Impact Modification and Fracture Mechanisms of Core–Shell Particle Reinforced Thermoplastic Protein

Abstract

Mechanical properties and fracture mechanisms of Novatein thermoplastic protein and blends with core–shell particles (CSPs) have been examined. Novatein is brittle with low impact strength and energy‐to‐break. Epoxy‐modified CSPs increase notched and unnotched impact strength, tensile strain‐at‐break, and energy‐to‐break, while tensile strength and modulus decrease as CSP content increases. Tg increases slightly with increasing CSP content attributed to physical crosslinking. Changes to mechanical properties are related to the critical matrix ligament thickness and rate of loading. Novatein control samples display brittle fracture characterized by large‐scale crazing. At high CSP content a large plastic zone and a slow crack propagation zone in unnotched and tensile samples are observed suggesting increased energy absorption. Notched impact samples reach critical craze stresses easily regardless of CSP content reducing impact strength. It is concluded that the impact strength of thermoplastic protein can be modified in a similar manner to traditional thermoplastics.

The relationship between morphology development and mechanical properties in thermoplastic protein blends

“…With the exception of CTNMA, all blends have a tensile strength less than that of the Novatein control regardless of PE content. [31] At low PE inclusions all blends showed an increase in secant modulus. However, this was not the case because after yielding neat polyethylene would typically undergo extensive strain hardening, which was T A B L E 3 Selected mechanical properties for Novatein and NTP-PE blends.…”

Manipulating morphology in thermoplastic protein/polyester blends for improved impact strength

“…[13] Similarly, increased glycerol plasticizer content in TPS increased the impact resistance of TPS/polycaprolactone blends, albeit that the mechanism of modification is different to when relying on morphology. In a previous study, [2] using core-shell reinforced Novatein, the critical matrix ligament thickness was achieved at a particle content of 20 wt%, after which significant improvements were observed. [15] For example, the inclusion of 20-30 wt% PBAT in a PLA matrix caused the impact strength to double compared to neat PLA, and triple when epoxy functionalized compatibilizer was added.…”

“…However, it is known that for Novatein reinforced with elastomeric core-shell particles, the critical reinforcement level needed for improvement in energy absorption was ~15-20 wt%, [2] while in reactive Novatein/polyethylene blends, this point was >20 wt% for some blends. However, it is known that for Novatein reinforced with elastomeric core-shell particles, the critical reinforcement level needed for improvement in energy absorption was ~15-20 wt%, [2] while in reactive Novatein/polyethylene blends, this point was >20 wt% for some blends.…”

Structural changes and energy absorption mechanisms during fracture of thermoplastic protein blends using synchrotron FTIR

“…Novatein thermoplastic protein, a biodegradable polymer produced from bloodmeal , has poor energy absorbing properties depending on plasticizer content and protein denaturant levels. The injection molding grade of Novatein shows high tensile strength and modulus but has low strain at break and impact strength . In comparison, increased plasticizer and protein denaturant content brings about better energy absorbing properties in Novatein, but a reduction in strength and modulus are observed .…”

“…The addition of an elastomeric polymer into a rigid matrix, either through blending or the incorporation of synthesized particles are common techniques for improving energy absorption . Impact modification of Novatein has been achieved in a number of ways; nano‐scale core‐shell particles with an elastomeric core and rigid shell were shown to improve the unnotched impact strength by an order of magnitude . Similarly, reactively blending high contents (∼40 wt%) of modified polyethylene (PE) with Novatein, doubled the elongation at break and increased impact strength by ∼350%, while decreasing tensile strength by less than 25% .…”