Zhaobin Tang

Bio-based epoxy resin from itaconic acid and its thermosets cured with anhydride and comonomers

A novel itaconic acid (IA) based epoxy resin with curable double bonds (EIA) was synthesized by the esterification reaction between IA and epichlorohydrin (ECH). Its chemical structure was confirmed in detail by FT-IR, 1H-NMR and ESI-ION TRAP MS before being cured by methyl hexahydrophthalic anhydride (MHHPA). In order to manipulate the properties of the cured resin, divinyl benzene (DVB) and acrylated epoxidized soybean oil (AESO) were employed here to act as comonomers. The results demonstrated that EIA showed a higher epoxy value of 0.625 and higher curing reactivity toward MHHPA compared with the commonly used diglycidyl ether of bisphenol A (DGEBA). The glass transition temperature, tensile strength, flexural strength and modulus of the cured EIA without comonomers were 130.4 °C, 87.5 MPa, 152.4 MPa and 3400 MPa, respectively, which were comparable or better than those of DGEBA cured by the same curing agent. After being copolymerized with DVB or AESO, the properties of the cured EIA could be regulated further. The results indicated that EIA has great potential to replace the petroleum-based thermosetting resin, such as DGEBA.

Preparation and characterization of poly(lactic acid)/starch composites toughened with epoxidized soybean oil.

Blends of entirely bio-sourced polymers, namely polylactide (PLA) and starch, have been melt-compounded by lab-scale co-extruder with epoxidized soybean oil (ESO) as a reactive compatibilizer. The starch granules were grafted with the maleic anhydride (MA) to enhance its reactivity with ESO. The ready reactions between the epoxy groups on ESO, the MA groups on MA-grafted starch (MGST) and the end carboxylic acid groups of PLA brought blending components together and formed a compatible compound. An elongation at break (EB) of 140% was obtained in the blend of PLA/MGST/ESO (80/10/10), increased from 5% of a pure PLA. The grafting content of the MA on the starch granules primarily determined the compatibility and properties of the ternary blends, which was also affected by the relative amount of MGST and ESO.

Effect of castor oil enrichment layer produced by reaction on the properties of PLA/HDI-g-starch blends

Blends of entirely bio-sourced polymers, namely polylactide (PLA) and starch, have been melt-compounded by lab-scale co-extruder with castor oil (CO) as a plasticizer. The enrichment of castor oil on starch had great effect on the properties of the blends. If the castor oil was mainly dispersed in PLA matrix, the properties of the blends were poor, but when the hexamethylenediisocyanate (HDI) was grafted on starch granules the ready reactions between the hydroxyl on CO and the isocyante on the HDI-grafted starch (HGSTs) brought CO molecules enriched on starch particles. DSC analysis shows that the CO layer on starch has a positive effect on the crystallization of PLA in the ternary blend. The accumulation of CO on starch greatly improves the toughness and impact strength of PLA/starch blends. The grafting content of HDI on the starch granules primarily determined the compatibility and properties of the resulted blends.

Preparation and characterization of thermoplastic starches and their blends with poly(lactic acid)

Two different thermoplastic starches (TPS), namely maleic anhydride grafted starch (MA-g-starch) and epoxidized cardanol grafted starch (Epicard-g-starch), were successfully prepared by chemical modification without the addition of any plasticizer. The structure and properties were characterized by nuclear magnetic resonance (NMR), X-ray diffraction (XRD), hot press testing, scanning electron microscopy (SEM) and contact angle meter, respectively. Results from XRD showed that the highly crystalline structure of native starch was destroyed after modification. Continuous phase was obtained from both of the chemically modified starches after hot pressing at 130°C, indicating that they have good thermoplasticity. Subsequently, they were melt-blended with PLA. It was found that the Epicard-g-starch had a much finer dispersed phase size than MA-g-starch in PLA matrix due to its better hydrophobicity. As a result, the mechanical properties of PLA/Epicard-g-starch blend were superior to those of PLA/MA-g-starch blend.

Research progress in the heat resistance, toughening and filling modification of PLA

Due to its high strength, high modulus, excellent clarity, good biodegradability and biocompatibility, poly(lactic acid) (PLA), a bio-based thermoplastic polyester, has evolved into a competitive commodity material with potential to replace conventional petrochemical-based polymers. However, the wide applications of PLA have been hampered by its native drawbacks, such as low heat distortion temperature (HDT), inherent brittleness and relatively high cost. In recent years, researchers have devoted to breaking above-mentioned bottleneck and attempted to extend the application of PLA. This review will summarize recent work about the modification of PLA, especially focusing on enhancing HDT, toughening and reducing cost.