**10.1 Abbreviations**


mf-TM modulated force thermomechanometry

MWCNT multi-wall carbon nano-tube


Improved processing techniques due to equipment design (screw element design, feed stages, steam release and plasticiser addition) to accommodate retention of water content. Plasticiser structures that are specific to starch and can be used with starch–filler composites, while limiting moisture susceptibility are required. Where plasticisers are not able to enhance properties, polymer blends may be more suited due to the large size of polymer molecules compared with plasticisers. The primary limitations to TPS are moisture variation and retrogradation causing embrittlement during storage that is not desired for packaging materials. A challenge is for starch with more specific initial properties to be available. The structure of synthetic properties can be controlled better than that of biopolymers causing a major set-back for materials from natural resources where properties may change with source, season or plant variant. This makes preparation of commercial

Native starch has complex supra-molecular structures that must be disrupted and dissociated to form amorphous thermoplastic starch. Water, other plasticisers, temperature and shear are important in gelatinising starch to form TPS. TPS is processed using extrusion then formed using injection moulding or thermoforming, the same as synthetic thermoplastics. TPS can be combined with other polymers in blends and fillers to form composites. Problems with TPS are water sorption and retrogradation, causing properties to change over time and under prevailing ambient conditions. There are many varieties of starch with differing composition, processing behaviour and properties. This makes development of TPS materials highly specific to particular starch types during development and application. Starch has interesting theoretical properties as a polymer. There is not theoretical distinction between synthetic and natural polymers, except for the complex intermolecular interactions resulting from polarity and hydrogen bond formation and the multileveled hierarchy of ordered structures that form. Starch presents many characteristics, found in synthetic polymers, in the one polymer: linear chains with a single repeat unit, branching, hydrogen bonding, crystallinity, gelatinisation, melting and glass transition phenomena, liquid crystalline characteristics, retrogradation, upper critical solution temperature behaviour, solubility, gelation all combined to form the

**8. Future directions** 

**9. Conclusion** 

**10. Appendix** 

**10.1 Abbreviations** 

PCL poly(caprolactone) PLA poly(lactic acid)

products with precise tolerances difficult.

technology of thermoplastic starch production.

DMA dynamic mechanical analysis DSC differential scanning calorimetry FTIR Fourier transform infrared

LCST lower critical solution temperature mf-TM modulated force thermomechanometry MWCNT multi-wall carbon nano-tube PBAT poly(butylene adipate-*co*-terephthalate)


#### **11. References**


**7** 

 *Canada* 

**Retrogradation and Antiplasticization** 

Petrochemical-based plastics are widely used in modern society due to their high effective mechanical and barrier properties (Farris et al., 2009; Siracusa et al., 2008). However, petrochemical-based plastics have become an environmental concern as they are not biodegradable or recyclable. Replacing the petrochemical-based polymers with biopolymers which are renewable has become an attractive idea and necessitates research on bioplastics (Debeaufort et al., 1998). Among the biopolymers, starch is considered as one of the most promising candidates for bioplastics due to its abundant availability, annually renewability, competitive price, and potential performance, including thermoplasticity (Lai & Padua, 1997; Mali et al., 2005). Native starch does not have thermoplastic properties. However, when additional plasticizers, elevated temperatures and shear are present, native starch does exhibit thermoplastic properties. Standard techniques, such as extrusion and injection moulding, used for producing petrochemical-based plastics, can be used in thermoplastic processing of starch (Guilbert et al., 1997). Some of thermoplastic starch (TPS) has been developed into commercial products, like compost bags, packaging materials (loose fillers and films), coatings, mulch films and disposable diapers (Jovanovic et al., 1997; Lai et al., 1997). TPS film and coating are being developed for the meat, poultry, seafood, fruit, vegetable, grains and candies industry sectors (Debeaufort et al., 1998). A drawback for use of starch is that TPS products age with time during storage due to starch retrogradation, which significantly changes quality, acceptability, and shelf-life of the TPS products. This review will summarize the current knowledge of TPS pertaining to its plasticization,

Native starch does not have any thermoplastic properties without addition of plasticizer(s) (e.g., water, glycerol, sorbitol, etc.). The products made from native starch are readily broken into fragments when they are dried in ambient conditions due to strong intermolecular hydrogen bonding in the amylose and amylopectin macromolecular chains (Ma et al., 2007). But in the presence of plasticizers and elevated temperatures and shear, native starch readily melts and flows, allowing for its use as an extruding, injection moulding, or blowing material, similar to most conventional synthetic thermoplastic polymers (Ma et al., 2007). The role of

**1. Introduction** 

retrogradation, and antiplasticization.

**2. Basics of starch plasticization** 

*Richardson Centre for Functional Foods and Nutraceuticals,* 

 *University of Manitoba, Winnipeg, MB, R3T 2N2,* 

 **of Thermoplastic Starch** 

Yachuan Zhang and Curtis Rempel

glass transition and the water activity behavior. *Journal of Polymer Science Part B: Polymer Physics*, 49, 1041-1049.

