Renewable poly(lactic acid) (PLA) exhibits high strength and stiffness PLA is fully biodegradable and has received great interest However, the inherent brittleness of PLA largely impedes its wide applications In this article, the recent progress in PLA toughening using various routes including plasticization, copolymerization, and melt blending with flexible polymers, was reviewed in detail PLA toughening, particularly modification of impact toughness through melt blending, was emphasized in this review Reactive blending was shown to be especially effective in achieving high impact strength The relationship between composition, morphology, and mechanical properties were summarized Toughening mechanisms were also discussed © 2011 Wiley Periodicals, Inc J Polym Sci Part B: Polym Phys, 2011

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/polb.22283

Research progress in toughening modification of poly(lactic acid)

Failure mechanisms in toughened epoxy resins—A review

We present chain structure, phase morphology, and toughness relationships in thermoplastic polymers and polymer/rubber blends. In neat polymers, molecular aspects of craze/yield behavior are controlled by two chain parameters: entanglement density ν e and characteristic ratio C ∞ . The crazing stress is proportional to ν e 1/2 , and the yield stress is proportional to C ∞ . The dispersed rubber toughens a polymer/rubber blend mainly by promoting energy dissipation of the matrix. The toughening efficiency correlates with the rubber phase morphology and the chain structure of the matrix

Chain structure, phase morphology, and toughness relationships in polymers and blends

This paper describes the fatigue behaviour of newly developed all-polypropylene (all-PP) tapes and composites, with reference to the composite processing conditions, testing temperature and making a comparison with commercial alternatives. All-PP tapes are highly oriented and their failure behaviour follows that of other highly oriented polymers. All-PP woven composites fail ultimately due to PP tape failure. However, this failure mode is accompanied by delamination of fabrics in the woven structure. Consolidation pressure plays a decisive role in controlling the interlaminar properties and hence the delamination resistance and furthermore the fatigue limit of the composite. Comparison of all-PP woven composites with commercial alternatives based on glass and natural fibres reveals the excellent relative performance of all-PP composites under fatigue loads. Fatigue properties of all-PP composites are however sensitive to the testing temperature, and elevated temperatures can lead to a rapid reduction of the fatigue resistance of these all-polymer systems.

Fatigue Properties of Highly Oriented Polypropylene Tapes and All-Polypropylene Composites:

Deformation and fracture behaviour of a rubber-toughened epoxy: 2. Failure criteria

Criterion for craze nucleation in polycarbonate

The brittle fracture behavior of round-notched poly(methyl methacrylate), poly(vinyl chloride), and polystyrene bars has been studied at varying temperatures and bending rates. Brittle fracture originating from internal crazes occurs in a restricted range of temperature. When the plastic deformation zone at the tip of the notch reached a certain size, which decreased with decreasing temperature or increasing bending rate, the internal crazes nucleated at the elastic-plastic boundary. The extrapolation of the position of internal craze nucleation versus temperature plots showed that the nucleation of well defined internal crazes developed above the temperature of the 3 loss peak in each glassy polymer. The mechanism of the ductile-brittle fracture transition at the β-transition temperature in glassy polymers can be understood in terms of variation of the position of internal craze nucleation with temperature and/or strain rate.

Brittle fracture in glassy polymers

The development of plastic deformation and crazing in the neighborhood of a notch has been studied in connection with nonlinear fracture processes of crystalline ductile polymers, polyethylene, polypropylene, and propylene-ethylene block copolymers. After revealing the morphology of plastic deformation around the notch and studying the effects of crystalline structure on ductile fracture processes, the J-energy analysis was applied to give a criterion for crack initiation in the fracture of these elastic-plastic materials. The material resistance to stable and unstable cracking was characterized using the curves of J against crack extension Δα.

Fracture and toughness of crystalline polymer solids

This paper deals with prediction of the temperature rise in the stress-controlled fatigue process of a glass-fiber-reinforced polyamide and the application of a temperature and frequency superposition procedure to the S-N curve An experimental equation was derived to predict the temperature rise from calculations based on the fatigue test conditions and viscoelastic properties of the material The temperature rise (ΔT) can be expressed as a product of a coefficient term Φ(L, κ) concerning heat radiation and the test-specimen shape and a function term Pfat concerning the viscoelastic properties and fatigue test conditions Φ(L, κ) was found experimentally to derive the equation for predicting the temperature rise blow or above the glass transition temperature (Tg) of the material The equation σR = −STfA log NfR + STfB was obtained as a procedure for applying temperature and frequency superposition to S-N curves in consideration of ΔT This procedure was obtained by combining both temperature- and frequency-superposition techniques Here, σR and log NfR represents the stress and the fatigue lifetime calculated at a given temperature and frequency, A and B denote the slope and intercept of any arbitrarily chosen S-N curve, and STf is a shift factor for temperature and frequency superposition © 1999 John Wiley & Sons, Inc J Appl Polym Sci 72: 1783–1793, 1999

Fatigue characteristics of a glass‐fiber‐reinforced polyamide

The brittle fracture behaviour of ductile glassy polycarbonate, poly(vinyl chloride) and poly(methyl methacrylate) notched bars subjected to plane strain tension has been studied at varying strain rates. Morphological observations of thin sections and fracture surfaces revealed that a disc-type craze was nucleated at the tip of the plastic zone which spread from the notch root. A slip-line theory modified so that the yield criterion is influenced by a hydrostatic stress component allows the calculation of the stress components at the elastic-plastic boundary, where the hydrostatic stress is highest, from the knowledge of the location of the fracture origin. An analysis of the data resulted in the conclusion that Orowan's analysis for notch brittleness is appropriate.

Ikuo Narisawa

Papers

Criterion for craze nucleation in polycarbonate

Brittle fracture in glassy polymers

Fracture and toughness of crystalline polymer solids

Fatigue characteristics of a glass‐fiber‐reinforced polyamide

Notch brittleness of ductile glassy polymers under plane strain