High strength and toughness of double physically cross-linked hydrogels composed of polyvinyl alcohol and calcium alginate

The weak mechanical properties of hydrogels, especially physically cross-linked hydrogels are usually a major factor to hinder their application. To solve this problem, in this work, we prepared a high strength and toughness of double physically cross-linked (PDN) hydrogels composed of crystalline domain cross-linked polyvinyl alcohol (PVA) and Ca²⁺-cross-linked alginate (Alg). With a further annealing treatment, the noncovalent cross-linked network via the formed crystalline promote the as-prepared PDN PVA/Alg hydrogel to exhibit well mechanical properties with the tensile strength of ~1.94 MPa, elongation at break of ~607% and Young's modulus of ~0.45 MPa (above 70 wt% of water content). By analyzing the mechanism of improving the hydrogel mechanical properties, it is found that annealing can effectively improve the crystallinity of PVA in the hydrogel, and then greatly improve the mechanical properties of the hydrogel. This provides a general method for improving the mechanical properties of PVA PDN hydrogels. In addition, the PDN PVA/Alg hydrogel was also proved to have good ionic conductivity of 1.70 S m⁻¹. These desirable properties make the prepared physically cross-linked hydrogels promising materials for medical and biosensing fields.     

Experimental investigation of the influence of the compounding process and the composite composition on the mechanical properties of a short flax fiber–reinforced polypropylene composite

Polypropylene (PP) composites containing 20 wt% short flax fibers are prepared, and the process parameters such as throughput, rotational speed, and screw configuration are varied during melt compounding with a corotating intermeshing twin‐screw extruder. The investigations reveal that low rotational speeds, high throughputs, and moderate shear energy inputs by the screw configuration led to an optimum set of mechanical properties. To investigate the influence of different composite compositions on the mechanical properties, composites with fiber contents between 0 and 40 wt% and maleic anhydride‐grafted PP (PP‐g‐MA) contents between 0 and 7 wt% are prepared. Increasing fiber contents enhance the Young's modulus and decrease the elongation at break and the notched impact strength. The tensile strength is barely affected. The addition of PP‐g‐MA increases the tensile strength as well as the elongation at break, whereas the Young's modulus is not influenced. Thus, PP‐g‐MA enhances the adhesion between PP and flax fibers significantly. POLYM. COMPOS., 36:2282–2290, 2015. © 2014 Society of Plastics Engineers     

Proanthocyanidin‐Induced Horizontal Arrangement in Poly(vinyl alcohol)/Graphene Composites with Enhanced Mechanical Properties

A green approach is employed to prepare mechanically enhanced composites by adding noncovalently proanthocyanidin (PC)‐modified graphene (PC‐rGO) into poly(vinyl alcohol) (PVA). Ascorbic acid (AA) is used as the reducing agent, and PC is used as a dispersant to synthesize low‐defect and fully dispersed graphene. After static treatment, the PC‐rGO sheets in the composite form a horizontally arranged structure. Compared with neat PVA, the Young's modulus of the graphene‐modified composites is significantly enhanced by approximately 79.3% with incorporation of 0.9 wt% PC‐rGO. The composites incorporated with GO or AA‐rGO (without PC) have randomly distributed GO structures and apparent rGO agglomeration, resulting in a weaker mechanical property. The dispersibility, degree of defects, distribution state of graphene, and interactions with the polymer matrix are directly related to the final mechanical performance. This new approach to mechanically enhance graphene‐embedded PVA composites provides the possibility for large‐scale production of graphene‐reinforced composite materials.     

Experimental investigation on the influence of the composition on the morphology and the mechanical properties of short glass fiber‐reinforced polypropylene nanocomposites

Polypropylene composites containing 0–5 wt% layered silicate and 0–30 wt% short glass fibers are prepared by melt compounding. To investigate the influence of different compositions on the mechanical properties of short glass fiber‐reinforced polypropylene nanocomposites, materials with various filler contents are prepared. At a glass fiber content of 10 wt% Young's modulus of the layered silicate‐containing composites decreases by around 30% compared to conventional glass fiber‐reinforced polypropylene. But at higher glass fiber loadings, an increasing modulus of up to 10% is observed. However, the addition of layered silicate results in large decreases of the tensile and the notched impact strength. A maleic anhydride‐grafted polypropylene enhances Young's modulus and the tensile strength. © 2012 Society of Plastics Engineers     

Preparation of well‐dispersed reduced graphene oxide and its mechanical reinforcement in polyvinyl alcohol fibre

The current work reports the preparation and characterization of polyvinyl alcohol (PVA) composite fibres reinforced with graphene reduced from graphene oxide (GO) by using oligomeric proanthocyanidin (OPC) as a reductant. After reduction, most of the oxygen‐containing groups were removed from the GO and reduced graphene oxide (rGO) was prepared. As a result of combined OPC as a dispersant, rGO could be well dispersed in a dimethyl sulfoxide/H₂O mixed solvent and in PVA matrix, and the PVA/rGO dispersion was wet spun followed by hot drawing to prepare continuous PVA/rGO composite fibres. The PVA/rGO composite fibres exhibited a significant enhancement of mechanical properties at low rGO loadings; in particular the tensile strength and Young's modulus of the 2.0 wt% rGO and PVA composite fibre increased to 244% and 294% respectively relative to neat PVA fibre. Moreover, the storage modulus (?10 °C) and T_g increased to 300% and 7.2 °C, respectively. © 2016 Society of Chemical Industry     

Study of effect of old corrugated cardboard in properties of polypropylene composites: Study of mechanical properties,thermal behavior,and morphological properties

The investigation of the economical use of lignocellulose waste, which is one of the environmental problems facing nations, is ongoing. In this study, waste cardboard paper fiber reinforcing polypropylene (PP) composites was developed. In order to modify the PP matrix maleated PP (MA‐g‐PP) a 5 wt% and a grafting rate of 1 and 2 wt% was used as a compatibilizer. The effects of fiber and compatibilizer content as well as graft content are evaluated by mechanical, thermal property measurements, and scanning electron microscopy (SEM). The compatibilizer improved all mechanical properties significantly. Thus, the tensile strength of MA‐g‐PP‐containing composites increases compared to PP/cardboard composites paper content increases. However, the tensile modulus of a PP‐based composite increases with an increase in paper fiber with the compatibilizer having little effect. SEM revealed that the addition of MA‐g‐PP generates strong interactions between a PP matrix and paper fibers. However, the addition of the MA‐g‐PP compatibilizing agent gives a significant improvement on the crystallization of the composites, whereas the compatibilized PP/old corrugated cardboard (OCC) composites have higher crystallinity (Xc) than uncompatibilized PP/OCC composites. The MA‐g‐PP also diminished the water absorption in the composites. J. VINYL ADDIT. TECHNOL., 22:231–238, 2016. © 2014 Society of Plastics Engineers     

Mechanical reinforcement of electrospun water‐soluble polymer nanofibers using nanodiamonds

Optimization of the mechanical properties is necessary in the applications of electrospun nanofibrous matrices. In this work, mechanical reinforcement of electrospun nanofiber membranes of water‐soluble polymer by the incorporation of commercial nanodiamonds (NDs) was studied. Through an ND/poly(vinyl alcohol) (ND/PVA) model system, it is demonstrated that 155% improvement of Young's modulus, 89% increase in tensile strength, and 336% elevation in energy to break are achieved by the addition of only 2 wt% ND. Fourier transform infrared spectroscopy results suggest the existence of molecular interactions between NDs and PVA matrix, which contributes to the effective load transfer from the polymer matrix to the fillers. However, higher level of ND addition (>2 wt%) aggravates the agglomeration of nanofillers in PVA matrix and offsets the reinforcing effect, as ND agglomerates may act as flaws in composite nanofibers. Furthermore, NDs have optimizing effect on the morphology of ND/PVA nanofibers through increasing the conductivity of the electrospinning solution. Therefore, ND nanofillers possess the potential to improve the mechanical performance of water‐soluble polymer‐based nanofiber membranes. POLYM. COMPOS., 34:1735–1744, 2013. © 2013 Society of Plastics Engineers     

Effect of maleated polypropylene on the performance of polypropylene/cellulose composite

Composites consisting of a polypropylene (PP) and highly crystalline cellulosic microfibers were prepared by melting mixing with the maleic anhydride grafted polypropylene (MAPP) as a compatibilizer. The results show that even with addition of a small amount of MAPP, the mechanical properties of the composites improved dramatically. The improvement is attributed to stronger interfacial adhesion caused by esterification between anhydride groups of MAPP and hydroxyl groups of cellulose, although the number of the ester bonds is too few to be detected by FT‐IR spectroscopy. It was also found that tensile strength and Young's modulus increased with the increasing MAPP contents in the composites, and the optimum MAPP content is about 10 wt% for the composite with cellulose content of 30 wt%. SEM indicated that the interfacial adhesion between cellulose fibers and PP improved in MAPP‐containing composites. The DSC results showed that MAPP has little effect on melting and crystallization temperatures of PP in the composites. POLYM. COMPOS., 26:448–453, 2005. © 2005 Society of Plastics Engineers     

剑麻纤维/长玻纤混杂增强PP复合材料的力学性能研究

采用剑麻纤维(SF)和长玻璃纤维(LGF)混杂增强聚丙烯(PP)复合材料,考察了SF/LGF的比例和含量对PP复合材料力学性能的影响。结果表明:SF/LGF在聚丙烯树脂基体中呈交叉网状分布,这有利于提高复合材料的冲击强度、弯曲模量、拉伸强度和软化点。在SF/LGF质量比为2 2∶,二者总质量分数为30%时,SF/LGF混杂增强PP复合材料的综合力学性能较好。     

Morphology and mechanical and electrical properties of oriented PVA-VGCF and PVA-MWNT composites

The composites poly(vinyl alcohol) (PVA) and vapor growth carbon fiber (VGCFs) and multi wall carbon nanotubes (MWNTs) were prepared by gelation/crystallization from the mixture of dimethyl sulfoxide (DMSO) and water (H₂O). The composite films were elongated to 5-10-fold uniaxially. The mechanical properties of PVA composites were improved significantly by introduction of VGCFs and MWNTs and also by the orientation of fillers. Compared to VGCFs, MWNTs was more effective to improve the electric conductivity of the composites because of its network structure. The change in the electrical conductivity for the PVA/MWNT composites containing 5 wt% MWNT was independent of the draw ratio up to eight-fold indicating no disruption of the network formation. A certain high level of filler content was proved to be necessary for the promotion of both mechanical and electrical properties in oriented composite.     

Crosslinked poly(vinyl alcohol) composite films with cellulose nanocrystals: Mechanical and thermal properties

In this work, poly(vinyl alcohol) (PVA) and cellulose nanocrystals (CNCs) were crosslinked using sodium tetraborate decahydrate (borax) to improve the mechanical and thermal properties of the neat PVA. The results showed that the CNCs affected the crystallization behavior of the crosslinked PVA. The crystallization temperature of the crosslinked PVA with CNCs increased considerably from ～152 to ～187 °C. The continuous improvement of the thermal stability was observed with the increasing content of CNCs in the crosslinked PVA films. Additionally, the strong interaction between the CNCs and PVA was theoretically estimated from the Young's modulus values of the composites. Thermodynamic mechanical testing revealed that the crosslinked PVA composite films with CNCs could bear higher loads at high temperature compared to the films without the CNCs. At 60 °C, 2.7 GPa was reported for the storage modulus of the crosslinked composites with 3 wt % of CNCs, twice as high as that for the crosslinked films without CNCs. Moreover, creep results were improved when CNCs were added in the crosslinked nanocomposites. The materials prepared in this work could broaden the opportunities for applications in a wide range of temperatures. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45710.     

Effect of electron beam irradiation on the mechanical,thermal, and dynamic mechanical properties of flyash and nanostructured fly ash waste polyethylene hybrid composites

The effect of electron beam irradiation on the technical properties of fly ash (FA) and nano fly ash (NFA)‐filled waste polyethylene (WPE) composites have been investigated in this article. It is observed that the FA/NFA at 5 wt% imparted enhanced technical properties. The modified composites were prepared by three different methods (1) modification of WPE matrix first by grafting with maleic anhydride (MA) and preparing the composite (2) Preparing WPE‐FA/NFA composites and subjecting to electron beam irradiation. (3) Subjecting the FA/NFA to electron beam radiation first and then preparing composites with WPE. Of the three methods, the composite prepared and then electron beam irradiated gave the best balance in the physico‐mechanical properties. The tensile and flexural strength of WPE increased from 21.2 MPa and 25.4 MPa to 33.0 MPa (57.8%) and 45.8 MPa (72%) respectively at 5 wt% FA‐filled WPE composites, which further increased to 34.5 MPa (65%) and 47.7 MPa (87.8%) respectively with 5 wt% of NFA‐filled WPE composites, after electron beam irradiation. The thermal stability was enhanced upon electron beam irradiation of the composites. The dynamic mechanical properties reveal that the storage modulus reaches the highest value for the irradiated composite corroborating with the flexural modulus throughout the temperature range studied. The fractured surfaces were examined under SEM and were correlated with the mechanical properties. The results indicate that FA/NFA reinforced WPE composites act as an excellent stress raisers preventing crack propagation and enhancing the performance properties on electron beam irradiation. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

The Effect of Accelerated Weathering on the Mechanical Properties of Alkali Treated Hemp Fibre/Epoxy Composites

In this study, 65 wt% aligned untreated long hemp fibre/epoxy (AUL) and aligned alkali treated long hemp fibre/epoxy (AAL) composites cured at 70°C using compression moulding were subjected to accelerated weathering using an accelerated weathering chamber with UV-irradiation and water spray at 50°C for four different time periods (250, 500, 750 and 1000 h). After accelerated weathering, tensile strength (TS), flexural strength, Young's modulus (YM), flexural modulus and fracture toughness (K _Ic) were found to decrease and impact energy (IE) was found to increase for both AUL and AAL composites. AUL composite had greater overall reduction in mechanical properties than that for AAL composite upon exposure to accelerated weathering environment. FTIR, TGA and WAXRD analyses of the accelerated weathered composites support the results of the deterioration of mechanical properties upon exposure to accelerated weathering environment.     

Prestretching effect and recovery process of polyvinyl alcohol film crosslinked with tartaric acid

The tartaric acid (TA)/polyvinyl alcohol (PVA) composite films were prepared with various TA concentrations from 5 to 20 wt%. The crosslinking due to TA improved the tensile characteristics such as tensile strength and the Young's modulus, and thermal stability of the films. The addition of TA in PVA led to a decrease in the crystallinity. Application of prestretching or preliminary deformation resulted in significant changes in both stress–strain behavior and tensile characteristics of both pure PVA and TA/PVA composite films. Although low preextension levels such as 5% strain did not change much the tensile characteristics, higher preextension levels improved the tensile strength but decreased the extensibility of the films. The recovery processes of the stretched films consisted of a fast recovery process for which most of the recoverable elastic deformation is seen took place within almost 30 min and a time-dependent long-lasting recovery process continued in time very slowly, which resulted in undesirable residual deformation. It was also observed that increasing TA concentration accelerated the recovery process, hence, improved the recovery properties of PVA. The use of TA in the membrane applications can be considered to improve the mechanical properties and reusability of the membrane technology.     

Preparation and mechanical properties of composite of fibrous cellulose and maleated polyethylene

Fibrous cellulose and maleated polyethylene (FC–MPE) composites were prepared under melt mixing by maleation of polyethylene (PE) to obtain maleic anhydride (MA) grafted PE (MPE) and successive compounding of the resultant MPE with fibrous cellulose (FC). When increasing the content of added MA to 2 wt %, the grafting efficiency of MA decreases gradually to 84% and the grafted MA chains become longer. Scanning electron microscopy (SEM) reveals strong adhesion of MPE to FC in the FC–MPE composite, which is probably due to the increased compatibility between MPE and FC, in contrast to no adhesion of unmaleated PE (UPE) to FC in the FC–UPE composite. This difference in interfacial structure between the FC–MPE and FC–UPE composites results in quite different mechanical properties for them. With an increase in the FC content to 60 wt %, the tensile strength of the FC–MPE composite increases significantly and reaches 125% that of pure PE. Furthermore, the larger Young's modulus, larger bending elastic modulus, and smaller elongation of the FC–MPE composite strongly indicate effective transfer of the high tensile strength and elasticity of FC to the MPE matrix through the strong adhesion between FC and MPE. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1971–1980, 2002; DOI 10.1002/app.10428     

Reinforcing effect of nanocrystalline cellulose and office waste paper fibers on mechanical and thermal properties of poly (lactic acid) composites

Nanocrystalline cellulose (NCC) was prepared from office waste paper (OWP) by sulfuric acid hydrolysis method in this paper and it was used to prepare a series of poly (lactic acid) PLA/NCC composites by using a dissolution method in solvent N, N-dimethylformamide solution. The results indicated that with the addition of only 3 wt% NCC, the composites exhibited outstanding mechanical property. The tensile, bending and impact properties of the PLA/3NCC composite were improved by 8.2%, 13.1%, and 35.9% than those of pure PLA, respectively. On this basis, office waste paper fibers (OWF) were also used as a physical blended filler to enhance PLA/NCC composites to reduce the preparation cost of PLA composites and the perfect PLA/NCC/OWF sample was easily manufactured by melting–blending and injection molding. According to the crystallization and melting performance table, both NCC and OWF can act as nucleating agent to promote the crystallization properties on composites, while the blends did not have positive effect on thermal stability. Furthermore, the water absorption and degradation properties of PLA composites were also studied. This work not only provided a novel idea for the utilization of office waste paper but also successfully produced environment friendly composites with favorable mechanical properties and crystallization performance.     

Structurally different short aramid fiber–reinforced thermoplastic polyurethane

The reinforcing effect of two structurally different Aramid short fibers, Technora and Twaron on the mechanical, dynamic mechanical, and thermal properties of an ester‐based thermoplastic polyurethane (TPU) was investigated. A fixed fiber length of 6 mm is used by varying the fiber loading ranging from 3 to 10 phr. The Young's modulus and the low strain modulus of Technora–TPU composite was found three times higher than that of Twaron–TPU composite at all ranges of fiber loading. Optical microscopic analysis revealed that a severe processing‐induced fiber breakage of Twaron is the primary reason behind the inferior properties shown by these fiber‐reinforced TPU composite. A brittle kind of failure has been observed during tensile testing in both the composite at a fiber loading of 10 phr. To solve this problem, an economic pretreatment with maleic anhydride‐grafted polybutadine (PB‐g‐MA) has been applied on the Aramid fiber surface before mixing it with the TPU matrix. A good quality of fiber dispersion with significant improvement in mechanical properties could be achieved with the addition of only 5 phr of PB‐g‐MA. Morphological analyses on the tensile‐fractured and cryogenically fractured surfaces of these composites offer strong evidences for the dispersing and coupling action of PB‐g‐MA with these Aramid fibers and the TPU matrix. POLYM. COMPOS., 35:1767–1778, 2014. © 2013 Society of Plastics Engineers     

Poly(vinyl chloride)/single wall carbon nanotubes composites: Investigation of mechanical and thermal characteristics

Composites of polyvinylchloride (PVC) with single wall carbon nanotubes (SWCNTs) were prepared by plastisol curing. Scanning electron microscopy (SEM) observations revealed that appropriate dispersion of the nanotubes was achieved. The mechanical properties showed that SWCNT improved the Young's modulus and tensile strength of the PVC. The composites have higher elongation at break and toughness as well. By comparing the mechanical properties of the composites, it is found that there is a critical SWCNT loading (about 1 wt%) below which the tensile properties increase with increasing nanofiller concentration. For the composites containing 0.25–0.75 wt% of SWCNT, this situation was observed, whereas for a sample with 1 wt% SWCNT, the mechanical properties decreased due to the agglomeration of the nanotubes. Thermogravimetric analysis indicated that the SWCNT increased T_5%, T_10%, T_50%, T_onset, and T_max and decreased weight loss in the degradation process of the PVC. In addition, by adding SWCNT to the polymer, residual mass at 600°C increased significantly. These results are advantages for the applications of the polymer in which high mechanical properties, including high tensile modulus and toughness, and good thermal properties are needed. J. VINYL ADDIT. TECHNOL., 22:128–133, 2016. © 2014 Society of Plastics Engineers     

Rice husk powder–filled polystyrene/styrene butadiene rubber blends

Natural fibers are rich in cellulose and they are a cheap, easily renewable source of fibers with the potential for polymer reinforcement. The presence of large amounts of hydroxyl groups makes natural fibers less attractive for reinforcement of polymeric materials. Composites made from polystyrene (PS)/styrene butadiene rubber (SBR) blend and treated rice husk powder (RHP) were prepared. The RHP was treated by esterification and acetylation. A similar series of composites was also prepared using maleic anhydride–polypropylene (MA–PP) as a coupling agent. The processing behavior, mechanical properties, effect of thermooxidative ageing, and surface morphology of untreated and chemically modified RHP were studied. There was a decrease in tensile strength (except MA–PP composites), elongation at break, and Young's modulus in chemically treated RHP composites. The postreaction process during thermooxidative ageing enhanced the tensile strength and Young's modulus of the esterified and MA–PP composites. Acetylation treatment was effective in reducing the percentage of water absorption in RHP/PS–SBR composites. In general chemically treated RHP/PS–SBR composites and MA–PP showed a better matrix phase and filler distribution. However, the degree of filler–matrix interaction was mainly responsible for the improvement of mechanical properties in the composites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3320–3332, 2004     

Preparation and characterization of high strength and high modulus PVA fiber via dry-wet spinning with cross-linking of boric acid

To improve the mechanical properties of polyvinyl alcohol (PVA) fibers, a series of PVA fibers were prepared via dry-wet spinning with cross-linking of boric acid (BA) (PVA/BA fibers), and using the mixed solvent of dimethyl sulfoxide and water. Moreover, the final PVA/BA fibers were characterized by Fourier transform infrared spectra (FTIR), scanning electron microscopy (SEM), differential scanning calorimetery (DSC), thermogravimetric analyzer (TGA), powder X-ray diffraction (XRD) and yarn strength tester. Furthermore, with the increasing of BA content, FTIR analysis showed that the degree of crosslinking of BA with PVA increased. SEM images of final PVA/BA fibers presented smooth surfaces, and the diameters decreased firstly and then increased. DSC, TGA, and XRD analysis indicated that the melting temperatures, thermal properties and crystallinities first increased and then decreased with the increasing of BA content. In addition, mechanical properties measurements illustrated that the cross-linking existed at an optimal BA content of 0.3 wt%, and PVA/BA-0.3 fiber had the highest tensile strength and Young's modulus of 13.1 ± 0.4 and 360.2 ± 10.4 cN/dtex, respectively.