Thermoplastic Starch

The thermoplastics processing of native starch in the presence of water is a recent development with very wide possible applications. Eventually, oil-based polymer materials have to be replaced in many applications by sustainable, inexpensive, natural materials from renewable resources. The present contribution focuses on the injection moulding of starch. The bases of the processing and the thermal and molecular changes occurring are described. In addition, the rheological behaviour of starch-water melts during processing is analysed quantitatively to give apparent melt viscosities. The dimensional, thermal and mechanical properties of moulded thermoplastic starch polymer (TSP) materials and the products presently being produced from them are discussed.     

A state-of-the-art review on particulate wood polymer composites: Processing,properties and applications

In the present decade, the demands for recyclable, environmentally friendly and low-cost with good strength composites materials have been significantly increased. In this context, the particulate wood polymer composites have attracted the researchers owing to their eco-friendliness, low-cost as they are prepared using waste wood particles, and good mechanical and physical properties. These composites were prepared by filling the waste wood particles into the polymers using different fabrication methods such as extrusion, hand layup, compression moulding, injection moulding and additive manufacturing (3D printing). A good number of research works have been reported on the testing and characterization of wood composites for the various applications so far. This fact motivated to prepare a state-of-the-art review on the recent developments in processing, characterization, and applications of wood composites. This paper presents a discussion on the chemical structure and properties of different types of wood species. The mechanical, thermal and water absorption behaviour of thermosets, thermoplastics and biopolymers based wood composites have also been discussed. Further, characterization of the nano biocomposites prepared using nanocellulose/nanoparticles of wood are also presented. The outcomes of the present review provide a good understanding of wood composites that will encourage the researchers for further research works & developments of novel wood composites for the advanced applications.     

Selecting polymers for medical devices based on thermal analytical methods

This biomaterials overview for selecting polymers for medical devices focuses on polymer materials, properties and performance. An improved understanding of thermoplastics and thermoset properties is accomplished by thermal analysis for device applications. The medical applications and requirements as well as the oxidative and mechanical stability of currently used polymers in devices are discussed. The tools used to aid the ranking of the thermoplastics and thermosets are differential scanning calorimetry (DSC), thermogravimetry (TG), thermal mechanical analysis (TMA) and dynamic mechanical analysis (DMA) as well as a number of key ASTM polymer tests. This paper will spotlight the thermal and mechanical characterization of the bio-compatible polymers e.g., olefins, nylon, polyacetals, polyvinyl chloride and polyesters.     

Preparation and Characterization of Electroactive Biopolymers

Biopolymers have the potential for use as a matrix for applications such as controlled release devices, environmentally sensitive membranes, mimic materials and energetic applications. Renewable resources (such as starch) can be utilized as polymer matrices for electroactive materials that are sensitive to their environment. Natural polymers are generally more environmentally-friendly and biocompatible than existing synthetic products. Thermoplastic starch is naturally insulative; however, the chemical, electrical, and mechanical properties of the biopolymer matrix can be tailored for specific functionality in a continuous process utilizing reactive extrusion. Conductance can be measured in the solid state by a direct-current resistance method. Ion-conducting materials, produced by doping thermoplastic starch and biopolymers with metal halides, have 5 orders of magnitude greater conductance than native materials. There is a correlation between polymer mobility and conductance. Plant or microbial biopolymers with ionic functional groups have shown promise for higher levels of conductance. The conductance approaches the level of synthetic polymer electrolytes.     

Thermodynamics of starch-water systems: An analysis from solution-gel model on water sorption isotherms

The water sorption of several starch samples and resistant starch (RS) samples were analyzed using an equilibrium solution-gel structure model and the results were compared to various sorption theories. It is found that the water sorption relations to water activity in starch in the high water content region could be properly described by the equilibrium two-phase structural model. The results suggested that favorable starch-starch interaction determined the formation of starch gel in water. The gel structure had a high molecular modulus of 10⁸ Pa and thus had limited water sorption capability. Part of the starch also exhibited the solution properties with water due to chain ends and defects of the gel structure. Despite the unfavorable starch-water interaction, starch-water solution might be formed due to the predominant contributions from the entropy of mixing. The solution phase was responsible for the rapid increase of water sorption at high water activity. It was also demonstrated that the starch could maintain a maximum dynamic unfreezable water up to ≈ 36%, which was consistent with the DSC measurements. © 1996 John Wiley & Sons, Inc.     

Novel Thermoplastic Composites from Commodity Polymers and Man-Made Cellulose Fibers

Summary: A new class of fibre reinforced commodity thermoplastics suited for injection moulding and direct processing applications has been developed using man-made cellulosic fibres (Rayon tire yarn, Tencel, Viscose, Carbacell) and thermoplastic commodity polymers, such as polypropylene (PP), polyethylene (PE), high impact polystyrene (HIPS), poly(lactic acid) (PLA), and a thermoplastic elastomer (TPE) as the matrix polymer. For compounding, a specially adapted double pultrusion technique has been employed which provides composites with homogeneously distributed fibres. Extensive investigations were performed with Rayon reinforced PP in view of applications in the automotive industry. The Rayon-PP composite is characterized by high strength and an excellent impact behaviour as compared with glass fibre reinforced PP, thus permitting applications in the field of engineering thermoplastics such as polycarbonate/acrylonitrile butadiene styrene blends (PC/ABS). With the PP based composites the influence of material parameters (e.g. fibre type and load, coupling agent) were studied and it has been demonstrated how to tailor the desired composite properties as modulus and heat distortion temperature (HDT) by varying the fibre type or adding inorganic fillers. Man-made cellulose fibers are also suitable for the reinforcement of further thermoplastic commodity polymers with appropriate processing temperatures. In case of PE modulus and strength are tripled compared to the neat resin while Charpy impact strength is increased five-fold. For HIPS mainly strength and stiffness are increased, while for TPE the property profile is changed completely. With Rayon reinforced PLA, a fully biogenic and biodegradable composite with excellent mechanical properties including highly improved impact strength is presented.     

Recent advances in starch–clay nanocomposites

Biological nanocomposites are a valuable addition to the existing nanocomposite materials and eventually can substitute petroleum-based composite materials in numerous applications due to their inherent advantages such as biodegradability, eco-friendliness, low cost, and easy availability to name a few. Recently, polymer–clay nanocomposites have achieved much more attention due to their enhanced properties such as size dispersion and significant enhancement in physicochemical and mechanical properties in comparison to the pure polymer systems. Among various biopolymers, starch is one of the most abundant natural polymers on the earth and is highly valuable due to its chemical and physical properties. Starch polymer has highly increased potential as an alternative to petroleum-based materials. However, starch cannot be used alone and starch–clay nanocomposite has emerged as a new potential green sustainable material. This article focuses on recent progress in starch-based nanocomposites with particular emphasis on starch–clay nanocomposite preparation, properties, and applications.     

Bulk plastic materials obtained from processing raw powders of renewable natural polymers via back pressure equal channel angular consolidation (BP-ECAC)

Renewable natural polymers wheat starch (WS) and wheat gluten (WG) were successfully processed into plastic bulk materials using back pressure equal channel angular consolidation (BP-ECAC) without using any additional plasticizers at relatively low temperatures. The strong shear deformation occurred during the process caused an effective deformation of WS or WG granular structures and resulted in an efficient gelatinization of starch or plasticization of gluten with the natural moisture content. Sufficient chain entanglement was formed in both WS and WG materials for achieving strong cohesion among the macromolecule matrixes. The mechanical strength of the obtained plastic materials was comparable to that of conventional polymers but stronger than the strength of thermoplastic WS or plasticized WG. The processing temperature played an important role in determination of morphologies and properties of the plastic materials. Increasing processing temperature would cause more effective gelatinization or plasticization of the natural polymers, enhance the interactions among different components in the systems, and form materials with improved mechanical properties. Thermal cross-linking might play a positive role in the improvement of mechanical properties when processing temperature was increased. However, thermal decomposition could also occur under such severe shearing especially at high temperatures. The optimum temperature for conducting such process was around 100-120 °C for WS and WG. The BP-ECAC method provides a potential to manufacture natural polymer based plastic materials efficiently on an industrial scale for various applications.     

Characterizations of modified cassava starch with long chain fatty acid chlorides obtained from esterification under low reaction temperature and its PLA blending

In contrast to typical starch esterification in an aqueous solution, which are carried out at elevated to ambient reaction temperatures, a low reaction temperature was applied in this study to minimize the starch chain hydrolysis. The physical properties of the modified starch, obtained from an esterification of cassava starch with long-chain fatty acid chlorides carried out in aqueous media at 4°C, were characterized using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and contact angle measurements. The modified starches show improvement in thermal stability and hydrophobicity, which can be further optimized by varying the types of acid chlorides and the reaction conditions. The starch products have high potential for use as fillers for biodegradable polymers, especially polylactic acid (PLA), as their tunable hydrophobicity can impose strong effect on controlling of the PLA's hydrolytic degradation rate for specific applications. Results on mechanical properties of the blends between the modified starch and PLA show an improvement in modulus of the polymer.     

The Influence of Pair Spiral Extrusion Equipment on Thermoplastic Potato Starch

Owing to contain a great deal of hydroxyl in Potato Starch, between the molecules and inside of molecules have very strong hydroxyl action. Thus, the liquate temperature is higher than disintegrate temperature, so it is difficult to process. Under the microscope, the microcosmic construction is a polar crystal molecule, and it appears globe predicament.To make the original potato starch into possession thermoplastic, we must make molecule of starch to change construct into amorphous state to form thermoplastic starch colophony. Besides auxiliary agent, shearing stress, temperature, time, pressure and hydrous quantity can affect the quality of starch thermoplastic too. The pair spiral extrude machine is used widely as the machines that are based of the pressure difference, and this extrude course may suffice require.Using the machine of pair spiral extrude of specific combination in the test of thermoplastic starch, the potato starch can be turned into thermoplastic starch of denaturalization preferably under auxiliary agent, shearing stress, temperature, pressure and the certain hydrous quantity.By the action of the technology process condition and the spiral combination, potato starch grains expand and fragmentate; hydroxyl bond cleave between and inside of molecules. Thus, crystallize state is changed into amorphous state. The transmutation of starch molecule property may be seen clearly from X diffraction chart and analyses of the construction property,By means of the denaturation, the crystal area of potato starch is broken,its crystallization degree is decreased,and its molecular chains are in amorphous state. The hydrogen bond among the molecular chain is broken or removed so that the starch structure is changed, making the starch thermoplastic.The processing of thermoplastic starch advances a higher requirement of ingredient water content, and technical conditions. A remodeled twin-screw extruder is used to create an environment to realize the condition of denaturalizing and plasticizing reactions. After the continuous probing, we have successfully developed three types of thermoplastics starch plastic from the potato starch (starch content of all of them is greater than 90%). The fluidity of the thermoplastics starch will be better if the processing is performed under the condition of 4.0-6.0Mpa (pressure) and 80-110℃ (temperature). By doing so, it is shown that there is the possibility of further thermoplastic fabrication upon it.     

Online monitoring of thermoset post-curing by dynamic mechanical thermal analysis DMTA

Thermosetting moulding compounds are synthetic materials which can be easily formed in the molten state and achieve high temperature stability due to a cross-linking process which takes place during manufacture. To ensure thermal and mechanical properties, post-curing of moulded phenolic resin components is necessary for high quality applications. In the industrial practice, post-curing time–temperature-programs are heuristically acquired. In this paper, dynamical mechanical thermal analysis is employed to determine optimal post-curing conditions for injection moulded parts from phenolic resin.     

Design and synthesis of self-healing polymers

Self-healing polymers represent a class of materials with built-in capability of rehabilitating damages. The topic has attracted increasingly more attention in the past few years. The on-going research activities clearly indicate that self-healing polymeric materials turn out to be a typical multi-disciplinary area concerning polymer chemistry, organic synthesis, polymer physics, theoretical and experimental mechanics, processing, composites manufacturing, interfacial engineering, etc. The present article briefly reviews the achievements of the groups worldwide, and particularly the work carried out in our own laboratory towards strength recovery for structural applications. To ensure sufficient coverage, thermoplastics and thermosetting polymers, extrinsic and intrinsic self-healing, autonomic and non-autonomic healing approaches are included. Innovative routes that correlate materials chemistry to full capacity restoration are discussed for further development from bioinspired toward biomimetic repair.     

Phase behaviour of SMA/PMMA blends: the influence of processing at low and high deformation rates

The influence of processing parameters (deformations) on SMA/PMMA blend phase behaviour is studied. It is found that injection moulding does change polymer blend phase behaviour. Phase separation kinetics are important to understand the injection moulding experiments and the kinetics are probably influenced by the deformations caused by the injection moulding proces. Capillary flow causes a complex change of polymer blend phase behaviour showing both deformation induced mixing and redemixing. Short capillaries, causing almost only uniaxial elongation in combination with pressure, cause no change to polymer blend phase behaviour. This is probably due to the short time the deformation is imposed to the material: it is expected that elongation is a main parameter causing changes in polymer blend phase behaviour. Parallel plate rheometer experiments show that applying only shear causes a complex change of phase behaviour showing both shear induced mixing and redemixing.     

Clustering and percolation effects in microcrystalline starch-reinforced thermoplastic

The use of starch microcrystals as biodegradable particulate filler is evaluated by processing composite materials with a weight fraction of starch ranging from 0 to 60%. In a previous work [Macromolecules, 29, 7624] the preparation technique of a colloidal suspension of hydrolyzed starch and the processing of composite materials by freeze drying and molding a mixture of aqueous suspensions of starch microcrystals and synthetic polymer matrix were presented. Starch microcrystals with dimensions of a few nanometers were obtained from potatoes' starch granules, and it was found that this filler produces a great reinforcing effect, especially at a temperature higher than T_g of the synthetic matrix. Classical models for polymers containing nearly spherical particles based on a mean field approach could not explain this reinforcing effect. The morphology of these nanocomposite systems is discussed in light of aggregate formation and percolation concepts. The sorption behavior of these materials is also performed. Starch is a hygroscopic material, and it is found that the composites absorb more water, as the starch content is higher. The diffusion coefficient of the penetrant is predicted from modified mechanical three branch series-parallel model based on a percolation approach. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2211–2224, 1998     

Starch swelling and its role in modern ceramic shaping technology

A microscopic real-time visualisation of potato starch swelling in aqueous media at 56°C is performed. The viscosity increase of a starch-water mixture during the swelling step is documented by viscometric measurements. The mechanism of ceramic green-body formation in a new ceramic shaping process, called “starch consolidation”, is discussed. In particular, the rheological changes during swelling and their concomitant structural background can explain certain discrepancies between model predictions and experimental findings observed in previous work.     

Product design for productivity and innovation with engineering thermoplastics and their blends in the nineties

Companies must constantly improve their technologies to survive the competitive battle in the nineteen nineties and beyond. This now holds more than ever for producers of engineering thermoplastics, who traditionally have enjoyed significantly higher margins than the commodity plastic producers. In today's competitive environment it is vital to be the high quality, low cost producer. At the same time products and processes need to become “greener”. The drivers call for specific R&D approaches focused at cost and ecological improvements of processes and products. Examples are: (i) novel catalysis with fewer process steps, higher yields and selectivity for the production of monomers and polymers. (ii) solvent-free polymerisation processes, resulting in lower investment cost, lower operating cost and the lack of solvent traces in the final product (iii) design of polymer modifications, e.g. higher flow and/or higher heat co-polymers such that products can be produced in existing equipment resulting in acceptable Return-on-Investment (ROI). Higher flow products are specifically needed for thin-wall designs to allow optimum use of the high mechanical properties of engineering thermoplastics, making shorter processing cycles possible during moulding and bringing less material in the environment. This paper reviews various routes to high flow technology, such as improving processing window, molecular engineering and blends. The pull for these technology developments come from optical data storage, thin wall bumper and super thin note bloc computer applications. The need for greener products is addressed through improved flame and fire retardant product design.     

Effect of Charge and Hydrophobicity on Adsorption of Modified Starches on Polyester

Polyester fabric (poly(ethylene terephthalate)) is a hydrophobic polymer. Its hydrophobic nature can be a disadvantage for certain applications like dyeing, finishing, detergency, etc. Physical or chemical modification of the polyester to make it more hydrophilic is therefore desirable for certain performance characteristics. Surface modification of polyester to make it hydrophilic can be achieved by adsorbing polymers on the polyester surface. Starch is a commonly available, hydrophilic polymer used in many textile applications that can be used to modify polyester. However, it needs to be chemically modified so that it can adsorb on the polyester fabric and physically modify the fabric characteristics. The polymers used in this study are two different modified starches—cationic and anionic starches and mixtures of the two. The adsorption kinetics on a polyester substrate was studied. The effect of charge and hydrophobicity on adsorption was investigated. Cationic starches were shown to readily adsorb on polyester and this was attributed to electrostatic interactions. Hydrophobic substituents on the cationic moiety resulted in increased adsorption. This was attributed to the weak hydrophobic interaction between the polymer chains which could result in a more coiled polymer conformation. It is hypothesized that more starch molecules are required for surface coverage of the polyester, resulting in an increase in adsorption. Anionic starch was adsorbed on the substrate but at a slower rate than the cationic starches. It is likely that there is a H bonding between acid groups on the starch and the ester groups of the polyester. However, the anionic starch is desorbed when the polyester is placed in an aqueous medium. When a blend of cationic starch and anionic starch was used, a low concentration of anionic starch was seen to increase adsorption, indicating that the polyelectrolyte complex itself may be adsorbing on the substrate. Further increases cause a decrease in adsorption as no sites may be available on the complex for adsorption. When hydrophobic substituents are present, addition of the anionic starch causes a decrease in adsorption at all concentrations. This was attributed to the “crosslinking” between the hydrophobically modified starch and the anionic polymer.     

Absolute Rate Constants of Radiation-Induced Polymerization of Isobutyl Vinyl Ether

A basic limitation in the processing of thermoplastics lies in the high viscosity of their melts. Since high viscosity is largely a consequence of high average molecular weight, this problem would be solved if a polymer could be provided in the form of polymer blocks which are essentially independent at elevated temperatures and which bond together reversibly at ambient temperatures. The theoretical possibility of achieving such a system is considered from the point of view of thermodynamic arguments as applied to an idealized system of monodisperse polymer blocks linearly connected by weak chemical bonds. Average molecular weights are expressed in terms of a molar Gibbs function contribution associated with a weak bond in the polymer. Assuming a requirement for substantial decomposition at 500°K, arguments are presented for an entropy contribution of ca. 200 J °K^?1 mole^?1 for such bonds, and on this basis an optimum weak bond energy of 60 ± 20 kJ mole^?1 is indicated. Possible block terminations giving energies of this magnitude are considered.     

Effect of thermal treatment on potato starch evidenced by EPR,XRD and molecular weight distribution

Effect of heating of the potato starch on damages of its structure was investigated by quantitative electron paramagnetic resonance (EPR) spectroscopy, X‐ray diffraction and determination of the molecular weight distribution. The measurements were performed in the temperature range commonly used for starch modifications optimizing properties important for industrial applications. Upon thermal treatment, because of breaking of the polymer chains, diminishing of the average molecular weights occurred, which significantly influences generation of radicals, evidenced by EPR. For the relatively mild conditions, with heating parameters not exceeding temperature 230 °C and time of heating equal to 30 min a moderate changes of both the number of thermally generated radicals and the mean molecular weight of the starch were observed. After more drastic thermal treatment (e.g. 2 h at 230 °C), a rapid increase in the radical amount occurred, which was accompanied by significant reduction of the starch molecular size and crystallinity. Experimentally established threshold values of heating parameters should not be exceeded in order to avoid excessive damages of the starch structure accompanied by the formation of the redundant amount of radicals. This requirement is important for industrial applications, because significant destruction of the starch matrix might annihilate the positive influence of the previously performed intentional starch modification. Copyright © 2015 John Wiley & Sons, Ltd.