Fracture Toughness of Poly(Methyl Methacrylate) Blends

  • R. P. Kusy
  • W. F. Simmons
Part of the Polymer Science and Technology book series (PST, volume 20)


A series of acrylic blends was prepared from three feedstocks having number average molecular weights (M n) of 4X103 (L), 3X104 (M) , and 1X105 (H). After single-edge-notched tension bars were machined from molded sheets, the fracture surface energy (γ) was determined using the Brown and Srawley equation. When the mean γ was plotted against the blend composition, results showed a different dependence for each binary combination: H/M suggested a linear relationship, while H/L and M/L appeared concave downward and upward, respectively. Further reduction of this data to a molecular weight basis permitted analysis via three general approaches: that a property, P ∝ M n -1, that P ∝ log M w, and that P ∝ log x n (where x n = M n/Mo). The first two relationships gave straight line segments for each binary combination and provided interesting parallels with several previous investigators--Sookne, Flory, Nielsen, and Berry. In the second case, moreover, the intersection of the H/L and M/L data lines suggested a common origin, which corresponded to γ = 525 erg/cm2 at M w = 26,000 (the entanglement molecular weight, Moε?). Of the three models, however, the last (P ∝ log x n) was most informative. Like the earlier single component materials, the binary blends followed a sigmoidal relationship; however, the effective molecular weight necessary for plastic deformation (x) had decreased. For these blends this shift corresponded to an increase in the strain energy release rate (GI c = 2γ) for a given x n. These observations are consistent with Manson’s fatigue test results on acrylic blends and provide confirmation that the fracture morphology is dependent upon γ and not x n.


Fracture Toughness Methyl Methacrylate Fracture Morphology Strain Energy Release Rate Number Average Molecular Weight 
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Copyright information

© Plenum Press, New York 1983

Authors and Affiliations

  • R. P. Kusy
    • 1
  • W. F. Simmons
    • 1
  1. 1.Dental Research CenterUniversity of North CarolinaChapel HillUSA

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