Dependence of the fracture and fatigue performance of polyolefins and related blends and composites on microstructural and molecular characteristics

Abstract

This article surveys the influence of microstructural, morphological and molecular variables on the fracture and fatigue behavior of polyolefins, related blends and composites. The effects of major parameters of the structural hierarchy on the fracture mechanics (FM) response were considered and the related model descriptions reviewed. Emphasis was put on how important is to select the right FM approach for the toughness determination. It was pointed out that a clear distinction between crack initiation and growth is the essential prerequisite to differentiate between effects of the initial structure and its alteration due to mechanical loading. Although the microstructural dependence of the fracture and fatigue properties in reinforced, filled and impact modified polyolefins is quite well explored, this information is still missing for the neat polymers. This is due to a strong interlinking among molecular and morphological variables in neat polyolefins. Recommendations were given how to overcome this difficulty.

Investigation of the microstructures, properties, and toughening mechanism of polypropylene/calcium carbonate toughening masterbatch composites

“…The tie molecules interconnect crystalline regions and thus cause the deformation and failure of PP. The concentration of the tie molecules is increased with increasing MW, which accounts for the high fracture strength of high‐MW PP . In addition, Lin and co‐workers found that the improvement in impact strength of PP/nano‐CaCO 3 composites, and the enhancement of higher‐MW PP are more significant because of the higher concentrations of tie molecules.…”

The mechanism for fracture resistance in β‐nucleated isotactic polypropylene

“…The mechanical performance of a semicrystalline polymer is mainly dependent on its intrinsic molecular architecture (e.g., MW, tacticity, polydispersity etc) and on extrinsic parameters such as the test speed, the test temperature, the stress state, and the processing conditions 35, 36. Reviewed for β ‐PP, it is usually studied with the effects of MW, crystallinity, spherulitic size, and the crystalline structure on the fracture resistance 16, 36–38. With the increasing MW of β ‐PP, it results in large enhancement of fracture resistance, which is due to the dense density of intra‐ and interspherulitic tie molecule 1, 11, 39–41.…”

Towards the understanding of the molecular weight dependence of essential work of fracture in semi-crystalline polymers: A study on poly(ε-caprolactone)

“…Channel and Clutton [31] studied the effect of molecular weight and chain branching in a series of polyethylenes under impact conditions and found that fracture toughness (G c ) increases linearly with increasing molecular weight. It was stated that the increase in molecular weight increases the number of tie molecules, that is accompanied by increased toughness [18]. Based on this literature overview it can be deduced that the raise in tie molecule density and lamellae thickness seem to increase the resistance to crack initiation and the value of w e .…”

“…The reason is that several factors influence the structure and amount of crystalline phase and these are strongly interrelated. These include [18]: molecular structure, molecular weight and its distribution; crystalline phase and structure; the amount, order and orientation of crystalline fraction; spherulite size; lamellae thickness; chain branching; number and density of tie molecules; etc. By starting with molecular structure and related glass transition temperature, the investigated materials can be divided into two groups.…”