Using the essential work of fracture method for studying physical aging in thin, ductile, polymeric films

Abstract

Water‐filled, drop impact tests on full‐scale, blow‐molding polyester bottles showed that impact properties change significantly after 30 days of aging at 50°C. To quantify this deleterious effect of aging, we did small‐scale laboratory experiments using the essential work of fracture method (EWFM). We measured the essential work of fracture of thin specimens cut from the sides of blow‐molded bottles and aged under various conditions. Similar to the impact results, significant drops in essential work occurred after relatively short amounts of aging. Additional experiments confirmed that the decreases in essential work were due to physical aging and not to chemical degradation. A comparison of the essential work results to the full‐scale, bottle‐drop impact tests showed some inconsistencies that need to be resolved before EWFM can be recommended as a quantitative method for studying physical aging of blow‐molding polyester resins.

Effect of thermal and hygrothermal aging on the plane stress fracture toughness of poly(ethylene terephthalate) sheets

“…[1,2,4,7] and references therein), credited to Broberg, splits the total energy required to the fracture of a pre-cracked specimen into two components: the essential (W e ) and non-essential work (W p ) of fracture. W e is needed to fracture the polymer in the crack propagation zone and thus to generate new surfaces.…”

“…The embrittlement induced by physical aging can be assessed by determining of the change in the yield stress (σ y -tensile tests) [2][3][4]. Furthermore it can be characterized by measuring the enthalpy relaxation (ΔH -differential scanning calorimetry, DSC) [2,[5][6][7]. Physical aging also influences the fracture mechanical properties of the polymer but only relatively few studies have been published so far.…”

“…Physical aging also influences the fracture mechanical properties of the polymer but only relatively few studies have been published so far. [1][2][3][4]7]. For assessing the fracture characteristics of ductile, tough polymers the Essential Work of Fracture (EWF) method has gained acceptance recently [1][2][3][4][7][8][9][10][11][12][13][14][15], which has been developed mainly for in-plane load on single-and doubleetched notched tensile specimens (SEN-T [12,13] and DEN-T [1,14,15], respectively) and used widely.…”

In-plane and Out-of-plane Fracture Toughness of Physically Aged Polyesters as Assessed by the Essential Work of Fracture (EWF) Method

“…The latter is assessed by differential scanning calorimetry (DSC) -see later. Interestingly up to now little work has been done to find correlation between fracture mechanical and aging parameters (Liu and Nairn, 1998;Karger-Kocsis and Moskala, 2002;Karger-Kocsis et al, 2003).…”

Fracture behavior of quenched poly(lactic acid)

“…The sudden cooling freezes this less ordered structural state and hampers a chain reorganization such as the one caused by aging during slow cooling. Even though physical aging on toughness behaviour of polymers has been little investigated using fracture mechanics approaches, the essential work of fracture method (EWF) has been reported as a successful technique to follow the effect of physical aging on polymer films [12][13][14][15][16]. The aim of this work consists in the application of a de-aging thermal treatment to two commercial grades of PLA with different D-lactic monomer fractions and studying their fracture behavior applying the EWF method.…”