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In this paper the viscoelastic behavior of different soft adhesives with substantially similar adhesive performance is analyzed in the light of a Slip-Tube Model. In this model, the junction points between network chains and virtual chains are replaced by slip-links attached to fluctuating ends of virtual chains. The slip-links are allowed to slide along the contour of the network chains but not pass through each other. The predictions of the slip-tube model are in excellent agreement with the experimental data on uniaxial deformation of soft adhesive networks. Furthermore, the study shows that some adhesive performances can be described qualitatively by Small Amplitude Oscillatory Shear (SAOS), and the in-service properties can be described with adhesives with different viscoelastic spectra. Highly nonlinear uniaxial stretching tests reveal deeper insights into the description of the adhesives performances. Some well-established models are adopted and slightly modified by introducing the rate-dependence of their physical parameters to describe the response of soft adhesive to stretching.

A new method for calculating the retardation spectra for linear viscoelastic materials is presented. The method uses the analytical expressions among the viscoelastic functions through the numerical evaluation of the Inverse Laplace Transform (ILT) with the Gaver–Wynn–Rho (GWR) algorithm. It is applied to study three polymers' relaxation mechanisms: a star Polystyrene and two Polycyanurate networks with two different crosslink densities. The shear spectrum is de-convoluted to separate the segmental and the chain modes responsible for the softening dispersion. The retardation mechanisms extracted from the shear response are then compared with the volumetric bulk response. The results show that the shear segmental contribution is narrower than the volumetric bulk response and finishes about two decades before the shoulder's appearance in the shear retardation spectrum. Thus, the volumetric bulk response, mainly exerted by the segmental mode, is also affected at long times by the short time chain mechanism, usually claimed to be Sub-Rouse modes.

In this work the effect of melt mixing condition and of a trans-esterification catalyst on miscibility of poly(methyl methacrylate) (PMMA)/polycarbonate of bisphenol A (PC) blends is studied. In particular, at high temperature chemical reactions between PMMA and PC phases can take place; these strongly change the compatibility in the blend and materials having single Tg can be obtained. FT-IR analyses, coupled with solvent extraction, suggest that a grafting reaction of PC on PMMA is involved. SEC and DSC data are consistent with spectroscopic results, and some decrement of the molar weight distribution (MWD) of PC phase is observed. On the other hand, the presence of a fraction of modified material having higher MWD of starting PMMA is also noticed. The single Tg characteristic of some materials has been confirmed by experimental data of structural relaxation performed by differential scanning calorimetry (DSC). These materials showed optical clarity and the morphological analysis performed by scanning electron microscopy (SEM) confirm the homogeneity of these materials.

The principal features of the volumetric as well as the viscoelastic response of mechanically stimulated glasses can be summarized as follows: i) the time-aging time shift factors contract upon increasing the probe stress (i.e. the stress apparently modifies the volume recovery kinetics), ii) the volume recovery baseline remains unaltered (i.e. the underlying structure of the stimulated glass remains unchanged) iii) yielding scales linearly with the logarithmic of the strain rate. Here we present a review of the above features with aid of a series of numerically simulated results concerning the responses of glassy polycarbonate. Simulations are obtained coupling a modified KAHR equation with the constitutive law for linear viscoelasticity within the domain of the reduced time. It will be shown that by using a minimum of experimental (PVT and linear viscoelastic) data inputs even the subtle intricacies can be predicted. Furthermore a new class of results concerning the stress-strain behaviour of glassy polymers is presented that never appeared before.

The origin of internal stresses in a polymeric component, subjected to an arbitrary cooling, will be described. The differential volume relaxation arising as a result of the different thermal history suffered by each body point was considered as the primary source of stresses build up. A numerical routine was developed accounting for the simultaneous stress relaxation processes and implemented within an Ansys® environment. The volume relaxation kinetics was modelled by using the four-parameter TNM (Tool-Narayanaswamy-Moynihan) phenomenological theory using the PVT (Pressure-Volume-Temperature) data obtained on a polystyrene sample. The numerical algorithm translates the specific volume theoretical predictions at each body point as applied non-mechanical loads acting on the component. Thermorheological complexity emerged due to coupling of volume and stress relaxation phenomena. A linear dependence of Poisson's ratio on the tensile relaxation modulus was postulated. A quantitative predictions of time dependent stress distribution was realized for two specific test cases.

Linear and cross-linked polymers capable of responding to both temperature and pH changes were synthesized by radical copolymerization of N-isopropylacrylamide (NIPAAm) and N-methacryloyl-L-leucine (MALEU) in different NIPAAm/MALEU molar ratios. The solution behavior of linear polymers was investigated in 0.1 M NaCl and in citrate buffers pH 4.0, 4.5. 5.0 and 6.0. A sharp increase in the cloud point temperature (T CP ) was observed to occur around pH 4-5, Hydrogels were synthesized employing N,N'-methylenebisacrylamide as cross-linking agent. The influence of composition and degree of cross-linking on water absorption was investigated in 0.1 M NaCl and in citrate buffers pH 4.0 and 5.0. A reversible phase transition within a wide range of temperatures, depending on the composition and the pH, in accordance with the behavior of linear polymers, was observed.

Tension-tension fatigue tests were conducted on unnotched injection moulded poly(phenylene ether ketone) (PEK-C) specimens with two stress ratios, R. The fatigue behaviour of this material is described. The S-N curves (S = alternating stress, N = number of cycles to failure) for different R values have the same general shape, but the curve for bigger R is shifted to long cycles. A fatigue lifetime inversion is observed from constructed S-N curves. Examinations of failure surfaces and analyses of the fatigue data reveal that the fatigue failure mechanism of the material studied is crack growth dominated. But the manner of the fatigue crack initiation and propagation depends on the maximum cyclic stress applied. At higher stresses, the fatigue crack originates at the corner of the specimen and propagates inward; at lower stresses, the fatigue crack nucleates at an internal flaw of the specimen and propagates outward. The fatigue lifetime inversion corresponds to the transition of crack initiation and propagation from one mode to the other.

The density evolution of a semi-crystalline Poly(lactic acid) under ultra/high pressure histories in the region of alpha relaxation has been studied. It was found that the degree of crystallinity does not change in the temperature and pressure ranges under concern and consequently it is assumed that the volume relaxation kinetics involves only the amorphous part of the polymer. The scaling law for relaxation times, recently proposed by Casalini and Roland, has been utilized in the framework of KAHR (Kovacs Aklonis Hutchinson and Ramos) phenomenological theory in order to model the volume relaxation behavior. With this approach the model contains only two fitting parameters, (namely the relaxation time in the reference state, τg, and the fractional exponent, β, that describes the dispersion of the alpha relaxation) instead of the five parameters of the classical KAHR theory. The model predicts accurately both the density evolution of the PLA during the sterilization and Pasteurization treatments simulated in a pressure dilatometer and the density changes occurring in the PLA films utilized as packaging material in the HP industrial processes.

Diglycidyl terminated 4,4′-oxydiphenyl cured with an aromatic diamine exhibits liquid crystalline properties, even if the amount of hardener is used in defect with respect to the stoichiometric amount. Physical properties of the resin, hardened with different quantities of amine are presented and discussed. In particular the high values of fracture toughness of this class of thermoset has been explained on the basis of the biphasic nature of the crosslinked resin.The differences in mechanical properties are analyzed taking into account the different crosslink densities.

Non-equilibrium glasses, including polymer glasses, spontaneously tend to approach the equilibrium state. The time-dependent phenomena occurring in glassy polymers below the glass transition are commonly referred to as physical aging. Since the physical aging results primarily in a volume relaxation (or densification), our efforts have been focused on the measurements of the time-dependent behavior of the specific volume. The dependence of the storage and loss moduli upon aging have been related to the progressive loss of mobility associated with the volume relaxation. A Williams-Watts type equation has been adopted to model the volume relaxation data at different temperatures, and a numerical procedure has been developed in order to predict the kinetics of volume relaxation subjected to complex thermal histories.

In this paper the source of non linearity in amorphous materials will be analyzed and verified with phenomenological approaches. A series of simulated results, replicating the relevant experimental data presented in literature along the years, will be reported.

Macrocyclic oligomers (MCOs) of some commercial alkyl aromatic polyesters (PET, PTT, PBT) were prepared by cyclo‐depolymerization (CDP) of the polymers in refluxing 1, 2‐dichlorobenzene with di‐n‐butyltin oxide as a transesterification catalyst. The mixtures of MCOs and residual polymer obtained at varying polymer/solvent ratios were separated and characterized by thorough GPC and DSC analyses. The higher the initial polymer concentration the lower was the yield of MCOs, and vice versa. Rheological measurements carried out on polymer/MCO mixtures showed a decrease in the melt viscosity with increasing amount of MCOs. Moreover, the MCOs present in these systems easily underwent entropically‐driven ring‐opening polymerizations (ED‐ROPs) to reform the parent polyesters.

A kinetic model for lifetime prediction of polyethylene pipes transporting pressurized water disinfected by chlorine dioxide (DOC) has been elaborated. This model is composed of three sub‐models:—A system of differential equations, derived from a realistic mechanistic scheme for radical chain oxidation in the presence of DOC of stabilized polyethylene (PE), giving access to the spatial distribution of structural changes in the pipe wall and its evolution against time of exposure;—The classical Saito’s equation to predict the profiles of average molar masses from the spatial distribution of chain scissions and crosslinking events;—An empirical creep equation and an empirical fracture criterion derived from regression curves obtained in pure water. It is assumed that chemical degradation modifies only the time to transition tc between ductile and brittle regimes of failure, and that tc is linked to the weight average molar mass by a power law.By combining these three sub‐models, it is possible to predict th...

Methacrylate‐terminated Poly (1,3dioxolane) (PDXL) macromonomers were synthesized by cationic ring‐opening polymerization in the presence of 2‐hydroxypropyl methacrylate (2‐HPMA) as transfer agent. Molecular weights and polydispersity index of the PDXL macromonomers were evaluated by size exclusion chromatography (SEC) and 1H‐NMR. Copolymerizations of PDXL macromonomers with styrene (St) and methyl methacrylate (MMA) were carried out using various feed molar ratios. Monomer reactivity ratios between the macromonomers and the comonomers were estimated from the copolymerization results. Glass transition temperatures of the copolymers were found to decrease with an increase in the amount of PDXL in the copolymers.

The development of synthetic biodegradable polymers, such as poly(lactic acid), is particularly important for constructing medical devices, controlled drug release matrix, including scaffolds and sutures, and has attracted growing interest in the biomedical field. Here, we report a novel approach to preparing poly (D, L‐lactic acid) (PDLA) as a biodegradable polymer. We investigated in detail the reaction conditions for the simple direct polycondensation of D, L‐lactic acid, including the reaction times, temperatures, and catalyst. The molecular weight of synthesized PDLA is dependent on both the reaction temperature, amount of catalyst and time. The optimum reaction condition to obtain PDLA by direct polycondensation using Maghnite‐H+[1,2], a proton exchanged Montmorillonite clay, as catalyst was thus determined to be 120 °C, 5% amount of Maghnite‐H+ for 28 h with a molecular weight of 7970. The method for PDLA synthesis established here will facilitate production of PDLA of various molecular weights, wh...

Plastics depend strongly on underground resources such as petroleum. To produce novel wood materials as a substitute for plastics, the fine structure of wood impregnated with various organic solvents—ethylene glycol(EG), tri‐ethylene glycol, dimethyl folmamyde(DMF), dimethyl sulfoxide(DMSO)—was examined. The dynamic Young’s modulus and tanδ—frequency curves of every sample indicated that the relaxation process due to the glass transition of lignin in wood exists. To obtain basic data about the processes, the apparent activation energies (ΔE) were examined. The values of ΔE of the sample impregnated with water and EG were higher than that with DMSO and DMF. These results may not only be due to the hydrogen bonding per volume, but also the confined effect in wood. In fact, the CP/MAS spectra of EG—Wood sample indicates the existence of slow movement EG at higher temperatures of the melting point.

The development of synthetic biodegradable polymers, such as poly(α‐hydroxy acid), is particularly important for constructing medical devices, drug delivery systems, including scaffolds and sutures, and has attracted growing interest in the biomedical field. Here, we report a novel approach to preparing poly(D, L‐lactic acid) (PDLA) as a biodegradable polymer. We investigated in detail the reaction conditions for the simple direct polycondensation of lactic acid, including the reaction times, temperatures, and catalyst. The molecular weight of synthesized PLA is dependent on both the reaction temperature and time. The optimum reaction condition to obtain PDLA by direct polycondensation using Maghnite‐H+, a proton exchanged Montmorillonite clay, as catalyst was thus determined to be 120 °C for 28h with a molecular weight of 7970.The method for PDLA synthesis established here will facilitate production of PDLA of various molecular weights, which may have a potential utility as biomaterials.

With the aim to investigate the influence of slight differences in the chemical structure of a family of polymers on the response of these to electric perturbation fields, the relaxation behavior of three dimethoxy phenyl isomers of poly(benzyl methacrylate) have been studied.

Hyperbranched polymers are highly cascade branched polymers easily accessible via one‐pot procedure from ABm type monomers. A key property of hyperbranched polymers is their molecular architecture, which allows core‐shell morphology to be manipulated for further specific applications in material and medical sciences. Since the discovery of hyperbranched polymer materials, an increasing number of reports have been published describing synthetic procedures and technological applications of such materials, but their physical properties have remained less studied until the last decade.In the present work, different esterified hyperbranched polyglycerols have been prepared starting from polyglycerol precursors in presence of acetic acid, thus generating functionalization degree with range from 0 to 94%. Thermal analysis of the obtained samples has been studied by Differential Scanning Calorimetry (DSC). Dielectric Spectroscopy measurements have been analyzed by combining loss spectra deconvolution with the mod...

Researches involving ecofriendliness materials are growing up, as well as, a current interest in developing materials from inexpensive and renewable resources. Vegetable oils show a number of excellent properties, which could be utilized to produce valuable polymeric materials. In this work is described the synthesis of polymeric materials from linseed oil (Linum usitatissimum L.) and passion fruit oil (Passiflora edulis) and their characterization by thermogravimetry (TG), differential scanning calorimetry (DSC) and Raman spectroscopy. The TG curve shows that those polymeric materials present two stages of decomposition. DSC plots of the vegetable oils showed some endothermic and exothermic transitions which are not present in the DSC curves corresponding to oil‐based polymers. The Raman spectra of the polymers indicate declining of absorbance in the region of C = C stretching (∼1600 cm−1). This absorption was used to estimate the degree of polymerization (79% and 67.5% for linseed and passion fruit oils...

The most popular and important biodegradable polymers are aliphatic polyesters, such as polylactic acid (PLA), polyglycolic acid (PGA), polycaprolactone (PCL), polyhydoxyalkanoates (PHA’s) and polyethylene oxide (PEO). However, each of these has some shortcomings which restrict its applications. Blending techniques are an extremely promising approach which can improve or tune the original properties of the polymers[1]. Aliphatic polyesters are a central class of biodegradable polymers, because hydrolytic and/or enzymatic chain cleavage of these materials leads to α‐hydroxyacids, which in most cases are ultimately metabolized in human body. This is particularly useful for controlled release devices and for other biomedical applications like suture fibers and ligaments. For aliphatic polyesters, hydrolysis rates are affected by the temperature, molecular structure, and ester group density as well as by the species of enzyme used. The degree of crystallinity may be a crucial factor, since enzymes attack main...

Mass transport mechanism of low molecular weight compounds (water and carbon dioxide) into polyimide films has been analysed and modelled on the basis of the relevant findings of an in situ FTIR spectroscopic analysis. In particular, in the case of water, it has been assumed that concurrent diffusion occurs of single water molecules and water dimers, which display different mobilities. A non‐linear instantaneous equilibrium between the local concentrations of these two species has been imposed, based on a two layers BET theory. The proposed approach is able to give a good qualitative and quantitative interpretation of both sorption equilibrium and of sorption/desorption kinetics data.

The behavior of the wing of an aircraft is characterized by the complex interaction among dynamic (distribution of the masses), elastic (ownership of the materials) and aerodynamic (shapes, forces and moments) phenomena. As a rule it is expected from us that the aerodynamic actions damp the oscillations (natural or forced) of the wing. However, above given speeds a lot of undesired aero-elastic phenomena, among which the divergence of the wings, occur and became of considerable importance in view of safety. To potentially prevent dangerous situations, generally the speed of the aircraft is limited; a possible alternative is to endow the “system wing” of proper devices (passive or active, i.e. controls) in order to prevent that the energy transfer of aerodynamic actions amplifies its instability. The forward swept wings are extremely efficient in terms of aerodynamics performance (stall and supersonic behavior) and therefore of maneuverability of the aircraft, even if, unfortunately, they are extremely critic under the profile of the aero-elastic stability. The solution of the technical-scientific and technological problems associated with the use of innovative configurations of wings prefigures a meaningful breakthrough in the international aerospace sector. Within this work the authors aim to determine a particular configuration of composite material for the realization of a forward swept wing in such a way that, under the action of the effective aerodynamic loads, the wings structural response provides a coupled bending-torsion deformations with stability effects. It will be shown that by using a recursive analysis of the composite lay-up one can tailor the overall bending/torsion deformation ratio value.

Organic-inorganic hybrid materials with excellent heavy metal ions chelating properties are synthesized by covalent bonding of multifunctional polymers of polyamidoamine (PAA) type onto silica. Two series of polyamidoamine-silica hybrid materials differing in the PAA chemical structure are prepared and their thermal properties are investigated. Differential Scanning Calorimetry (DSC) is used to study the effects of chain immobilization and ion chelation on the glass-transition temperature (Tg) of the polymers. The Tg of PAA-hybrid materials is elevated with respect to ungrafted PAAs, but when the linear and the corresponding hybrid PAAs are in the complex form with metal ions such as Cu2+ and Co2+, the materials arrive to the decomposition temperature and no Tg is detected. To highlight the effect of metal ion on the molecular mobility of these systems, an oligomeric plasticizer is added. The behaviour in the Tg region is analyzed and discussed in term of Tool-Narayanaswamy-Moynihan (TNM) model. In particular the apparent activation energy (Δh*) is used to discuss overall segmental co-operativity in order to better understand the effect of complex formation on structural mobility.

Statistical copolycarbonates containing different bisphenol A/tetramethyl bisphenol A (BPA/TMBPA) molar ratios were synthesized by polycondensation reaction between a mixture of the two bisphenols and phosgene. The reaction conditions were selected for producing polymers having comparable molecular weights (M n ≃ 9000 g/mol) but different composition, and the same composition but different molecular weights. The calorimetric properties of the products were investigated by differential scanning calorimetry (DSC) and dynamical-mechanical thermal analysis (DMTA). In particular, the effect of the copolymers molecular characteristics on the glass transition temperature (Tg) and the related relaxation processes were studied. DMTA was employed for evaluating the effect of macromolecular structure on the γ low temperature relaxation peak.

Mass-variation measurements were carried out on carbon black (CB)-poly(vinyl chloride) (PVC) composite film with 40% by weight of di(2-ethylhexyl)-phthalate (DOP), cast on resonant piezo-layer (RPL) elements of lead zirconat titanate (PZT). Even if anomalous diffusion is predicted by fitting the data with M t /M∞=kt α , the fractional uptake M t /M∞ is linear with the square root of the time up to M t /M∞=0.6, suggesting Fickian behavour. The anomalous values of a are probably due to experimental time lag. A dependence of the diffusion on the morphology of the material and the penetrant shape and flexibility has been found.

Binary blends based on poly(vinyl chloride) (PVC) were prepared both by casting from tetrahydrofuran (THF) and by mixing in the melt form, in a discontinuous mixer, PVC and multi-block copolymers containing poly(e-caprolactone) (PCDT) and poly(ethylene glycol) (PEG) segments. PCDT-PEG copolymers were synthesized using a polycondensation reaction where the α,ω-bis-chloroformate of an oligomeric poly(e-caprolactone) diol terminated (PCDT) and oligomeric PEG were employed as macromonomers. For comparison purposes, blends PVC with starting oligomers as well as with mixtures containing a typical low molecular plasticizer, dioctylphthalate (DOP), were also prepared. The copolymer miscibility was studied by differential scanning calorimetry (DSC) and FT-IR spectroscopy. The blend morphology was investigated by polarized light microscopy (PLM). A higher miscibility with PVC was observed for copolymers compared to PEG.

Thermodegradative investigations of two classes of multi-block copolymers containing poly(D,L-lactic-glycolic acid) (PLGA) and either poly(ethylene glycol) (PEG) or poly(e-caprolactone) diol-terminated (PCDT) segments were performed. In particular, the influence of the type and length of the segments as well as of the molar ratio between the D,L-lactic acid (LA) and glycolic acid (GA) residues was investigated at 180°C in air by viscometry, FT-IR analysis and isothermal thermogravimetry. The thermal oxidative degradation of these materials is largely affected by the LA/GA ratio, a higher LA content generally imparting higher stability. The FT-IR analysis suggests that, depending on the composition of the PLGA segments, degradative processes are triggered which can lead to a preferential degradation of the blocks.

Polymers capable of responding to both temperature and pH changes were synthesised by radical copolymerisation of N-isopropylacrylamide (NIPAAm) and N-methacryloyl- l -leucine (MALEU) in different NIPAAm/MALEU molar ratios (15:1, 10:1, 2:1 and 1:1). The polymers were characterised by Size Exclusion Chromatography, acid–base titrations, FT-IR and 1H-NMR analyses. Their solution behaviour was studied in 0.1 M NaCl and in citrate buffers (pH 4.0, 4.5, 5.0 and 6.0). At pH 4.0 and 4.5 the cloud point temperature (TCP) of copolymers was depressed proportionally to their MALEU content. In contrast, at pH 5.0 and 6.0 the phase transition temperature increased linearly. The behaviour of the copolymers with NIPAAm/MALEU ratios 15:1 and 10:1 was investigated also between pH 3 and 11 in 0.1 M NaCl. In both cases a sharp increase in TCP was observed around pH 4–5. The TCP vs. pH curve was linearised and the acidity constants were determined by the linearisation procedure. Furthermore, it was possible to demonstrate that the phase transition temperature increases linearly with the ionic content of the polymers.

The loss of orientation is a much more rapid phenomenon than the thermal shrinkage of drawn polystyrene, as shown by birefringence and FTIR measurements. The properties imparted by the orientation can be lost before the complete shrinkage occurs. The implications of this fact are discussed.