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Structural, mechanical, thermal and surface properties comprising biodegradable aromatic–aliphatic polymer poly(butylene adipate-co-terephthalate) (PBAT) and the wheat stalk-based nanocellulose (NCC) were studied. The materials were found to comprise the compatible and yet phase-segregated constituents which kept their identity in the nanocomposite materials. The NCC phase was found to be homogeneously dispersed in the PBAT matrix inside. Similar to the corresponding microcomposites, the investigated nanocomposites were found to be stable within their desired application temperature as packaging materials. The tensile properties of the nanocomposites degraded in terms of strain at break, tensile strength and tensile modulus. At higher filler content, the reinforcing effect dominated leading to an increase in indentation modulus and hardness, and a decrease in the work of elastic deformation. The wettability and the water absorption capacity of the materials increased with NCC content thereby enhancing the biodegradability of the composites.

In this work, peel tests inside the chamber of an ESEM ( in situ peel tests) are described with heat-sealed test specimens of packaging systems made of multilayer films that simulate different flexible packaging types, according to the packaging line used. The in situ peel tests provided evidence to describe the influence of three different main aspects of the packaging process in relation to the opening behavior of the sealing packages. The investigated aspects are the peel angle, the alignment angle between the orientation of the multilayer films and the seal, and the bulge formation as a consequence of inadequate sealing parameters. In situ peel tests enabled the differentiation between peel angle and local (micro) peel angle, which results from the overall stiffness of the multilayer structure film. Alignment angles of 90° and 45° were found to produce similar opening forces. Images showing the formation of various new local micro fissures on new planes during the in situ peel test explained how the opening force can be dramatically increased during the tearing of two sealed multilayer films.

Further developed methods based on an indenter penetration into a material allow generalised quantitative statements on the composition, the depth-dependent mechanical properties and the delamination behaviour of multilayer polymer films, which is demonstrated on gelatine-coated polyethylene terephthalate and polyethylene films. These highly sensitive polymer testing methods, include the recording microindentation test and the recording adhesion test, describe the material behaviour multi-parametrically and are fast (raw data acquisition within several minutes) and relatively simple, requiring a minimum 1 gram sample depending on the film thickness. Based on the Vickers hardness under load approach, the hardness–depth diagrams calculated from the recording microindentation test provide information about the structure, the thickness and the coating hardness and the substrates. The tangential load vs. tangential path length diagrams from recording adhesion test can detect different scratch processes such as continuous scratching or non-continuous stick-slip layer delamination. Furthermore, they form the basis to quantitatively analyze adhesion, i.e. to determine the critical tangential load and the critical tangential delamination work. Both are highly dependent on the substrate type and treatment.

Star-shaped polystyrene-block-polybutadiene-block-polystyrene (SBS) block copolymer (BCP) was subjected to epoxidation reaction using m-chloroperoxy benzoic acid (MCPBA). The epoxidized SBS block copolymer (eSBS) was then blended with diglycidyl ether of bisphenol-A based epoxy resin (EP) and cross-linked with methylene dianiline (MDA). The materials were characterized by different techniques such as Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The FTIR spectrumwith the peak located at 890 cm−1 and 1230 cm−1 attested the occurrence of epoxidation reaction. The nanophase separated structures as demonstrated by transmission electron microscopy were induced in the eSBS/EP blends by epoxidized eSBS.

Structural, thermal and mechanical properties of the compostable composites comprising a biodegradable aliphatic-aromatic copolyester (namely, the poly(butylene adipate-co-terephthalate; PBAT), and microcrystalline cellulose (MCC) derived from agricultural waste, the wheat stalk, were investigated. Purely physical interaction between the components was found to be responsible to get the MCC phase quite uniformly embedded in the PBAT matrix, the latter being the dominating component of the composites surface. There were two distinct thermally activated degradation regimes characterized by separate activation processes corresponding to the decomposition of the MCC and the PBAT phases, respectively. The physically bound and rather weak but large PBAT-MCC interfacial areas provoked more rapid thermal degradation of the composites compared to the pure components. While the PBAT acted as a highly ductile material upon tensile loading, the composites maintained high ductility only up to 20% by weight of the MCC. The drastic reduction in the ductility for higher filler loading was attributed to the possible void formation at the interfacial region followed by crack initiation and propagation leading eventually to the premature specimen fracture. The composite materials thus fabricated were hence found to suit for low-load bearing applications.

Nanocomposites of multiwalled carbon nanotubes (MWCNTs) with poly(butylene adipate-co-terephthalate) (PBAT), a flexible aromatic–aliphatic copolyester, were prepared by melt mixing followed by compression moulding to investigate their spectroscopic, morphological, mechanical and electrical properties. A comparison of the Fourier transform infrared (FTIR) spectra of the neat polymer matrix and the composites showed no difference, implying a physical mixing of the matrix and the filler. A morphological investigation revealed the formation of a continuous and interconnected MWCNT network embedded in the polymer matrix with partial agglomeration. Increasing Martens hardness and indentation modulus and decreasing maximum indentation depth with increasing filler concentration demonstrated the reinforcement of the polymer by the MWCNTs. A volume resistivity of 4.6 × 105 Ω cm of the materials was achieved by the incorporation of only 1 wt.-% of the MWCNTs, which confirmed a quite low percolation threshold (below 1 wt.-%) of the nanocomposites. The electrical volume resistivity of the flexible nanocomposites was achieved up to 1.6 × 102 Ω cm, depending on the filler content. The elongation at the break of the nanocomposites at 374% and the maximum relative resistance changes ( Δ R/ R 0 ) of 20 and 200 at 0.9 and 7.5% strains, respectively, were recorded in the nanocomposites (3 wt.-% MWCNTs) within the estimated volume resistivity range. A cyclic strain experiment shows the most stable and reproducible Δ R/ R 0 values in the 2%–5% strain range. The electrical conductivity and piezoresistivity of the investigated nanocomposites in correlation with the mechanical properties and observed morphology make them applicable for low-strain deformation-sensing.

Rising raw materials prices and increasing customer demands for reliability and durability mean that there is huge interest in finding more and more ways of improving the service life of elastomeric products, for economic and environmental reasons, by boosting their resistance under the relevant operating conditions. The material-dependent oxygen absorption capacity and oxygen permeability play an important role in oxidative ageing processes and their modelling. Thus, ageing resistance is substantially dependent on the rate of oxygen diffusion into the bulk of the material in the case of thermo-oxidative attack. To evaluate the resistance of materials to external influences, artificial ageing methods are used in practice. The advantage of these methods is that, as a result of intensifying the test parameters, e.g. temperature and humidity, the ageing processes in the vulcanisate are accelerated. Within the scope of this study, the influence of accelerated ageing on the mechanical and viscoelastic properties of mainly carbon-black-filled natural rubber (NR) vulcanisates was studied in an oxygen atmosphere at elevated temperature and in oxygen with solar radiation. The filler content was varied and the antioxidant IPPD was used. The analyses showed that, as well as mechanical properties such as hardness and tensile strength, the viscoelastic properties are also affected, depending on the ageing time and the type of ageing. In addition to the investigation of mechanical properties, a direct evaluation of the material change was carried out for selected samples by means of analytical tests. The investigations showed the deterioration of the antioxidant activity.

The overall stable crack initiation and propagation behaviour of specimens cut from plastic pipes that were composed of different polyolefin materials were investigated using concepts of elastic–plastic fracture mechanics including the crack propagation kinetics. The effect of specimen shape, orientation, welding, lading rate, composition/microstructure and direction of crack propagation on the crack resistance (R) behaviour of these materials has been thereby assessed.

Summary The prototype of a depth-sensing macrohardness testing system with temperature chamber and temperature controlling unit for contact heating/cooling was upgraded in terms of control and software in such a way, that it allows application of the Stepped Isothermal Method (SIM) as for now. The SIM is a single-specimen method, for which the temperature is raised stepwise at constant load and kept constant for a given time for each step, where the changes in indentation depth are measured as a function of time in this case. After correction of the thermally induced change in indentation depth and mathematical procedures a master curve construction is realised along a logarithmic time axis. The method was successfully applied to the assessment of the long-term creep behaviour of different thermoplastic polymers such as PP, PE-HD, PET and PVDF. The results obtained were compared with results of the SIM using tensile testing and the short-term creep test using the depth-sensing macrohardness testing system.

Chitin was prepared from prawn shells waste by chemical treatments viz. demineralization, deproteinization and decolorization. Chitosan was prepared by deacetylation of chitin with 50% NaOH at 100 °C in the presence of nitrogen. Deacetylation was performed at different intervals of time to get a series of chitosans having different degrees of deacetylation. Prepared chitosans were characterized by molecular weight determination, degree of deacetylation, Fourier transform infrared (FTIR) spectroscopy and Scanning electron micrography (SEM). The degree of deacetylation of chitosans was calculated by acid base titration and potentiometric titration. The molecular weights of commercial and prepared chitosan (CS-4.0) samples were determined using the Mark- Houwink equation and were found to be 3.5 × 105 (g/mole) and 3.3 × 104 (g/mole), respectively. The degree of deacetylation was found to linearly increase with the increase of reaction time. FTIR spectra showed the characteristic peaks of chitin and chitosan. Antimicrobial screening results revealed that the prepared chitosan (CS-4.0) was equally or more biologically active than the commercial chitosan.

Conventional test procedures, such as the S4 test to analyze the resistance against rapid crack propagation (RCP) of plastic pipe materials are characterized by usage of a lot of material, are far from saving of time and they are-in need of special experimental set-ups. Therefore, in the last decade, small-scale accelerated reliable tests (SMART) are developed - worldwide to overcome the disadvantage of such conventional tests. In this paper fracture mechanics based analysis of instrumented Charpy impact test data for a set of bimodal high-density polyethylene pipe grades are compared with data of the conventional Charpy impact test. From this comparison the Charpy impact strength at −30°C comes forth as a robust reproducible measure of the resistance to RCP and it is therefore proposed as a SMART method to rank materials with respect to RCP resistance. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers

The selective wetting behavior of silica in emulsion styrene butadiene rubber (ESBR)/solution styrene butadiene rubber (SSBR) blends is characterized by the wetting concept, which is further developed for filled blends based on miscible rubbers. It is found that not only the chemical rubber–filler affinity but also the topology of the filler surface significantly influences the selective filler wetting in rubber blends. The nanopore structure of the silica surface has been recognized as the main reason for the difference in the wetting behavior of the branched ESBR molecules and linear SSBR molecules. However, the effect of nanopore structure becomes more significant in the presence of silane. It is discussed that the adsorption of silane on silica surface constricts the nanopore to some extent that hinders effectively the space filling of the nanopores by the branched ESBR molecules but not by the linear SSBR molecules. As a result, in silanized ESBR/SSBR blends the dominant wetting of silica surface by the tightly bonded layer of SSBR molecules causes a low-energy dissipation in the rubber–filler interphase. That imparts the low rolling resistance to the blends similar to that of a silica-filled SSBR compound, while the ESBR-rich matrix warrants the good tensile behavior, i.e., good abrasion and wear resistance of the blends.

The main aim of the paper is to study the influence of both material inhomogeneity and weld bead geometry on crack propagation in welded polyolefin pipes. Axially and circumferentially oriented cracks are studied and the stress intensity factors are compared considering different positions of the cracks. Two cases of the welded pipe system are compared, one considering the optimal weld bead geometry and the other one considering the geometry after removing the weld bead once the welding process is finished. In both cases the inhomogeneous distribution of material properties inside the welded region is considered. The results show that the weld might have a negative effect on the lifetime especially when the weld bead is removed. Though the weld bead increases the stress concentration near the notches due to which a circumferential crack may appear the resulting lifetime is still comparable to that of an axial crack propagating in a homogeneous pipe. Keywords: Slow crack growth, Butt weld, Lifetime estimation, Polyolefin pipes, Weld bead

The qualitative and quantitative assessment of the aging behavior of polymers and polymeric products depends on a substantial characterization of the materials properties and is linked to a multi-parametric approach. However, the choice of suitable polymer diagnostics test methods as well as parameters for the characterization of the material behavior are important. The aging of products can be attributed to complex factors and due to the superposition of different factors, the generation of simple relationships is impossible. Important materials for the automotive industry are fiber-reinforced PA6 materials, which can fulfill the requirements related to the mechanical properties like stiffness, strength, toughness as well as other properties. However, the knowledge for the assessment of different climate conditions as well as media on the aging behavior of such materials is not complete. For this reason, it is essential to describe the behavior with a material-physical approach.

Polymeric stretch films are wrapped around a packaging unit to keep it bundled and safe for transportation and storage. To maintain the generated retention forces and prevent a peel-off of the film, adhesive interactions between the film layers are required. Fracture mechanics investigations have been done in order to characterise the autohesive (cling) properties of the linear low density polyethylene/α-olefin copolymer based stretch wrap films. Resistance against initiation and stable peel front propagation across the interface of the cold-welded peel films are supposed to indicate detailed adhesive interactions. Next to the energy release rate G IC that considers all kind of deformations during the peel process, the adhesive energy release rate G aIC was determined using the standard peel cling test for polymeric stretch films according to ASTM D 5458. As a function of the peeling angle, an independence of G aIC between 10° and 90° could be observed for the investigated stretch films. The crack resistance curve concept was applied and crack initiation values could be determined next to stable crack propagation. The results might indicate multiple adhesive interactions due to the surface morphology and viscoelastic behaviour of the investigated films. In accordance to the calculated crack initiation, a physical crack initiation could be observed.

The aim of this study was to develop new opportunities to measure crack resistance curves at conditions of high ductility of reinforced polyamide 6 (PA6) compounds with high glass fibre content. The addition of toughening modifiers in glass fibre-reinforced compounds, the hygroscopic behaviour of polyamides as well as raised temperatures limit the validity range of conventional toughness evaluation with the experimental methods of linear elastic fracture mechanics and the J-integral method. The determination of J-crack resistance (R)-curves is necessary for a complete toughness evaluation. The fluorescence dyeing technique showed to be an efficient, accurate and reliable method to enhance the measurement of stable crack growth portions on roughly structured fracture surfaces. Within the study a fractional factorial statistical design of experiments was used to prove the reliability and accuracy of the method. Fluorescence microscopy has its definite advantages compared to light microscopy or scanning electron microscopy (SEM) especially when it is applied by use of a 3D digital microscope with depth from defocus which was used for the study. Finally additional information about the toughness behaviour of highly reinforced PA6 compounds with different amounts of elastomeric modifier could be revealed by means of the newly developed fluorescence adsorption-contrast method (3D-FAC method).

The acoustic emission (AE) analysis is a structure-sensitive test method of plastic diagnostics, which enables the characterisation of the damage kinetics as well as damage mechanisms under specific conditions. The AE analysis is linked to release of stored elastic energy, which propagates as spherical volume wave in the material. In this work, short-glass fibre-reinforced thermoplastic materials were examined in the quasi-static tensile test in the environmental scanning electron microscope (ESEM) with simultaneously recording of the AE as well as under impact-loading conditions in the instrumented Charpy impact test (ICIT). Therefore, it was possible to couple the mechanical, the acoustic and the micromechanical results to describe the damage kinetic as well as the damage mechanisms. In dependence on the bonding conditions of the glass fibre in the polymer matrix, different mechanisms of damage to be related to typical frequency ranges can be detected: (i) fibre fracture, (ii) matrix deformation with slipping of fibres in the delamination area and friction processes of the fibres in the matrix, (iii) debonding and pull-out with/without matrix yielding. The coupling of the AE analysis with the ICIT allows the assessment of the damage kinetic and therefore, the determination of the damage initiation under impact-loading conditions. However, in dependence on various bonding conditions, different results could be found. For good bonding conditions, the damage initiation takes placed before the material behaviour changes from elastic to elastic–plastic behaviour. This could be found for the short-glass fibre-reinforced high-density polyethylene materials. For the fibre-reinforced polybutene materials, the first AE takes place at the point of elastic–plastic material behaviour. An energetic approach of the damage initiation by the parameter J Si shows an independent behaviour from the polymer matrix as well as from the glass fibre content. For all investigated thermoplastics, a J Si-value of 0.8 N/mm as resistance against stable crack propagation could be determined.

During the reported project work, ca. 200 different SSBR and SSBR/BR vulcanisates were produced and investigated. During compounding, for each mixture, various processing-related parameters were recorded. Afterwards, the vulcanisation behaviour was characterised by using vulcametry and the last step was to quantify the mechanical and fracture mechanical properties by selected methods. The general aim was to optimise the material properties regarding a possible application in car tires. Mainly, the type of polymer, type and content of filler as well as the surface modification of the used alternative filler TROVO®powder were varied to get a preferably balanced property level. It could be stated that the different main components of the rubber mixture (polymer, filler, coupling agent) have a large influence on the physical properties. Basing on the results, most promising combinations of polymer and filler were defined and further investigated. It was found that the silica filler can be replaced by maximal 10 phr TROVO®powder BK3 without loss in application-related properties or to get an increase in properties, respectively. From the processing-related properties, it could be concluded that due to the reduced polymer filler interaction, the processing requires less energy to get a homogeneous mixture. This can be an advantage. Further, for some application-related properties such as tear strength, an increase due to the substitution of small amounts of silica by TROVO®powder BK3 was observed. This means, TROVO®powder BK3 can contribute to an enhancement of the processing behaviour. Due to the large particle size and the low specific surface area, only small amount of polymer–filler interaction as a basis of reinforcement can be expected. However, the surface modification of TROVO®powder with silane or zinc for example is an elegant way, to transport critical substances into the mixture and distribute them very well.

The overall stable crack initiation and propagation behaviour of fracture mechanics specimens cut from plastic pipes that were composed of different polyolefin materials were investigated using concepts of elastic–plastic fracture mechanics including the crack propagation kinetics. The effect of specimen shape, orientation, welding and lading rate on the crack resistance (R) behaviour of these materials has been thereby assessed. It was found in principle that specimen shape, orientation and welding have an influence indeed but only an unexpected small one on crack initiation behaviour and, particularly, on crack propagation behaviour. The crack initiation toughness is not sensitive to the orientation in most cases. In contrast, the crack propagation toughness is significantly affected by the orientation where the values for crack propagation in extrusion direction are larger than ones for crack propagation crosswise to that. This confirms that the morphology affects the stable crack propagation behaviour more than the stable crack initiation behaviour. In agreement with results of the microindentation test, fracture mechanics investigations also show that a lower welding pressure and a larger welding temperature, respectively, have no or a positive effect on the mechanical and fracture mechanics properties, whereas a larger pressure and a lower temperature, respectively, result in deterioration of the performance of the welded joint. Furthermore, the R-curve behaviour was investigated using specimens cut from bilayer pipe segments. It has been shown that an additional layer has a clear impact on the R-curve behaviour compared to the crack propagation in single-layer pipes, which can be explained thereby that the plastic constraint was affected by this additional layer. For clarification of the toughness-in- or -decreasing effect of an additional layer (with differing mechanical characteristics) on the layer where the crack was growing, R-curve ratios were introduced, that showed that the asymmetric mechanical properties of different layers were directly reflected in an asymmetric impact on the stable crack initiation and propagation behaviour.

The present article gives a comparison of the peel behaviour of the adhesive peel system ethylene vinyl acetate copolymer/polyethylene (EVA/PE) and the cohesive peel system low-density polyethylene/isotactic polybutene-1 (LDPE/iPB-1) using the fracture mechanics values energy release rate G Ic and adhesive energy release rate G aIc. The influence of the content of the peel component and the influence of the peel angle on the peel behaviour was investigated. In case of the adhesive peel system, an independence of the adhesive energy release rate on the peel angle was found. In case of the cohesive peel system, two zones of G aIc could be identified, (1) G aIc is independent of the peel angle and (2) G aIc depends linearly on the peel angle. This difference in G aIc could be strongly addressed to the type of crack propagation. In general the results revealed that fracture mechanics values like G Ic and G aIc can be used to get further and deeper structure-sensitive information of the investigated material system.

Short-glass fibre-reinforced polyamide 6 (PA6/GF) materials have been used for many decades successfully in the automotive industry, especially for components in exterior and interior area. Due to the required product qualification testing in the automotive field, components are exposed to, among others, a hygrothermal stress of 1000 h or more during the development phase. This work aims to contribute to enhanced understanding of the mechanical properties of stiffness, tensile strength, hardness and fracture toughness of short-glass fibre-reinforced polyamide 6 materials at hygrothermal aging. The results show a decrease in properties, which is more characterised by the absorption of moisture and less than by other aging processes.

Summary Chitosan was prepared from shells of locally available fresh water prawns with variation of sodium hydroxide concentration and reaction time. The biopolymer was melt-mixed with a commercially available biodegradable polymer, the poly(butylene adipate-co-terephthalate) (PBAT). The chitosan and blend films were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The glass transition temperature (Tg) and melting point of the materials remained unchanged implying complete incompatibility of the blend components. Kinetic study showed that activation energy of the degradation process, i.e., thermal stability of the blends, decreased with increasing chitosan content in the blends. As the thermal properties of all the samples were found to be identical, it can be concluded that there was no effect of the added chitosan on the crystallization and melting behavior of the PBAT. These findings support the notion of the absence of interactions among the blend components. The rate of biodegradation was found to be higher in blends compared to pure PBAT polymer.