Cytoxicity, dynamic and thermal properties of bio-based rosin-epoxy resin/ castor oil polyurethane/ carbon nanotubes bio-nanocomposites

Recent advancement in synthesizing bio-epoxy nanocomposites using lignin, plant oils, saccharides, polyphenols, and natural rubbers: A review

Due to environmental issues, production costs, and the low recycling capability of conventional epoxy polymers and their composites, many science groups have tried to develop a new type of epoxy polymers, which are compatible with the environment. Considering the precursors, these polymers can be produced from plant oils, saccharides, lignin, polyphenol, and natural resins. The appearance of these bio-polymers caused to introduce a new type of composites, namely bio-epoxy nanocomposites, which can be classified according to the synthesized bio-epoxy, the used nanomaterials, or both. Hence, in this work, various bio-epoxy resins, which have the proper potential for application as a matrix, are completely introduced with the synthesis viewpoint, and their characterized chemical structures are drawn. In the next steps, the bio-epoxy nanocomposites are classified based on the used nanomaterials, which are carbon nanoparticles (carbon nanotubes, graphene nanoplatelets, graphene oxide, reduced graphene oxide, etc.), nano-silica (mesoporous and spherical), cellulose (nanofibers and whiskers), nanoclay and so on. Also, the features of these bio-nanocomposites and their applications are introduced. This review study can be a proper guide for developing a new type of green nanocomposites in the near future.

Sustainable cycloaliphatic polyurethanes: from synthesis to applications

Polyurethanes (PUs) are a versatile and major polymer family, mainly produced via polyaddition between polyols and polyisocyanates. A large variety of fossil-based building blocks is commonly used to develop a wide range of macromolecular architectures with specific properties. Due to environmental concerns, legislation, rarefaction of some petrol fractions and price fluctuation, sustainable feedstocks are attracting significant attention, e.g., plastic waste and biobased resources from biomass. Consequently, various sustainable building blocks are available to develop new renewable macromolecular architectures such as aromatics, linear aliphatics and cycloaliphatics. Meanwhile, the relationship between the chemical structures of these building blocks and properties of the final PUs can be determined. For instance, aromatic building blocks are remarkable to endow materials with rigidity, hydrophobicity, fire resistance, chemical and thermal stability, whereas acyclic aliphatics endow them with oxidation and UV light resistance, flexibility and transparency. Cycloaliphatics are very interesting as they combine most of the advantages of linear aliphatic and aromatic compounds. This original and unique review presents a comprehensive overview of the synthesis of sustainable cycloaliphatic PUs using various renewable products such as biobased terpenes, carbohydrates, fatty acids and cholesterol and/or plastic waste. Herein, we summarize the chemical modification of the main sustainable cycloaliphatic feedstocks, synthesis of PUs using these building blocks and their corresponding properties and subsequently present their major applications in hot-topic fields, including building, transportation, packaging and biomedicine.

Effects of a graphene oxide-alginate sheet scaffold on rotator cuff tendon healing in a rat model

BACKGROUND

Natural polymer scaffolds used to promote rotator cuff healing have limitations in terms of their mechanical and biochemical properties. This animal study aimed to investigate the effects of combined graphene oxide (GO) and alginate scaffold and the toxicity of GO on rotator cuff healing in a rat model.

METHODS

First, the mechanical properties of a GO/alginate scaffold and a pure alginate scaffold were compared. The in vitro cytotoxicity of and proliferation of human tenocytes with the GO/alginate scaffold were evaluated by CCK-8 assay. For the in vivo experiment, 20 male rats were randomly divided into two groups (n = 10 each), and supraspinatus repair was performed: group 1 underwent supraspinatus repair alone, and group 2 underwent supraspinatus repair with the GO/alginate scaffold. Biomechanical and histological analyses were performed to evaluate the quality of tendon-to-bone healing 8 weeks after rotator cuff repair.

RESULTS

The GO/alginate scaffold exhibited an increased maximum load (p = .001) and tensile strength (p = .001). In the cytotoxicity test, the cell survival rate with the GO/alginate scaffold was 102.08%. The proliferation rate of human tenocytes was no significant difference between the GO/alginate and alginate groups for 1, 3, 5, and 7 days. Biomechanically, group 2 exhibited a significantly greater ultimate failure load (p < .001), ultimate stress (p < .001), and stiffness (p < .001) than group 1. The histological analysis revealed that the tendon-to-bone interface in group 2 showed more collagen fibers bridging, tendon-to-bone integration, longitudinally oriented collagen fibers, and fibrocartilage formation than in group 1.

CONCLUSION

A small amount of GO added to alginate improved the mechanical properties of the scaffold without evidence of cytotoxicity. At 8 weeks after rotator cuff repair, the GO/alginate scaffold improved tendon-to-bone healing without causing any signs of toxicity in a rat model.

Improving Epoxy Resin Performance Using PPG and MDI by One-Step Modification

The toughening modification of epoxy resin by polyurethane prepolymer (PU) can effectively solve the disadvantage of high brittleness in its application. In this study, a convenient way to toughen epoxy resins was explored, and the monomers PPG and MDI for the synthesis of polyurethane prepolymers were used for a one-step modification of epoxy resins. The test results of viscosity and elongation at break showed that P-M reduced the viscosity of the epoxy resin and improved the toughness. Especially when the content of P-M was 25%, the elongation at the break of the modified EP reached 196.56%. From a thermogravimetric and pyrolysis kinetic analysis, the P-M modification had better thermal stability than the PU modification. These findings have particular implications for the toughening and engineering applications of epoxy resins.

Synthesis and Characterization of Crosslinked Castor Oil-Based Polyurethane Nanocomposites Based on Novel Silane-Modified Isocyanate and Their Potential Application in Heat Insulating Coating

An isocyanate with trimethoxysilane groups at the side chains (IPDI-M) was synthesized via an addition between the mercaptopropyl trimethoxysilane groups (MPTMS) and IPDI tripolymer (IPDI-T). Then, silane grafted isocyanate as the functional hard segment, castor oil as the soft segment, poly (ethylene adipate) diol (PEA) as the chain extender, and MPTMS as an end-capping reagent were applied to form a series of organosilicon hybrid bio-based polyurethane (CPUSi). The effect of the IPDI-M contents on the thermal stability, mechanical properties, and surface properties of the resulting product was systematically investigated. Profit from the Si–O–Si crosslinked structures formed from MPTMS curing, the tensile strength, and Young’s modulus of the resulting products increased from 9.5 MPa to 22.3 Mpa and 4.05 Mpa to 81.59 Mpa, respectively, whereas the elongation at break decreased from 342% to 101%. The glass transition temperature, thermal stability, transparency, hydrophobicity, and chemical resistance were remarkably strengthened for the obtained organosilicon-modified polyurethane with the increasing MPTMS content. At the end of the work, the thermal insulation coating that was based on CPUSi and ATO can effectively block near-infrared rays, and the temperature difference between the inside and outside of the film reached 15.1 °C.

Polymers and Composites Derived from Castor Oil as Sustainable Materials and Degradable Biomaterials: Current Status and Emerging Trends

Recent years have seen rapid growth in utilizing vegetable oils to derive a wide variety of polymers to replace petroleum-based polymers for minimizing environmental impact. Nonedible castor oil (CO) can be extracted from castor plants that grow easily, even in an arid land. CO is a promising source for developing several polymers such as polyurethanes, polyesters, polyamides, and epoxy-polymers. Several synthesis routes have been developed, and distinct properties of polymers have been studied for industrial applications. Furthermore, fillers and fibers, including nanomaterials, have been incorporated in these polymers for enhancing their physical, thermal, and mechanical properties. This review highlights the development of CO-based polymers and their composites with attractive properties for industrial and biomedical applications. Recent advancements in CO-based polymers and their composites are presented along with a discussion on future opportunities for further developments in diverse applications.

Epoxidation of Kraft Lignin as a Tool for Improving the Mechanical Properties of Epoxy Adhesive

Owing to its chemical structure, wide availability and renewable nature, lignin is a promising candidate for the partial replacement of fossil-based raw material in the synthesis of epoxy resins. Its poor compatibility has been reported to be one of the main drawbacks in this domain. On the other hand, a well-established modification method for lignin epoxidation has been used for many years for the improvement of lignin compatibility. However, the extent of the effect of lignin epoxidation on the improvement of bio-based epoxy mechanical properties, applied as adhesives, is still an open question in the literature. In this context, a pristine and industrial grade kraft lignin (AKL) was reacted with epichlorohydrin to yield epoxidized lignin (E-AKL) in this work. Afterwards, AKL or E-AKL were separately blended with petroleum-based epoxy resin at 15 and 30 wt% and cured with a commercial amine. The adhesive curing kinetic was evaluated using a novel technique for thermal transition characterization, Temperature Modulated Optical Refractometry (TMOR); the results showed that the incorporation of AKL reduces the crosslinking rate, and that this effect is overcome by lignin modification. Mechanical tests revealed an improvement of impact and practical adhesion strength for samples containing 15 wt% of E-AKL. These results elucidate the effect of lignin epoxidation on the application of lignin-based epoxy adhesives, and might support the further development and application of these bio-based materials.

Advances in Rosin-Based Chemicals: The Latest Recipes, Applications and Future Trends

A comprehensive review of the publications about rosin-based chemicals has been compiled. Rosin, or colophony, is a natural, abundant, cheap and non-toxic raw material which can be easily modified to obtain numerous useful products, which makes it an excellent subject of innovative research, attracting growing interest in recent years. The last extensive review in this research area was published in 2008, so the current article contains the most promising, repeatable achievements in synthesis of rosin-derived chemicals, published in scientific literature from 2008 to 2018. The first part of the review includes low/medium molecule weight compounds: Especially intermediates, resins, monomers, curing agents, surfactants, medications and biocides. The second part is about macromolecules: mainly elastomers, polymers for biomedical applications, coatings, adhesives, surfactants, sorbents, organosilicons and polysaccharides. In conclusion, a critical evaluation of the publications in terms of data completeness has been carried out with an indication of the most promising directions of rosin-based chemicals development.

In Vitro Evaluation of Resilient Liner after Brushing with Conventional and Experimental Ricinus communis-Based Dentifrices

PURPOSE

To evaluate the effect of experimental (Ricinus communis) and commercial dentifrices used for denture cleaning on abrasiveness (gravimetric method; roughness), hardness, and color stability of a resilient relining material.

MATERIALS AND METHODS

Sixty circular (15 × 3 mm) specimens were distributed into four groups: C (control; brushing with water); CO (brushing with Colgate - for natural teeth); CB (brushing with Corega Brite - for complete dentures); RC (brushing with experimental dentifrice). Brushing was performed in a toothbrushing machine with a soft brush and a dentifrice suspension for 50 minutes, calculated to correspond to 1 year of regular brushing. Variables were measured initially and after the trial period. For the gravimetric method, the difference in mass was considered. The surface roughness was measured by a rugosimeter, and the hardness test was performed by a Shore A durometer. Color changes (ΔE; CIE L*a*b* and NBS systems) were measured by a portable spectrophotometer. Results were analyzed by ANOVA/Tukey's test (α = 0.05).

RESULTS

The largest mass variation (μg; p < 0.0001) occurred in C (-6.21 ± 3.18). Concerning roughness, CB (0.26 ± 0.04) showed the lowest value, followed by RC (0.29 ± 0.08) and CO (0.34 ± 0.24) (p < 0.0001). Group C produced the greatest surface roughness (0.72 ± 0.25). Hardness values decreased after brushing with water (p = 0.014). No significant differences were found among RC (50.31 ± 1.03), CO (49.11 ± 1.31), CB (49.17 ± 1.23), and C (48.02 ± 1.26). Color stability was similar in all groups (p = 0.135; C: 2.3 ± 0.77; CO: 2.6 ± 0.54; CB: 2.2 ± 0.44; RC: 2.9 ± 1.56).

CONCLUSIONS

The use of experimental dentifrice could be indicated, as it showed similar results to the specific dentifrice, keeping the resilient material properties within acceptable values.

Clinical trial for evaluation of Ricinus communis and sodium hypochlorite as denture cleanser

Objective

This study evaluated Ricinus communis and sodium hypochlorite solutions in terms of biofilm removal ability, remission of candidiasis, antimicrobial activity, and participant satisfaction.

Material and Methods

It was conducted a controlled clinical trial, randomized, double-blind, and crossover. Sixty-four denture wearers with (n=24) and without candidiasis (n=40) were instructed to brush (3 times/day) and immerse their dentures (20 min/day) in different storage solutions (S1 / S2: 0.25% / 0.5% sodium hypochlorite; S3: 10% R. communis; S4: Saline).The trial period for each solution was seven days and a washout period of seven days was used before starting the use of another solution. The variables were analyzed at baseline and after each trial period. The biofilm of inner surfaces of maxillary dentures was disclosed, photographed, and total and dyed areas were measured (Image Tool software). The percentage of biofilm was calculated. Remission of candidiasis was assessed by visual scale and score were attributed. Antimicrobial activity was assessed by the DNA-Checkerboard hybridization method. Patient satisfaction was measured using a questionnaire.

Results

S1 (4.41±7.98%) and S2 (2.93±5.23%) were more effective then S3 (6.95±10.93%) in biofilm remotion(P<0.0001). All solutions were different from the control (11.07±11.99%). S3 was the most effective solution in remission of candidiasis (50%), followed by S1 (46%). Concerning antimicrobial action, S1/S2 were similar and resulted in the lowest microorganism mean count (P=0.04), followed by S3. No significant differences were found with patient's satisfaction.

Conclusions

10% R. communis and 0.25% sodium hypochlorite were effective in biofilm removal, causing remission of candidiasis and reducing the formation of microbial colonies in denture surfaces. All solutions were approved by patients.