Low-intensity mixing process of high molecular weight polymer chains leads to elastomers of long network strands and high fatigue threshold.

Many polymer networks are prepared by crosslinking polymer chains. The polymer chains and crosslinkers are commonly mixed in internal mixers or roll mills. These intense processes break the polymer chains, lower viscosity, and ease mixing. The resulting polymer networks have short chains and a fatigue threshold of ∼100 J m-2. Here, we show that a low-intensity process, a combination of kneading and annealing, preserves long chains, leading to a network of polybutadiene to achieve a fatigue threshold of 440 J m-2. In a network, each chain has multiple crosslinks, which divides the chain into multiple strands. At the ends of the chain are two dangling strands that do not bear the load. The larger the number of crosslinks per chain, the lower the fraction of dangling strands. High fatigue threshold requires long strands, as well as a low fraction of dangling strands. Once intense mixing cuts chains short, each short chain can only have a few crosslinks; the strands are short and the fraction of dangling strands is high-both lower the fatigue threshold. By contrast, a low-intensity mixing process preserves long chains, which can have many crosslinks; the strands are long and the fraction of dangling strands is low-both increase the fatigue threshold. It is hoped that this work will aid the development of fatigue-resistant elastomers.

Study on hydroxypropyl corn starch/alkyl ketene dimer composite film with enhanced water resistance and mechanical properties.

This study aimed to address the limited applicability of starch-based films in food packaging due to their inherent hydrophilicity, by developing a highly hydrophobic and mechanically reinforced film through compositing with alkyl ketene dimer (AKD). The FTIR analysis confirmed the successful introduction of AKD into the starch backbone via esterification by forming a ß-keto ester linkage. Notably, the incorporation of AKD resulted in significant improvements in the modified film (S80A20), by exhibiting a higher water contact angle (WCA) of 128.28° and a reduced water vapor permeability (WVP) to 0.81×10-10 (g m/m2 s Pa). These enhancements were attributed to the inherent low surface energy of AKD and the increased surface roughness caused by AKD recrystallization. Moreover, the mechanical properties of the films were also enhanced due to the chemical crosslinking and intermolecular hydrogen bonding, as supported by the results of relaxation temperatures and molecular dynamics simulations. Considering the environmentally friendly and biodegradable nature of all components, the prepared hydrophobic films will hopefully be applied in food packaging.

Harnessing nitrogen-doped graphene quantum dots for enhancing the fluorescence and conductivity of the starch-based film.

The flexible film is widely applied in the modern electronic industry, whilst it is still challenging to use biopolymer substrates (e.g., starch) to prepare flexible film well-performed in conductivity and fluorescence. In the study, a novel conductive, fluorescent, and flexible biopolymer film was prepared via a cost-effective method by fabricating the nitrogen-doped oxide-reduced graphene quantum dots (N-rGO-QDs) into the thermoplastic starch (TPS) substrate. TPS/N-rGO-QDs film with 10 wt% N-rGO-QDs showed the desirable lowest resistivity (0.082 Ω·m), acceptable light transmittance (60-80 %), and durable fluorescence intensity (9000 CPS). The results reveal a novel starch-based multifunctional film with satisfactory electrical and fluorescent performances, which is hypothesized potential to be applied in some frontier domains, like human wearable devices.

Predicting the Glycemic Index of Biscuits Using Static In Vitro Digestion Protocols.

In vitro digestion methods that can accurately predict the estimated GI (eGI) values of complex carbohydrate foods, including biscuits, are worth exploring. In the current study, standard commercial biscuits with varied clinical GI values between 9~30 were digested using both the INFOGEST and single-enzyme digestion protocols. The digestion kinetic parameters were acquired through mathematical fitting by mathematical kinetics models. The results showed that compared with the INFOGEST protocol, the AUR180 deduced from digesting using either porcine pancreatin or α-amylase showed the best potential in predicting the eGI values. Accordingly, mathematical equations were established based on the relations between the AUR180 and the GI values. When digesting using porcine pancreatin, GI= 1.834 + 0.009 ×AUCR180 (R2= 0.952), and when digesting using only α-amylase, GI= 6.101 + 0.009 ×AUCR180 (R2=0.902). The AUR180 represents the area under the curve of the reducing-sugar content normalized to the total carbohydrates versus the digestion time in 180 min. The in vitro method presented enabled the rapid and accurate prediction of the eGI values of biscuits, and the validity of the formula was verified by another batch of biscuits with a known GI, and the error rate of most samples was less than 30%.

Making Highly Elastic and Tough Hydrogels from Doughs.

A hydrogel is often fabricated from preexisting polymer chains by covalently crosslinking them into a polymer network. The crosslinks make the hydrogel swell-resistant but brittle. This conflict is resolved here by making a hydrogel from a dough. The dough is formed by mixing long polymer chains with a small amount of water and photoinitiator. The dough is then homogenized by kneading and annealing at elevated temperatures, during which the crowded polymer chains densely entangle. The polymer chains are then sparsely crosslinked into a polymer network under an ultraviolet lamp, and submerged in water to swell to equilibrium. The resulting hydrogel is both swell-resistant and tough. The hydrogel also has near-perfect elasticity, high strength, high fatigue resistance, and low friction. The method is demonstrated with two widely used polymers, poly(ethylene glycol) and cellulose. These hydrogels have never been made swell-resistant, elastic, and tough before. The method is generally applicable to synthetic and natural polymers, and is compatible with industrial processing technologies, opening doors to the development of sustainable, high-performance hydrogels.

Characterization of a novel starch-based foam with a tunable release of oxygen.

Here, we used techniques of extrusion and coating to produce starch-based foams with a combined function of buffering and controlled release of oxygen. The foams presented open-cell structures and showed a compression recovery ratio of 94%. After coating with poly(vinyl alcohol) solution, in which calcium peroxides were loaded, the developed functional foams showed a behavior of controllable oxygen release under a wet condition, as well as a high compression strength (≥2.2 MPa). Also, these foams showed an improved moisture resistance with a reduction in maximum moisture absorption from 25 to 14%. Under a vibrated storage condition to simulate food transportation, guavas packaged with functional foams showed a reduced physical damage, and browning index from 5.00 to 2.97, owing to the foams' superior buffering ability and self-regulation of storage atmosphere. The functional packaging system of the starch-based foams developed in our work is promising for fruit and vegetable preservations.

Effect of NaCl addition on alcohol-alkali-treated waxy rice starch: Structural and physicochemical functionality.

The physicochemical and structural properties of waxy rice starch (WRS) and alcohol-alkali-treated waxy rice starch (AAT-WRS) were determined in the presence of different concentrations of NaCl (0, 2, 4, 6 and 8%). The results showed that NaCl decreased the transparency of WRS and AAT-WRS pastes, but enhanced both freeze-thaw stability and apparent viscosity (p < 0.05). The rheological measurement results showed that the addition of NaCl could improve the modulus values of both WRS and AAT-WRS, and the effect on WRS was more significant than that on AAT-WRS. The textural parameters of WRS pastes were evidently enhanced by NaCl, but the presence of NaCl had no significant effect on the firmness of AAT-WRS pastes. The results of SEM and FT-IR revealed that NaCl could protect the granular morphology and increase the degree of short-range order of WRS and AAT-WRS.

Quantitative study of starch swelling capacity during gelatinization with an efficient automatic segmentation methodology.

A novel image segmentation methodology combined with optical microscopy observation was developed for qualifying starch swelling. Starch granules in the micrograph were successfully segmented based on high-precision edges extraction achieved by Canny edge detection together with mathematical morphology operation. Granules were automatically identified by computer vision and characterized by giving quantifiable area of these granules. The evolved swelling process could be generally divided into two phases. During the first phase, starch granules were only swollen up by 2.56 %, which is hard to be identified by conventional naked eye. During the following narrow temperature interval (60-66 ℃), these starch granules were detected to swell up significantly by 9.08 %. Through the granule area variable, swelling capacity was high-throughput characterized, which allows for the whole evaluation to be completed within a couple of minutes. The proposed methodology showed a high accuracy and potential as a novel technique for characterizing gelatinization.

Effect of starch microstructure on microwave-assisted esterification.

Dry modification of starch, especially by microwave-assisted heating, has attracted increasing attention due to its various advantages, including energy saving, high conversion, rapidity, and avoidance of volatile organic solvents in organic synthesis. This work focuses on two fundamental issues: 1) effect of starch microstructure on dry modification; 2) effect of acid anhydride in solid and liquid states on the dry reaction, since their interfaces with solid starch are significantly different. Cornstarches with different amylose/amylopectin ratios were used to demonstrate the effect of starch microstructure, while two acid anhydrides, maleic (solid) and acetic (liquid) anhydrides, were used to study the reaction mechanisms. FTIR, SEM, XRD, and DSC were used to study the performance of modified starches and the mechanisms. It was found that the degree of substitution (DS) of starches modified by maleic anhydride generally increased with increasing amylose content since amylose contains more hydroxyl groups, resulting in higher sensitivity to microwaves. On the other hand, the DS of starches modified by acetic anhydride increased with increasing amylopectin content, since liquid acetic acid can diffuse into high-amylopectin starch granules. The higher amylopectin starches, waxy and maize, showed higher RC(%) and ∆H(%) than that of higher amylose starches G50 and G80.

How rheological behaviors of concentrated starch affect graft copolymerization of acrylamide and resultant hydrogel.

Corn starches with different amylose/amylopectin ratios were used to explore the effect of rheological behaviors of concentrated system on the graft copolymerization of acrylamide and resultant hydrogels, which sheds a light on their reactive extrusion process. The viscoelastic moduli of starch melts increased with increasing amylose content (AC), leading to a decreased extent of micro-mixing detected by a reduced rheokinetic rate. With increasing AC, the graft efficiency was decreased but with almost similar monomer conversion (about 87.5%) and nearly equivalent graft content. XRD and SAXS spectra revealed that the extent of retrogradation of the starches were increased and two-phase separation was enhanced for hydrogels with increasing AC. Interestingly, microscopic analysis showed the superabsorbent hydrogel from the starch with AC of 50% exhibited a gridding membrane porous structure, resulting in a higher water absorbent capacity of 550 g/g. This was attributed to the moderate crosslinking and the slightly greater graft content.

Influence of crosslinker amount on the microstructure and properties of starch-based superabsorbent polymers by one-step preparation at high starch concentration.

This work concerns how crosslinker amount (N, N'-methylene-bisacrylamide) affects the microstructural, absorbent and rheological features of one-step prepared starch-based superabsorbent polymers at a high starch concentration (0.27:1 w/w starch-water). The increased crosslinker amount evidently altered the microstructure and the absorbent and rheological features. Then, the variations in starch-based superabsorbent polymer properties were discussed from a microstructure viewpoint. Particularly, the higher crosslinker quantity rose the crosslinking density and the ratio (GR) of grafted anhydroglucose unit on starch backbone (from 27% to 52%), but short the average polyacrylamide (PAM) chain length (LPAM). These structural features suppressed the chain stretch within starch-based superabsorbent polymer fractal gels (confirmed by smaller Rg value) and promoted the formation of smaller chain networks, thus weakening the water absorption to the starch-based superabsorbent polymer chain networks. Also, the increased GR and reduced LPAM, with lowered chain extension and elevated crosslinking density, probably decreased the flexibility and mobility of chain segments in starch-based superabsorbent polymer gel matrixes. This caused the enhanced robustness and storage modulus of the gels with reduced chain energy dissipation ability.

Rheokinetics of graft copolymerization of acrylamide in concentrated starch and rheological behaviors and microstructures of reaction products.

A widely recognized challenge in starch chemistry is to manipulate the graft copolymerization onto starch melt by reactive extrusion (REX). To understand the complex in-situ graft copolymerization in highly concentrated systems, we firstly used a mixer to achieve a homogeneous viscous starch melt, and then undertook dynamic rheological measurements to study the rheokinetics of the reaction. The in-situ synthesis also facilitated the characterization of the microstructures of reaction products. The melt mixture could be regarded to be completely micromixed since the rheokinetics was predominated by the reaction kinetics. The rheological characterization revealed that G'of hydrogels followed a linear progression with the crosslinker concentration. Nevertheless, the reaction temperature and initiator content had little influence on the final microstructure of hydrogels, most likely due to the strong chain transfer reaction in the melt. Additionally, high-amylose starches tended to form grafted hydrogels with a high physical crosslinking density.

Development and preparation of active starch films carrying tea polyphenol.

Starch films incorporated with tea polyphenol (TP) were developed to produce active food packaging. The effect of the incorporation of TP with different content on the structure, physicochemical properties, antioxidant activity and antimicrobial activity of the starch films was systematically evaluated. Results showed that TP was well dispersed in the starch matrix, which induced a slight influence on the surface and barrier properties of the films. TP addition led to an important improvement in antioxidant capability, as well as inhibition efficiency against the microorganisms of S. aureus and E. coli. However, a decrease in mechanical properties of films was observed. Moreover, a new automatic counting method which combined the computer vision and machine learning algorithm was developed to identify and count the colonies, and the method performed much faster without subjective uncertainty.

Understanding the microstructure and absorption rate of starch-based superabsorbent polymers prepared under high starch concentration.

From a microstructural view, the focus of this work was on the water absorption rate of starch-based superabsorbent polymers (starch-SAPs) prepared under high starch concentration (0.27:1w/w starch:water). The effects of starch amylose/amylopectin ratio were disclosed. The increase in amylopectin reduced the amount (CPAM) of polyacrylamide (PAM) in starch-SAPs but increased the ratio of starch carbons grafted with PAM, which eventually decreased the average length (LPAM) of PAM chains. The shorter PAM chains could reduce starch-SAP chain flexibility, thus inducing larger mass fractal gels in swollen starch-SAPs. In general, the increases in CPAM and LPAM were preferable for a higher water absorbent capacity (WAC), whereas the denser fractal gels reduced WAC. Interestingly, all starch-SAPs had a dual-phase absorption process with the first stage showing a higher rate than the second phase (k1>k2). The shorter PAM chains caused increases in k1 and k2.

Preparation and characterization of slow-release fertilizer encapsulated by starch-based superabsorbent polymer.

To enhance the effectiveness of fertilizers, a novel double-coated slow-release fertilizer was developed using ethyl cellulose (EC) as inner coating and starch-based superabsorbent polymer (starch-SAP) as outer coating. For starch-SAPs synthesized by a twin-roll mixer using starches from three botanical origins, a reduced grid size and an increased fractal gel size on nano-scale (i.e., increased stretch of 3D network) contributed to increasing the water absorbing capacity with a reduced absorbing rate and thus improving the slow-release property of fertilizer. The fertilizer particles coated with starch-SAP displayed well slow-release behaviors. In soil, compared to urea particles without and with EC coating, the particles further coated with starch-SAP showed reduced nitrogen release rate, and in particular, those with potato starch-SAP coating exhibited a steady release behavior for a period longer than 96h. Therefore, this work has demonstrated the potential of this new slow-release fertilizer system for improving the effectiveness of fertilizers.