Shish-kebab stmctures

When polymers are crystallized under flow (stirring, extensional, etc.), the ubiquitous morphology [23] is the shish-kebab structure, consisting of central core (shish) surrounded by lamellae (kebabs) attached along the shish. What is the underlying mechanism behind the formation of shish-kebab stmcture ... 

The epitaxial growth and the formation of a shish-kebab stmcture were also investigated in high molecular weight iPP (HMW-iPP)/low-molecular-weight LLDPE (LMW-LLDPE) blends [21]. The formation of the initial crystallization precursor structure was investigated by using synchrotron WAXS/SAXS techniques at 130 and 140 °C. Shear was applied at temperatures above the cloud points of these blends, and therefore, the HMW-iPP chains could form a flow-induced crystalline stmcture in the blends only at 6 and 9 wt% of HMW-iPP LMW-LLDPE merely served as the amorphous matrix (Fig. 5.3). When the HMW-iPP... 

A shear flow field can facilitate the formation of a shish-kebab stmcture, which consists of shish (extended chains that align along the flow direction) and kebabs (transversely grown lamellae perpendicular to shish). The skin layers are usually dominated by shish-kebabs.20... 

At the same time Pennings (DSM, later of the University of Groningen, The Netherlands) studied the fiber formation from dilute solutions of high molecular weight polyethylene. He started with fibers formed in a Couette device these were stirring-induced fiber crystals, with the famous shish-kebab stmcture [16]. The best properties were obtained when fibers were slowly withdrawn from a gel layer on a rotor. The molecular weight was above 10 , the polymer concentration about 1%, the fiber growth rate below 1 m min, the moduli around 125 GPa [17], and tenacities far above 1 GPa. 

The subject of crystallization from stressed melts has been reviewed (Kumaraswamy 2005) and one frequent occurrence in the time sequence of this crystallization is the formation of row nuclei which give rise to structures known as shish-kebabs . Polypropylene is the polymer best known for its remarkable propensity for forming row structures, which often contain considerable amounts of P-phase material (Olley et al. 2014), and are a major feature of the skin-core stmcture of injection-moulded polypropylene (Shinohara et al. 2012), but they are also found in polyethylene (An et al. 2006), isotactic polystyrene (Azzurri and Alfonso 2008), poly(phenylene sulfide) (Zhang et al. 2008) and polylactide (Xu et al. 2013). 

---