Degradation and lifetime prediction of plastics in subsea and offshore infrastructures.

Engineering and civil developments have relied on synthetic polymers and plastics (including polyethylene, polypropylene, polyamide, etc.) for decades, especially where their durability protects engineering structures against corrosion and other environmental stimuli. Offshore oil and gas infrastructure and renewable energy platforms are typical examples, where these plastics (100,000 s of metric tonnes worldwide) are used primarily as functional material to protect metallic flowlines and subsea equipment against seawater corrosion. Despite this, the current literature on polymers is limited to sea-surface environments, and a model for subsea degradation of plastics is needed. In this review, we collate relevant studies on the degradation of plastics and synthetic polymers in marine environments to gain insight into the fate of these materials when left in subsea conditions. We present a new mathematical model that accounts for various physicochemical changes in the oceanic environment as a function of depth to predict the lifespan of synthetic plastics and the possible formation of plastic debris, e.g., microplastics. We found that the degradation rate of the plastics decreases significantly as a function of water depth and can be estimated quantitatively by the mathematical model that accounts for the effect (and sensitivity) of geographical location, temperature, light intensity, hydrostatic pressure, and marine sediments. For instance, it takes a subsea polyethylene coating about 800 years to degrade on ocean floor (as opposed to <400 years in shallow coastal waters), generating 1000s of particles per g of degradation under certain conditions. Our results demonstrate how suspended sediments in the water column are likely to compensate for the decreasing depth-corrected degradation rates, resulting in surface abrasion and the formation of plastic debris such as microplastics. This review, and the complementing data, will be significant for the environmental impact assessment of plastics in subsea infrastructures. Moreover, as these infrastructures reach the end of their service life, the management of the plastic components becomes of great interest to environmental regulators, industry, and the community, considering the known sizeable impacts of plastics on global biogeochemical cycles.

Halophyte biorefinery for polyhydroxyalkanoates production from Ulva sp. Hydrolysate with Haloferax mediterranei in pneumatically agitated bioreactors and ultrasound harvesting.

The present study tested the outdoor cultivation of Haloferax mediterranei for PHA production from green macroalgae Ulva sp. in pneumatically agitated bioreactors and applied ultrasonic separation for enhanced settling of archaeal cells. Scaled-up cultivation (40 L) yielded maximum biomass productivity of 50.1 ± 0.11 mg·L-1·h-1 with a PHA productivity of 27 ± 0.01 mg·L-1·h-1 and conversion yield of 0.107 g PHA per gram UlvaDW. The maximum mass fraction of PHA achieved in biomass was calculated to be 56% w/w. Ultrasonic harvesting of Hfx. mediterranei cells approached 30% removal at energy inputs around 7.8 kWh·m-3, and indicated no significant aggregation enhancement by Ca2+ addition. Molecular weight analysis showed an increase in Polydispersity Index (PDI) when the corresponding air velocities were increased suggesting that the polymer was more homogeneous at lower mixing velocities. The current study demonstrated scalable processes for PHA production using Ulva sp. feedstock providing new technologies for halophilic biorefinery.

Advantages and Disadvantages of Bioplastics Production from Starch and Lignocellulosic Components.

The accumulation of plastic wastes in different environments has become a topic of major concern over the past decades; therefore, technologies and strategies aimed at mitigating the environmental impacts of petroleum products have gained worldwide relevance. In this scenario, the production of bioplastics mainly from polysaccharides such as starch is a growing strategy and a field of intense research. The use of plasticizers, the preparation of blends, and the reinforcement of bioplastics with lignocellulosic components have shown promising and environmentally safe alternatives for overcoming the limitations of bioplastics, mainly due to the availability, biodegradability, and biocompatibility of such resources. This review addresses the production of bioplastics composed of polysaccharides from plant biomass and its advantages and disadvantages.

Flexible starch-polyurethane films: Effect of mixed macrodiol polyurethane ionomers on physicochemical characteristics and hydrophobicity.

One of the most critical limitations in synthesizing starch-polyurethane (PU) hybrid materials is their microphase separation caused by physical incompatibility. This paper reports that the physical incompatibility and microphase separation between starch and PU can be overcome by using specifically designed anionic poly(ether-ester) polyurethane (AEEPU). The AEEPU was synthesised by preparing isocyanate (NCO)-terminated prepolymer using Isophorone diisocyanate (IPDI), 2,2-bis(hydroxymethyl)propionic acid (BMPA), poly (ethylene glycol) (PEG) and polycaprolactone (PCL). This AEEPU was physically mixed with glycerol plasticized high amylose starch (HAGS) at HAGS to AEEPU mass ratios of 90/10, 80/20, 70/30, 60/40, 50/50. Higher AEEPU content in HAGS-AEEPU increased surface hydrophobicity and elasticity while the Young's modulus remained unaffected. HAGS-AEEPU film at 50:50 ratio was comparable to LDPE film in terms of elongation at break (187%), Young's modulus (383 MPa), and contact angle (112°) and good transparency. These starch-PU films are expected to find increased application as biodegradable packaging materials.

Optimizing Prednisolone Loading into Distiller's Dried Grain Kafirin Microparticles, and In vitro Release for Oral Delivery.

Kafirin microparticles have potential as colon-targeted delivery systems because of their ability to protect encapsulated material from digestive processes of the upper gastrointestinal tract (GIT). The aim was to optimize prednisolone loading into kafirin microparticles, and investigate their potential as an oral delivery system. Response surface methodology (RSM) was used to predict the optimal formulation of prednisolone loaded microparticles. Prednisolone release from the microparticles was measured in simulated conditions of the GIT. The RSM models were inadequate for predicting the relationship between starting quantities of kafirin and prednisolone, and prednisolone loading into microparticles. Compared to prednisolone released in the simulated gastric and small intestinal conditions, no additional drug release was observed in simulated colonic conditions. Hence, more insight into factors affecting drug loading into kafirin microparticles is required to improve the robustness of the RSM model. This present method of formulating prednisolone-loaded kafirin microparticles is unlikely to offer clinical benefits over commercially available dosage forms. Nevertheless, the overall amount of prednisolone released from the kafirin microparticles in conditions simulating the human GIT demonstrates their ability to prevent the release of entrapped core material. Further work developing the formulation methods may result in a delivery system that targets the lower GIT.

Different characteristic effects of ageing on starch-based films plasticised by 1-ethyl-3-methylimidazolium acetate and by glycerol.

The focus of this study was on the effects of plasticisers (the ionic liquid 1-ethyl-3-methylimidazolium acetate, or [Emim][OAc]; and glycerol) on the changes of starch structure on multiple length scales, and the variation in properties of plasticised starch-based films, during ageing. The films were prepared by a simple melt compression moulding process, followed by storage at different relative humidity (RH) environments. Compared with glycerol, [Emim][OAc] could result in greater homogeneity in [Emim][OAc]-plasticised starch-based films (no gel-like aggregates and less molecular order (crystallites) on the nano-scale). Besides, much weaker starch-starch interactions but stronger starch-[Emim][OAc] interactions at the molecular level led to reduced strength and stiffness but increased flexibility of the films. More importantly, [Emim][OAc] (especially at high content) was revealed to more effectively maintain the plasticised state during ageing than glycerol: the densification (especially in the amorphous regions) was suppressed; and the structural characteristics especially on the nano-scale were stabilised (especially at a high RH), presumably due to the suppressed starch molecular interactions by [Emim][OAc] as confirmed by Raman spectroscopy. Such behaviour contributed to stabilised mechanical properties. Nonetheless, the crystallinity and thermal stability of starch-based films with both plasticisers were much less affected by ageing and moisture uptake during storage (42 days), but mostly depended on the plasticiser type and content. As starch is a typical semi-crystalline bio-polymer containing abundant hydroxyl groups and strong hydrogen bonding, the findings here could also be significant in creating materials from other similar biopolymers with tailored sensitivity and properties to the environment.

Extrusion induced low-order starch matrices: Enzymic hydrolysis and structure.

Waxy, normal and highwaymen maize starches were extruded with water as sole plasticizer to achieve low-order starch matrices. Of the three starches, we found that only high-amylose extrudate showed lower digestion rate/extent than starches cooked in excess water. The ordered structure of high-amylose starches in cooked and extruded forms was similar, as judged by NMR, XRD and DSC techniques, but enzyme resistance was much greater for extruded forms. Size exclusion chromatography suggested that longer chains were involved in enzyme resistance. We propose that the local molecular density of packing of amylose chains can control the digestion kinetics rather than just crystallinity, with the principle being that density sufficient to either prevent/limit binding and/or slow down catalysis can be achieved by dense amorphous packing.

Lubrication of starch in ionic liquid-water mixtures: Soluble carbohydrate polymers form a boundary film on hydrophobic surfaces.

Soluble starch polymers are shown to enhance the lubrication of ionic liquid-water solvent mixtures in low-pressure tribological contacts between hydrophobic substrates. A fraction of starch polymers become highly soluble in 1-ethyl-3-methylimidazolium acetate (EMIMAc)-water solvents with ionic liquid fraction ≥60wt%. In 65wt% EMIMAc, a small amount of soluble starch (0.33wt%) reduces the boundary friction coefficient by up to a third in comparison to that of the solvent. This low-friction is associated with a nanometre thick film (ca. 2nm) formed from the amylose fraction of the starch. In addition, under conditions where there is a mixture of insoluble starch particles and solubilised starch polymers, it is found that the presence of dissolved amylose enhances the lubrication of starch suspensions between roughened substrates. These findings open up the possibility of utilising starch biopolymers, as well as other hydrocolloids, for enhancing the performance of ionic liquid lubricants.

Understanding the structural disorganization of starch in water-ionic liquid solutions.

Using synchrotron X-ray scattering analyses and Fourier transform infrared spectroscopy, this work provides insights into the solvent effects of water : [C2mim][OAc] solutions on the disorganization of a starch semi-crystalline structure. When a certain ratio (10.2 : 1 mol/mol) of water : [C2mim][OAc] solution is used, the preferential hydrogen bonding between starch hydroxyls and [OAc](-) anions results in the breakage of the hydrogen bonding network of starch and thus the disruption of starch lamellae. This greatly facilitates the disorganization of starch, which occurs much easier than in pure water. In contrast, when 90.8 : 1 (mol/mol) water : [C2mim][OAc] solution is used, the interactions between [OAc](-) anions and water suppress the solvent effects on starch, thereby making the disorganization of starch less easy than in pure water. All these differences can be shown by changes in the lamellar and fractal structures: firstly, a preferable increase in the thickness of the crystalline lamellae rather than that of the amorphous lamellae causes an overall increase in the thickness of the semi-crystalline lamellae; then, the amorphous lamellae start to decrease probably due to the out-phasing of starch molecules from them; this forms a fractal gel on a larger scale (than the lamellae) which gradually decreases to a stable value as the temperature increases further. It is noteworthy that these changes occur at temperatures far below the transition temperature that is thermally detectable as is normally described. This hints to our future work that using certain aqueous ionic liquids for destructuration of the starch semi-crystalline structure is the key to realize green processes to obtain homogeneous amorphous materials.

Biodegradation of starch films: the roles of molecular and crystalline structure.

The influences of molecular, crystalline and granular structures on the biodegradability of compression-molded starch films were investigated. Fungal α-amylase was used as model degradation agent. The substrates comprised varied starch structures obtained by different degrees of acid hydrolysis, different granular sizes using size fractionation, and different degrees of crystallinity by aging for different times (up to 14 days). Two stages are identified for unretrograded films by fitting degradation data using first-order kinetics. Starch films containing larger molecules were degraded faster, but the rate coefficient was independent of the granule size. Retrograded films were degraded much slower than unretrograded ones, with a similar rate coefficient to that in the second stage of unretrograded films. Although initially the smaller molecules or the easily accessible starch chains on the amorphous film surface were degraded faster, the more ordered structure (resistant starch) formed from retrogradation, either before or during enzymatic degradation, strongly inhibits film biodegradation.

Characteristics of starch-based films with different amylose contents plasticised by 1-ethyl-3-methylimidazolium acetate.

Starch-based films plasticised by an ionic liquid, 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]), were prepared by a simple compression moulding process, facilitated by the strong plasticisation effect of [Emim][OAc]. The effects of amylose content of starch (regular vs. high-amylose maize) and relative humidity (RH) during ageing of the samples on a range of structural and material characteristics were investigated. Surprisingly, plasticisation by [Emim][OAc] made the effect of amylose content insignificant, contrary to most previous studies when other plasticisers were used. In other words, [Emim][OAc] changed the underlying mechanism responsible for mechanical properties from the entanglement of starch macromolecules (mainly amylose), which has been reported as a main responsible factor previously. The crystallinity of the plasticised starch samples was low and thus was unlikely to have a major contribution to the material characteristics, although the amylose content impacted on the crystalline structure and the mobility of amorphous parts in the samples to some extent. Therefore, RH conditioning and thus the sample water content was the major factor influencing the mechanical properties, glass transition temperature, and electrical conductivity of the starch films. This suggests the potential application of ionic liquid-plasticised starch materials in areas where the control of properties by environmental RH is desired.

Establishing whether the structural feature controlling the mechanical properties of starch films is molecular or crystalline.

The effects of molecular and crystalline structures on the tensile mechanical properties of thermoplastic starch (TPS) films from waxy, normal, and high-amylose maize were investigated. Starch structural variations were obtained through extrusion and hydrothermal treatment (HTT). The molecular and crystalline structures were characterized using size-exclusion chromatography and X-ray diffractometry, respectively. TPS from high-amylose maize showed higher elongation at break and tensile strength than those from normal maize and waxy maize starches when processed with 40% plasticizer. Within the same amylose content, the mechanical properties were not affected by amylopectin molecular size or the crystallinity of TPS prior to HTT. This lack of correlation between the molecular size, crystallinity and mechanical properties may be due to the dominant effect of the plasticizer on the mechanical properties. Further crystallization of normal maize TPS by HTT increased the tensile strength and Young's modulus, while decreasing the elongation at break. The results suggest that the crystallinity from the remaining ungelatinized starch granules has less significant effect on the mechanical properties than that resulting from starch recrystallization, possibly due to a stronger network from leached-out amylose surrounding the remaining starch granules.

Characteristics of starch-based films plasticised by glycerol and by the ionic liquid 1-ethyl-3-methylimidazolium acetate: a comparative study.

This paper reports the plasticisation effect of the ionic liquid, 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]), as compared with the traditionally used plasticiser, glycerol, on the characteristics of starch-based films. For minimising the additional effect of processing, a simple compression moulding process (which involves minimal shear) was used for preparation of starch-based films. The results show that [Emim][OAc] was favourable for plasticisation, i.e., disruption of starch granules (by scanning electron microscopy), and could result in a more amorphous structure in the starch-based materials (by X-ray diffraction and dynamic mechanical analysis). (13)C CP/MAS and SPE/MAS NMR spectroscopy revealed that not only was the crystallinity reduced by [Emim][OAc], but also the amorphous starch present was plasticised to a more mobile form as indicated by the appearance of amorphous starch in the SPE/MAS spectrum. Mechanical results illustrate that, when either glycerol or [Emim][OAc] was used, a higher plasticiser content could contribute to higher flexibility. In spite of the accelerated thermal degradation of starch by [Emim][OAc] as shown by thermogravimetric analysis, the biodegradation study revealed the antimicrobial effect of [Emim][OAc] on the starch-based materials. Considering the high-amylose starch used here which is typically difficult to gelatinise in a traditional plasticiser (water and/or glycerol), [Emim][OAc] is demonstrated to be a promising plasticiser for starch to develop "green" flexible antimicrobial materials for novel applications.

Crystallisation and fractionation of selected polyhydroxyalkanoates produced from mixed cultures.

Poly[R-3-hydroxybutyrate-co-(R-3-hydroxyvalerate)] (PHBV) copolymers were produced from mixed cultures of biomass (activated sludge) fed with acetic acid (HAc) and propionic acid (HPr). Feeding was performed in such a way as to produce materials with a wide range of monomer compositions and microstructures. Solvent-cast thin films of these materials have recently been shown to exhibit a narrow range of mechanical properties similar to those of the homopolymer poly(R-3-hydroxybutyrate) (PHB) [1]. In this work, more detailed analyses of the thermal and crystallisation properties of these mixed-culture polyesters have revealed that they like comprise complex blends with broad compositional distribution of random and/or blocky copolymers of very different 3-hydroxyvalerate (3HV) contents and melting temperatures and thus have very different respective crystallisation kinetics. This blend complexity was confirmed by solvent fractionation of selected samples. The findings support the hypothesis that overall mechanical properties of these complex copolymer blend materials will be strongly influenced by the more rapidly crystallising components that form the matrix within which the slower crystallising components exist as microdomains. New opportunities in the material development of PHAs are likely to be found in establishing and exploiting such structure-function relationships.

In-line monitoring of thermal degradation of PHA during melt-processing by Near-Infrared spectroscopy.

Polyhydroxyalkanoate (PHA) biopolymer processing is often challenged by low thermal stability, meaning that the temperatures and time for which these polymers can be processed is restrictive. Considering the sensitivity of PHA to processing conditions, there is a demand for in-line monitoring of the material behaviour in the melt. This paper investigates the application of Near-Infrared (NIR) spectroscopy for monitoring the thermal degradation of PHAs during melt-processing. Two types of materials were tested: two mixed culture PHAs extracted from biomass produced in laboratory and pilot scale after an acidic pre-treatment, and two commercially available materials derived from pure culture production systems. Thermal degradation studies were carried out in a laboratory scale extruder with conical twin screws connected to a NIR spectrometer by a fibre optic to allow in situ monitoring. Multivariate data analysis methods were applied for assessing thermal degradation kinetics and predicted the degree of degradation as measured by (1)H NMR (proton nuclear magnetic resonance spectroscopy). The pre-treated mixed culture PHAs were found to be more thermally stable when compared with the commercial pure culture PHAs as demonstrated by NIR, (1)H NMR and GPC (gel permeation chromatography).

Encapsulation of hydrocortisone and mesalazine in zein microparticles.

Zein was investigated for use as an oral-drug delivery system by loading prednisolone into zein microparticles using coacervation. To investigate the adaptability of this method to other drugs, zein microparticles were loaded with hydrocortisone, which is structurally related to prednisolone; or mesalazine, which is structurally different having a smaller LogP and ionizable functional groups. Investigations into the in vitro digestibility, and the electrophoretic profile of zein, and zein microparticles were conducted to shed further insight on using this protein as a drug delivery system. Hydrocortisone loading into zein microparticles was comparable with that reported for prednisolone, but mesalazine loading was highly variable. Depending on the starting quantities of hydrocortisone and zein, the average amount of microparticles equivalent to 4 mg hydrocortisone, (a clinically used dose), ranged from 60-115 mg, which is realistic and practical for oral dosing. Comparatively, an average of 2.5 g of microparticles was required to deliver 250 mg of mesalazine (a clinically used dose), so alternate encapsulation methods that can produce higher and more precise mesalazine loading are required. In vitro protein digestibility revealed that zein microparticles were more resistant to digestion compared to the zein raw material, and that individual zein peptides are not preferentially coacervated into the microparticles. In combination, these results suggest that there is potential to formulate a delivery system based on zein microparticles made using specific subunits of zein that is more resistant to digestion as starting material, to deliver drugs to the lower gastrointestinal tract.

Effect of the ionic liquid 1-ethyl-3-methylimidazolium acetate on the phase transition of starch: dissolution or gelatinization?

This work revealed that the interactions between starch, the ionic liquid 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]), and water might contribute to the phase transition (gelatinization, dissolution, or both) of native starch at reduced temperature. Using mixtures of water and [Emim][OAc] at certain ratios (7.2/1 and 10.8/1 mol/mol), both the gelatinization and dissolution of the starch occur competitively, but also in a synergistic manner. At lower [Emim][OAc] concentration (water/[Emim][OAc] molar ratio≥25.0/1), mainly gelatinization occurs which is slightly impeded by the strong interaction between water and [Emim][OAc]; while at higher [Emim][OAc] concentration (water/[Emim][OAc] molar ratio≤2.8/1), the dissolution of starch is the major form of phase transition, possibly restricted by the difficulty of [Emim][OAc] to interact with starch.

Preparation and in vitro release of zein microparticles loaded with prednisolone for oral delivery.

Zein has been proposed as a polymer for targeted-drug delivery via the oral route. Zein microparticles were loaded with prednisolone and evaluated as an oral delivery system. Microparticles were formulated using phase separation. Starting quantities of zein and prednisolone, along with the agitation method and temperature were found to significantly impact drug loading and loading efficiency. Vortex mixing produced the highest drug loading and loading efficiency. Drug release was measured in simulated conditions of the stomach and small intestine using the microparticles made with the method that best improved drug loading. In simulated stomach and small intestine conditions, prednisolone release reached almost 70% over 3 and 4 h, respectively. While a clinically relevant dose may be delivered using c. 100 mg of zein microparticles, prednisolone release from the microparticles indicates that they may not be suited as a controlled- or targeted-delivery system.

Synthesis, characterization and biocompatibility of novel biodegradable cross-linked co-polymers based on poly(propylene oxide) diglycidylether and polyethylenimine.

Novel biodegradable cross-linked co-polymers were prepared from poly(propylene glycol) diglycidylether (PPGDGE) and poly(ethylene imine) (PEI). PPGDGE and PEI were mixed at ambient temperature with varying PEI concentrations of 10, 15, 18.5, 25, 30, 40 and 50 wt%; the homogenous PPGDGE/PEI mixtures obtained were cured at elevated temperatures, resulting in formation of PPG-PEI cross-linked co-polymers via ring-opening reaction of PPGDGE with PEI. The physicochemical and biological properties of these co-polymers were dependent on the PEI content and the extent of curing reaction. The glass transition temperature of PPG-PEI cross-linked co-polymers varied in the range from -14 to +42°C, while the co-polymers displayed composition-dependent mechanical behavior, from brittle to ductile with increasing PEI content from 18.5 wt% to 40 wt%. Chinese hamster ovary (CHO) cells were cultured on the PPG-PEI co-polymers; the MTT assay was used to measure cell viability and determine the cytotoxicity. The cell viability rate, relative to tissue-culture polystyrene (TCPS), increased from 49% to 125% with increasing PEI content from 18.5 wt% to 40 wt%. Although epoxy monomers usually exhibit cytotoxicity, the epoxy groups were exhausted via curing reaction in the fully cross-linked co-polymers. The PEI-cured PPG epoxy resin, i.e., PPG-PEI cross-linked co-polymers obtained in this study, showed excellent biocompatibility.

The anaerobic degradability of thermoplastic starch: polyvinyl alcohol blends: potential biodegradable food packaging materials.

A systematic study on the anaerobic degradability of a series of starch:polyvinyl alcohol (TPS:PVOH) blends was performed to determine their fate upon disposal in either anaerobic digesters or bioreactor landfills. The aims of the study were to measure the rate and extent of solubilisation of the plastics. The extent of substrate solubilisation on a COD basis reached 60% for a 90:10 (w/w) blend of TPS:PVOH, 40% for 75:25, 30% for 50:50 and 15% for PVOH only. The rate of substrate solubilisation was most rapid for the 90:10 blend (0.041 h(-1)) and decreased with the amount of starch in the blend in the following order 0.034 h(-1)(75:25); 0.023 h(-1)(50:50). The total solids that remained after 900 h were 10 wt.% (90:10); 23 wt.% (75:25); 55 wt.% (50:50); 90 wt.% (0:100). Starch containing substrates produced a higher concentration of volatile fatty acids (VFAs) and biogas, compared to the 0:100 substrate. The major outcome was that PVOH inhibited the degradation of the starch from the blend.