New stabilizers & fillers boost polyolefin performance.

The recent biennial SPE Polyolefins RETEC in Houston provided a few hints of coming metallocene-based resin developments (see Technology Newsfocus). As for news of more immediate impact, polyolefin additives were the highlights of the meeting.

Speakers introduced novel uv and antioxidant chemistries, including reactive and polymer-bound types, as well as a developmental HALS for longer-lasting agricultural films. Also new is a line of talcs said to provide good appearance and high heat stability in PP. Formulators of mica-filled PP may be able to optimize the balance of toughness and stiffness with the aid of a comprehensive study of performance-enhancing additives.

MORE PERMANENT STABILIZERS

In their aim to invent stabilizers that are both highly soluble in resins and have very low extractability, some additive suppliers have focused their R&D on polymer-bound HALS and antioxidants. The most recent commercial example is Sanduvor PR31, a low-molecular-weight methylated tertiary HALS from Clariant Corp., Charlotte, N.C. This monomeric HALS remains mobile within the polymer, allowing it to migrate to the surface, where a photo-reaction with light causes it to graft onto the host polymer. In this manner, the additive becomes anchored where it can do the most good.

In recent field studies, blue-pigmented stadium seats of PP copolymer with this stabilizer achieved a [Delta]E of 9.6 after 5000 hr of Xenon-arc exposure. That beats a [Delta]E of 10.4 with a threefold greater concentration of the conventional stabilizer package (Tinuvin 770 monomeric HALS plus Tinuvin T-327 benzotriazole, both from Ciba Specialty Chemicals, Tarrytown, N.Y.).

Color change from light exposure was also reduced in blue-pigmented HDPE plaques containing 0.15% of the new stabilizer. After 9000 hr of natural accelerated weathering, [Delta]E was 5 versus 9.1 for a commonly used oligomeric HALS at the same concentration.

Polysiloxane-bound uv stabilizers and phenolic antioxidants from Great Lakes Chemical Corp., West Lafayette, Ind., are said to provide outstanding resistance to extraction in PP fiber and PE cable. Polysiloxane technology has so far yielded one commercial product, Uvasil299, an oligomeric HALS said to be highly compatible with PP.

Currently being evaluated are three Silanox antioxidants, designated SiAO2 (2700 molecular weight), SiAO3 (3200 MW), and SiAO4 (3900 MW). Heptane extractability of these phenolic polysiloxanes in HDPE plaques surpasses that of two workhorse monomeric stabilizers - Anox 20, equivalent to Ciba's Irganox 1010, and Anox PP 18, equivalent to Ciba's 1076 [ILLUSTRATION FOR FIGURE 1 OMITTED].

A new generation of these silicone-bound stabilizers is being developed with reactive sites to permit grafting. This will lower their extractability even further, says technical manager Robert Gray. Polyolefin food containers, water pipe, and medical applications will be targeted.

HALS FOR AGRICULTURAL FILM

Ciba Specialty Chemicals is developing a family of alkoxyamine-based' HALS that are expected to be the next generation of agricultural-film stabilizers. They will provide superior chemical resistance and stabilization, Ciba says. These solid, high-molecular-weight HALS (currently designated NOR-HALS) are said to have less tendency to interact with acidic pesticide derivatives because of their very low basicity (NOR-1, for example has a Pka of 4.2). In severe pesticide exposure tests, greenhouse films with 4% NOR-1 reportedly outlast films with 8% of an HMW tertiary-amine HALS that Ciba says is the best-performing conventional HALS in this type of test.

Films containing NOR-1 are as chemically resistant as films stabilized with a benchmark nickel quencher. However, the nickel quencher fails dramatically after 21 months, while film with NOR-1 retains 50% elongation after 31 months. Nickel quenchers are being phased out for environmental reasons, Ciba says.

GET MORE OUT OF FILLERS

Five high-heat-stable appearance grades of reinforcing talcs have been developed by Specialty Minerals, Inc., Easton, Pa. Aimed at PP homopolymers, TPOs, and engineering thermoplastics and alloys, the domestically produced PolyTalc AG series is said to outperform both conventional domestic talcs and high-end grades from China and Canada.

PolyTalc AG ranges from 44-micron top size to an ultrafine version with 6-micron top size. The latter is said to be the finest talc commercially available. Compounds with these talcs reportedly show exceptional thermal stability. Both 44-micron and 10-micron grades of PolyTalc AG far outperform competitors in long-term heat-aging of PP copolymer [ILLUSTRATION FOR FIGURE 2 OMITTED].

Colorant costs when formulating with these talcs are said to be competitive with those of high-end imports and much lower than when using conventional U.S. talcs. In fact, PolyTalc AG requires only one-fourth as much TiO2 as is typically needed with U.S. talcs to achieve a given Hunter L* brightness value.

Ultrafine PolyTalc AG 609 reportedly outperforms conventional fine and coarse talcs. At a 40% loading in both medium-impact and super-high-impact PP copolymers, this filler provides higher flex modulus and HDT, lower mold shrinkage, and enhancements in both falling-weight impact (at ambient temperature and at-22 F) and notched Izod values.

Looking for ways to increase impact/stiffness balance and other properties of mica-reinforced poly-olefins, Franklin Industrial Minerals, Inc., Kings Mountain, N.C., examined the effects of 16 additives and compatibilizers in PP and TPOs. The additives included maleic anhydride-modified PP homopolymers and copolymers and rubbers, fatty acid/amide blends, and silicones.

Some additives produced significant changes in impact/stiffness balance and also affected properties such as HDT and flexural and tensile strengths. Franklin found that results varied with the resin system and with the type of impact test used. For example, in PP homopolymer with 30% mica, Polydis TR 016 (a blend of fatty-acid metal salt and an amide) from Struktol Co., Stow, Ohio, gave the best balance of flex modulus with notched Izod or Gardner impact. In TPO [ILLUSTRATION FOR FIGURE 3 OMITTED], Polydis TR 016 was also the only additive to give significant improvement in stiffness/notched Izod balance. But to achieve good Gardner impact and unnotched Izod, best results were achieved with 6% of Unite MP 1000, a maleic anhydride-modified PP homopolymer from Aristech Chemical Corp., Pittsburgh. This additive also raised HDT.

Further studies are under way to see how metallocene-catalyzed poly-olefins behave as modifiers in mica-filled PP. Franklin hints that even better impact/stiffness balances may result.