Tensile Breaking Stress Research Articles

Enhancing the strength of tissue paper through pulp fractionation and stratified forming

Abstract The potential of combining stratified paper forming with pulp fractionation was investigated to improve the balance between low density, which enhances water absorbency and softness, and the dry strength of tissue papers. The selected fractionation approaches allowed us to separate especially stiff, low-fibrillated fibers (A fractions) from flexible, fibrillated fibers containing fines (detached segments of fibers, fibrils, or lamellae fragments) (B fractions). After characterizing the morphological properties of each fiber fraction, 20 g/m2 model papers were produced with and without wet pressing to tune the paper density. At a density of 0.3 g/cm³, the tensile breaking stress of B papers was at least three times higher than that of A papers. The strain at break of B papers was also close to two times higher than that of A papers. Interestingly, bilayer papers A/B exhibited breaking stress values intermediate between those of A and B papers, while native pulp papers, i.e., without fractionation and stratified forming, followed the trend of A papers. Notably, bi-layering the paper improved the breaking stress by up to twice as much without increasing the paper density, which could be highly beneficial in improving the balance of properties in tissue paper grades.

Ultra-stretchable and conductive polyacrylamide/carboxymethyl chitosan composite hydrogels with low modulus and fast self-recoverability as flexible strain sensors

There is a great demand for the fabrication of soft electronics using hydrogels due to their biomimetic structures and good flexibility. However, conventional hydrogels have poor mechanical properties, which restricts their applications as stretchable sensors. Herein, a facile one-step strategy is proposed to fabricate tough and conductive hydrogels by making use of the graftability of carboxymethyl chitosan without extra conductive matter and crosslinking agent. The obtained polyacrylamide/carboxymethyl chitosan composite hydrogels possess outstanding transmittance and excellent mechanical performances, with tensile breaking stress of 630 kPa, breaking strain of 4560 %, toughness of 8490 kJ/m3. These hydrogels have low modulus of 5–20 kPa, fast recoverability after unloading, high conductivity of ∼0.85 S/m without the addition of other conductive substances and good biocompatibility. The ionic conductivity of the gels originates from the counterions of carboxymethyl chitosan, affording the hydrogels as resistive-type sensors. The resultant hydrogel sensors demonstrate a broad strain window (0.12–1500 %), excellent linear response, high sensitivity with the gauge factor reaching 11.72, and great durability, capable of monitoring diverse human motions. This work provides a new strategy to develop stretchable conductive hydrogels with promising applications in the fields of artificial intelligence and flexible electronics.

Comparative Structure-Property Relationship between Nanoclay and Cellulose Nanofiber Reinforced Natural Rubber Nanocomposites.

Natural rubber (NR) nanocomposites reinforced with five parts per hundred rubber (phr) of two different nano-fillers, i.e., nanoclay (abbrev. NC) and cellulose nanofiber (abbrev. CNF), were prepared by using latex mixing approach, followed by mill-compounding and molding. The morphology, stress–strain behavior, strain-induced crystallization, and bound rubber of the NR nanocomposites were systematically compared through TEM, tensile test, WAXS, DMA, and bound rubber measurement. The aggregated CNFs were observed in the NR matrix, while the dispersed nanosized clay tactoids were detected across the NR phase. The reinforcement effects of NC and CNF were clearly distinct in the NR nanocomposites. At the same nano-filler content, the addition of NC and CNF effectively accelerated strain-induced crystallization of NR. The high tensile strength obtained in the NC-filled NR nanocomposite was attributed to strain-induced crystallization of NR accelerated by well-dispersed NC. However, the larger tensile modulus and low strain for the CNF-filled NR were related to the formation of immobilized NR at the interface between CNF aggregate and NR. The immobilization effect of NR at the CNF surface offered by a mutual entanglement of CNF aggregate and NR chain led to local stress concentration and accelerated strain-induced crystallization of CNF/NR nanocomposite. From the present study, the NR nanocomposites combined with 5 phr CNF shows high-tensile modulus and acceptable breaking tensile stress and strain, suggesting the application of CNF/NR based nanocomposite in automotive and stretchable sensors for next-generation electronic devices.

Crystallization, microstructure and mechanical properties of directionally oriented films prepared using a novel blowing‐film process

AbstractA novel process of film preparation using a self‐made internal mandrel and external mold reverse rotation die is proposed. In this process, the mold's inner mandrel and outer parts rotate in opposite directions to achieve melt circumferential shear flow. In the blowing‐film process, a polymer melt is subjected to a flow field composed of extruded pressure extrusion and the reverse rotation of the die. The equipment has been used to successfully prepare low‐density polyethylene films. The microstructure and properties of films obtained under various internal and external reverse rotation speeds were studied. The results show that the rotation speeds are beneficial for forming a highly ordered crystalline structure of the film. As a result of microstructure evolution, the transverse direction (TD) tensile strength was enhanced by 39.4% and the machine direction (MD) tensile strength was enhanced by 47.4%. TD and MD breaking elongation increased by 38% and 43%, and the TD tensile breaking stress from 7.41 MPa was enhanced up to 10.79 MPa and the MD tensile breaking stress from 7.24 MPa was enhanced up to 11.26 MPa. The TD and MD tear strength increased by 38.2% and 28.3%. This novel blowing‐film process can be used to control the microstructure of films by controlling process parameters to improve the mechanical properties of films. © 2022 Society of Industrial Chemistry.

Tough and fluorescent hydrogels composed of poly(hydroxyurethane) and poly(stearyl acrylate‐co‐acrylic acid) with hydrophobic associations and hydrogen bonds as the physical crosslinks

AbstractFluorescent hydrogels have promising applications in biomedical and engineering fields. However, they are usually mechanically weak. Here, we report a fluorescent composite hydrogel with high toughness, which is facilely prepared by solution casting ethanol solution of poly(hydroxyurethane) (PHU) and poly(stearyl acrylate‐co‐acrylic acid) (P[SA‐co‐AAc]) followed by swelling the casted film in water. The composite hydrogels with water content of 62–78 wt% possess remarkable mechanical performances, with tensile breaking stress of 0.3–1.1 MPa, breaking strain of 280%–400%, Young's modulus of 0.2–0.7 MPa, and tearing fracture energy of 1250–2630 J/m2. The high toughness is attributed to the effective energy dissipation of the network with hydrophobic association of SA units and hydrogen bonds between PHU and P(SA‐co‐AAc) as the physical crosslinks. The intense aggregation of carbamates and the formation of carbamate clusters through intra‐ and intermolecular hydrogen bonds endow the composite hydrogel with strong fluorescence. These hydrogels with high toughness and strong fluorescence should find applications in flexible electronics, information display, and biomedical devices.

Grafted Polyurethane Copolymers with Notable Changes in Tensile and Shape Memory Properties upon Addition of Acid and Base

Ionic cross-linking of polyurethane (PU) was performed using grafted glutaric acid (GA) or dimethylamino propanol (DAP) to enhance the mechanical properties and control the degree of interaction using acid or base. The effect of ionic cross-linking on the water compatibility, thermal phase transition of soft segments, tensile mechanical strength, and shape memory properties were determined by comparison with ordinary PU. The water compatibility of PU could be improved by grafted acidic or basic functional groups. The breaking tensile stress and shape recovery capability increased significantly relative to ordinary PU due to ionic cross-linking but notably decreased upon the addition of acid or base due to the disruption of ionic cross-linking. It was demonstrated that the water compatibility and mechanical properties of PU could be controlled using ionic cross-linking and the disruption of ionic cross-linking by adding acid or base.

A breathable waterborne poly-(urethane/urea) coating containing PO-EO-PO triblock copolymer

A breathable waterborne poly-(urethane/urea) (WPU) coating for textiles was synthesized by a pre-polymer method with 4,4′-Diisocyanate dicyclohexylmethane (H12MDI), Poly(propylene oxide)-b-poly(ethylene oxide)-b-poly(propylene oxide) triblock diols (PO-EO-PO diols), and Polyteramethylene glycol (PTMG). The PO-EO-PO diols were incorporated into the WPU to improve the swelling issue of frequently observed in the polyethylene glycol (PEO) segments. The stability, mechanical property, thermal properties, and breathability of PO-EO-PO, including WPUs were investigated by varying PTMG/PO-EO-PO diol ratios. The PO-EO-PO incorporated WPUs showed excellent mechanical properties: 250% of tensile elongation and breaking stress of 15–27 MPa. The breathability reached 620–15 000 mm of water pressure resistance H2O and 2717–63 822 g H2O 24 h m−2 of vapor permeability. The highly breathable, WPU coating contained with different PO/EO fraction of PO-EO-PO diols will play an essential role in the garment-textile industry to convert to a greener process.

The Preparation and Characterization of an Epoxy Polyurethane Hybrid Polymer Using Bisphenol A and Epichlorohydrin

Epoxy polymers composed of bisphenol A (BPA) and epichlorohydrin (ECH) were grafted onto polyurethane (PU) using the graft-polymerization method to prepare the epoxy PU hybrid polymer. The main series contained the epoxy polymer grafted onto PU; however, the epoxy polymer was not bound to PU in the control series. The breaking tensile stress steeply increased at low BPA and ECH contents and then decreased as more BPA and ECH were included in the main series, whereas the control series did not display an incline in the breaking tensile stress irrespective of the BPA and ECH contents. The percent shape recovery also steeply increased after the grafting of epoxy polymer in the main series but increased at a slower rate in the control series. The flexibility of the main series at a freezing temperature was not enhanced compared with the plain PU because the grafted epoxy polymers did not effectively disrupt the molecular interaction between PUs. Therefore, the grafting of epoxy polymers noticeably enhanced the breaking tensile strength and percent shape recovery of PU.

The Graft-Polymerization of Poly(Ethylene Glycol) Phenyl Ether Acrylate onto Polyurethane and Its Impact on the Mechanical Properties and Chain Packing

The poly(ethylene glycol) phenyl ether acrylate (PEPA) monomers are graft-polymerized onto polyurethane (PU), and its impacts on water compatibility, chain packing, tensile stress, and shape recovery capability are evaluated. The grafted poly(PEPA)s slightly increase the degree of cross-linking due to the linking between themselves. The water compatibility (water contact angle, water swelling, and water vapor permeation) are affected slightly by the grafted poly(PEPA). The grafted poly(PEPA) does not notably influence the melting of soft segments, but the crystallization of soft segments is reduced significantly. The grafted poly(PEPA) does not significantly affect the glass transition of soft segments. The grafted poly(PEPA) notably increases the breaking tensile stress with the increase in PEPA content, but the breaking tensile strain decreases slowly with increasing PEPA content. The grafted poly(PEPA) rapidly improves the shape recovery capability of PU and slowly decreases the shape retention capability with the increase in PEPA content. Therefore, the grafted poly(PEPA) slightly modifies the water compatibility but notably enhances the breaking tensile stress and shape recovery capability of PU.

ON BURR (4P) DISTRIBUTION: APPLICATION OF BREAKING STRESS DATA

In many problems of quality and reliability engineering processes and designs, fitting of a probability distribution to the tensile strength or breaking stress data may be helpful in predicting the probability or forecasting the frequency of occurrence of the breaking stress, and planning beforehand. In this paper, Burr (4P) distribution functions was fitted to such breaking stress data, and compared with Burr (3P), Dagum (3P) and Dagum (4P) distribution functions. Goodness of fit has been tested using the Kolmogorov-Smirnov, Anderson-Darling and Chi-Squared distribution tests. It is observed that the Burr (4P) distribution fits the best among these four distributions.

Tough physical hydrogels reinforced by hydrophobic association with remarkable mechanical property, rapid stimuli-responsiveness and fast self-recovery capability

Tough hydrogels with tunable mechanical properties and multi-functional properties have been attracted increasing attention in recent years. Herein, we report a series of tough physical hydrogels (poly (BEM-co-acrylamide-acrylic acid, P-BAA) reinforced by hydrophobic association derived from a novel amphiphilic and eco-friendly monomer - behenyl ether methacrylate (BEM). The tunable mechanical properties of P-BAA hydrogels obtained by varying the contents of sodium dodecyl sulfate (SDS) and BEM, with tensile breaking stress, breaking strain and Young’ modulus being 720 kPa, 2850% and 210 kPa, respectively. P-BAA hydrogels also exhibited significant responsive to salt and pH as well as rapid self-rolling ability. Furthermore, the P-BAA hydrogel exhibited abilities of good self-healing, satisfied thermal-remolding and fast self-recovery, due to the synergy of the hydrophobic association and hydrogen bonds. Such hydrogels with remarkable mechanical performances and multi-functional properties should be acted as promising candidates in soft actuators, flexible sensors, etc.

Insertion of a Cardo Structure into a Polyurethane Framework Using a pH Indicator and Its Impact on Tensile and Shape Memory Properties

Perpendicular cardo structural units were inserted into a polyurethane (PU) framework from the pH indicator (phenolphthalein (PP), phenol red (PR), or bromocresol green (BG)) sharing a triphenylmethyl group. The thermal transitions, mechanical properties, pH-sensitive color change, and low temperature flexibility of the PU modified with the cardo structural units were compared with those of the ordinary PU. Slight cross-linking between PU chains was performed because the insertion of the indicator moieties deteriorated the mechanical properties. The breaking tensile stress and shape recovery capability at 0 °C of the BG-PU series surpassed those of the PP-PU and PR-PU series. The inserted pH indicator moieties did not show the color change under different pH conditions because the isomerization under basic conditions was blocked. Among the three series of PUs, the BG-PU demonstrated the best low temperature flexibility compared with that of the PP-PU and PR-PU due to the functional groups on the phenyl rings of BG. Insertion of a cardo structural unit from the pH indicator reduced the molecular interaction between PU chains.

Conversion of the Hydrophobic Surface of Polyurethane into a Hydrophilic Surface Using the Graft Polymerization of 2-(dimethylamino) ethyl Methacrylate and the Resulting Antifungal Effect

A hydrophobic polyurethane (PU) was altered to obtain a hydrophilic characteristic using the graft polymerization of 2-(dimethylamino)ethyl methylmethacrylate (DAMA) onto the PU surface and the subsequent ionization of the dimethylamino group on poly(DAMA). The grafted poly(DAMA) chain influenced numerous properties, such as the cross-link density, thermal transitions of soft segments, and tensile and shape memory characteristics. The grafting of poly(DAMA) noticeably enhanced the breaking tensile stress and shape recovery capability through the cross-linking between the grafted poly(DAMA)s, but the breaking tensile strain and the shape retention did not noticeably decline after the grafting of poly(DAMA). Additionally, the poly(DAMA)-grafted PU exhibited a significant enhancement in its low temperature flexibility and antifungal effectiveness against a mixture of fungi.

The effect of attached tetracycline and hydrophilic groups on the enhancement of antibacterial effectiveness and low temperature flexibility of polyurethane

Tetracycline was chemically attached to polyurethane (PU) to enhance its antimicrobial activity, and a carboxyl group or polyol was also attached to PU to enhance the hydrophilicity. The attached groups affected cross‐linking, viscosity of PU solution, glass transition of soft segment, breaking tensile stress, reliable shape recovery capability, flexibility at very low temperature, surface hydrophilicity, and antibacterial effectiveness. The glass transition temperature could go up from −67.5°C for unmodified PU to −48.8°C due to the attached tetracycline. The attachment of tetracycline boosted breaking tensile stress and shape recovery by 345% and 186%, respectively, relative to unmodified PU. The attached carboxyl group and polyol improved the hydrophilicity as confirmed by water swelling and water contact angle data. Finally, PU samples with the attached tetracycline demonstrated excellent flexibility at freezing temperature compared with ordinary PU and absolutely inhibited the bacterial growth of S. aureus and K. pneumoniae on PU.

The preparation of hydrogel-like polyurethane using the graft polymerization of N,N-dimethylaminoethyl methacrylate and acrylic acid

The surface of polyurethane (PU) was modified by the graft polymerization of N,N-dimethylaminoethyl methacrylate (DAMA) and acrylic acid (AA) to enhance its water compatibility. Portions of poly(DAMA) and poly(AA) could be ionized by mutual acid–base neutralization and could notably improve the surface hydrophilicity of PU. The water contact angle, water absorption, and water vapor permeation test results jointly demonstrate the increase in water compatibility resulting from the inclusion of poly(DAMA) and poly(AA) in PU. The melting and glass transition temperatures of PU were not significantly influenced by the grafting of poly(DAMA) and poly(AA) onto PU. Small portions of the grafted poly(DAMA) and poly(AA) were involved in the cross-linking of PU, which sharply increased the shape recovery and the breaking tensile stress while maintaining high shape retention and breaking tensile strain.

Ultrastiff and Tough Supramolecular Hydrogels with a Dense and Robust Hydrogen Bond Network

Design of tough hydrogels has made great progress in the past two decades. However, the synthetic tough gels are usually much softer than some biotissues (e.g., skins with modulus up to 100 MPa). Here we report a new class of ultrastiff and tough supramolecular hydrogels facilely prepared by copolymerization of methacrylic acid and methacrylamide. The gels with water content of approximately 50–70 wt % possessed remarkable mechanical properties, with Young’s modulus of 2.3–217.3 MPa, tensile breaking stress of 1.2–8.3 MPa, breaking strain of 200–620%, and tearing fracture energy of 2.9–23.5 kJ/m2, superior to most existing hydrogels, especially in terms of modulus. Typical yielding and crazing were observed in the gel under tensile loading, indicating the forced elastic deformation of these hydrogels in a glassy state, as confirmed by dynamic mechanical analysis. The ultrahigh stiffness was attributed to the dense cross-linking and reduced segmental mobility caused by the robust intra- and interchain hydr...

A Tough and Stiff Hydrogel with Tunable Water Content and Mechanical Properties Based on the Synergistic Effect of Hydrogen Bonding and Hydrophobic Interaction

Hydrogels are usually recognized as soft and weak materials, the poor mechanical properties of which greatly limit their applications as structural elements. Designing of hydrogels with high strength and high modulus has both fundamental and practical significances. Herein we report a series of tough, stiff, and transparent hydrogels facilely prepared by copolymerization of 1-vinylimidazole and methacrylic acid in dimethyl sulfoxide followed by solvent exchange to water. The equilibrated hydrogels with water content of 50–60 wt % possessed excellent mechanical properties, with tensile breaking stress, breaking strain, Young’s modulus, and tearing fracture energy of 1.3–5.4 MPa, 40–330%, 20–170 MPa, and 600–4500 J/m2, respectively. These tough hydrogels were also stable over a wide pH range (2 ≤ pH ≤ 10), resulting from the formation of dense and robust hydrogen bonds between imidazole and carboxylic acid groups. Moreover, the water content and mechanical properties of one gel can be adjusted over a wide r...

The temperature-sensitive water vapor permeation control of polyurethane membrane using the graft-polymerized poly(N-isopropylacrylamide) and the impact on the tensile strength and shape recovery effect

ABSTRACTPoly(N-isopropylacrylamide) (poly(NIPAM)) was grafted onto polyurethane (PU) using a graft-polymerization method to develop a thermo-responsive PU and to investigate the impact on cross-link density, solution viscosity, soft segment thermal transitions, tensile properties, shape memory effect, and water vapor permeation through PU membrane. The soft segment crystallization peak sharply decreased with the increase in NIPAM content, whereas the glass transition temperature (Tg) slightly increased with the increase of NIPAM content. The breaking tensile stress rapidly increased with the increase in NIPAM content due to the cross-linking effect between the grafted poly(NIPAM) chains, whereas the strain at break did not significantly decreased as the NIPAM content increased. The shape recovery at 10°C rapidly increased from 46.9% for plain PU to above 90% after the grafting of poly(NIPAM) onto PU, and the shape retention at −25°C slightly decreased with the increase in NIPAM content. Finally, the grafting of poly(NIPAM) onto PU demonstrated the temperature-responsive control of water vapor permeation through PU film due to the conformational change of the grafted poly(NIPAM) with the increase of temperature and the potential applications of the resulting PUs are discussed.

Grafting of niclosamide and salicylanilide onto hydrophilic polyurethane for the control of fungal and barnacle growth

Grafting of niclosamide or salicylanilide onto polyurethane (PU) was executed to develop antifungal effectiveness and barnacle repelling capability in seawater compared with underivatized PU. The PU surface was simultaneously modified to improve the surface hydrophilicity by inserting dimethylolpropionic acid into PU frame or by grafting recycled polyols onto PU. Surface modifications of PU significantly affected its properties, such as cross-link density, tensile and shape memory properties, and flexibility under freezing conditions relative to the unmodified PU. The modification of PU surface also notably influenced the glass transition and the melting and crystallization related to soft segments. The breaking tensile stress and the shape recovery were enhanced significantly after the grafting of polyol due to chemical cross-linking, whereas the breaking tensile strain was not reduced. Some PU samples demonstrated complete antifungal effectiveness against a mixture of fungi, and barnacle growth on PU films was limited in the specifically modified PUs.

Synthesis and characterizations of antifungal polyurethanes with enhanced tensile and shape recovery performances

AbstractBenzimidazole as an antifungal agent and poly(acrylic acid) as a hydrophilic group were grafted together onto polyurethane (PU) to synthesis the antifungal PU. Benzimidazole was chosen as a key antifungal agent because of its proven fungal growth control against a wide spectrum of fungi. The hydrophilicity of antifungal PU was notably escalated after the grafting of poly(acrylic acid) based on the water contact angle results, but the melting and glass transition of soft segment in PU did not notably change by the grafting of benzimidazole and poly(acrylic acid). The synthesized antifungal PUs exhibited a sharp increase in the breaking tensile stress and shape recovery due to the slight chemical cross‐linking between PUs. The benzimidazole‐grafted PUs containing the poly(acrylic acid) demonstrated a clear suppression in the growth of a group of fungi. Therefore, the antifungal PUs with enhanced tensile strength and shape recovery capability were successfully synthesized using the combined grafting of benzimidazole and poly(acrylic acid) onto PU.