Polypropylene failure

Figure 7 Effect of phosphate coating level on failure strength and crystallinity for talc filled polypropylene failure strength crystaUinity.

The model has also been found to work well in describing the mechanics of the interface between the semicrystalline polymers polyamide 6 and polypropylene coupled by the in-situ formation of a diblock copolymer at the interface. The toughness in this system was found to vary as E- where E was measured after the sample was fractured (see Fig. 8). The model probably applied to this system because the failure occurred by the formation and breakdown of a primary craze in the polypropylene [14],... 

Low surface energy substrates, such as polyethylene or polypropylene, are generally difficult to bond with adhesives. However, cyanoacrylate-based adhesives can be effectively utilized to bond polyolefins with the use of the proper primer/activa-tor on the surface. Primer materials include tertiary aliphatic and aromatic amines, trialkyl ammonium carboxylate salts, tetraalkyl ammonium salts, phosphines, and organometallic compounds, which are initiators for alkyl cyanoacrylate polymerization [33-36]. The primer is applied as a dilute solution to the polyolefin surface, solvent is allowed to evaporate, and the specimens are assembled with a small amount of the adhesive. With the use of primers, adhesive strength can be so strong that substrate failure occurs during the course of the shear tests, as shown in Fig. 11. 

The hypothesis of stereochemical control linked to catalyst chirality was recently confirmed by Ewen (410) who used a soluble chiral catalyst of known configuration. Ethylenebis(l-indenyl)titanium dichloride exists in two diaste-reoisomeric forms with (meso, 103) and C2 (104) symmetry, both active as catalysts in the presence of methylalumoxanes and trimethylaluminum. Polymerization was carried out with a mixture of the two isomers in a 44/56 ratio. The polymer consists of two fractions, their formation being ascribed to the two catalysts a pentane-soluble fraction, which is atactic and derives from the meso catalyst, and an insoluble crystalline fraction, obtained from the racemic catalyst, which is isotactic and contains a defect distribution analogous to that observed in conventional polypropylenes obtained with heterogeneous catalysts. The failure of the meso catalyst in controlling the polymer stereochemistry was attributed to its mirror symmetry in its turn, the racemic compound is able to exert an asymmetric induction on the growing chains due to its intrinsic chirality. 

Texas, USA 1965 Propylene Pipeline failure in polypropylene polymerization plant caused 3M damage in an explosion and fire FB CVE... 

The agreement between heats of fusion of the same polymer is excellent in some cases, but very poor in others. Obviously, in the case of polypropylene more work needs to be done before the heat of fusion of this substance will be known with any certainty. Heats of fusion calculated from the copolymer equation, Eq. (6), are uniformly low, except in the case of Rybnikar s data. As pointed out by Dole and Wunderlich (1957) this is probably due to the failure to measure the maximum melting of carefully annealed samples. Thus, Dole and Wunderlich (1959) found that the calorimetrically estimated melting point in the case of the carefully annealed copolyester, the 80/20 polyethylene terephthalate and sebacate, was 240° C, whereas the value calculated from Eq. (6) using the heat of fusion estimated from the calorimetric data of Smith and Dole (1956) was 245° C. The unannealed sample had a melting point of ca. 210°. 

Most of the data are presented as plots of the time to failure for the polypropylene as a function of the size of the alkyl group derived from the a-olefin. These comparisons are made on an equal antioxidant weight basis, and as the size of the alkyl group is increased, the molar concentration of antioxidant decreases. Presented in this customary way the data are weighted in favor of lower molecular weight compounds because their molar concentration is higher. 

Figures 8.51 and 8.52 show differences between the behavior of polypropylene filled with glass beads at different temperatures. In both cases, the debonding between filler and the matrix requires the lowest level of energy and confirms that this is the most likely mode of failure. The volume fraction of filler has little effect on debonding, cavitation, and yielding at 0°C. At -6()°C, yielding is improved by increasing concentration of filler. Debonding is initiated at the poles and begins plastic yielding in the matrix which ultimately leads to failure. Strain required to initiate failure is reduced when the filler concentration is increased. ...

The polymer lifetime of the HHP based additive (9) was encouraging, as the earlier failure of diisocyanate adduct (10) was attributed to its lower compatibility in the polypropylene film. 

Precision of time-to-failure measurements in controlled conditions, when the said test procedure is closely followed, is rather fair. ASTM D 3012-00 lists an example with three polypropylene samples, apparently, of different origin, tested in seven different laboratories (a ronnd robin test). They showed oxidative stability of the samples (time to failnre) at 150°C as 14.0 0.8,35 3, and 63 5 days, respectively, for within-laboratory standard deviations of the average, that is, within 6-9% of the average, and 14 + 3, 35 + 7, and 63 + 19 days, respectively, for between-laboratory standard deviations of the average, that is, within 20-30% of the average. 

L. Woo, S.Y. Ding, A Khare, and M.T.K. Ling. Failure progression and mechanisms of irradiated polypropylenes and other medical polymers. In G. Wypych (Ed.), Weathering of Plastics. Testing to Mirror Real Life Performance, Plastic Design Library, 1999. 

The severe degradation of polypropylene following sterilizing doses of irradiation can be characterized mechanically by its failure to undergo the necessary work in practice. Embrittlement increases with time for an irradiated polypropylene, thus rendering an acceptable formulation totally unacceptable a few months after irradiation. Naturally, the decay of radicals can be accelerated by thermal annealing, limited by the geometrical distortion temperature. 

---