Resiliencies starch-based foams

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. 

The resiliencies of starch-based foams, with values between 69.5 and 71.2%, are, as a group, about 10% lower on a relative basis than those of EPS foams. Although starch-based foams absorb 13 to 16 wt% moisture after conditioning at 80% r.h. (relative humidity) and 23 °C, these products retain between 62 and 67% resiliency. 

All starch-based foams have significantly higher foam and bulk densities and open-cell and moisture contents than EPS-based foams. Both product types have similar compressive stresses, resiliencies, and friabilities. Starch-based foams are more sensitive to changes in relative humidity and temperature than EPS-based foams, but the larger amounts of absorbed moisture do not compromise mechanical integrity. 

Foams Wave by Mater-Bi, foamed sheet packaging is a biodegradable alternative to conventional protective foam packaging such as polystyrene, polyurethane and polyethylene. Wave by Mater-Bi is starch-based, and is expanded using water, extruded into sheets and then assembled into blocks that can be cut into any shape. The foams have a robust and resilient closed-cell structure. 

Potato Starch Based Resilient Thermoplastic Foams... 

Potato Starch Based Resilient Thermoplastic Foams 3.2.2 The influence of the water content... 

Mechanical testing on the foam is performed to measure the compressive stress and the resiliency. The results from diese tests are shown in table 2, in which the properties of extruded polystyrene foam (XPS) and commercial starch-based loose-frll foams (Eco-foam and Mater-Bi) together with EPS loose-fill foam (Pelaspan Pac) are added for conq>arison. The values of XPS are obtained from tests on typical XPS retail packaging trays. The table shows that the compressive stress reached with potato starch foam is comparable with that of XPS. Through the cell structure of the potato starch foam (high cell density, very small cells) a good resiliency can be obtained, although pure starch plastics exhibit brittle fracture behavior. This brittle fracture still is present on the microscopic scale of the individual cells but due to the cell density, the foam exhibits resiliency on macroscopic scale. 

The combination of starch with a water soluble polymer such as PVOH (or polyalkylene glycols) has been widely considered since 1970 [100]. Since the early 1990s these compositions have been mainly studied for starch-based loose-fill production as a substitute for expanded PS [101-107], using compositional water as expanding gas. In this kind of blends, not only natural starch but also modified ones such as hydroxy propylated high amylose starch can be used, especially to improve foam resilience and density [101-105]. 

The combination of starch with a soluble polymer such as polyvinyl alcohol (PVOH) and/or polyalkylene glycols has been widely considered since 1970 [137]. In recent years the system, thermoplastic starch/PVOH has been mainly studied for producing starch-based loose fillers as a substitute for expanded polystyrene [138-144]. As an example, Altieri and Lacourse developed a technology based on hydroxypropylated high amylose starch containing small amounts of PVOH for improving foam resiliency and density [138-142]. In this case loose fillers were produced directly by a twin screw extruder. 

Use of unmodified starches in combination with mild acids and carbonates has been claimed.214 Starch moisture content should be no greater than 25%. Acids such as tartaric, citric or malic acids are added at levels between 0.2% and 7%, while the carbonate level is 0.1% to 2%, both based on total starch composition. The acid is stated to serve a two-fold function it depolymerizes the starch during extrusion via hydrolysis, improving expansion at the same time, it liberates carbon dioxide, which acts as a blowing agent, from the carbonate. A typical formula extruded in a twin-screw extruder at 170-195°C yielded a product with a density of approximately 1 lb/ft3 (16kg/m3) and resilience of 60-85%. The foam had a continuous skin with a closed cell structure. 

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