Fracture and impact properties of polycarbonates and MBS elastomer‐modified polycarbonates

Abstract

SYNOPSISMechanical properties of polycarbonates ( PCs ) and elastomer-modified polycarbonates with various molecular weights (MW) are investigated. Higher MW PCs show slightly lower density, yield stress, and modulus. The ductile-brittle transition temperature (DBTT) of the notched impact strength decreases with the increase of PC MW and with the increase of elastomer content. The elastomer-modified PC has higher impact strength than does the unmodified counterpart if the failure is in the brittle mode, but has lower impact strength if the failure is in the ductile mode. The critical strain energy release rate (G,) measured at -30°C decreases with the decrease of PC MW. The extrapolated zero fracture energy was found at M , = 6800 or MFR = 135. The G, of the elastomer-modified PC (MFR = 15, 5% elastomer) is about twice that of the unmodified one. The presence of elastomer in the PC matrix promotes the plane-strain localized shear yielding to greater extents and thus increases the impact strength and G, in a typically brittle fracture. Two separate modes, localized and mass shear yielding, work simultaneously in the elastomer-toughening mechanism. The plane-strain localized shear yielding dominates the toughening mechanism at lower temperatures and brittle failure, while the plane-stress mass shear yielding dominates at higher temperatures and ductile failure. For the elastomer-modified PC ( 10% elastomer), the estimated extension ratio of the yielding zone of the fractured surface is 2 for the ductile failure and 5 for the brittle crack. A criterion for shifting from brittle to ductile failure based on precrack critical plastic-zone volume is proposed.

Effect of Rubber Content in Acrylonitrile–Butadiene–Styrene and Additional Rubber on The Polymer Blends of Polycarbonate and Acrylonitrile–Butadiene–Styrene

“…The blend with SAN (no rubber) fractured in brittle mode even at 40°C. Similar to the rubber-toughened polycarbonates, 43 two separate modes, plane-strain localized energy dissipations and plane-stress mass shear yielding, function simultaneously in the PC/ ABS blends. The localized energy dissipations take place mainly near the fracture surfaces with relatively less volume involved.…”

“…47 On the contrary, the mass shear yielding ductile failure dominates at high temperature plane-stress conditions which involves significantly greater volume but less extension ratio relative to the brittle failure. 43 .... Critical Strain Energy Release Rate, Ge A fracture mechanics approach by notched impact testing was independently developed by Brown 48 and Marshall et al 49 by assuming the specimen to exhibit bulk linear elastic behavior. The experiments were purposely carried out at low temperature ( -40°C) and with a sharper notch (0.125 mm notch radius) to meet the criteria of this method as close as possible.…”

Rubber-Toughened polymer blends of polycarbonate (PC) and poly (ethylene terephthalate (PET)

“…The main emphasis in toughening these pseudo-ductile polymers is to promote the failure mechanism from the localized shear yield brittle mode to the mass shear yield ductile mode [32].…”

Core–shell particles of poly(methyl methacrylate)‐block‐poly(n‐butyl acrylate) synthesized via reversible addition–fragmentation chain‐transfer emulsion polymerization and the polymer's application in toughening polycarbonate

“…22 Elastomers such as styrenebutadiene-styrene block copolymer (SBS), 23 acrylonitrilebutadiene-styrene copolymers, [24][25][26] and core-shell structured particles of poly(methyl methacrylate/styrene) (MBS) 21,23,27,28 and PnBA/PMMA 22,29,30 have been used as impact modifiers. 22 Elastomers such as styrenebutadiene-styrene block copolymer (SBS), 23 acrylonitrilebutadiene-styrene copolymers, [24][25][26] and core-shell structured particles of poly(methyl methacrylate/styrene) (MBS) 21,23,27,28 and PnBA/PMMA 22,29,30 have been used as impact modifiers.…”