Thermoplastic Protein Research Articles

Shear and extensional viscosity of thermally aggregated thermoplastic protein

AbstractNovatein is a thermoplastic produced from blood meal and is used in different agricultural applications. Novatein has some unique processing challenges and its rheology was studied using screw‐driven capillary rheometry, with a particular focus on sheet extrusion using ethylene glycol, glycerol, propylene glycol (PG), or triethylene glycol (TEG) as plasticizers. The entrance pressure drop contributed up to 44% of the total pressure drop (entrance and capillary pressure drop), but this was significantly reduced by plasticization or increased temperature. Polyol addition led to higher shear viscosities in comparison to no polyol plasticization, most likely due to improved chain mobility resulting in orientation effects. Elongational flow was dominated by primary plasticization of the protein‐rich phase and changes in secondary structure, whereas secondary plasticization (phase separation into a polyol‐rich phase) played a significant role in the reduction of the shear viscosity. Of the selected plasticizers, PG showed the most efficient plasticization in both shear and elongational flow. When combined with the beneficial secondary structural changes brought about by TEG, the sheet forming ability of Novatein was drastically improved.

Decoloured Novatein® and PLA Blends Compatibilized with Itaconic Anhydride

Poly (lactic acid) (PLA) was modified through free radical grafting of itaconic anhydride to create reactive side-chain groups. Modified PLA was blended with Decoloured Novatein® (DNTP), a thermoplastic protein material using reactive extrusion to produce a degradable material with improved properties compared to neat Decoloured Novatein®. Varying ratios of blends were prepared. Blending DNTP with PLA was found to increase tensile strength between 22% to 538% and modulus between 201 GPa to 3193 GPa, whereas the strain at break decreased between 80% to 94% depending on the blend ratio. The glass transition temperature of the blends which was measured as the tan δ peak, also revealed an increase when compared to neat DNTP. Scanning electron microscope revealed an enhanced interfacial adhesion between the two phases in the blends with PLA-g-IA suggesting a more homogenous microstructure. The results show the possibility and feasibility of blending DNTP with PLA for use in agricultural and packaging applications.

The role of water in plasticizing thermally aggregated protein‐based thermoplastics

ABSTRACTBlood meal‐based thermoplastic protein (Novatein) is made from a highly aggregated protein network, and as a result, water plays a significant role during plasticization. Novatein was plasticized with up to 40 parts tri(ethylene glycol) or glycerol and equilibrated at different relative humidities. The equilibrium moisture content (EMC) was the dominant factor determining mechanical properties, with a brittle to ductile transformation observed at 8% EMC. However, EMC was not sufficient to explain this behavior and the point of equivalence (POE) was introduced to differentiate between primary and secondary plasticization. It was shown that the constraint theory, which relates to hydrogen bonding plasticizers, was more applicable below the POE whereas the free volume theory, and the formation of the microscale phase separation, described material behavior above the POE. Water played a critical role improving ideal mixing conditions in the material and was also related to the brittle‐to‐ductile transition. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46746.

Morphology and compressive behaviour of foams produced from thermoplastic protein

Novatein® is a patented thermoplastic biopolymer produced from denatured haemoglobin and serum albumin proteins, in blood meal. This material is biodegradable after processing, and when foamed could provide an alternative to expanded polystyrene and polyurethane for short-term applications such as packaging. This study aims to investigate the effect of processing temperature on foam density and morphology and how these properties effect compression behaviour. Unconstrained rapid expansion produced a range of foam densities, 0.28–0.45 g/cm3, which were strongly dependant on temperature. The foams had compressive strengths between 200 and 600 kPa and an elastic moduli between 2.2 and 8 MPa. Under compression, high-density foams behaved like traditional plastic foams, while at low density they behaved more elastomeric. Models for open and closed cells successfully predicted the compression modulus and strength in the linear elastic region. The foams demonstrated a mixed mode morphology (open and closed cells) and an irregular distribution of cells, which explained the deviation from the models.

Classification of recyclables using laser-induced breakdown spectroscopy for waste management

With the ever-increasing amount of generated waste governments around the world are looking for, and implementing, ways to minimize waste output and maximize waste recovery. The main difficulties are sorting waste items, identifying the different types of plastics, and the time taken to sort them manually. Bioplastics such as polylactic acid and Novatein thermoplastic protein can be incorporated into the recycling stream to minimize waste. Laser-induced breakdown spectroscopy spectra analyzed by k-nearest neighbor and soft independent modeling by class analogy were investigated as methods that can rapidly identify recyclables. Raw, peak normalized, and total intensity normalized spectra were used to identify which would improve classification. Laser-induced breakdown spectroscopy spectra were generated by single laser shots to different locations on nine samples, glass (brown, green, and clear), tin, aluminum, polylactic acid, Novatein, polyethylene terephthalate, and high-density polyethylene. To prove that the system has the potential to be used on a waste sorting stream an autofocus unit was developed to move the laser-induced breakdown spectroscopy beam into focus on the different sample geometries. Two classification methods were investigated, soft independent modeling by class analogy and the k-nearest neighbors algorithm. k-Nearest neighbors on raw spectra produced the best results. Discrimination between bioplastics and plastics were 100%. Glass samples could not be reliably distinguished from each other. Surface contamination produced three misclassifications from 450 spectra. Similar results were obtained when the spectral range was reduced from 182.26–908.07 nm to 313.20–495.12 nm.

The Role of Extrusion Conditions on the Mechanical Properties of Thermoplastic Protein

Abstract Mechanical properties of Novatein thermoplastic protein compounded at different extrusion temperatures and processing water contents have been examined in a factorial experiment. Thermoplastic proteins are moisture sensitive and can be prone to thermal degradation during processing. Processing water was varied between 30 and 45 parts per hundred parts bloodmeal while the extrusion temperature was varied between 120 and 150 °C to identify a processing window suitable for process scale up. To resolve any effects processing water had on protein-protein interactions from its plasticising effect, injection molded specimens were mechanically tested both as molded and after conditioning at controlled temperature and humidity. Despite all conditioned samples having approximately the same moisture content, mechanical properties were different. Tensile strength and modulus decreased with increasing processing water at the same equilibrium moisture content. DMA and WAXS suggested this was due to changes in chain mobility within the amorphous phase of the material, rather than conformational change towards a more ordered state. Properties of unconditioned specimens were mostly dependent on the plasticising effect of different amounts of processing water remaining in the material after injection molding. Extrusion temperature had very little effect on mechanical properties, suggesting that Novatein is robust enough to handle some temperature variations during processes such as injection molding.

Morphology and Mechanical Properties of Itaconic Anhydride Grafted Poly(lactic acid) and Thermoplastic Protein Blends

Abstract Blends between Novatein thermoplastic protein and polylactic acid (PLA) have been prepared by reactive extrusion using itaconic anhydride grafted PLA. At equal proportions of Novatein and PLA, the absence of a compatibilizer formed a dispersed phase morphology of Novatein in PLA and the incorporation of compatibilizer formed a co-continuous morphology. Incorporating PLA in Novatein can improve the tensile strength of Novatein by 42% and the impact strength by 36% at an equal proportion blend (50/50) in the presence of a compatibilizer. Thermal analysis revealed that 50/50 was the phase inversion point, above and below this composition the material behaved similarly. The effect of compatibilizer was evident in wide-angle X-ray scattering. In the absence of compatibilizer three phases were detected: crystalline Novatein, amorphous Novatein, and amorphous PLA phases. With compatibilizer, the blend was moving towards two phases: crystalline Novatein, and an amorphous blend of Novatein and PLA. Itaconic anhydride grafted PLA improved miscibility between Novatein and PLA, and its use can potentially lead to the production of Novatein/PLA foams.

Phase separation of plasticizers in thermally aggregated protein‐based thermoplastics

AbstractBlood meal‐based thermoplastic protein (Novatein) was plasticized with up to 40 parts ethylene glycol, glycerol, propylene glycol, or tri(ethylene glycol) per hundred parts blood meal. The effect of plasticizers was investigated by relating the effect of equilibrium moisture content, phase separation, and protein secondary structure to the glass transition temperature and the mechanical properties. Plasticizers can diffuse through the polymer network and either be part of a protein‐rich phase where primary plasticization dominates or a plasticizer‐rich phase where secondary plasticization dominates. Equilibrium moisture content and added theoretical hydrogen bonding sites had the strongest correlation with the results. The point at which the equilibrium moisture content reached an equivalent moisture content (POE) to that of compositions without a plasticizer was found to be a critical point at which plasticization changes from primary to secondary, with a corresponding change in mechanical properties from brittle to ductile.

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

AbstractNovatein thermoplastic protein was blended with 10 wt% poly(butylene adipate‐co‐terephthalate) (PBAT) compatibilized with Joncryl ADR‐4368 and 2‐methylimidazole (2MI). Morphology was tailored for favorable impact strength through changing viscosity ratio (λ) and interfacial tension (γ12). For uncompatibilized blends, λ decreased and γ12 increased with increasing Novatein water content, whereas compatibilizers caused a decrease in both λ and γ12. PBAT continuity was high when uncompatibilized, but dispersion improved with decreasing λ and increasing γ12. The dispersed domain size decreased in all compatibilized blends; PBAT continuity was lowest in samples with the smallest λ. Compatibilized blends had higher impact strength than Novatein and uncompatibilized blends through improved interfacial adhesion, smaller domain size, and increased dispersion. By altering λ and γ12, and with appropriate chemical interaction, a morphology can be created for improved impact strength. Increasing PBAT content showed further increases in impact strength; however, a cocontinuous morphology formed, demonstrating that composition can override the effect of λ and γ12.

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

Novatein thermoplastic protein embrittles quickly after processing due to desorption of plasticizer, leading to poor energy absorbing properties such as impact strength. However, impact modified Novatein blends, containing functionalized polyethylene or nano‐scale core‐shell particles exhibit increased energy absorbing properties. The phase distribution of reinforced blends, and the protein secondary structure changes as a result of blending and fracture was investigated using synchrotron FT‐IR microspectroscopy. Morphological changes in Novatein/polyethylene blends were responsible for variations in mechanical properties, rather than changes in secondary structure. In contrast, a greater impact strength was correlated to an increase of disordered secondary structures in core‐shell particle reinforced Novatein. Blends which exhibited greater elongation or yielding during fracture showed a significant difference between protein secondary structure in the bulk matrix and the yielded material after fracture. It was concluded that the change in conformation of protein structures during fracture is an energy absorbing mechanism that acts in conjunction with the free elongation of the matrix due to decreasing interparticle distance for materials reinforced with nano‐particles. POLYM. ENG. SCI., 58:E124–E134, 2018. © 2017 Society of Plastics Engineers

Compatibilization effects in thermoplastic protein/polyester blends

ABSTRACTNovatein thermoplastic protein was extrusion blended with poly(butylene adipate‐co‐terephthalate) (PBAT) in the presence of dual compatibilizers to produce blends with greater energy absorbing properties than pure Novatein. Compatibilizer pairs were Joncryl ADR‐4368 (glycidyl methacrylate‐functionalized) with 2‐methylimidazole (2MI), and poly‐2‐ethyl‐2‐oxazoline (PEOX) with polymeric diphenyl methane diisocyanate (pMDI). Uncompatibilized Novatein/PBAT blends had decreased tensile mechanical properties, attributed to phase separation, and poor interfacial adhesion. PBAT became finely dispersed in both compatibilized systems, but PEOX/pMDI blends showed embrittlement and large Novatein domains, which acted as stress concentrations. Tensile strength and elongation at break for Joncryl/2MI blends did not decrease compared with Novatein, even at 10 wt % PBAT, and impact strength increased threefold. Dynamic mechanical analysis and solvent extraction showed that PBAT coalesced in all systems, at compositions as low as 2 wt %. It was concluded that using Joncryl/2MI as a dual compatibilizer system can successfully produce a morphology that enhances energy absorption during fracture. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45808.

Biopolymer foams from Novatein thermoplastic protein and poly(lactic acid)

ABSTRACTA batch processing method is used to fabricate foams comprising of a blend of poly(lactic acid) (PLA) and Novatein, a protein‐based thermoplastic. Various compositions of Novatein/PLA are prepared with and without a compatibilizer, PLA grafted with itaconic anhydride (PLA‐g‐IA). Pure Novatein cannot form a cellular structure at a foaming temperature of 80 °C, however, in a blend with 50 wt % of PLA, microcells form with smaller cell sizes (3.36 µm) and higher cell density (8.44 × 1021 cells cm−3) compared to pure PLA and blends with higher amounts of PLA. The incorporation of 50 wt % of semicrystalline Novatein stiffens the amorphous PLA phase, which restrains cell coalescence and cell collapse in the blends. At a foaming temperature of 140 °C, NTP30–PLA70 shows a unique interconnected porous morphology which can be attributed to the CO2‐induced plasticization effect. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45561.

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

AbstractNovatein thermoplastic protein was blended with modified polyethylene (containing either epoxy, carboxylic acid functionalities partially neutralised to produce zinc carboxylate salts, or maleic anhydride functionalities) to alter blend morphology and to manipulate thermal and mechanical properties. Up to 40 pphNovatein polyethylene (PE) was blended with Novatein by extrusion and injection moulding. Using zinc ionomer resulted in optimal properties and was compatible with a finely dispersed morphology at high content; high interfacial tension (σ) and a viscosity ratio (λ) of ~1 was observed. Unmodified blends and those containing epoxy functionalities showed co‐continuity at low PE content. Whilst co‐continuity appeared to increase impact resistance, other mechanical properties decreased due to lack of phase interaction. Maleic anhydride‐grafted‐polyethylene blends showed a finely dispersed PE phase, yet was less compatible. Zinc ionomer was deemed to be the most appropriate for modification of mechanical properties in Novatein.

Characterizations of Thermoplastic Protein Films from Down Feather Fiber

Down feather fiber was modified by formamide which acts as a plasticizer and then hot-pressed into thermoplastic down films. After hot-pressed, the mechanical properties of thermoplastic down films had a close relationship with the exposure time periods. The maximum tensile strength of thermoplastic down films can reach 28.74 MPa after exposure to atmosphere for 40 days. ATR-FTIR curves proved that there were hydrogen bonds forming between amino and amide groups of down feather fiber and formamide. WXRD patterns showed that the crystalline region of down feather fiber was destroyed by formamide during hot-pressing and then reformed after exposure to atmosphere for several days. TGA curves showed that thermoplastic down films has lower moisture compared with down feather fiber suggesting that high temperature removed the most of hydrogen-bound water in down feather fiber and then there are chemical reaction between down feather fiber and formamide.

The role of water on the structure and mechanical properties of a thermoplastic natural block co-polymer from squid sucker ring teeth

Hard biological polymers exhibiting a truly thermoplastic behavior that can maintain their structural properties after processing are extremely rare and highly desirable for use in advanced technological applications such as 3D-printing, biodegradable plastics and robust composites. One exception are the thermoplastic proteins that comprise the sucker ring teeth (SRT) of the Humboldt jumbo squid (Dosidicus gigas). In this work, we explore the mechanical properties of reconstituted SRT proteins and demonstrate that the material can be re-shaped by simple processing in water and at relatively low temperature (below 100 °C). The post-processed material maintains a high modulus in the GPa range, both in the dry and the wet states. When transitioning from low to high humidity, the material properties change from brittle to ductile with an increase in plastic deformation, where water acts as a plasticizer. Using synchrotron x-ray scattering tools, we found that water mostly influences nano scale structure, whereas at the molecular level, the protein structure remains largely unaffected. Furthermore, through simultaneous in situ x-ray scattering and mechanical tests, we show that the supramolecular network of the reconstituted SRT material exhibits a progressive alignment along the strain direction, which is attributed to chain alignment of the amorphous domains of SRT proteins. The high modulus in both dry and wet states, combined with their efficient thermal processing characteristics, make the SRT proteins promising substitutes for applications traditionally reserved for petroleum-based thermoplastics.

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

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. image

Nonisothermal Curing of DGEBA with Bloodmeal-based Proteins

Differential scanning calorimetry (DSC) was used to study the curing reaction of bisphenol A diglycidyl ether (DGEBA) and Novatein thermoplastic protein (NTP). NTP is made from bloodmeal and is ∼60% protein. Activation energy (Eα), pre-exponential factor (ln Ao) and order of reaction (m + n) were calculated using the Kissinger, model-free isoconversional and autocatalytic models. Curing kinetics were almost independent of concentration and the addition of plasticizers and protein denaturants to bloodmeal caused a decrease in Eα of ∼50%. Increasing protein denaturants had little effect on the reaction; however, inclusion of salt proved detrimental. At NTP’s maximum processing temperature (∼450 K), using an equal molar ratio of epoxy groups to reactive amino acids, 75% conversion can be reached in 3 min based on the modeling done here.

Compatibilization of Protein Thermoplastics and Polybutylene Succinate Blends

AbstractReactive extrusion was used to prepare blends of Novatein thermoplastic protein (NTP) and poly(butylene succinate) (PBS) compatibilized with poly‐2‐ethyl‐2‐oxazoline (PEOX) and polymeric methylene diphenyl diisocyanate (pMDI). PEOX improved the dispersion of NTP in PBS and in conjunction with pMDI led to improved water resistance and a tensile strength exceeding that of NTP and PBS. The secant modulus, elongation as well as energy to break were also improved. The glass transition temperature (Tg) of compatibilized blends remained unchanged, however, the melting enthalpy and temperature decreased. This suggested that the crystalline structure of PBS has been disrupted by NTP as a result of compatibilization.

Pressure Sensitive Adhesion of an Elastomeric Protein Complex Extracted From Squid Ring Teeth

The pressure sensitive adhesion characteristic of a protein complex extracted from squid ring teeth (SRT), which exhibits an unusual and reversible transition from a solid to a melt, is studied. The native SRT is an elastomeric protein complex that has standard amino acids, and it does not function as adhesives in nature. The SRT can be thermally shaped into any 3D geometry (e.g., thin films, ribbons, colloids), and it has a glass transition temperature of 32 °C in water. Underwater adhesion strength of the protein film is approximately 1.5–2.5 MPa. The thermoplastic protein film could potentially be used in an array of fields, including dental resins, bandages for wound healing, and surgical sutures in the body.

Effect of Formamide on the Mechanical Properties of Thermoplastic Protein Films

To manufacture the biodegradable protein films available for potential environmentally friendly application, down feather fiber was prepared and modified by formamide which acts as a plasticizer and then hot-pressed into films. The influence of formamdie on the mechanical properties of thermoplastic down films was investigated. The protein films modified by formamide were tough and showed excellent mechanical properties compared to the films without formamide. The down thermoplastic films modified by formamide showed lower weight loss of formamide indicating formamide is a good plasticizer for protein application.