Starch expandable thermoplastic

The introduction of gelatinized starch expanded considerably the use of starch as a polymeric material, but this technology based on water processing was limited by the necessity of more than one step, some of which were discontinuous. Nonetheless, these developments showed that it was possible to produce blends of synthetic thermoplastic materials with gelatinized starch, affording new prospects of the utilization of starch as a plastic material in the production of films and injection-moulded goods. 

As an alternative to these materials the objective in this research will be to produce starch based resilient thermoplastic foams based totally on native potato starch. This is done in two steps the production of expandable thermoplastic starch beads by extrusion and foaming of the expandable beads after conditioning in a successive foaming step. The properties of these foams will be studied as a function of processing parameters and material composition. A further objective is to determine the ultimate properties of pure starch based foams. 

Some commercial thermoplastic starch polymer based products were highlighted in Table 6.1, and some of them can be examined in more detail in this section. Probably one of the first starch based products developed was the National Starch expanded starch foam packaging material ECO-FOAM . ECO-FOAM materials are derived from maize or tapioca starch and include modified starches. This relatively short-term, protected-environment packaging use is ideal for thermoplastic starch polymers. National starch now has additional thermoplastic starch materials, blends and speciality hydrophobic thermoplastic starches for a range of apphcations including injection moulded toys, extruded sheet and blown film apphcations. [http //www.eco-foam.com/ loosefill.asp]. 

Cooked but unexpanded thermoplastic starches (TPS) have wider applications, because of the fact that approx. 8% of water can be removed after the cooking process by devolatilization at 300 mbar, corresponding to a cooling by approx. 70 °C down to 100°C. That means that the exiting strand does not expand but yields a glassy, plastic-like pellet that can be dried in a fluidized-bed dryer. 

EcoFoam (National Starch) Thermoplastic high amylose starch to be used as loose-fiUers and other expanded materials. Possible blends of starch with PVAl or PEG. 

Starch is one of these renewable resources. Starch is widely available and is especially suited for the production of foamed thermoplastic materials due to the intrinsic presence of a blowing agent. Destructurization of starch by means of extrusion compounding will facilitate the formation of expandable beads or foams of thermoplastic starch. 

The combination of starch with a water-soluble pol5mier such as poly(vinyl alcohol) (PVOH) and/or polyalkylene glycols has been widely considered since 1970 (151). More recently, the thermoplastic starch/PVOH system has been mainly studied for producing starch-based loose fillers as a substitute for expanded polystyrene (152-158). As an example, Altieri and Lacoin-se developed a technology based on hydroxy propylated high amylose starch containing small amounts of... 

Polylactide has high potential in agricultural applications such as mulch films either in pure form or blended with other polymers such as thermoplastic starch. In addition, polylactide is used in compostable yard bags and dog poop bags. Lactic acid based hot-melt adhesives have also been developed (90). Foamed PLA could be used as structural protective foams, loose-fill packaging and insulation material as an alternative for expanded polystyrene (EPS). While packaging is currently the high volume application... 

Ecofoam Thermoplastic high amylose starch Nich teclinology with W-L license National Starch 5000 Loose-fillers and other expanded materials... 

Another field of starch converted to thermoplastic material has caught much attention. The so-called starch plastics offer an interesting alternative for synthetic polymers achieving rapid degradation instead of long-term durability. Thermoplastic starch is generally processable as a traditional plastic however, its sensitivity to humidity restricts it to some applications, including loose-fillers, expanded trays, shape moulded parts — mainly as a replacement for polystyrene. ... 

Thermoplastic extrusion Name of the continuous extrusion process in which raw materials, generally refined milled fractions, are cooked and plasticized due to heat and pressure occurring inside the extruder barrel. The starch is gelatinized, and the exiting extrudate is usually formed into predetermined shapes. This process is widely used to produce direct-expanded-products and pellets or intermediate products used for production of many breakfast cereals and snacks. 

Thermoplastic starches find use mainly in water soluble compostable foams, expanded trays, shape molded parts, and expanded layers as a replacement for polystyrene. TPS products with different viscosity, water solubility, and water absorption have been prepared by altering the moisture/plasticizer content, amylose/amylopectin ratio of raw material, and the temperature and pressure in the extruder (Mohanty et al, 2000). Several studies have focused on the plasticization of TPS using glycerol (Forssell et al, 1997), sorbitol (Gaudin et al, 1999), urea, formamide (Ma et al, 2004), dimethyl sulfoxide (Nakamura and Tobolsky, 1967), and low molecular weight sugars (Kalichevsky et al, 1993). Plasticizers can increase the flexibility and processibility of TPS. 

---