PC Blends

To meet new market requirements, including technical performance and cost, compounders have designed polymer blends that balance the excellent inherent properties of polycarbonate with the unique characteristics of other matrices such as Acrylonitrile-Butadiene-Styrene (ABS), (mold flow/impact resistance) or polyesters (mold flow/chemical resistance).

PC/ABS: A blend to overcome poor flow behavior and brittleness
When used at low temperature, in thick parts or in the presence of fillers (pigments, fibers, mineral charges), high flow PC becomes notch sensitive and brittle. High impact grades of polycarbonates are available but often come at the expense of poor flow behavior due to high viscosity characteristics.

In order to improve the flow behavior in opaque high impact grade PC, a rubbery phase, such as ABS, may be blended with the PC matrix.  PC/ABS is the fastest growing PC alloy.  ABS balances high impact strength, surface finish and high flow for better processing. As a drawback, PC/ABS blends often do not meet the new flame retardancy standards.  To pass the standard, flame retardants are added, which have a deleterious effect on impact strength.  The proper ratio of impact modifier then needs to be added to the compound to bring the impact back up. 

The most common end-use applications for PC/ABS compounds are automotive parts, office equipment housings, computers and mobile phones.

PC/Polyester: A blend to overcome low chemical resistance
Polycarbonate is known to have very low chemical resistance, which is a critical performance in automotive applications where contact with oil and gasoline is inevitable. In order to overcome this drawback, polycarbonate is often blended with polyesters such as PBT or PET, materials with an inherent chemical resistance.  Unfortunately, in addition to enhancing the chemical resistance, polyesters lower the impact performance of the blend, making it necessary to add impact modifiers. 

Impact Modifiers are the Solution
In today’s market, it is exceedingly common to add fillers, pigments and/or flame retardants to compounded resins.  Each of these products impart beneficial properties to the end products, however they also deteriorate physical properties, particularly impact strength. To solve this problem, Arkema has designed high performance impact modifiers to restore these properties - modifiers that have the correct balance of compatibility and toughening efficiency.

Benefits of Arkema technology in impact modifiers for PC/ABS:

Improved Compatibility
The high impact performance of PC/ABS alloys will greatly depend on the ability to correctly disperse the various polymer phases (PC, PB, SAN) through compounding. Clearstrength^® E920 impact modifier facilitates this dispersion by compatibilizing the PC and SAN domains as seen on the picture below.

Great compatibility of Clearstrength^® impact modifier in PC blends:

                                                                                         Atomic Force Microscopy photo 
                                                                                           of Clearstrength^® E920 impact 
                                                                                           modifier dispersion in PC/ABS

IZOD Impact Strength
Based on Arkema's research in this area, a high level of IZOD impact strength can be achieved. 

Impact strength performance of PC/ABS modified with Clearstrength^® E920 impact modifier:

Improved Elongation
As Clearstrength^® E920 impact modifier is designed to act as a compatibilizer for PC/ABS blends, it is possible to disperse the Clearstrength^® E920 along the interfaces created in the blend.  In this regard, the morphology of the blend becomes co-continuous. As a result, the ductility of the resin is dramatically improved.

Improved elongation performance of PC/ABS modified with Clearstrength^® E920 impact modifier:

Benefits of Arkema technology in impact modifiers for PC/Polyester:

Better Impact Performance
Clearstrength^® E920 impact modifier is exceptionally compatible with PC/PBT and PC/PET - as a result, it is possible to get improved dispersion leading to improved impact performance.  Clearstrength^® E920 impact modifier is specifically designed to maximize the impact strength of blends with a PC concentration higher than 60%.

Impact strength in blends modified with Clearstrength^® E920 impact modifier:

Retained Properties
The addition of Clearstrength^® E920 impact modifier into PC/polyester blends has negligible effects on colorability, modulus, and MFI.  Clearstrength^® E920 impact modifier has the ability to improve impact performance over a wide range of temperatures without sacrificing appearance, other mechanical properties or processability across normal usage levels. 

Table 1: Retained Properties

Mechanical Property*	PC/PBT (No IM)	PC/PBT (15% Clearstrength® E-920)
Yield Stress, MPa (kpsi)	61 (8.8)	48 (7.0)
Yield Strain, %	12	11
Break Stress, MPa (kpsi)	64 (9.3)	53 (7.7)
Strain @ Break %	330	310
Young's Modulus, MPa (kpsi)	890 (130)	720 (100)

*ASTM D-638

Polyester Blends
For high content polyester (PBT/PET/PLA) blends, Arkema has designed the Lotader^® CX series molding compounds.  Lotader^® CX8902 molding compound is specifically designed for cold temperature impact performance  applications where thermal and UV stability is the greatest concern.  Find more information here.