Crystallisation nucleating agents

Polypropylene molecules repeatedly fold upon themselves to form lamellae, the sizes of which ate a function of the crystallisa tion conditions. Higher degrees of order are obtained upon formation of crystalline aggregates, or spheruHtes. The presence of a central crystallisation nucleus from which the lamellae radiate is clearly evident in these stmctures. Observations using cross-polarized light illustrates the characteristic Maltese cross model (Fig. 2b). The optical and mechanical properties ate a function of the size and number of spheruHtes and can be modified by nucleating agents. Crystallinity can also be inferred from thermal analysis (28) and density measurements (29). 

PET does not crystallise well in the unoriented state even in a hot mold unless nucleating agents and/or plasticisers are added. Commercial PET ... 

The growth rate shows a maximum at Tk 0.825 Tm. This therefore is the "optimum temperature" for a rapid crystallisation. Tg/Tm and Tm are determined by the constitution of the polymer and cannot be influenced by process parameters. The parameter vQ may be influenced by the average molecular weight and by the addition of nucleation agents. So the practical way to influence the "free" crystallisation of polymers is by choosing ... 

The crystallisation behaviour of PA-6/MMT nanocomposites is complicated to analyse because its polymorphic nature produces a monoclinic a and psuedohexagonal y structure, both of which are affected by the presence of clay particles in the matrix (9). The clay particles themselves have been shown to act as nucleating agents, increasing the crystallisation process in some instances while retarding crystal growth in others. Clearly, the cause of these phenomena must be understood so some measure of control can be employed to produce useful nanocomposite materials with desired properties. 

Nucleating agents help to increase crystallinity in crystallisable polymer systems, and thus they also can be considered as optical property modifiers . 

PCL was also blended with poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) copolymers on a small two-roll mill for 5 min at 140 °C (12% HV) or 128 °C (20% HV). The blends were injection moulded to produce tensile test samples. Samples were prepared in the presence of 1 wt % hydroxyapatite as a crystal nucleating agent and to reduce sample preparation time. For both copolymers, the addition of PCL (10 wt %) reduced the initial modulus and tensile strength (Table 12). Samples containing 90 wt % of PCL exhibited properties very similar to those of PCL and the effects were attributed to phase separation from the blends brought about by PHBV crystallisation at temperatures exceeding T for PCL. That is, the samples show immiscibility. Even blends containing 10 wt % PCL samples aimealed in aqueous media or in an oven showed the presence of crystalline PCL. 

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