國立交通大學應用化學研究所 Topic: Polymer blends Speaker: Yi-Hong Lin Polymer Research Center Institute of Applied Chemistry of NCTU

Basic Concepts of Mechanical Properties

Polymer-Polymer Systems Why blend polymers? Cost extending engineering resins by diluting it with a low cost polymer less expensive than the development of new products by synthesis Performance a balanced set of desired properties a custom-made products Variety Choices and options of current commercial products

Properties of Blends If we take polymer A and blend it with polymer B, the Tg will depend on the ratio of polymer A to polymer B in the blend. Mechanical properties, resistance to chemicals, radiation, or heat; they all generally plot the same way as the Tg does with respect to the relative amounts of each polymer in the blend.

Minor component versus major component relative amount of polymer B in the immiscible blend

Miscibility vs Compatibility Miscible If a polymer blend is miscible, a single composition dependent Tg will be observed between those of the component polymers Compatible A blend is said to be compatible if it exhibits the required properties. A compatible blend need not be miscible

Miscibility vs Compatibility Fox equation for a binary system Gordon and Taylor (GT) equation Kwei equation Fig. 1. A schematic representation of the dependence of Tg on composition in binary polymer blends:—fullymiscible system;–––compatible system; – · – · – immiscible system.

Blend preparation methods Blends can be prepared by dissolving the polymers in a common solvent. A thin film can be created by simply allowing the common solvent to evaporate. Blends can also be prepared in the ‘melt’. The component polymers (in pellet form) are pre-mixed and fed into an extruder which heats the polymers to temperatures above either the Tg or Tm (depending on the polymers) and introduces a high degree of mechanical work into the blend to ensure intimate mixing.

Detection of miscibility using DSC -miscible Blend A single Tg between those of the component polymers !!!

Fox-Flory prediction Example for PMMA and PVC

Miscible blend –DSC Polycarbonate/Poly(methyl methacrylate) Blend improved mechanical properties !!!

Miscible blend –SEM two-phase structure, indicating the expected immiscibility of the components. the size of the dispersed PC particles was reduced significantly upon the addition of C20A Figure 1. SEM images of the fracture surfaces of unmodified and C20A modified (40/60) PC/PMMA blends.

Detection of miscibility using DSC -immiscible Blend An immiscible blend exhibits two separate glass transitions at temperatures that correspond to the homopolymerTgs !!!

Detection of miscibility using DSC -immiscible Blend Fig. 3. SEM of PC/PS (30/70) blends (room temperature fracture surface)

Detection of miscibility using DSC - partially miscible Blend Partial miscibility is demonstrated by a broadening of the Tg in the direction of the other blend component ie the Tg of polymer A broadens in temperature towards the Tg of polymer B and vice versa.

Thermodynamics of Mixing Why do some polymers mix during blending? Need to consider some thermodynamics ΔG=ΔH−TΔS For miscibility to occur, ΔG must be negative. Now consider the entropy (S) and enthalpy (H) changes on mixing

Entropy change on mixing ΔS tends to zero…

What about the enthalpy change? ΔH is negative when the polymer blend components exhibit intermolecular interactions in the form of hydrogen bonds, dipole-dipole interactions or even ion-dipole interactions.

Introduction of Specific Interactions enthalpic terms free-energy change Contributed by the hydrogen bonding entropy terms Flory Huggins expression

Introduction of Specific Interactions Kwei-equation: negative deviation !!!

Introduction of Specific Interactions PVPh PVP

Introduction of Specific Interactions Kwei-equation: Positive deviation !!!

Compatibilization of Immiscible Polymer Blends: General concept Modification of the interface in immiscible polymer blends (white: polymer matrix A; black: disperse phase B) by compatibilization (gray: interface between disperse phase B and matrix A)

Reactions Between the Polymer Phases in the Blend Reactions of two polymers via pendant reactive groups substituents):

Reactions Between the Polymer Phases in the Blend Exchange reactions between two different polymer chains: which can be, for example, transesterification:

Block Copolymers as Compatibilizers Arrangement of block copolymers at the interface of polymer blends (left: segmented block copolymers; right: diblock copolymers)

Compatibilization in Polymer Blends: Example Chemical structure of maleic anhydride grafted polypropylene (PP-g-MA) the reaction between PP-g-MA and the amino end groups of polyamide (PA)

Compatibilization in Polymer Blends: Example Morphology of PP/PA blends (90/10 wt %), thin cuts of extruded strands, etched with formic acid, SEM micrographs: (a) PP/PA, (b) PP-g-MA/PA

Thanks for your attention Polymer Research Center Institute of Applied Chemistry of NCTU