Reduction In Mechanical Performance Research Articles

Optimizing self-sensing performance of conductive mortar via gradation of graphene coated aggregate

With the increasing focus on structural health monitoring of concrete during its service life, self-sensing functional concrete has emerged as an effective method for real-time detection and assessment of structural conditions. We recently proposed a new methodology of preparing conductive cementitious mortar with graphene-coated aggregates (Gr@Ag). Instead of the traditional approach, where conductive fillers are directly intermixed and uniformly distributed in the binding matrix, the development of Gr@Ag has created a more efficient path for electron transport through the connections of aggregates. The main objective of this study is to understand the effect of aggregate gradation on the electrical performances of conductive mortars, and the piezoresistivity is optimized by adjusting the aggregate packing. Electrochemical impedance spectroscopy was employed to investigate the underlying mechanisms of how aggregate gradation affects the mortar's electrical conductivity. It was found that both the internal resistance and resistivity of the conductive mortar considerably decreased with the reduction in Gr@Ag particle size. The contribution of conductive sand to the conductivity of mortar can reach 80.89–92.36 %, effectively transforming the conductive path from a disconnected state to a connected state. Reducing the particle size of the conductive aggregates contributes to an increase in particle contact rate, with the particle contact rate reaching up to 59 %. The presence of completely isolated conductive aggregates is noticeably reduced. As the particle size decreases, there is a significant reduction in mechanical performance. The conductive aggregates become relatively isolated from the matrix, and both the size of the conductive aggregates and the interfacial transition zone play vital roles to affect the mechanical properties.

Mechanical impact of regional structural deterioration and tissue-level compensation on proximal femur trabecular bone.

Osteoporosis-induced changes in bone structure and composition significantly reduce bone strength, particularly in the human proximal femur. This study examines how these changes affect the mechanical performance of trabecular bone to enhance diagnosis, prevention, and treatment strategies. A proximal femur sample was scanned using micro-CT at 40μm resolution. Five regions of interest were selected within the femoral head, femoral neck, and greater trochanter. Structural models simulating various stages of osteoporosis were created using image processing software. Micro-finite element analysis evaluated the mechanical properties of trabecular bone under different conditions of structural deterioration and tissue-level elastic modulus variations. The combined effects of structural deterioration and tissue-level mechanical properties on trabecular bone mechanical performance were further analyzed. The mechanical performance of trabecular bone generally follows a power-law relationship with its microstructural characteristics. However, in any specific region, the apparent mechanical properties linearly decrease with structural deterioration. The femoral neck and greater trochanter are more sensitive to structural deterioration than the femoral head. A 5% bone mass loss in the femoral head led to a 7% reduction in mechanical performance, while the femoral neck experienced a 12% loss. Increasing tissue-level elastic modulus improved mechanical performance, partially offsetting bone mass reduction effects. Trabecular bone in low bone mass regions is more affected by bone mass loss. Structural deterioration primarily reduces bone strength, but improvements in tissue-level properties can mitigate this effect, especially in early osteoporosis. Targeted assessments and interventions are crucial for effective management. Future research should explore heterogeneous deterioration models to better understand osteoporosis progression.

Life-Cycle Assessment and Environmental Costs of Cement-Based Materials Manufactured with Mixed Recycled Aggregate and Biomass Ash.

The development of new building elements, such as concrete and mortar with sustainable materials, which produce a lower carbon footprint, is an achievable milestone in the short term. The need to reduce the environmental impact of the production of cement-based materials is of vital importance. This work focuses on the evaluation of the life-cycle assessment, production costs, mechanical performance, and durability of three mortars and three concrete mixtures in which mixed recycled aggregates (MRAs) and biomass bottom ash from olive waste (oBBA) were included to replace cement and aggregates. Powdered MRA and oBBA were also applied as complementary cementitious materials with a reduced environmental footprint. Chemical and physical tests were performed on the materials, and mechanical performance properties, life-cycle assessment, and life-cycle cost analysis were applied to demonstrate the technical and environmental benefits of using these materials in mortar and concrete mixtures. This research showed that the application of MRA and oBBA produced a small reduction in mechanical strength but a significant benefit in terms of life-cycle population and environmental costs. The results demonstrated that finding long-term mechanical strength decreases between 2.7% and 14% for mortar mixes and between 1.7% and 10.4% for concrete mixes. Although there were small reductions in mechanical performance, the savings in environmental and monetary terms make the feasibility of manufacturing these cement-based materials feasible and interesting for both society and the business world. CO2 emissions are reduced by 25% for mortar mixes and 12% for concrete mixes with recycled materials, and it is possible to reduce the cost per cubic meter of mortar production by 20%, and the savings in the cost of production of a cubic meter of concrete is 13.8%.

Tribological behavior of poly(ether ether ketone)/synthetic Eucommia rubber composites

AbstractOur previous study (Polymer Composites 2023, 44: 1252–1263) revealed the positive role of rubber in modifying the tribological properties of polymer composites. This concept was applied here by incorporating synthetic Eucommia rubber (TPI) to 3D printed polyether ether ketone (PEEK) skeletons with different infill densities. The formation of TPI/PEEK composite improved the friction and wear of PEEK matrix with some reduction in mechanical performance. The composite with 70% infill density is recommended in terms of its overall performance. Based on the morphological and chemical analysis, the composite's wear mechanism was discussed. The findings of this present study could pave a new route to modify friction‐reduction and anti‐wear performance of PEEK.Highlights Novel composites were successfully prepared from thermodynamically incompatible synthetic Eucommia rubber (TPI) and polyether ether ketone (PEEK). The tribological properties of TPI/PEEK composites were studied in association with the infill density of PEEK. The TPI rubber helped improve the friction and wear properties of PEEK thanks to its role in enhancing the formation of transfer films on the counter steel surface.

Microstructural Evolution and Mechanical Behavior of Pure Aluminum Ultra-Thin Strip under Roller Vibration

As the demand for lithium-ion batteries increases, higher quality requirements are being placed on pure aluminum ultra-thin strips, one of the main materials used in lithium-ion battery current collectors. Roller vibration during the rolling process of pure aluminum ultra-thin strips is unavoidable and significantly affects the quality of the strips. This paper uses 1A99 pure aluminum ultra-thin strips as raw materials and employs a controlled vibration method during the rolling process to obtain products under two conditions: stable rolling and vibrational rolling. The surface and cross-section of the aluminum strips were characterized using scanning electron microscopy (SEM), and the microstructure of the surface and cross-section was studied using electron backscatter diffraction (EBSD) technology. The results show that, during stable rolling, the surface quality of the aluminum strip is good without defects. Under vibration, obvious vibration marks appear on the surface of the aluminum strip, showing characteristics of peaks and troughs. With the increase in strain at the trough position, there is a transition from low-angle grain boundaries to high-angle grain boundaries, and the grain size is uneven at the peak and trough positions, with noticeable grain refinement at the troughs. At the same time, under the influence of vibration, the aluminum strip induces a different texture morphology from conventional rolling. Due to the different plastic strains at the peak and trough positions, a texture alternation phenomenon occurs at these positions. The tensile test results indicate that aluminum strips exhibit poor mechanical properties under roller vibration, with the reduction in mechanical performance primarily attributed to the uneven microstructure distribution caused by roller vibration.

A novel approach utilising phosphorylated casein for fire-retardant and formaldehyde-free medium density wood fibreboards

Casein has been employed in composite materials as a flame retardant (FR). However, in the current research, casein has not been applied to a medium density fibreboard (MDF) material system, especially in a formaldehyde-free MDF material system, to investigate its impact on mechanical and fire-resistant performance. Polyamidoamine-epichlorohydrin (PAE) resin has been utilised as a binder to manufacture formaldehyde-free MDF samples in this research. Phosphorylation was conducted to enhance the flame-retardant ability of casein. This chemical treatment resulted in the significant improvement on the char-forming performance of the casein, leading to the dramatic reduction of the peak heat release rate (PHRR) by ⁓45% compared with non-treated casein. The char formation of the phosphorylated casein in the MDF sample also decreased its PHRR more effectively by ∼18% with the drop of the THR value (∼40 MJ/m2) than that of the casein. Besides, the addition of the phosphorylated casein to the MDF based on the PAE binder did not diminish the binder`s bonding performance, resulting in the improvement of the flexural modulus by ∼23% and flexural stress by ∼16%, while the IB strength retained compared with that of the control MDF sample. The current study clearly demonstrates that the jointly use of phosphorylated casein and PAE is a promising avenue to overcome one of the ongoing challenges in the MDF material system with regard to mitigating the reduction in mechanical performance associated with the introduction of flame-retardant materials.

A multi-functional polyurethane elastomer with high damping, water resistance and flame retardancy

Polyurethane elastomer has become a current focal point in the field of damping materials due to superior comprehensive properties. However, its effective damping temperature range is limited, and existing methods often lead to a reduction in mechanical performance. Moreover, polyurethane exhibits poor water resistance and flame resistance, constraining its applications. In this study, we introduce a small amount of dangling chain and aromatic dynamic disulfide bond into polyurethane to achieve a balance between damping and mechanical performance. Notably, the fluorinated dangling chain improves water resistance of the material synchronously and effectively. Additionally, ammonium polyphosphate modified by melamine and diethyl bis(2-hydroxyethyl)aminomethylphosphonate are introduced into polyurethane to improve flame resistance. The prepared polyurethane elastomer exhibits excellent comprehensive performance, featuring an effective damping (tanδ≥0.3) temperature range of 153.2 °C (−53.2 °C ∼ 100 °C), V-0 level flame resistance and excellent water resistance. Meanwhile, the heat stability of the polyurethane elastomer has been significantly enhanced, while maintaining a certain level of mechanical performance (9.72 ± 0.25 MPa, 602.4 ± 30.1%). These improvements extend the service life of polyurethane and expand its range of potential applications.

A fully healable, mechanical self-strengthening and antibacterial Poly(thiocarbamate-urethane) elastomer constructed via dual reversible dynamic networks

Crosslinked polyurethane elastomers may irreversibly suffer from some external damage such as chemical corrosion, stress and long-term heat treatment, inducing the formation of the microcracks and reduction of mechanical performance. Herein, a novel, fully healable and mechanical self-strengthening crosslinked poly(thiocarbamate-urethane) elastomers (PTU) are constructed by dual reversible dynamic networks, which are based on the thiol-isocyanate click reaction and 2, 4-diamino-6-hydroxy-pyrimidine-Zn2+ (HPM-Znx) coordination effect. Interestingly, the tensile strength and toughness of PTU-HPM-Zn1/4 reached 24.2 MPa and 46.3 MJ/m3, which are 3.6 and 1.6 times higher than those of PTU-HPM, due to the coordination effect between Zn2+ and pyrimidine that formed a denser cross-linking network. Interestingly, the snipped specimen of PTU-HPM-Zn1/4 are fully healable within 12 h at 70 °C. Moreover, the hot-reprocessed PTU-HPM-Zn1/4 sample were further increased to 25.0 MPa and 51.5 MJ/m3, showing a mechanical self-strengthening phenomenon. These impressive mechanical properties of PTU-HPM-Zn1/4 elastomer are attributed to the hierarchical structure evolution including the microphase separation between crystallized and amorphous regions, and the multi reversible dynamic networks reconstruction of thiocarbamate, coordination and hydrogen bonds in the system. Meanwhile, PTU-HPM-Zn1/4 showed excellent antibacterial property against E. Coli. In order to expand their application as flexible and wearable sensor devices, two PTU-HPM-Zn1/4 based conductive films were prepared, which exhibited fast and stable sensing characteristics.

Multi-objective optimization of mix proportions for mass concrete with enhanced resistance to cracking and reduced temperature rise

The objective of this study is to investigate the influence of fly ash (FA), granulated blast furnace slag (GBFS), and a high-efficiency crack-resistant agent (HECRA) on the workability, mechanical properties, hydration heat (HH), adiabatic temperature rise (ATR), and volume stability of mass concrete (MC). Preliminary experiments determined that the total replacement of FA and GBFS in dual blending should be within 35% to 40%, with the GBFS content not exceeding 15%. A total of 16 concrete mix designs (MD) were formulated, including a control mix (comprising only cement (C)) and ternary blends (comprising C, FA, and GBFS), with the HECRA added at 0%, 4%, and 8% of the mass of cementitious materials. The workability of the MC was assessed through tests for air content (AC), bulk density (BD), slump, flow, and setting time. The mechanical strength, HH, ATR, and shrinkage rate of the MC were individually evaluated through compressive strength (CS) tests, HH experiments, ATR tests, and shrinkage measurements. A grey relational evaluation model was employed to establish correlations between C, FA, GBFS, and the HECRA concerning overall performance. Supported by the entropy value method, a comprehensive performance evaluation model was created. The results indicate that, compared to the control mix, the other groups exhibited reductions in mechanical performance, rates of HH, cumulative ATR, and increased self-volume deformation (SVD). These findings suggest that including FA, GBFS, and a HECRA can mitigate the HH and SVD of MC, albeit at the expense of its strength. According to the comprehensive performance evaluation model, when the C-to-FA-to-GBFS ratio is 6:3:1, and the HECRA constitutes 8% of the mass of cementitious materials, the specimens demonstrate the best overall performance. At 28d, the CS is 48.46 MPa, satisfying the design strength requirements for C35 concrete. The comprehensive performance of the large volume crack-resistant concrete with low temperature rise (LCCT) produced in this study meets engineering needs. It provides theoretical references for the mixed design of MC.

A simple method to address the high water absorption of recycled aggregates in cementitious mixes

The high water absorption of recycled concrete aggregates (RCA) can cause a significant reduction in the flow properties of cement-based materials in relation to mixes produced with natural aggregate. In order to compensate for this adverse effect, two extreme and simple approaches based on the water absorption of RCA in pure water are often used: using RCA in a saturated surface-dry (SSD) state or adding extra water based on the 24-hour water absorption of RCA in pure water (WA24h). However, these approaches can result in a significant drop in mix’s strength due to excessive water being used. Therefore, this study proposes a simple method to accurately evaluate the water absorption of RCA in cement paste (WAP) based on the variation in the mortar’s apparent density resulting from the RCA absorption of water from the cement paste. This study also investigates the effects of the aforementioned two approaches on the mortars’ performance. Recycled concrete sand (RCS) was adopted as the object of the study. The results show that, after an initial increase, the WAP of RCS stabilizes at 24 min. WAP also increases with the mortar’s W/C and WA24h, and decreases with the aggregate’s volume fraction. In addition, the maximum water absorption of RCS in cement paste (WAP_30min) is lower than WA24h, and the WAP at 6 min (WAP_6min) can reach 80% of the WAP_30min. A campaign of mortars was produced using the WAP_30min as previously assessed. It is found that the flowability of mortar prepared with RCS is poorer than that of mortar prepared with natural sand at the same effective W/C, but their strength is higher. Using RCS in a SSD state or adding extra water based on the WA24h of RCS can compensate for the flowability loss of the mortars to some extent, but at the expense of an excessive reduction in mechanical performance. Based on the results of this study, the authors suggest that the mix design of mortars prepared with RCA can be improved using WAP, namely adjusting the initial W/C to balance flowability and mechanical properties.

Influence of E‐beam irradiation on compounds from linear low density polyethylene and thermoplastic vulcanized rubber consisting of a polypropylene and ethylene propylene diene monomer rubber phase

AbstractLinear low‐density polyethylene (LLDPE) crosslinks under irradiation in the range of up to 250 kGy. Crosslinking leads to better chemical and thermal resistance but causes reduction in mechanical performance. To counter this reduction, compounds of LLDPE with thermoplastic elastomers (TPV) were made. Specimens were irradiated with doses reaching from 99 to 231 kGy. Gel content shows a decrease of around 12% for compounds with 20 wt% of TPV compared to pure LLDPE. It is also found that compounds containing 10 wt% TPV experience a 4% higher gel content than predicted. For higher amounts of TPV elongation at break increases from 689% for pure LLDPE to 769% and tensile strength decreases from 31.9 to 30.5 MPa. Under irradiation, a trend to lower elongations and tensile strengths is observed. Elongation at break decreased around 200% and tensile strength around 5 MPa under irradiation. Thermal analysis of TPV showed that while the melting temperature decreases, its crystallinity first rises for doses up to 165 kGy before decreasing. Infrared spectroscopy was used to identify changes in the chemical structure, where evidence of surface oxidation under irradiation is found for all compounds with LLDPE.

Effect of nano-silica on the mechanical performance and microstructure of silicon-aluminum-based internal-cured concrete

This study explores the effect of nano-silica on the performance of internal-cured concrete (ICC) with silicon-aluminum-based lightweight aggregate (LWA) by evaluating the mechanical behavior, microstructure of the matrix and the ITZ between LWA and the surrounding paste and phases of hydration products. Adding nano-silica significantly increased the compressive, split-tensile and flexural strength with a maximum increase of 63.7%, 17.6% and 11.3%, respectively, at a 1.0 wt% dosage. Although nano-silica presented a good filling, nucleation and pozzolanic effect, a higher dosage of 2.5 wt% resulted in a minor negative consequence on concrete microstructure given that a visible gap was identified between LWA and the neighboring paste, leading to a reduction in mechanical performance. The additional water provided by the pre-wetted LWA can compensate for the decreased water absorbed by nano-silica to prevent the decline of relative humidity and promote hydration reactions. In addition to the internal curing effect, the silicon-aluminum-based LWA also presented pozzolanic reactivity and exhibited a good coupling effect with nano-silica, contributing to a strengthened microstructure with a large amount of C–S–H gel tightly bonded and intertwined with other morphologies of hydration products. An increase in internal-water to binder ratio from 0.012 to 0.036 improved the densification of the paste and the composition of hydration products but the impact is less significant. With the good combined effect of nano-silica and internal curing, the mixture with 40% LWA presented excellent mechanical properties.

Residual stress effects during additive manufacturing of reinforced thin nickel–chromium plates

Additive manufacturing (AM) is a powerful technique for producing metallic components with complex geometry relatively quickly, cheaply and directly from digital representations; however, residual stresses induced during manufacturing can result in distortions of components and reductions in mechanical performance, especially in parts that lack rotational symmetry and, or have cross sections with large aspect ratios. Geometrically reinforced thin plates have been built in nickel–chromium alloy using laser-powder bed fusion (L-PBF) and their shapes measured using stereoscopic digital image correlation before and after release from the base-plate of the AM machine. The results show that residual stresses cause potentially severe out-of-plane deformation that can be alleviated using either an enveloping support structure, which increased the build time substantially, was difficult to remove and wasted material, or using buttress supports to the reinforced edges of the thin plate. The buttresses were quick to build and remove, minimised waste but needed careful design. Plates built in a landscape orientation required out-of-plane buttresses while those built in a portrait orientation required both in-plane and out-of-plane buttresses. In both cases, out-of-plane deformation increased on release from the baseplate but this was mitigated by incremental release which resulted in out-of-plane deformations of less than 5% of the in-plane dimensions.

Experimental investigations on flexural performance of polymer composites with non-uniform out-of-plane waviness defect

Fibre waviness is frequently observed manufacturing defect which leads to a reduction of mechanical performance of the fibre reinforced polymer (FRP) composites. The current study investigates the effect of out-of-plane fibre waviness as a manufacturing defect on the flexural performance of carbon fibre reinforced polymer (CFRP) composites. Specimens with the non-uniform hump and non-uniform indentation waviness were fabricated using the transverse strip method. Experimental tests were conducted in the three-point flexural configuration using specimens with and without fibre waviness to investigate the flexural behaviour. Each of the above type of non-uniform waviness was investigated to evaluate the effect of the extent of the wave for three severity levels. Load-displacement response and digital optical microscopy were used to identify typical failure modes and damage initiation and progression in flexural specimens under test. Fibre kinking leading to delamination and fibre fracture were observed as prominent failure modes in hump as well as indentation waviness. Experimental investigation revels 12–30% reduction in flexural strength with increase in wave severity for the range considered in this study.

Evaluation of the Effect of a Combined Chemical and Thermal Modification of Wood though the Use of Bicine and Tricine

The effects of thermal modification of wood have been well established, particularly in terms of reductions in mechanical performance. In recent years, there has been an increase in studies related to the Maillard reaction. More commonly associated with food chemistry, it involves the reaction of amines and reducing sugars during cooking procedures. This study has attempted to combine the use of amines and thermal modification, with subsequent properties investigated for the treatment of spruce (Picea abies (L.) H. Karst) and beech (Fagus sylvatica L.). In this initial study, the combined effects of chemical treatments by tricine and bicine were investigated with thermal modification. Along with some preliminary data on mechanical properties, the modifications which appeared in the wood structure were evaluated by infrared spectroscopy and biological studies according to EN113 and EN117 methodologies. The hierarchal study interpretation of FTIR suggested interactions between the bicine or tricine and the wood, which was partly supported by the analysis of volatile organic compounds (VOC), though other tests were not as conclusive. The potential of the method warrants further consideration, which will be described.

Mechanical behaviour of carbon fibre reinforced polymer composite material at different temperatures: Experimental and model assessment

In the present study, temperature and frequency effects are studied involving carbon fibre reinforced polymeric materials with unidirectional fibers. Before testing, laminates were preserved in a deep freezer at −80, −20, 0, and 25°C for 60 days. Compressive, tensile, and stiffness behaviors of the laminates were assessed. The results confirmed that the compressive strength, tensile strength, and tensile modulus of laminates severely deteriorate at high temperatures. This might happen because of the weakening of the fibre/matrix interface, resulting in the load-carrying capacity of the carbon fibre being severely reduced. Lower temperatures did not significantly affect the mechanical performance of the laminates. This is due to minor deformation of the frozen laminates and closely compacted epoxy chain segments. The effects of temperature and vibration on the storage modulus, loss modulus, and damping behaviour of laminates are discussed. The results confirm that a reduction in mechanical performance is a strongly temperature-dependent phenomenon. Laminate damping properties are also evaluated. According to the results of the experiments, −80°C has the greatest permanence. Finally, the accuracy of the results on storage modulus was compared with empirical models. The model suggested by Gibson et al. provided the most accurate estimates for the storage modulus of the laminates. Other models were less accurate and gave non-conservative estimates.

Impact of Wetting and Drying Cycles on the Mechanical Properties and Microstructure of Vegetation-growing Concrete

Vegetation-growing Concrete (VC), as a new type of cemented soil, is usually used for plants growing on the surface of high and steep rocky slopes. With the widespread application of VC substrate, a pressing problem arises to ensure its durability under wetting and drying conditions. To explore the greatest possible impact on the mechanical properties and microstructure features of VC substrate, an experimental program including triaxial test, SEM analysis, and ultrasonic testing was implemented. The results showed that wetting and drying cycles can significantly decrease more than 40-percent of peak strength, 60-percent of residual strength, and 50-percent of cohesion for VC substrate under ultimate conditions. The fundamental cause of reduction in mechanical performance was found to be the weakening of the bond between soil particles. And it was discovered that structural damage increased as the number of wetting and drying cycles increased but at a slower rate. Based on the tested results, linear functions between the loss extent parameters of mechanical performance and the structural damage variable were established for the VC substrate. Finally, the action mechanisms of wetting and drying cycles for VC substrate were discussed, and the main influential factors were proposed.

Influence of X-rays and gamma-rays on the mechanical performance of human bone factoring out intraindividual bone structure and composition indices.

Doses of irradiation above 25 ​kGy are known to cause irreversible mechanical decay in bone tissue. However, the impact of irradiation doses absorbed in a clinical setting on the mechanical properties of bone remains unclear. In daily clinical practice and research, patients and specimens are exposed to irradiation due to diagnostic imaging tools, with doses ranging from milligray to Gray. The aim of this study was to investigate the influence of irradiation at these doses ranges on the mechanical performance of bone independent of inter-individual bone quality indices.Therefore, cortical bone specimens (n ​= ​10 per group) from a selected organ donor were irradiated at doses of milligray, Gray and kilogray (graft tissue sterilization) at five different irradiation doses. Three-point bending was performed to assess mechanical properties in the study groups.Our results show a severe reduction in mechanical performance (work to fracture: 50.29 ​± ​11.49 Nmm in control, 14.73 ​± ​1.84 Nmm at 31.2 ​kGy p ​≤ ​0.05) at high irradiation doses of 31.2 ​kGy, which correspond to graft tissue sterilization or synchrotron imaging. In contrast, no reduction in mechanical properties were detected for doses below 30 ​Gy. These findings are further supported by fracture surface texture imaging (i.e. more brittle fracture textures above 31.2 ​kGy).Our findings show that high radiation doses (≥31.2 ​kGy) severely alter the mechanical properties of bone. Thus, irradiation of this order of magnitude should be taken into account when mechanical analyses are planned after irradiation. However, doses of 30 ​Gy and below, which are common for clinical and experimental imaging (e.g., radiation therapy, DVT imaging, CT imaging, HR-pQCT imaging, DXA measurements, etc.), do not alter the mechanical bending-behavior of bone.

Chemical and physical interactions of regenerated cellulose yarns and isocyanate-based matrix systems

In the development of structural composites based on regenerated cellulose filaments, the physical and chemical interactions at the fibre-matrix interphase need to be fully understood. In the present study, continuous yarns and filaments of viscose (rayon) were treated with either polymeric diphenylmethane diisocyanate (pMDI) or a pMDI-based hardener for polyurethane resins. The effect of isocyanate treatment on mechanical yarn properties was evaluated in tensile tests. A significant decrease in tensile modulus, tensile force and elongation at break was found for treated samples. As revealed by size exclusion chromatography, isocyanate treatment resulted in a significantly reduced molecular weight of cellulose, presumably owing to hydrolytic cleavage caused by hydrochloric acid occurring as an impurity in pMDI. Yarn twist, fibre moisture content and, most significantly, the chemical composition of the isocyanate matrix were identified as critical process parameters strongly affecting the extent of reduction in mechanical performance. To cope with the problem of degradative reactions an additional step using calcium carbonate to trap hydrogen ions is proposed.

Catalytic C–H Oxidation Enhances Polyethylene Bonding

Selectively adding functionality to commodity plastics is an abiding challenge in polymer science. In this issue of Chem, Hartwig and co-workers describe a selective, catalytic oxidation of polyethylene C–H bonds by using high-valent ruthenium-oxo species. The transformation increases polyethylene’s adhesive properties without significantly modifying its thermal stability or mechanical strength.