Mechanical Behavior of Thermoplastic Starch: Rationale for the Temperature-Relative Humidity Equivalence

Abstract

This paper aimed at understanding and rationalizing the influence of both temperature and relative humidity on the mechanical behavior of thermoplastic starch (TPS). DMA experiments revealed that water molecules impact the crosslinking network by reducing the intermolecular hydrogen bond density, resulting in a less dense entanglement network. In addition, the in-situ X-ray characterization during hydration of starch revealed structural changes, which were ascribed to conformational changes in the starch chain, due to their interaction with the uptake water molecules. Finally, the study of TPS uniaxially stretched at different temperatures and humidity showed that the mechanical behavior of TPS could be rationalized by considering the ΔT parameter, which corresponds to the temperature difference between the drawing temperature and the glass transition temperature of TPS.

Influence of Air Humidity Level on the Structure and Mechanical Properties of Thermoplastic Starch-Montmorillonite Nanocomposite during Storage

“…In summary, we can say that high water content in the samples stored at 85% RH caused reduction in starch intermolecular H-bond density after seven weeks of storage. A similar effect was reported by Leroy et al [33] who analyzed thermal and structural (WAXS) behavior of thermoplastic potato starch stored under 58 and 89% RH.…”

“…The starch-based materials are very sensitive to storage conditions, especially to relative humidity, because starch can easily uptake water from ambient [35]. The water content then strongly influences the structure, recrystallization, and mechanical properties of these materials [33,36,37]. In TPS samples, mobile molecules of water denoted as free water and immobilised water molecules create strong bonds with starch chains [20,38] and present in MMT interlayer galleries termed bound water can be found.…”

“…On the other hand, samples stored at 11% RH exhibited a slight decrease in T g compared to the dried samples, whereas the T g values for the samples stored at 55% RH decreased substantially. The presence of more water may decrease the intermolecular hydrogen bond density [33]. However, low water content could not significantly affect the starch chain mobility, leading to preventing recrystallization during storage.…”

Obtaining and Characterizing New Types of Materials Based on Low-Density Polyethylene and Thermoplastic Starch

“…Additional water molecules are eliminated by the dehydration process of starch up to 250 • C. After this temperature the degradative oxidation processes start to break up the polymer backbone, and a strong exothermic effect can be observed on the DSC curve. The residual carbonaceous mass is burned away between 350 and 500 • C. Figure 6 presents the details of thermal analysis of thermoplastic starch up to 250 • C. An apparent glass transition can be observed around 50 • C, which is similar to some values reported in the literature [61,62].…”

Solid-State Luminescence with a Large Stokes Shift in Starch Functionalized with Low-Content ESIPT Dye

“…Due to its hydrophilic nature, TPS is highly susceptible to moisture absorption, which affects its mechanical properties. Efforts to alleviate this sensitivity involve blending TPS with other materials to enhance its final properties and reduce vulnerability to environmental factors such as humidity, temperature, and radiation exposure [13][14][15][16].…”