Effects of Water and Chemical Solutions Ageing on the Physical,Mechanical, Thermal and Flammability Properties of Natural Fibre-Reinforced Thermoplastic Composites

Biocomposites comprising a combination of natural fibres and bio-based polymers are good alternatives to those produced from synthetic components in terms of sustainability and environmental issues. However, it is well known that water or aqueous chemical solutions affect natural polymers/fibres more than the respective synthetic components. In this study the effects of water, salt water, acidic and alkali solutions ageing on water uptake, mechanical properties and flammability of natural fibre-reinforced polypropylene (PP) and poly(lactic acid) (PLA) composites were compared. Jute, sisal and wool fibre- reinforced PP and PLA composites were prepared using a novel, patented nonwoven technology followed by the hot press method. The prepared composites were aged in water and chemical solutions for up to 3 week periods. Water absorption, flexural properties and the thermal and flammability performances of the composites were investigated before and after ageing each process. The effect of post-ageing drying on the retention of mechanical and flammability properties has also been studied. A linear relationship between irreversible flexural modulus reduction and water adsorption/desorption was observed. The aqueous chemical solutions caused further but minor effects in terms of moisture sorption and flexural modulus changes. PLA composites were affected more than the respective PP composites, because of their hydrolytic sensitivity. From thermal analytical results, these changes in PP composites could be attributed to ageing effects on fibres, whereas in PLA composite changes related to both those of fibres present and of the polymer. Ageing however, had no adverse effect on the flammability of the composites.     

Macromolecular Architecture-Nature as a Model for Degradable Polymers

Abstract

Nature usually combines polymers with short degradation times with polymers having long degradation times in an energy and material optimized process involving hierarchical systems. Sometimes a natural system of polymers has evolved to degrade in a month, sometimes in many years. The building blocks of the plant and animal kingdom are biopolymers which are either oxidizable or hydrolyzable. In natural composites, combinations of the two are common, e.g., in wood. Current trends in polymer research and marketing of plastics indicate an increasing demand for the development of a diversity of degradable polymer products with a predetermined service-life. We identify four main routes to design degradable polymers. The goal is to tailor-make a material which is more susceptible to environmental degradation factors (e.g., hydrolysis, biodegradation, photooxidation). The most convenient route is to use cheap synthetic bulk polymers and add a biodegradable or photooxidizable component. A more expensive solution is to change the chemical structure by introducing hydrolyzable or oxidizable groups in the repetitive chain of a synthetic polymer. The third route to degradable polymers is to use biopolymers or derivatives of these where the bacterial polyhydroxyalkanoates are perhaps the most studied material of them all. The fourth route is to tailor-make new hydrolyzable structures e.g., polyesters, polyanhydrides, and polycarbonates.     

A review on flammability of epoxy polymer,cellulosic and non‐cellulosic fiber reinforced epoxy composites

Natural fiber is well‐known reinforcement filler in polymer‐matrix composites. Composite components like organic polymers and natural fibers are natural fire conductors as the natural fiber consists of cellulose, hemicellulose, and lignin, and hence are as highly flammable as wood. Natural fiber reinforced composite materials are progressively being used in a variety of applications where their fire response is a hazardous consideration, for example, in the automotive (transportation) and building‐construction industries. As a result, an awareness of their performance or response during a fire and the use of conventional fire retardants are of great importance, as they are subject to thermal decomposition when exposed to intensive high heat or fire sources. In this review paper, fire flammability is the main concern for cellulosic and non‐cellulosic fiber‐reinforced polymer composites, especially epoxy composites. This paper reviews the literature on the recent developments in flammability studies concerning polymers, epoxy polymers, cellulosic‐fibers, and non‐cellulosic fiber‐reinforced epoxy bio‐composites. The prime objective of this review is to expand the reach of “fire retardants for polymer materials and composites” to the science community, including physicists, chemists, and engineers in order to broaden the range of their applications. Copyright © 2015 John Wiley & Sons, Ltd.     

嵌段及接枝液晶高分子合成进展

本文概述了近年来嵌段及接枝液晶高分子的合成情况，分析了不同合成方法的优缺点，并对其对原位复合材料中的应用作了简单介绍。     

Hierarchical structures in natural and synthetic polymer science

The founders of our dynamic field uncovered the wonders of both natural and synthetic polymers by using relatively primitive instruments and techniques. They developed the foundations on which we now build complex materials systems. By using the lessons from macromolecular systems in biology, our scientific community is now designing synthetic polymers that mimic natural materials (1, 2). This paper is divided into two parts. 1. Hierarchical structure-property relationships in connective tissues-lessons from biology 2. Micro- and nano- layered polymeric systems     

Biomineralized polymer matrix composites for bone tissue repair: a review

Bone defects caused by trauma, infection or bone tumor resection, are highly prevalent. A small number(5%–10%) of these injuries fail to heal due to non-union and require surgical intervention. Currently, the principal treatment options for these defects are autografts, allografts, xenografts or synthetic grafts. The main problems associated with these therapies include pain,infection and donor site morbidity. Bone tissue engineering is a diverse field that focuses on the regeneration of bone by combining cells, scaffolds, growth factors and dynamic forces. There have been many recent studies utilizing biomineralized polymer matrix composites which mimic the natural structure of bone. The principal focus of this review is on recent advances in the synthesis of various types of biomineralized polymer matrix composite. Examples of the biomineralization of naturallyderived and synthetic polymers widely used for bone engineering are also summarized.     

Review: Raw Natural Fiber–Based Polymer Composites

The effective utilization of raw natural fibers as indispensable component in polymers for developing novel low-cost eco-friendly composites with properties such as acceptable specific strength, low density, high toughness, good thermal properties, and biodegradability is one of the most rapidly emerging fields of research in polymer engineering and science. In fact, raw natural fiber–reinforced composites are the subject of numerous scientific and research projects, as well as many commercial programs. Keeping in mind the immense advantages of raw natural fibers, in the present article we concisely review raw natural fiber/polymer matrix composites with particular focus on their mechanical properties.     

Self-assembly of polymer and molybdenum oxide into lamellar hybrid materials

We report on self-assembly of polymer and molybdenum oxide chains into a new class of lamellar hybrid materials. Aqueous ammonium molybdate and polyvinyl alcohol (PVA) or carboxymethyl cellulose (CMC) were used as the starting materials. Ammonium molybdate was hydrolyzed into layered molybdenum oxide under acidified conditions. The organic polymer chains and the inorganic molybdenum oxide layers self-assemble and pack into new hybrid composites. Scanning electron microscope (SEM) images and polarized microscopy show that these two new materials have typical lamellar structure. Transmission electron microscope (TEM) images show that the layer thickness is about 100 nm. X-ray diffraction (XRD) data confirm the formation of inorganic molybdenum oxide. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) data gave thermal behavior of these composites. The mechanism of this hybrid reaction and the templating function of polymers were discussed in this paper. A special entropy effect was discovered when polymer was used as guest species. This entropy effect makes polymers preferential candidates as guest species rather than small molecules when fabricating organic/inorganic layered hybrid materials. We believe that this opens a new way to create organic/inorganic hybrid superstructures.     

Photoelasticity of textured heterogeneous polymer materials

The photoelastic properties of textured polymer composites are considered for the high deformation limit. Photoelasticity equations for incompressible polymers are derived in the correlation function theory approximation. It is shown that the birefringence may be zero for critical stretching across the texture axis. This effect can be used to measure the dispersion of shear moduli of polymer composites. © 1993 John Wiley & Sons, Inc.     

Layered photoconductive polymers: anisotropic morphology and correlation with photorefractive reflection grating response

We demonstrate that the mesophase morphology of the layered photorefractive polymers has a substantial influence on the photorefractive properties, especially in reflection grating geometries with a minimal grating spacing. The layered morphology of the photoconductive polymers based on poly(p-phenyleneterephthalate) (PPT) with pendent carbazole (CZ) groups can be efficiently controlled by changing their molecular weight. Photorefractive composites based on PPT-CZ polymers with different chromophores, diethylaminodicyanostyrene (DDCST) or piperidinodicyanostyrene (PDCST), show anisotropic morphology induced by the squeezing flow during sample preparation. The contributions of the highest occupied molecular orbital levels of the chromophores and of the degree and anisotropy of the layered crystalline structure to the charge transport and trapping result in a high efficiency of the PDCST composite and a similar response speed in DDCST and PDCST composites in the reflection grating geometry, although of about six times lower photoconductivity in the less-ordered PDCST composite.     

Functionalization of single layers and nanofibers: a new strategy to produce polymer nanocomposites with optimized properties

Nanocomposites are the emerging materials of the 21st century in view of their possessing design uniqueness without any compromises, certain unusual property combinations that are not found in conventional composites, as well as a wide spectrum of applications. Polymer-based layered compound nanocomposites have special place in view of their best property enhancement. Hence, the objective of this article is to bring new ideas to optimize the design of polymer/layered compounds/fibrous nanocomposites, starting with a brief overview of the preparation, structure, properties and applications. The proposed strategy suggests the use of synthetic and natural layered compounds, taking into account their ability to be exfoliated in the form of single layers, which can be chemically grafted with key molecules. The same procedure can also be applied to fibrous materials. These surface-grafted molecules can carry reactive groups to be bonded to the polymer matrices. Thus adhesion between the reinforcement and the polymer matrix can be achieved. This methodology, which has not been explored systematically in the specialized literature, can be used to produce polymer nanocomposites with low-cost fibrous materials having similarity to expensive carbon nanotubes exhibiting optimized dispersion, interfacial bonding, and attractive physical and other properties.     

Preparation of bio-based polymers for materials applications

A new technology developed by us for the synthesis of well defined, tailored cellulose-synthetic polymer graft polymers and crosslinked cellulose graft polymers with control over the molecular weight of the synthetic polymer graft, a high degree of graft substitution, and knowledge of the backbone-graft linkage is reviewed. The potential of bio-based polymers using these new tailored cellulosic graft polymers for use in plastics, resins, and composite applications is discussed. The new graft polymers can function as compatibilizers/interfacial agents in the preparation of biopolymer-synthetic polymer composites and blends with the desirable properties of the constitutent polymers incorporated into the new material system.     

Experimentally-statistical estimation models and forecasting of nonmetal shipbuilding materials toxicity indexes under burning conditions

Experimentally-statistical models for estimation of oxygen index and an indicator of toxicity of combustion products of natural and synthetic polymers and their compositions treated with fire-retardants are suggested. Widely used and promising polymer binders for nonmetal shipbuilding materials of different functions are analyzed. The influence of inorganic and organic fire-retardants and fillers on the basis of glass and natural silicates on toxicity and fire resistance of polymer materials was studied.     

Electrostatic contributions in the increased compatibility of polymer blends

Successful blending of different polymers to make a structural or functional material requires overcoming limitations due to immiscibility and/or incompatibility that arise from large polymer-polymer interfacial tensions. In the case of latex blends, the combination of capillary adhesion during the blended dispersion drying stage with electrostatic adhesion in the final product is an effective strategy to avoid these limitations, which has been extended to a number of polymer blends and composites. This work shows that adhesion of polymer domains in blends made with natural rubber and synthetic latexes is enhanced by electrostatic adhesion that is in turn enhanced by ion migration, according to the results from scanning electric potential microscopy. The additional attractive force between domains improves blend stability and mechanical properties, broadening the possibilities and scope of latex blends, in consonance with the "green chemistry" paradigm. This novel approach based on electrostatic adhesion can be easily extended to multicomponent systems, including nonpolymers.     

Improvement of Fibre-Matrix-Adhesion of Natural Fibres by Chemical Treatment

Plastics, also called synthetic polymers, are playing an important role in daily living. To raise more applications it is necessary to modify known polymeric systems to reach improved materials/material systems. A possibility to create new optimised materials out of neat polymers is offered by compounding them with different filling material. Besides chemical modification of polymers, mixing, combining or use of different fillers, one possibility is given by the composite technique, whereas the combination of the polymeric matrix and the embedded reinforcement (e.g. fibre) are yielding in optimised materials adjusted to the required properties. Concerning the polymeric matrix, either thermoplastic or thermoset material can be used. In case of the reinforcement, either synthetic (carbon-, glass- or polymeric fibres) or natural fibres are introduced to composites. To obtain an appropriate adhesion of the matrix to the reinforcement system, synthetic fibres are equipped with an avivage. For natural fibres, there are no such materials available and the hydrophilic property of this system surface prevents an adhesion to hydrophobic polymers, as well as to sizings. In this paper, ways are shown to modify the natural fibres via chemical treatment to yield higher physical properties at better adhesion. Also we will explain activities on the use of natural fibres as reaction systems and processing tools as well as the attempt to isolate the different compounds of the neat fibre via selective work-up.     

Structural and mechanical study of elastomers under plane deformation

The plane shrinkage of various elastomers [natural rubber, synthetic isoprene rubber, and plasticized poly(vinyl chloride)] at room temperature has been studied via direct microscopic observations. Prior to deformation, the surface of polymer samples is decorated with a thin (several nanometers) metallic layer. Further deformation leads to formation of the surface relief in the coating. An analysis of the formed microreliefs allows one to visualize and characterize the induced stress field in the sample. The shrinkage of poly(vinyl chloride) samples is accompanied by development of the uniform surface relief over the whole surface of the deformed polymer. This fact suggests a homogeneous character of the stress field and, hence, a homogeneous structure of the polymer sample. In the case of crosslinked rubbers (natural rubber and synthetic isoprene rubber), their plane shrinkage leads to the development of an irregular pattern on the polymer surface. In addition to the folded surface relief that is typical of the poly(vinyl chloride) structure, one can observe 20-to 50-μm “islands,” which are characterized by their own morphological features. Information on structural inhomogeneity of rubbers that is obtained by scanning electron microscopy correlates with the data of DSC measurements. The advantages of electron microscopic procedure for studying structural rearrangements in polymers during strain recovery of elastomers are demonstrated.     

The effects of intralayer metal composition of layered double hydroxides on glass transition, dispersion, thermal and fire properties of their PMMA nanocomposites

A series of aluminum-containing layered double hydroxides (LDHs), containing Mg, Ca, Co, Ni, Cu and Zn as the divalent metals, have been prepared by the co-precipitation method and used to prepare nanocomposites of PMMA by in situ bulk polymerization. The additives were characterized by Fourier transform infrared spectroscopy, X-ray diffraction spectroscopy (XRD) and thermogravimetric analysis while the polymer composites were characterized by XRD, transmission electron microscopy, differential scanning calorimetry and cone calorimetry. Polymerization of methyl methacrylate in the presence of these undecenoate LDHs results in composites with enhanced thermal stability. The glass transition temperatures of the composites and the pristine polymers are found to be around 110 °C; this suggests that the presence of these additives has little effect on the polymer. It is found that the additive composition and the dispersion state of LDHs agglomerates in the polymer matrix influence the fire properties of composites as measured by cone calorimetry.     

高分子时代的天然高分子

本文从资源利用的战略角度讨论了发展及加强天然高分子研究的重要性。以几个天然高分子为例讨论了它们的研究动向及进展。与合成高分子相比，指出了天然高分子研究中存在的问题。文中对我国学者在这一领域中所作的卓越贡献做了简要介绍。     

Synthetic and biological polymers--merging the interface

The increasing control that synthetic chemists are able to exert over molecular architecture is allowing the design and preparation of macromolecular and polymeric systems of unprecedented sophistication. In form and function, synthetic polymers are able to mimic many biological polymers, in effect ‘blurring the boundaries’ between the worlds of artificial and natural materials. In this review, some key examples from the merging interface between synthetic and natural polymers are considered, and illustrations of both ‘bio-inspired’ synthetic macromolecular chemistry and new directions in polymer materials are given.     

Microbial aspects of the degradation of water-soluble synthetic polymers

This paper focuses on microbial aspects of degradation of synthetic polymers, especially of water-soluble specialty polymers. The polymer structures analogous to natural polymers suggest biodegradability which originates from enzymes which do not discriminate between natural and synthetic polymers. Hydrolysis and oxidation are the primary processes for biodegradation. Assimilation rates are determined by the conversion of the polymer carbons into common metabolic products whether degradation is exogenous or endogenous. Biochemical mechanisms in the degradation of polyethers are summarized. Microbial symbiosis was involved in the degradation of a copolymer and the availability of symbiotic processes is suggested for the degradation of all copolymers. Transportability of PEG 20 000 through cell walls was suggested and a chemical process using hydrogen peroxide and ferric ions is proposed for the depolymerization of PEG with Mn more than 20 000 and its copolymers.