Solvent - Toluene

14 Sohxlet Extraction ASTM standard D Wood specimens were extracted for 4 hours with two sets of solvents. Coupling Treatment Wood specimens were dipped in the coupling solutions of 0, 12.5, 25, and 50 g/l MAPP at 100 C for 5 min under a continuous stirring with a magnetic stirrer.

15 Wood Veneer under Sohxlet extraction

16 Manufacture of wood-pvc composites Pressure: MPa Pressing procedure: Heating 3 min at 178 C and then cooling at 70 C for 1 min Shear strength measurement Shear tests followed the ASTM standards D3163 and D3165

17 Wood-PVC Laminates under Shear Testing

18 DMA (Seiko Instruments, Model DMS 110)

19 DMA Procedure - Using three cycles Temperature [ o C] Specimen Test mode Test cycle Start Stop First heating Wood Bending First cooling Second heating PVC Woo-PVC composites Bending Bending First heating First cooling Second heating First heating First cooling Second heating Rate [ C/min]

20 TGA system (TA Instruments, Model TGA2950) Procedure: Heating from 25 o C to 600 o C under a N 2 flux at a pressure of 8 KPa

21 DSC (TA Instruments, Model DSC2920) Procedure For interphase samples, heating from 25 o C to 200 o C under a N 2 flux at a pressure of 8 KPa For modified wood veneer and wood-pvc composite samples, cooling at -10 o C for a while and then heating up to 200 o C in a N 2 flux

22 Summary Results on Thermal/Mechanical Properties Material E (GPa) a E (GPa) a Glass transition ( o C) a tanδ a Shear strength (MPa) Enthalpy (J/g) b TG at 600 o C (%) DTG max (%/ o C) c PVC o C 10.3 o C Wood o C 18.8 o C Wood-PVC composites: a 0% MAPP 2.95% E % E % E % G % G % G The value was measured in first heating at 1 Hz; b The value was measured at the glass transition; c Two maximum peaks were selected for wood-pvc composites o C - - o C o C, o C o C, o C o C, o C o C, o C o C, o C o C, o C o C, o C

23 DMA Results

24 Glass Transitions of Wood-PVC Composites o C tanδ o C 88.9 o C 89.3 o C PVC 0% MAPP 2.95% E % G Temperature ( o C)

25 Influence of Frequency on E' and tanδ of Wood-PVC Composites with 6.83% E x x x10 9 E' 0.01 Hz 0.1 Hz 1 Hz 10 Hz 100 Hz E' (Pa) 4.0x tanδ 2.0x10 9 tanδ Temperature ( o C) 0.0

26 Influence of MAPP Retention on E' and tanδ of Wood-PVC Composites (Freq = 1 Hz) 1.0x E' (Pa) 8.0x x x10 9 E' 0% MAPP 2.95% E % E % E % G % G % G tanδ 2.0x tanδ Temperature ( o C)

27 TGA Results

28 Influence of Maleation on Decomposition of Wood-PVC Composites by TG TG (%) PVC Wood 0% MAPP 2.95% E % E % E % G % G % G Temperature ( o C)

29 Influence of Maleation on Decomposition of Wood-PVC Composites by DTG DTG (%/ o C) PVC Wood 0% MAPP 6.83% E % G Temperature ( o C)

30 Comparisons on DTG Decomposition of Wood- PVC Composites with and without Maleation % MAPP 2.95% E % E % E % G % G % G DTG (%/ o C) Temperature ( o C)

31 DSC Results

32 Heat Flow (dq/dt) vs. Temperature For Wood-PVC Composites Heat flow (mw/mg) PVC: Tg=77.16 o C PVC Wood WPC with 4.12% E-43 WPC with 3.64% G Temperature ( o C)

33 Derivative DSC spectra for PVC, modified wood veneer, and wood-pvc composites Derivative heat flow (mw/mg o C) T g of PVC PVC Wood with 2.17% G-3015 W PC with 4.12% E-43 WPC with 3.64% G-3015 T m of PVC T g of wood Temperature ( o C)

34 DSC Spectra of PVC-MAPP Interphases Heat flow (mw/mg o C) T g of PVC T m of PVC PVC E-43 WPC with 0% E-43 WPC with 2.19% E-43 WPC with 3.64% E-43 WPC with 5.78% E-43 T m of E Temperature ( o C)

35 Conclusions Maleation significantly influenced the thermal behavior of wood-pvc composites. E' and E* increased with MAPP retention and graft rate. However, tanδ was independent of retention and graft rate. Wood-PVC composites with MAPP had significant shifts in DMA, DSC, and TG/DTG spectra compared with those without MAPP.