bluuebunny/crossref_metadata_2025 huggingface dataset:
Public Attitudes toward Private Military Companies: Insights from Principal–agent Theory
Authors: Ramirez Mark D. , Wood Reed M.
Published: September 2018

This article examines the distribution and correlates of mass attitudes toward the privatization of US military operations. Relying on insights from principal–agent theory, we form predictions about what beliefs are associated with a willingness to grant authority over military operations to private military companies (PMCs). The model predicts that citizens’ beliefs about actor motives, accountability, and costs are associated with attitudes toward PMCs. Using a nationally representative survey, we find that beliefs about the profit-oriented motives of private firms and perceptions of their lack of accountability reduce support for the use of PMCs, particularly in combat operations. By contrast, belief in private firms’ superior fiscal efficiency increases support for utilizing PMCs in both combat and noncombat operations. The results illustrate the usefulness of principle-agent theory for understanding mass attitudes and help to improve the field’s understanding of the contours of public attitudes toward US defense policy.
A reflection of Indian higher education system: An academic labour market perspective
Authors: Shome Samik , Gupta Yuvika
Published: September 2018

The education sector significantly affects the economic, political and social development of any nation and is a key to enhance country’s competitiveness in the global economy. Higher education is critical to India’s aspirations of emerging as a major player in the global knowledge economy. This paper takes a comprehensive look at the various stages of growth of higher education in India. It also examines the degree to which a labour market for academic staffs has developed in Indian education sector and explores its implications for academic professionals, their careers and work. It analyses the key elements and characteristics of this market. The paper draws and builds on findings from official national data and also evidence-based reports subject to secondary analysis. In conclusion the paper argues that there is a degree of insularity in the Indian academic market.
Pathways From Peer Victimization to Sexually Transmitted Infections Among African American Adolescents
Authors: Hong Jun Sung , Kim Jinwon , Lee Jane J. , Shamoun Celine L. , Lee Jeoung Min , Voisin Dexter R.
Published: September 2018

African American youths, especially those in low resource communities, are vulnerable to peer victimization, which can increase risk of sexually transmitted infections. However, few studies explored the relationship between these two health concerns and the pathways that may link them. The present study aimed to address this gap. We used descriptive statistics, correlation coefficients, and structural equation modeling to analyze data collected from 277 adolescents ages 13 to 24 years in Chicago. Primary results indicated that peer victimization was not directly related to acquisition of sexually transmitted infections. However, peer victimization was negatively associated with condom use, and condom use was negatively associated with sexually transmitted infections. Furthermore, affiliation with sexually active peers was positively associated with substance use. These findings have implications for bullying and sexual risk prevention and intervention of low-income youths. Attention to treatment approaches and interventions that are holistic and culturally feasible is recommended for practitioners working with urban youth.
Serum iron levels are an independent predictor of in-hospital mortality of critically ill patients: a retrospective, single-institution study
Authors: Xia Jian-jun , Wang Fei , Jiang Xiao-nan , Jiang Ting-ting , Shen Li-juan , Liu Yue , You Da-li , Ding Yong , Ju Xue-feng , Wang Li , Wu Xiao , Hu Shan-you
Published: September 2018

Objective

This study aimed to examine the relationship between serum iron levels and in-hospital mortality in critically ill patients.

Methods

We retrospectively studied 250 critically ill patients who received treatment at the intensive care unit between June 2015 and May 2017. Blood chemistry and hepatic and renal function were measured. Kaplan–Meier survival curves were plotted according to serum iron levels. Correlations between serum iron levels and other variables were analyzed.

Results

A total of 165 (66.0%) patients had abnormally low serum iron levels (<10.6 μmol/L). Patients who died during hospitalization had markedly higher Acute Physiology and Chronic Health Evaluation II scores and significantly lower serum iron levels compared with those who survived. Cumulative survival was significantly lower in patients with low serum iron levels than in those with normal serum iron levels in subgroup analysis of older patients (n = 192). Multivariate regression analysis showed that, after adjusting for relevant factors, low serum iron levels remained an independent risk for in-hospital mortality (odds ratio 2.014; 95% confidence interval 1.089, 3.725).

Conclusions

Low serum iron levels are present in a significant proportion of critically ill patients and are associated with higher in-hospital mortality, particularly in older patients.
A hierarchical framework for concepts in physical geography
Authors: Gregory KJ , Lewin J
Published: September 2018

The word concept is widely used in physical geography but seldom defined. Developing from an earlier proposal of concept types in geomorphology, this paper considers a structure for categorising concepts in physical geography in the light of sciences and philosophy more generally. It reviews where our concepts derive from, and their relation to kinds, universals and categories, whilst also indicating the lack of an agreed clear distinction between them. Because an unstructured diversity of concepts has previously been proposed in physical geography by different authors, a new provisional hierarchy is constructed. This is cognisant of specific developments in a range of disciplines, including formal concept analysis, lattice theory and hierarchy theory. A ‘concept of concepts’ hierarchy of six categories is proposed in which multidisciplinary (superordinate, contextual meta-concepts) and fundamental, operational and ancillary categories provide a 6 × 5 framework. This enables attention to be focused on stimulating conceptual underpinnings that can be tested at different levels in future learning, teaching and research. This can support the formation of knowledge structures and monitoring procedures that keep in step with ways that are characterising other disciplines.
The Influence of the Review of Radical Political Economics: Insights on Selected Key Articles
Authors: Schroeder Susan K.
Published: September 2018

The Review of Radical Political Economics ( RRPE) continues to offer cutting-edge contributions to radical political economics and, as such, is considered to be one of the leading journals for heterodox (nonmainstream) economics. The following mini-symposium reflects on three articles that were published by the RRPE during its, and Union for Radical Political Economics’ (URPE), first fifty years. These articles are examples of the RRPE’s seminal works that affected, and continue to affect, the literature of heterodox economics in various ways. The authors of these articles were asked to provide their reflections on them. This article provides a foundation for appreciating those contributions—both old and new.
The Review of Radical Political Economics at Its Half Century: A Retrospective
Authors: Wachtel Howard M.
Published: September 2018

Fifty years on, the Review of Radical Political Economics ( RRPE) lives on against the odds that such a quixotic 1968 adventure could survive for half a century. As the first managing editor of the RRPE and one of the founders of the Union for Radical Political Economics (URPE), I have compiled a history of the first five years of the journal and the organization. This retrospective is primarily based on archival research, supplemented by my recollections. It concludes with some thoughts on how URPE and the RRPE affected the study and uses of economics in the past half century.
What Is Radical Political Economics?
Authors: Kim Marlene
Published: September 2018

From interviews of Union for Radical Political Economics (URPE) members, founders, and activists, I discuss what radical political economics means. I argue that the meaning should go back to its original intent, so that it is broad and inclusive and examines the structure of the economy; the root of economic problems and conditions; issues of power; and oppression and inequality by race, gender, class, and nation. With a broad definition of radical political economics, we can continue to address problems of hegemony and inequality, which are as important today as they were fifty years ago.
URPE, Radical Political Economics, Social Movements, and Revolution—From Identity Politics to Solidarity Economics: Looking Backward, Looking Forward on the Occasion of URPE’s Fiftieth Anniversary
Authors: Matthaei Julie
Published: September 2018

This article traces the shift from the identity politics of the early worker, feminist, and antiracist movements to the solidarity politics embodied in a movement of movements, to the emergence of solidarity economy initiatives and organizing. It examines the important contributions which Union for Radical Political Economics (URPE) and radical political economics (RPE) have made to these developments, and advocates that they become actively involved in analyzing and promoting the shift toward the solidarity economy.

JEL Classification:
Two Coupled Circadian Oscillators Are Involved in Nonphotic Acceleration of Reentrainment to Shifted Light Cycles in Mice
Authors: Yamanaka Yujiro , Honma Sato , Honma Ken-ichi
Published: September 2018

The onset and offset of an activity band in the circadian behavioral rhythm are known to differentially reentrain to shifted light-dark cycles (LD). Differential reentrainment could be explained by different light responsivities of circadian oscillators underlying these phase-markers. In contrast, reentrainment is accelerated by exposure to nonphotic time cues such as timed wheel-running. However, the relationship between the 2 oscillators and nonphotic acceleration of reentrainment is largely unknown. We examined phase-shifts of the mouse behavioral rhythm in response to an 8-h phase-advanced shift of LD and effects of behavioral interventions: maintained in a home cage (HC), exposed to a running wheel (RW) in HC (HC+RW), transferred to a new cage (NC), and exposed to RW in NC (NC+RW). Each intervention was given for 3h from the beginning of the shifted dark period and repeated for 4 days. Following the last dark period, the mice were released into constant darkness (DD). As a result, activity onset and offset were differentially phase-shifted. The activity onset on the first day of DD (DD1) was phase-advanced from the baseline slightly in HC and HC+RW, substantially in NC+RW, but not significantly in NC. The amount of phase-shift was significantly larger in the NC+RW than in the other groups. In contrast, the activity offset was significantly advanced in all groups by 6 to 8 h. The differential phase-shifts resulted in shortening of the activity band (α compression). The α compression was gradually relieved upon exposure to DD (α decompression), and the activity band finally became stable. Interestingly, the magnitude of phase-shifts of activity offset, but not of activity onset, in the following DD was negatively correlated with the extent of α compression in DD1. These findings indicate that the 2 circadian oscillators underlying activity onset and offset are involved in asymmetric phase-shifts and nonphotic acceleration of reentrainment.
I’m Too Old for This: Time Demands and Older, Early-Career Employees’ Receptivity to Supervisor Support
Authors: Dust Scott B. , Wang Peng , Lai Lei
Published: September 2018

This study explores how age and career stage affect receptivity to supervisor support using a multi-wave field sample of 528 employees. Following conservation of resources theory, we suggest that for early-career employees, supervisor support will more strongly mitigate the negative relationship between time demands and satisfaction with work–family balance and career satisfaction. We argue, however, that prior research overlooks a demographic with unique resource valuations: older, early-career employees. We therefore hypothesize and test two-way and three-way interactions of time demands, supervisor support, and career stage on satisfaction with work–family balance and career satisfaction. Our findings illustrate that early-stage employees were more receptive to the buffering impact of supervisor support. Additionally, for early-career employees, older employees compared to younger employees were more receptive to the buffering impact of supervisor support with regard to satisfaction with work–family balance and less receptive with regard to career satisfaction.
Innovative design and analysis of a longitudinal-torsional transducer with the shared node plane applied for ultrasonic assisted milling
Authors: Wu Chenjun , Chen Shijin , Cheng Kai , Ding Hui , Xiao Caiwei
Published: September 2018

This paper presents an innovative design and development of a longitudinal-torsional ultrasonic vibration transducer. This longitudinal-torsional ultrasonic vibration transducer can be stimulated up by one group of longitudinal piezoelectric ceramics and it has a shared longitudinal and torsional vibration node plane. The longitudinal-torsional ultrasonic vibration transducer consists of two amplitude horns, a mounting flange, and four pieces of axially poled piezoelectric ceramics. Theoretical analysis and formulation of the share vibration node have been studied, which are used to guide the design of the transducer. Five helical grooves are cut off along the circumference of the amplitude horn so as to convert the longitudinal vibration to both longitudinal and torsional vibration at the same time. Simulations have confirmed that each longitudinal-torsional vibration mode has one shared node on the transducer. The vibration amplitude is measured by a laser displacement sensor and the largest longitudinal displacement of longitudinal-torsional ultrasonic vibration transducer reaches 6 µm and torsional displacement reaches 11 mrad when 500Vpp voltage is applied on the transducer. Ultrasonic vibration milling experiments have shown that the longitudinal-torsional ultrasonic vibration transducer has played a great role in the cutting process as the longitudinal-torsional ultrasonic vibration milling decreases the cutting force substantially compared to the convention milling operations.
Surface Free Energy Modification of Crude Rubber Using Oxygen Plasma and Uv Laser Treatment
Authors: Golob Gorazd , Gunde Marta Klanjšek , Kaplanová Marie , Lovreček Mladen , Mozetič Miran
Published: September 2018

A study has been made of the surface properties of nitrile-butadiene rubber and ethylene-propylene-diene monomer crude rubber, basic raw materials for offset lithographic printing blankets manufacturing. Increased surface free energy of the crude rubber was achieved by treatment with the low-pressure oxygen plasma. After plasma activation, samples were treated using a UV laser to deactivate the surface layer. The surface free energy was calculated on the basis of contact angles with different liquids. Plasma-treated samples had higher surface free energy, especially the polar component, and the effect was larger for nitrile-butadiene rubber samples. This surface free energy decreased after exposure to UV laser light. FTIR-ATR spectroscopy was used to detect possible changes in chemical structure of the surface, but no differences were obtained. Changes of surface free energy were thus most likely a consequence of changes in the surface structure.
Effects of Moulding Condition and Curing Atmosphere on the Flexural Properties of Vinyl Ester
Authors: Nouranian S. , Lee J. , Torres G.W. , Lacy T.E. , Toghiani H. , Pittman C.U.
Published: September 2018

The effects of moulding condition and curing atmosphere on the flexural properties of a neat 33 wt.%-styrene epoxy vinyl ester (VE) were investigated. Specimens were prepared using either open or closed moulds, and thermally cured under either air or nitrogen atmosphere. Four-point bending tests were performed with both the top (“air-side”) and the bottom (“mould-side”) surfaces of the cured specimens in tension. The mean flexural moduli for nitrogen-cured and closed-mould specimens were 3% and 9% higher than for air-cured specimens, respectively. However, the mean flexural strength for open-mould air-cured specimens with their air-sides loaded in tension were 65% lower than the mean flexural strengths of open-mould nitrogen-cured or closed-mould specimens. This likely resulted from partial VE resin curing inhibition due to oxygen diffusion into the free surface region of the open-mould air-cured specimens. This creates gradients in the local stiffness and strength in the near-surface region due to lower crosslink density. This effect may be particularly important for thin specimens. These results underscore the significance of exposure to air during open-mould curing on the cured VE flexural properties. Such assessments are crucial for composite part manufacturing utilizing VEs.
Rheological Behaviour of Styrene-Free Unsaturated Polyester-Clay Nanocomposites
Authors: Rezadoust Amir Masoud , Esfandeh Masoud , Beheshty Mohammad Hosain
Published: September 2018

The rheological behaviour of styrene-free unsaturated polyester resin-organoclay (Cloisite 15A) nanocomposites at various clay contents, prepared by melt mixing, was investigated. Styrene-free resin was used to achieve high-shear mixing and to avoid viscosity changes due to solvent evaporation. In order to compare the effects of shear- and diffusion-induced phenomena on the intercalation of nanoclay; samples were prepared at two different temperatures of 40 °C (cold-mixed) and 150 °C (hot-mixed) and tested in the range of 40-120 °C using dynamic rheometry. Complex viscosity-temperature curves for cold-mixed samples showed a decrease in viscosity with increasing temperature followed by the formation of a plateau at a particular temperature, depending on the clay content. This behaviour is characteristic of systems with a network structure. The results of small angle X-ray diffraction and TEM analysis confirmed the intercalation of the nanoclay particles as well as a reduction in their thickness. TEM images revealed that the size reduction happened through bending fracture followed by shear delamination of the fractured clay layers. On this basis, a structure of the physical network was proposed to be formed by sticking several nanoclay stacks inside a polymer chain and more involvement of polymer chains with the delaminated layers' ends. A dispersion model was used to quantify and interpret the dispersion status of nanoclay particles in the resin system.
Phase Transfer Catalyzed Polymerization of Styrene and Graft Copolymerization of Styrene onto Gelatin
Authors: Kaur Inderjeet , Anita  , Khanna N. Deepika
Published: September 2018

The use of tetrabutylammonium bromide (TBAB), as phase transfer catalyst during polymerization of styrene in the presence of water-soluble radical initiator, potassium persulfate (KPS), and graft copolymerization of styrene onto gelatin, a water soluble polymer, using a water-insoluble radical initiator, benzoyl peroxide (BPO), has been explored in a water-benzene biphasic system. The percentage conversion (Pc) of styrene to polystyrene and percent grafting (Pg) of styrene onto gelatin was studied as a function of various reaction parameters. Under optimum reaction conditions, maximum Pc (76%) was obtained at [KPS] = 12.9 × 10−4 moles/L, [Sty] = 4.3 ×10−3 moles/L, and maximum Pg (87%) was obtained at [BPO] = 4.6× 10−4 moles/L, [Sty] = 13.88 × 10−3 moles/L using [PTC] = 2.89 × 10−4 moles/Lin 10 mL each of water and benzene in 120 min at 60 °C. The graft copolymer, Gel-g-poly(Sty), was characterized by IR, Thermogravimetric Analysis, Scanning Electron Microscopy and swelling behaviour in different solvents. Metal uptake and degradation studies of the grafted sample were also carried out. The grafted sample showed maximum uptake for Cu2+ (88%), Ni2+ (80%) and Fe2+ (50%). Degradation studies of Gel-g-poly(Sty) were carried out by soil burial test and UV radiations. Photo-degradation showed better degradation (5.26% wt. loss) in 32 h of exposure to UV radiations as compared to soil burial degradation (8.46% wt. loss) in 30 days. Gelatin-styrene graft copolymers can thus be used as bio- and photo-degradable materials for environmental management.
Study on Chlorination of Maleic Anhydride Grafted Polypropylene
Authors: Fu Heqing , Yan Caibin , Wei Xiaoli , Deng Wei , Wang Lina
Published: September 2018

The non-polarity of polypropylene has restricted its use; therefore it needs to be modified. Maleic anhydride grafted polypropylene(PP-g-MAH) is such a kind of modified polypropylene; however its polarity is still low. In order to improve its polarity, chlorinated maleic anhydride-grafted polypropylene (Cl-PP-g-MAH) prepared by free radical polymerization was carried out using PP-g-MAH as reaction material, carbon tetrachloride (CCl4) as solvent and benzoyl peroxide (BPO) as initiator. The products were characterized by Fourier Transform Infrared Spectroscopy (FTIR) and Nuclear Magnetic Resonance Spectroscopy (NMR). The effects of the reaction temperature, reaction time, flow rate of chlorine and concentrations of PP-g-MAH and BPO initiator on the degree of chlorination were studied. The optimum technological conditions were obtained, and the surface tension, light transmission, particle size and tensile strength of chlorinated maleic anhydride grafted polypropylene were better than those of maleic anhydride grafted polypropylene. After modification by maleic anhydride and chlorine, PP could meet commercial needs in the fibre composites, adhesives, printing inks, coatings and plastics industries.
Interrelation between Contact Angle and Interlayer Spacıng of Montmorıllonıte Clay Used ın Polymer Nanocomposıtes
Authors: Savaş Lemiye Atabek , Savaş Soner
Published: September 2018

In this study, the effect of interlayer d-spacing on the contact angle (θc) of montmorillonite nanoclays was investigated. Three type of montmorillonites, pure hydrophilic, modified with 35-45 wt.% dimethyl dialkyl (C14-C18) amine (Nanomer I.44P) and modified with (1-hexadecyl) tri-methylammonium bromide (HDTMAB), were used for comparison. According to the results, it was found that cations can be replaced by organic cations and interlayer spacing increases. Although organophilic montmorillonite clays whose surface energy is lowered and is more compatible with organic polymers, they shows hydrophobic behavior with water. Modified clays were found to have a larger interlayer d-spacing and also a larger time-independent contact angle in comparison to the un-modified clay.
Molecularly Imprinted Polymers and Their Synthesis by Different Methods
Authors: Yemiş Fadim , Alkan Pinar , Yenigül Berin , Yenigül Mesut
Published: September 2018

Over the past thirty years, molecular imprinting has aroused great research interest for scientists. This attention can be explained by the serious potential advantages of using molecularly imprinted polymers in place of natural receptors and enzymes such as their superior durability, low-cost and easy preparation. Furthermore molecular imprinting is a promising technique for the preparation of polymer composites with predetermined selectivity and high affinity. This mini review examines and evaluates the preparation technique and utility application of molecularly imprinted polymers (MIPs) in several areas. The review begins with a brief introduction to MIPs with a focus on their preparations and continues with application areas.
Flexible Pvc-Silica Composites as An Adsorptive Material for Water Soluble Dyes
Authors: Ulutan Sevgi , Yetgin Senem , Balköse Devrim
Published: September 2018

Methylene Blue (MB) adsorption studies were performed on flexible Polyvinyl Chloride/Silica composites which were obtained by using plastisol-plastigel technology. Change of MB concentration in aqueous phase as the adsorption process advanced was followed by using visible spectroscopy. The diffusion of MB through the composites exhibited non-Fickian behavior with a diffusivity of 10−11m2s−1. Making use of such PVC-silica composite sheets as column packing, the packing time will be reduced and the surface available for diffusion will be increased.
Production and Characterization of Polyethylene/Calcium Carbonate Composite Materials by Using Calcium Carbonate Dry and Wet Coated with Different Fatty Acids
Authors: Ozen Ilhan , Simsek Suleyman , Eren Feride
Published: September 2018

In this study, calcium carbonate (CaCO3) was coated by suitable chemicals using aqueous or dry coating methods in the optimum conditions. Uncoated calcium carbonate having a mean particle size (d50) of 1.6 microns and a top cut (d98) of 8 microns was provided commercially and it was dry and wet coated with saturated fatty acids whose carbon numbers vary between 14 and 18. Coating amount was adjusted to 0.5-2%. Particle size and particle size distribution of the calcium carbonates before and after coating were investigated. After characterization of the coated calcium carbonates, they were incorporated into linear low density polyethylene (LLDPE) in changing amounts using a twin screw extruder. The effects of coating chemicals, coating conditions and filler amount on composite materials were studied by evaluating the thermal (DSC and TGA) and appearance (Scanning Electron Microscope (SEM)) analyses.
Comparison of the Performance of Newly Developed Hydrophobic Coatings with Trade One
Authors: Selli Neslihan Tamsu , Tunali Ayşe
Published: September 2018

There is a considerable demand for wall tiles with a hydrophobic surface. Because hydrophobic tile surfaces non-adhesive towards soil, ice, graffiti and other unwanted contaminants. In this study newly developed hydrophobic solution and commercially available solution was applied on the tiles to compare their performance. The two coated tiles were compared regarding their abrasion and chemical resistance. It has been observed that newly developed hydrophobic solution has higher contact angle after washability test. It also has higher durability against citric acid and hydrochloric acid.
Processing and Characterization of Natural Fibre Reinforced Composites Using Lignin Phenolic Binder
Authors: Mahendran Arunjunai Raj , Wuzella Günter , Aust Nicolai , Müller Uwe , Kandelbauer Andreas
Published: September 2018

Natural fibre-reinforced composites were prepared using a lignin-phenolic resol binder, in which 30 wt.-% of the phenol was substituted by a modified lignosulfonate from renewable resources. The reinforcement of the lignin phenolic binder matrix was accomplished by different natural fibres. The non-woven flax, flax/wood and flax/kenaf fibre mats were impregnated with the lignin-phenolic binder and they were compression-moulded at elevated temperature. The curing condensations of the synthesized lignin phenolic resins were characterized by differential scanning calorimetry. Water absorption, thickness swelling and flexural strengths of the natural fibre-reinforced composites were determined, as well as their thermal stability using thermogravimetric analysis. The flexural strengths of the flax/wood and flax/kenaf composites were higher than those of the flax reinforced composite. Morphological analysis using scanning electron microscopy showed an enhancement in fibre/matrix interaction for the flax/wood and flax/kenaf fibre mixtures.
Synthesis and Characterization of Bismaleimide Modified Vinyl Ester Monomer-Unsaturated Polyester Intercrosslinked Hybrid Matrices
Authors: Chandramohan A. , Mandhakini M. , Dinakaran K. , Alagar M.
Published: September 2018

Intercrosslinked hybrid matrices were developed from N,N′-bismaleimido-4,4′-diphenyl methane (BMI) modified vinyl ester monomer (VEM), namely cyclohexyl-1,1′-bis[4-(γ-2-methylphenoxy)-α-hydroxypropylacrylate]-unsaturated polyester (UP) resin. BMI-modified VEM-UP hybrid matrices were characterized for their mechanical properties, viz. tensile strength, flexural strength, unnotched izod impact strength and hardness as per ASTM standards. Data obtained from thermal studies indicated that the introduction of vinyl ester monomer into unsaturated polyester resin marginally reduced the values of heat distortion temperature and glass transition temperature compared with those of the neat UP resin. Scanning electron microscopy studies of BMI modified VEM-unsaturated polyester systems exhibited a homogeneous morphology, confirming efficient chemical interaction and the formation of intercrosslinked networks.
Thermal Degradation and Flammability Behaviour of Hdpe/Eva/Eg Composites
Authors: Sun Zhidan , Ma Yonghong , Xu Yang , Chen Xiaolang , Chen Man , Yu Jie , Hu Shuchun , Zhang Zhibin
Published: September 2018

In this work, high density polyethylene (HDPE), ethylene-vinyl acetate (EVA) copolymer and expandable graphite (EG) flame retardant composites were prepared by using a twin screw extruder technique. The thermal stability and flame retardant properties of the composites were investigated by the thermogravimetric analysis (TGA) and cone calorimeter, respectively. The char morphology after combustion was also further characterized. The experimental results indicated that intumescent EG greatly enhanced the thermal stability and fire resistance of polymer matrix materials. The presence of EG improved the degradation temperature of HDPE/EVA blend and increased its char residue at high temperature. The results from cone calorimeter demonstrated that the addition of EG led to the decrease of the heat release rate (HRR), total heat release (THR) and smoke production rate (SPR) of materials and could retard the emission of the toxic and flammability gases by promoting the formation of a compact char layer. This char layer will prevent the polymer matrix further degradation and protect it effectively from heat penetrating inside, resulting in lower weight loss rate and better flame retarded property.
Glass Fibres Recovered by Microwave Pyrolysis as a Reinforcement for Polypropylene
Authors: Åkesson Dan , Krishnamoorthi Ramesh , Foltynowicz Zenon , Christέen Jonas , Kalantar Adib , Skrifvars Mikael
Published: September 2018

Glass fibre composites were recycled by microwave pyrolysis. The glass fibres recovered were evaluated as a reinforcement agent for polypropylene (PP). Samples were prepared with a micro-compounder and the resulting compounds were evaluated with tensile testing, flexural testing, Charpy impact testing and scanning electron microscopy (SEM). The adhesion between fibre and glass was relatively poor, and an attempt was made to improve it. Various coupling agents were evaluated, in addition to the use of maleic anhydride-grafted PP (MA-PP). Tests showed that MA-PP had a relatively strong effect on the mechanical properties.
Glass Transition Behaviour of PMMA/PVA Incompatible Blend
Authors: Nakamura Yoshinobu , Kariya Eiji , Fukuda Tomoyoshi , Fujii Syuji , Fujiwara Kazuko , Hikasa Shigeki
Published: September 2018

Dynamic viscoelastic properties and morphology of poly(methyl methacrylate) (PMMA)/poly(vinyl alcohol) (PVA) blend prepared by melt kneading was investigated. These solubility parameter values differ greatly. Two kinds of PVA with saponification degrees of 88 and 98 mol.% were used. Micrometre-order domains were observed by scanning electron microscopy for 88 mol.% PVA, whereas no clear domain was observed for 98 mol.%. Both the blends were incompatible systems because two loss modulus peaks based on PMMA and PVA were observed by dynamic mechanical analysis. The loss modulus peak based on the PMMA-rich phase was higher than that of pure PMMA; the increase of the corresponding glass transition temperature (Tg) caused by blending was more remarkable for 98 mol.% PVA than 88 mol.%. It was thought that the intermolecular interaction of OH group in PVA and carbonyl group in PMMA caused the increase in Tg, but no clear evidence of the interaction for the blend was observed by a Fourier transform infrared spectroscopic analysis. The poly(vinyl acetate)/PMMA blend was incompatible. The unsaponificated vinyl acetate unit in PVA decreased the interaction between PMMA and PVA. This is the reason why the effect of Tg rising was lower for 88 mol.% PVA than for 98 mol.%.
Analysis of Mechanical Properties of Carbon/Epoxy Composites in the near Critical Water Decomposition
Authors: Jia Xuegang , Liu Yuyan , Li Lan
Published: September 2018

Carbon fiber/epoxy resin composites have been widely used in many fields. However, they hardly melt at high temperatures or dissolve in any regular solvents. The recycling of carbon fiber/epoxy resin composites is one of the top research priorities. Carbon fiber/epoxy resin composite laminates consist of layers which are made of different materials. In near critical water, layers experience different forces, which result in the separation of layers and then accelerate the decomposition. In order to reach our final goal, decomposition of carbon fiber/epoxy resin composite laminates in near critical water, the characteristics of stress and strain of carbon fiber/epoxy resin laminates are necessary to know to guide the further study of decomposition. In this project, the stress and strain of carbon fiber/epoxy resin laminates in nearly critical water were analyzed using the ANSYS software. The results showed that temperature and pressure affected stress and strain of laminates differently in X and Y directions. In addition, the increased number of layers of laminates will increase the interlaminar shear stress, peeling stress, and the strain in Y direction, but will decrease the strain in X direction.
Compression Buckling Response of Tow-placed, Variable Stiffness Composite Panels with Sine Curved and Tangent Curved Fibers
Authors: Yongli Qin , Yingdan Zhu , Yueping Yu , Chun Yan , Xiaoqing Zhang , Xinyu Fan
Published: September 2018

Tailoring of composite laminated panels by Variable Angle Tow (VAT) steering fibers in their optimal spatial orientations provides a unique opportunity to maximize performance. Increased buckling response of the laminates by VAT steering technique may directly provide significant weight savings by redistributing loads in a benign manner. The aim of this work is to design tow-placed, variable stiffness composite panels with resistance to buckling by steering sine curved and tangent curved fibers. Buckling behaviors of two types of VAT panels and three typical types of straight fiber panels ([45/-45/0/90]s,[±45]2s, [0/90]2s) are investigated by finite element numerical simulations. It is found that the VAT panels with sine curved and tangent curved fibers show much better buckling performance to traditional straight fiber panels, with 9.25%-30.75% and 8.18%-29.47% improvement in buckling load respectively and a more uniform stress distribution. These results demonstrate that the design of composite laminated panels with sine curved and tangent curved fiber formats has the potential for buckling performance improvements in structural efficiency, and sine curved fibers may enhance buckling property of composite laminates better than tangent curved fibers do.
Effect of Surface Properties of T800 Carbon Fibers on Epoxy/Fiber Interface Adhesion
Authors: Wang Li-li , Li Peng , Li Ling-cong , Yu Yun-hua , Yang Xiao-ping
Published: September 2018

The purpose of this paper is to study the effect of surface properties of domestic sized-T800 carbon fibers on the epoxy/fiber interfacial adhesion by comparing with Toray sized-T800 carbon fibers. Surface chemistry analysis of the fibers was carried out by using X-ray photoelectron spectroscopy (XPS). The surface roughness of the carbon fibers was characterized by scanning electron microscope (SEM) and atomic force microscope (AFM). Dynamic contact angle analysis (DCAA) was selected to characterize the surface energy of the two types of carbon fibers. The interlaminar shear strength (ILSS) test, SEM and Dynamic mechanical thermal analysis (DMTA) were used to study the interface adhesion of the two carbon fiber reinforced epoxy composites. The results show that Toray sized-T800 carbon fiber/epoxy composite has higher interlaminar shear strength than domestic sized-T800/epoxy composite because Toray sized-T800 carbon fibers have more active and rougher surface than the domestic sized-T800 carbon fibers.
Dynamic Analysis on Composite Laminates Subjected to Low-velocity Impact Damage
Authors: Qu Peng , Guan Xiaojun , Nie Jiaqi , Zhu Guowei , Jia Yuxi
Published: September 2018

The hierarchical and heterogeneous structure characteristics of composite laminates give rise to the difficulty in the study of the composite laminates damage under low-velocity impact. A numerical method for the evaluation of the impact damage was proposed on the basis of the continuum damage mechanics (CDM) and the cohesive zone model (CZM). The method can bring stable simulations and can effectively establish the relation between the mesoscale structure and the macroscopic response under impact. The evolution of the impact damage and the effect of single ply orientation on the impact damage resistance were investigated. It is found that the tangential delamination is the dominant form of the interface damage and more orientation of fiber can make the impact resistance improved. The prediction has a good agreement with the experimental results. The dynamic analysis is helpful for a thorough understanding of the evolution of low-velocity impact damages in composite laminates.
Preparation and Characterization of Silica/Polymer Antifogging Coatings
Authors: Chang Chao-Chin , Wang Kuan-Chung , Chen Ching-Chung , Cheng Liao-Ping
Published: September 2018

This research work concerns the preparation of a bi-layer antifogging (AF) coating on a polycarbonate plastic substrate. The bottom layer, serving as a mechanical support, is an organic-inorganic composite that is formed by embedding colloidal silica in a crosslinked network of γ-glycidoxypropyltrimethoxysiline. Atop this layer, a coating formulation incorporating glycidyl methacrylate and poly(ethylene oxide)-based hydrophilic species was applied and then UV-cured to yield a film exhibiting the AF effect. Solid-state 29Si-NMR and FTIR were employed to investigate the evolution of chemical bonds during the sol-gel and the UV-curing processes. Contact angles of water on the coatings were measured to examine the hydrophilicity of the coatings. Furthermore, industrial tests such as pencil hardness, tape adhesion, and steam tests were carried out to evaluate the performance of the coatings.
Atomistic Structure and Thermodynamic Properties of Siloxane Pyrolyzed Amorphous Silicon Oxycarbide
Authors: Luo Xiaoguang , Ai Bangcheng , Yu Jijun , Miao Wenbo
Published: September 2018

Atomistic models of amorphous silicon oxycarbide, a-SiCO with different compositional range between SiO2 and SiC are constructed by rapid quenching. Structural models consisting of 528–568 atoms are fully optimized by molecular mechanics based on ReaxFF force fields. The addition of carbon into SiO2 glass stiffens the network and increases the bulk modulus. For better understanding the thermodynamics properties of a-SiCO, the effect of pressure and temperature on the bulk modulus, heat capacity, Debye temperature and coefficient of thermal expansion are derived by the quasi-harmonic Debye model in virtue of standard thermodynamic relations.
Preparation and Characterization of Elastomeric Ethylene Terpolymer Reinforced Poly(Ethylene-Co-Isosorbide Terephthalate)/Multi-Walled Carbon Nanotube Composites
Authors: Park J.S. , Kim S.B. , Kim H.R. , Nam B.U.
Published: September 2018

Poly(ethylene-co-isosorbideterephthalate)(PEIT)/multi-walled carbon nanotube (MWCNT)/ethylene terpolymer composites were prepared by a melt mixing process. The effects of MWCNT and the ethylene terpolymer of nanocomposites on the mechanical, thermal and electrical properties were investigated. MWCNT and ethylene terpolymer from 1 to 5 phr and 5 wt.% and 10 wt.% were added to the PEIT matrix, respectively. The thermal properties were evaluated by DSC and TGA. The morphology, mechanical properties and electrical characteristics were assessed by FE-SEM, a notched Izod impact strength tester and a surface resistance meter. As a result, we found that the PEIT/MWCNT/ethylene terpolymer composites have higher conductivity and better mechanical properties than neat PEIT resin.
Dynamic Compressive Behaviors of Multi Directional Woven Composite Laminates at Different Strain Rates
Authors: Wang Na , Cho Chongdu
Published: September 2018

This paper discusses the experimental study on the response of multi directional satin weave E-glass/epoxy composite laminates subjected to quasi-static and high strain rate compression loading along in-plane direction. Composite laminates were fabricated from satin weave glass fabric reinforced epoxy matrix pre-impregnated tapes which were manually laid up into laminates with stacking sequence of [45/-45/0/90] The low strain rate tests were conducted with an INSTRON™ testing machine, and the high strain rate tests done using a pulse shaper modified compression Split Hopkinson Pressure Bar (SHPB) apparatus. Compressive strength, modulus and strain at peak stress are evaluated experimentally at different strain rates. The results show that compressive strength, modulus and strain at peak stress are rate sensitive and enhanced at high strain rate compared with those at quasi-static loading. Under high strain rate loading, compressive strength and modulus increase as the strain rate increases. Optical and microscopic graphs on the specimens are carefully examined to determine operative failure modes. With the studied strain rate regimes, the failure modes are observed to change from splitting followed by fiber kink buckling to predominantly delamination and shear fracture as the strain rate increases from quasi-static to high strain rate.
Study of the Microstructure and Mechanical Properties of Pbsn Alloys Deposited on Carbon Fiber Reinforced Epoxy Composites
Authors: Liu Chang , Song Dajun , Hao Lifeng , Yang Fan , Jiao Weicheng , Wang Rongguo , Chen Minghua
Published: September 2018

In this paper, four groups of the plasma spray process parameters (g1, g2, g3 and g4) of PbSn coatings deposited on carbon fiber reinforced epoxy composites (CFRE composites) were examined. The microstructure and phase composition of the as-sprayed coatings have been examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The bonding strength of the coatings to the substrates was detected on a RGD-5 tensile testing machine. Results indicate that the melting extent and the bonding strength of the coatings were evidently improved and the porosity decreased with the g3 parameters. However, the phases and the content of crystalline of PbSn coatings were slightly changed with all of the parameters.
Micro-Geometry Modeling Based on Monte Carlo and Permeability Prediction of Yarn
Authors: Yang Bo , Jin Tianguo
Published: September 2018

In order to simulate the resin filling process of Liquid Composite Modeling (LCM) such as Resin Transfer Molding (RTM) effectively, the permeability tensor field of preform is needed to be predicted accurately in advance. In the several existing micro-permeability prediction models, the fibers are assumed to be regularly arranged (quadratic or hexagonal) to simplify the flow analysis, they all ignore the randomness of the fiber distribution in yarn. The micro-permeability is a preform property depending strongly on the preform's micro-geometry, so building the micro-geometry close to the real structure is significant to predict the micro-permeability of preform. In this work, we present a Monte Carlo moving method to obtain the fiber random distribution on the front and rear cross sections of yarn segment, then build the geometry model of the yarn segment, adjust the center path line of fiber model by Bezier method, establish the micro-geometry model of yarn close to the real structure containing both axial and radial random factors. The micro-geometry model consisting of ∼100 fibers is built using the mentioned method, the fiber volume fraction varies from 0.15 to 0.90, and CFD simulations are carried out to determine their permeability values. The results show that compared to the regular fiber arrays, the disordered fiber arrays have a greater axial permeability, and two special transverse flow effects emerged as the disorder of fiber distribution, named local channeling effect and local obstructing effect. Relative to the theory predicted transverse permeability, the simulated permeability increases in the high porosity yarn as the channeling effect dominates the liquid flow, vice versa, the simulated permeability decreases in the low porosity yarn since the obstructing effect dominates the liquid flow, the simulation results agree well with the experimental ones, indicating the validity of the micro-geometry modeling method.
Interfacial Properties of Nano-Silica Modified Cfrps under Cryogenic Condition
Authors: Wang Rongguo , Zhang Chengwei , Hao Lifeng , Jiao Weicheng , Yang Fan , Liu Wenbo
Published: September 2018

The change of interface performance between carbon-fiber and matrix resin influence the properties of carbon-fiber reinforce polymer composites (CFRPs) when temperature was changed from room temperature to cryogenic conditions. In order to find the interfacial properties of epoxy/nano-silica matrix CFRPs under cryogenic conditions, the interfacial shear strength (IFSS) and the interlaminar shear strength (ILSS) were investigated at room temperatures and 77K respectively. The morphology of fractured interface was investigated by scanning electron microscope (SEM). The results show that there are higher mechanical properties of interface at 77K condition.
Tensile Properties of Epoxy with Microcapsules and Imidazoline Derivatives Curing Agent and Interlaminar Self-Healing Properties of Carbon Fiber Reinforced Epoxy Composites
Authors: Hu Honglin , Hao Lifeng , Wang Rongguo , Liu Wenbo , Yang Fan , Jiao Weicheng , Xu Zhonghai
Published: September 2018

Microcapsules are inevitable defects in the resin matrix, which would greatly influence on mechanical performance of structural material. Therefore, a balance value of microcapsule's content between self-healing properties and mechanical properties should be provided for fabricating adequate self-healing materials. Epoxy resin with epoxy-containing microcapsules and latent hardener 2MZ-AZINE, and carbon fiber reinforced epoxy composites were prepared. The tensile properties of epoxy resin with epoxy-containing microcapsules or 2MZ-AZINE were investigated. As the increase of content of latent hardener 2MZ-AZINE, tensile modulus and tensile stress of epoxy with 2MZ-AZINE decreases. The tensile stress of epoxy samples decreases with the enhancement of content of epoxy-containing microcapsules. Tensile modulus of epoxy with microcapsules decreases with the increase of microcapsule content below 10 wt.%, and tensile modulus increases above 10 wt.%. Considering the self-healing ability of epoxy sample, the content of microcapsules and latent hardener are concluded to 15 w% and 2 w%, respectively, offering a ∼24.7 MPa tensile stress. The maximum interlaminar self-healing efficiency in this research is only 31.98% recovery of interlaminar tensile stress (epoxy resin matrix with 15 w% microcapsule and 2 w% latent hardener 2MZ-AZINE). As a consequence, this research provided the mechanical parameter for fabricating carbon fiber reinforced epoxy composite.