Blends with functionalized polyolefins

An interesting class of condensation copolymers is the liquid crystalline polymers (LCP). From the viewpoint of practical applications, LCP are very attractive as 

In summary, the microhardness of PET/PHB and PEN/PHB quenched copolymers show minima for blends of 30/70 and 50/50, respectively, due to the fact that the samples are fully amorphous for these compositions. If the PET, or the PEN, content is increased, the microhardness will increase owing either to the additive microhardness behaviour of the single components for amorphous samples, or to the increasing crystal thickness in the case of crystallized samples. If, on the other hand, the PHB concentration is increased the samples always crystallize and the crystallite-reinforced material shows a microhardness increase which is proportional to the PHB content of the crystal (Baltd Calleja, 1991). 

Mechanical studies have also been performed on another non-LCP system -copolyesters of PET and PEN, where both copolymer units having flexible chain segments and lack a liquid-crystalline behaviour (Santa Cruz et al, 1992). The whole range of PET/PEN copolymers can therefore be prepared in the amorphous state. 

Samples of PET/PEN copolymers with 10, 20, 30, 50, 80 and 100 mol% PEN have been synthesized. Amorphous films of the samples were obtained by melt pressing above the melting point and quenching in ice-water. The samples were then crystallized by annealing the glassy materials at various temperatures. The degree of crystallinity was calculated from the amorphous density measured on quenched samples and from the crystal density derived from the crystal unit cell. 

Micromechanical studies have been carried out on thermoplastic elastomers. The latter are a special class of multiphase systems (block copolymers) exhibiting an unusual combination of properties they are elastic and at the same time tough and they show low-temperature flexibility and strength at relatively high temperatures (frequently ca 150 °C). In addition, they are easily processable. For this reason, they are nowadays of great commercial importance as engineering materials. In natural 

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Coltelli M-B, Savi S, Aghetto M, Ciardelh F. A chemical view onto post consumer poly(ethylene terephthalate) valorization through reactive blending with functionalized polyolefins. Polym SciA2009 51(ll) l-13. 

Property changes of PBT by blending with functionalized polyolefins... 

Bulk grafting of polyolefins with functionalized monomers can be performed by means of conventional processing equipment. Inherently stabilized polyolefins are formed when low concentrations of functionalized monomers are used [218]. Using high concentration levels of the latter, stabilizer masterbatch for blending with undoped polyolefins are created. -Functionalized polyolefins can be prepared by means of the radical grafting more successfully than via copolymerization. 

Specifically, PVC blends with polyethylene, polypropylene, or polystyrene could offer significant potential. PVC offers rigidity combined with flammability resistance. In essence, PVC offers the promise to be the lowest cost method to flame retard these polymers. The processing temperatures for the polyolefins and polystyrene are within the critical range for PVC. In fact, addition of the polyolefins to PVC should enhance its ability to be extruded and injected molded. PVC has been utilized in blends with functional styrenics (ABS and styrene-maleic anhydride co-and terpolymers) as well as PMMA offering the key advantage of improved flame resistance. Reactive extrusion concepts applied to PVC blends with polyolefins and polystyrene appear to be a facile method for compatibilization should the proper chemical modifications be found. He et al. [1997] noted the use of solid-state chlorinated polyethylene as a compatibilizer for PVC/LLDPE blends with a significant improvement in mechanical properties. A recent treatise [Datta and Lohse,... 

The tunable metallocene catalyst with a well-defined polymerization mechanism provides distinctive advantages in the preparation of new polymers with well-controlled molecular structures, especially functional polyolefins that are very difficult to prepare by other methods. Since the discovery of HDPE and i-PP about half a century ago, functionalization of polyolefin has been a scientifically challenging and industrially important area. The constant interest, despite lack of effective functionalization chemistry, is due to the strong desire to improve polyolefin s poor interactive properties. The hydrophobicity and low surface energy of polyolefin has limited its applications, especially in the areas of coating, blends, and composites, in which adhesion, comparability, dispersion, and paintability are paramount. 

Seo [1997] prepared compatibilized PA blends with LCP polyesteramide (Hoechst Vectra B950) in the presence of anhydride-functionalized polyolefin. Specifically, 60 parts PA-6 was mixed with 25 parts LCP and 15 parts EPDM-g-MA in a TSE at 290°C. The blend was characterized by SEM, optical microscopy, Raman spectroscopy, mechanical properties, selective solvent extraction, and FTIR. 

Extensive work has been reported by Spadaro and co-workers (Table 11.9), to examine the effects of gamma-radiation-induced functionalization of PE e.g., reactions (R-22), (R-26 to R-29), and (R-38)). It is known that polar groups on polyolefins help their compatibili-zation with polymers containing polar groups [Gaylord, 1989]. Use of chemically functionalized PE for preparing blends with PA-6 has also been examined [Chen et al., 1988 Xanthos, 1988 Raval et al., 1991]. 

Consequently, to create PA/PO blends with a high melt viscosity it is advisable to use fully functionalized polyolefins. It can be expected that proper dispersion in melt of PA blended with high viscosity g-PO can yield composites with satisfactory structural homogeneity and high melt viscosity. This possibihty is based on the above data showing that contact between the phases in a PA/g-PO blend is created instantaneously, and the development of contact zones between the polymeric phases depends much on the degree of mechanical dispersion of the components and not on the diffusion processes taking place in the mesophase. 

Thermoplastic starch is also blended with other polymers to improve its properties for particular applications. For example, a bag for collection of household food waste for composting that readily dissolved when it got wet would not function very well In applications such as this, the resins used for blending are also biodegradable, so that they do not interfere with the composting operation. In other cases, starch is blended with nonbiodegradable resins such as polyolefins. 

Valenza, A., Carianni, G., Mascia, L., Radiation grafting functionalization of poly(vinylidene fluoride) to compatibilize its blends with polyolefin ionomers. Polymer Engineering and Science 1998,38(3), 452 60. 

Renaut and co-workers [7] discussed the fire retardancy of PP - polycarbonate (PC) blends. Fire retardant (FR) properties of the blends were shown to be gradually affected by the presence of polyolefins grafted with functional groups as compatabilisers. 

Polyolefin (PO = PP, HOPE, EPR, or PMP) was blended with an impact modifier, 0.1-5 wt% colorant and/or 5-50 wt% of opadfios, and a styrene-diolefin block copolymer, grafted with 1-6 mol% of acrylic acid, maleic anhydride, or snlftniale functionality (SEBS, SEPS, radial SEB, or SEP). To improve scratch resistance the blend contained 100-3,000 ppm Zn stearate and 16-22C fatty acid amide. The alloys were injection molded into parts showing impact, scratch, and abrasion resistance. They were used to manufacture interior trim for vehicles and in other applications where a scratch- and scuff-resistant plastic material is required ... 

Most of these tie layers are based on modified polyolefins or their copolymers. lonomers such as Surlyn may also be used as a tie layer. The functionality of the adhesive layer derives from comonomers snch as acrylic acid, methacryUc acid, maleic anhydride or vinyl acetate. Styrene-isoprene-styrene thermoplastic block copolymers blended with polyolefins can be used as tie layers. The level of addition of these grafted units is... 

C. Albano, R. Perera, P. Silva, Effects of gamma radiation in polymer blends, in composites with micro and nano fillers and in functionalized polyolefins, Revista Latinoameri-cana de Metalurgia y Materiales 30 (1) (2010) 3-27. 

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