materials development | Compounding bioplastics
of such non-biodegradable modifi ers as ethylene acrylate and ABS.
Bioplasticizers
Metabolix can adjust the crystallinity of its Mirel grades by changing the level of comonomer
The Polymer Additives business unit at Belgium-based Proviron makes various ranges of phthalate-free plasticizers, preferably from renewable resources, for various plastics, including PVC and polyamides. One of its existing bio-based plasticizers, Proviplast 2624 acetyl tributyl citrate (ATBC), is suitable for PLA as well as PVC, but the company is also working on new molecules that are more effi cient in PLA. These are polar plasticizers with medium or medium-high molecular weight that break the strong interactions between lactide groups in neighbouring polymer chains. At the NatureWorks conference, development director José Vanheule introduced the Proviplast C series of ready-to-use plasticized compounds of PLA, based on either ATBC or on the new molecules. The compounds can be mixed by the converter with pure PLA to obtain modulus values that range from the equivalent of polystyrene to LDPE and below, he said. Proviron is at the R&D stage with fully bio-based grades, while grades that are either partially bio-based or not bio-based are in pre-launch or at pilot plant stage.
Amorphous PHA copolymers from Metabolix can be used to fi ne tune the properties of PLA
around -60°C. The Mirel modifi ers are immiscible in PLA, and compatibilizers may be needed to enable effective blending. They have no effect on Tg. Engle said the Mirel rubber modifi ers provide
performance that is comparable to traditional non- renewable rubber modifi ers without compromising the renewable nature of PLA or its clarity and compostability. In PLA fi lms, Metabolix modifi ers lower the modulus and improve tear resistance. In extruded and moulded parts, they improve ductility and reduce brittle fracturing. The new Mirel copolymers are claimed to have
several advantages over traditional plasticizers and mineral fi llers. Plasticizers such as citrate esters and low-molecular weight PEG provide modest toughening, Engle said, but may have drawbacks with migration. Mineral fi llers provide good toughening, but have drawbacks with ductility. Amorphous PHA can substantially increase the melt
elasticity of PLA, providing increased bubble stability, and in compatibilized systems its effects on impact strength at addition rates of 10-30% are between those
22 COMPOUNDING WORLD | June 2014
One very promising plasticizer will form the basis of the Proviplast C5000 series that will be launched commercially in Q3 of this year. Vanheule says that grades will vary according to such parameters as the grade of PLA used, the amount of plasticizer, and mixing capabilities at the customer.
One way of improving the properties of PLA to make
it suitable for durable applications is to add a nucleator to increase the crystallinity of the moulded product. This has the additional benefi t of having little effect on the bio-based content of the material. In Orlando, Masatoshi Sakata of Takemoto Oil & Fat described the company’s LAK 301 nucleating agent – which is available neat and as a 1% masterbatch – and its effect on various grades of Ingeo. He said it is possible to obtain a defl ection temperature under 0.45 MPa load of 147°C in one of NatureWorks new HP (High Productivity) grades, 3100HP. This compares with a typical value of 144°C (amorphous PLA has a DTUL of around 55°C).
Vinyl acetate modifi ers Wacker launched its new Vinnex vinyl-acetate-based binder system for bioplastics last year, saying that it allows polymers and blends based on renewables to be processed just like conventional thermoplastics. Vinnex is available in powder form and as transparent pellets (which are based on a resin with longer side chains). Resin grades are particularly suitable for transparent
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