Improving oxygen barrier properties of poly(ethylene terephthalate) by incorporating isophthalate. I. Effect of orientation

The present study examined poly(ethylene terephthalate) (PET) and a series of statistical and blocky copolymers in which up to 30% of the terephthalate was replaced with isophthalate by copolymerization and melt blending, respectively. Some level of transesterification during processing of melt blends resulted in blocky copolymers, as confirmed by NMR. Random and blocky copolymers exhibited similar properties in the glassy state, including a single glass transition, due to miscibility of the blocks. However, random copolymerization effectively retarded cold‐crystallization from the glass whereas blocky copolymers readily cold‐crystallized to a crystallinity level close to that of PET. The polymers were oriented at four temperatures in the vicinity of the T_g and characterized by oxygen transport, wide‐angle X‐ray diffraction, positron annihilation lifetime spectroscopy, and infrared spectroscopy. Orientation of all the copolymers resulted in property changes consistent with strain‐induced crystallization. However, blocky copolymers oriented more easily than random copolymers of the same composition and after orientation exhibited slightly lower oxygen permeability, higher density, and higher fraction trans conformers. Analysis of oxygen solubility based on free volume concepts led to a two‐phase model from which the amount of crystallinity and the amorphous phase density were extracted. Dedensification of the amorphous phase correlated with the draw temperature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1615–1628, 2005     

Sequence analysis and fiber properties of a blend of poly(ethylene terephthalate) and poly(ethylene terephthalate‐co‐4,4′‐bibenzoate)

Blends of poly(ethylene terephthalate) (PET) and poly(ethylene terephthalate‐co‐4,4′‐ bibenzoate) (PETBB) are prepared by coextrusion. Analysis by ¹³C‐NMR spectroscopy shows that little transesterification occurs during the blending process. Additional heat treatment of the blend leads to more transesterification and a corresponding increase in the degree of randomness, R. Analysis by differential scanning calorimetry shows that the as‐extruded blend is semicrystalline, unlike PETBB15, a random copolymer with the same composition as the non‐ random blend. Additional heat treatment of the blend leads to a decrease in the melting point, T_m, and an increase in glass transition temperature, T_g. The T_m and T_g of the blend reach minimum and maximum values, respectively, after 15 min at 270°C, at which point the blend has not been fully randomized. The blend has a lower crystallization rate than PET and PETBB55 (a copolymer containing 55 mol % bibenzoate). The PET/PETBB55 (70/30 w/w) blend shows a secondary endothermic peak at 15°C above an isothermal crystallization temperature. The secondary peak was confirmed to be the melting of small and/or imperfect crystals resulting from secondary crystallization. The blend exhibits the crystal structure of PET. Tensile properties of the fibers prepared from the blend are comparable to those of PET fiber, whereas PETBB55 fibers display higher performance. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1793–1803, 2004     

Improving the mechanical properties of clay/polymer aerogels by a simple dip‐coating procedure

Clay aerogels have many advantages as one of the lowest density family of materials current technology can provide; they possess very low thermal conductivities, high porosities, and high surface areas. Although the mechanical properties of native clay aerogels are rather low, incorporating water‐dispersible polymers into the clay gel before they are processed into aerogel forms can easily produce more robust, low‐density composites. Various processing modifications and additives can be employed to strengthen the aerogel material, but currently, the materials have some notable weaknesses in abrasion resistance, water absorption, and flexural properties. In this study, we employed a low‐cost rubber coating material to quickly and efficiently address all three of these problems. After coating, the aerogels gained significant mechanical reinforcement, a 20‐fold increase in flexural modulus and a 15‐fold increase in yield stress, while exhibiting an increase of only 8% in the thermal conductivity. Improvements such as these can improve the commercial applicability of clay/polymer aerogels as thermal insulation materials. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Incorporation of postconsumer polyurethane foam into a polymer/clay aerogel matrix

The feasibility of incorporating ground recycled polyurethane (PU) foam into clay/polymer aerogels was demonstrated, and a range of compositions were prepared and characterized to determine the effect of variation in the formulations on density and mechanical properties of the resulting materials. This study followed a modified combinatorial approach. Initially, experiments were performed in water using either sodium exchanged montmorillonite or laponite clay, poly(vinyl alcohol) (PVOH) solution as the polymer binder, and the recycled PU foam. Freezing and freeze‐drying the aqueous gels produced aerogels, which were characterized through density and mechanical testing, scanning electron microscopy, and thermal gravimetric analysis. The study was expanded by exploring alternative binder chemistries, including the use of an alginate polymer in place of the PVOH or adding a polyisocyanate as a crosslinking agent for PVOH. The effect of recycled PU foam content, clay type and level, and binder type and level on the mechanical properties of the aerogels were determined and will be discussed herein. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42586.     

Improving the flame retardancy of polypropylene foam with piperazine pyrophosphate via multilayering coextrusion of film/foam composites

A series of 16-layer polypropylene/flame retardant (PP/FR) film/foam composite structures were produced by microlayer coextrusion. A highly branched PP was used in the foam layers to increase strain hardening and cell stability, while the PP used in the film layers was a high shear viscosity grade to confine bubble growth. In addition to improved tensile properties, the PP/FR composite film/foams exhibited five times the compression modulus of PP/FR composite foams at each FR loading level. The thermal stabilities of the composites were investigated, exhibiting three step decompositions. The FR particles were effective in decreasing flammability by forming intumescent char. The PP/FR-film/foam-20 showed self-extinguishing behavior in a modified vertical burn test, while the PP/FR-foam-20 sample continued to burn. Cone calorimetry demonstrated that PP/FR film/foams had lower heat release than PP/FR foams due to the unique alternating film/foam structure of PP/FR film/foams. Scanning electron microscopy imaging of the residual chars from fire testing that the PP/FR composite film/foams showed a more continuous protective char surface when compared with PP/FR composite foams at each FR concentration. The combined data indicate that the formation of a surface film on top of a foam ensures a robust intumescent fire protective barrier for partly foamed materials and shows a new way toward lightweight materials with improved fire safety performance. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48552.     

Thermo-rheological analysis of various chain extended recycled poly(ethylene terephthalate)

Three chain extenders, pyromellitic dianhydride (PMDA), ethylene carbonate (EC), and a polymeric-epoxide, were investigated for improving recycled p(ethylene terephthalate) (r-PET) properties with melt extrusion. The amount of additives and processing temperatures were also varied to check for melt degradation. Small amplitude oscillatory shear experiments were performed to probe rheological changes with different chain extenders. Capillary rheometry with haul-off was also performed to measure extensional viscosity and melt strength. Higher loadings of the chain extenders were found to improve properties of r-PET. These chain extenders definitely increased melt viscosities when incorporated at the higher level of the ranges examined, matching that of virgin PET. EC addition resulted in high shear thinning of the polymer. Epoxy and PMDA added to r-PET produced products with the same extensional viscosity as v-PET. Haul-off experiments demonstrate superior performance by epoxy-modified r-PET compared to v-PET.     

A new ionic conductor from AgI and Ag2O.B2O3

A room temperature conductivity maximum was recognized in the system AgI:Ag₂O.B₂O₃ at 78.8 mole% AgI, the mobile species being silver ions.X-rays diffraction and DTA showed the glass-like nature of this material which maintains its good electrochemical performances in the temperature range 25–230°. The discharge behaviour of solid state galvanic cells containing this material is close to that obtained from 4AgI:Ag₂WO₄.     

Tin fluorophosphate nonwovens by melt state centrifugal Forcespinning

This report describes the direct melt processing of inorganic tin fluorophosphate (TFP) glass fibers with average diameters ranging from 2 to 4 µm via centrifugal Forcespinning. This was accomplished by using a TFP glass with low glass transition temperature (T _g) and the melt processing capability of Forcespinning. The thermal behavior of TFP glass fibers was investigated by differential scanning calorimetry and thermogravimetric analysis, while the compositional evolution of the fibers was studied using energy-dispersive spectrometry and Fourier-transform infrared spectroscopy. These fibers exhibited excellent thermal stability after thermal post-treatment at 300 °C. The T _g of the thermally treated fibers increased by 100 °C compared to the bulk material. The fibers were found to undergo dehydration and loss of fluorine during thermal treatment, resulting in a rigid and crosslinked glass network with enhanced thermal stability and increased T _g. The enhanced thermal stability demonstrated the potential of TFP fibers for high temperature catalysis and chemical filtration applications.     

Structure and property study of nylon‐6/clay nanocomposite fiber

The crystal structures of nylon‐6 and nylon‐6/clay fibers were investigated on annealing and drawing. Annealing increased the γ‐crystalline form of both fibers, as indicated by the DSC curves, and its effect was dominant in nylon‐6/clay fiber. On drawing, the γ‐crystalline form was easily converted into the α form in nylon‐6, whereas it was still observed at a relatively high spin‐draw ratio in nylon‐6/clay fiber. However, although the α‐crystal form was dominant in nylon‐6, the γ‐crystal form was dominant in nylon‐6/clay with annealing and drawing, on the basis of the XRD data. The fast crystallization rate of nylon‐6/clay compared with pure nylon‐6 was confirmed, on the basis of the Avrami exponent. The initial modulus of nylon‐6/clay fiber was 30 % higher than the neat nylon‐6 fiber. The reinforcing effect of clay on the dynamic storage modulus was observed. Copyright © 2004 Society of Chemical Industry