The acid-catalyzed reaction of acetic anhydride with some oxocanes

Three cyclic polymers of formaldehyde, namely, trioxane, 1,3,5,7-tetraoxocane, and 1,3,5,7,9-pentaoxocane, were reacted with acetic anhydride containing a catalytic amount of sulfuric acid. The progress of each reaction was followed by GLC. The cyclic compounds increased in reactivity with increasing molecular weight. The first step in each reaction was a ring opening, which produced a poly(oxymethylene diacetate) containing the same number of formaldehyde units as in the original cyclic compound. The poly(oxymethylene diacetate) then reacted with additional acetic anhydride to produce diacetates containing a smaller number of formaldehyde units. By controlling the time of reaction, the higher or lower molecular weight diacetates were made to predominate in the reaction mixture. Zine chloride can be used in place of sulfuric acid as the catalyst for the conversion of oxocanes to poly(oxymethylene diacetates). The reaction with ZnCl₂ at room temperature is less vigorous and easier to control, yielding as the main product poly(oxymethylene diacetate) containing the same number of formaldehyde units as in the starting oxocane.     

Development of continuous die drawing production process for engineered polymer cores for wire ropes

Abstract

The process of continuous die drawing has been adapted as the means of production of polymer cores for wire ropes. The cores have a precisely engineered cross-sectional shape, which is produced by the die drawing process. In order to control this shape accurately, the drawing is carried out in two stages, first drawing in a heated circular conical die and secondly in a cooled fluted conical die. A production line has been developed, which produces core at commercially acceptable rates and with precisely controlled dimensional and mechanical properties. The polymer core serves as a replacement for the three strand cores made from natural fibres.     

Fabrication of reinforced and toughened poly(lactic acid)/poly(butylene adipate-co-terephthalate) composites through solid die drawing process

In this study, poly(butylene adipate-co-terephthalate) (PBAT) was introduced to poly(lactic acid) (PLA) matrix to improve its inherent poor toughness. Besides, the orientation structure was also introduced via die drawing process to compensate for strength loss. The results indicate that die drawing process contributes to improve the mechanical properties of PLA. The tensile strength, modulus, and elongation at break of die-drawn pure PLA increased by 76.6, 36.1, and 1,375.0%, respectively, compared with those of isotropic PLA. Moreover, the tensile strength can be further improved by the addition of PBAT. The die drawing process can remarkably improve crystallinity, and the orientation factor is high when the PBAT content is less than 30 wt%. By combining the PBAT with highly oriented structure imported by die drawing process, it is possible to prepare simultaneously reinforced and toughened materials, which provides a new insight into the modification of PLA.     

Drawing of polymers through a conical die

A new process is described in which ultra-oriented polymers are produced by drawing a billet of initially isotropic polymer through a converging die. The process, called die-drawing, has been used to make oriented polypropylene rods with room temperature Young's moduli up to 20.6 GPa. The considerable advantages of this process compared with conventional tensile drawing and hydrostatic or ram extrusion are discussed.     

Thermal and mechanical properties of oxymethylene linked polymers

A series of novel polymers has been prepared by linking together copolymers of oxyethylene and oxypropylene with an oxymethylene link. Oxymethylene linked (OML) polymers have been made by a step polymerization reaction. Three different OML polymers have been synthesized starting from three different short chain triblock (ABA) copolymers of poly(oxyethylene) (A) and poly(oxypropylene) (B). These polymers have been characterized by gel permeation chromatography, differential scanning calorimetric analysis and Fourier transform infrared spectroscopy. The mechanical properties of the cast films and the rheological properties of aqueous solutions of these new polymers have been studied. It has been observed that it is possible to modulate the thermal and mechanical properties of these polymers by changing the starting materials. © 2000 Society of Chemical Industry     

Activated gas plasma surface treatment of polymers for adhesive bonding

Polyethylene, polypropylene, poly(vinyl fluoride) (Tedlar), polystyrene, nylon 6, poly(ethylene terephthalate) (Mylar), polycarbonate, cellulose acetate butyrate, and a poly(oxymethylene) copolymer were treated with activated helium and with activated oxygen. Mechanical strengths of adhesive-bonded specimens prepared from treated and from untreated coupons were compared. Polyethylene (PE) and polypropylene (PP) showed the greatest increases in bond strength. Oxygen and helium were both effective with polyethylene, but polypropylene showed no improvement when treated with activated helium. The results with excited helium parallel the effects of ionizing radiation on these two polymers, as does the appearance of unsaturation bands in the infrared (965 cm^?1 in PE, and 887 and 910 cm^?1 in PP). Active nitrogen produced excellent bond strength with polyethylene but not with polypropylene. Of the remaining polymers examined, Tedlar, polystyrene, and nylon 6 showed the greatest improvement in bondability after treatment, and Mylar showed moderate improvement. Polycarbonate, cellulose acetate butyrate, and the poly(oxymethylene) copolymer gave approximately two-fold increases in lap-shear bond strength. In several cases, significant differences in response to time of treatment and type of excited gas were found.     

Damage in large scale solid state deformation of thermoplastic polymers at elevated temperatures and varying strain rates

Abstract

A key factor which limits the production speed of the polymer die drawing process is the premature fracture of the material on exit from the die. In this paper, the growth of damage in the material during the die drawing process has been studied using a combination of thermoplastic finite element analysis and structural characterisation by means of scanning electron microscopy and small angle X-ray scattering for the specific case of die drawing of polyoxymethylene. It is demonstrated that special profiled dies offer a more beneficial strain rate distribution than the conventional conical dies and allow higher production speeds to be obtained. Voids grow in the material as a result of the tensile stresses pertaining near the die exit and then, crazes appear from within the material at a critical stress level leading ultimately to final fracture. The results suggest that although the crazes initiate at a critical stress, the extent of crazing at the maximum draw ratio obtained (～13) is independent of the type of die and hence the stress level. Fracture of the drawn product occurs at different stresses for different die profiles but always at the maximum draw ratio of 13, suggesting that this relates to the limiting extensibility of a molecular network.     

The Effect of Processing Parameters on the Crystalline,Orientation, and Mechanical Properties of Two‐Stage Die‐Drawn Polypropylene

An investigation specifically focusing on the relationship among processing parameters, structure, and mechanical properties of solid two‐stage die‐drawn polypropylene (PP) has been done in this study, which aimed at providing a reliable reference in the choose of appropriate conditions that can be able to meet a specific processing requirement. PP sheets were drawn through a self‐design solid two‐stage die‐drawing apparatus to various drawing ratios (DRs) at different speeds and with different die‐exit thicknesses. The results showed that tensile strength, modulus, and the degree of orientation significantly increased with the nominal DR and could be further improved by increasing the drawing speed. While the crystallinity increased prior and decreased to near a constant value when the drawing speed was over 150 mm/min in the researched scope. Larger the die‐exit thickness was, lower the orientation degree was but higher the crystallinity could be obtained. Compared with crystallinity, orientation degree plays a leading role in the final product properties during a two‐stage solid die‐drawing process. POLYM. ENG. SCI., 59:2347–2355, 2019. © 2019 Society of Plastics Engineers     

Heat capacities of polyethylene and linear aliphatic polyoxides

Heat capacities at constant pressure and volume are calculated from full and partially approximated normal mode frequency spectra for crystalline polyethylene, poly(oxymethylene), poly(oxyethylene), poly(oxytrimethylene), poly(oxytetramethylene), poly(oxyoctamethylene), poly(oxymethyleneoxyethylene), and poly(oxymethyleneoxytetramethylene). A calculation scheme using a Tarasov-function for 2N skeletal modes and approximation of the residual normal modes from known data on polyethylene and poly(oxymethylene) is developed for all homologous, linear, aliphatic polyoxides. N is the number of CH₂-groups in the repeating unit. Calculations can be carried out over the whole temperature range OK to melting. For θ-temperatures and constant A_o for the C_v? to ?C_p conversion, oxygenconcentration dependent curves are given. Recommended experimental data bank heat capacities agree to ±5% or better.     

The production and properties of poly(aryletherketone) (PEEK) rods oriented by drawing through a conical die

Oriented poly(aryletherketone) (PEEK) rods have been produced by drawing isotropic polymer through a conical die. Room temperature Young's moduli were measured by three-point bending and ranged from 5 GPa at a draw ratio of about 2 to 11 GPa at a draw ratio of about 4. Dynamic mechanical properties were explored in the range ?150 to 200°C; two loss peaks were observed, with the higher corresponding to T_g.     

Dynamic mechanical behaviour of highly oriented poly(oxymethylene) produced by microwave heat-drawing

Dynamic mechanical measurements on highly oriented poly(oxymethylene) produced by microwave heat-drawing have been undertaken at four frequencies (3.5, 11, 35 and 110 Hz) over the temperature range from −150°C to the melting point. The dynamic modulus at 110 Hz reached a value of 85 GPa at −150°C for the most highly-oriented sample (draw ratio, 41). The α and γ absorptions are clearly discernible, even at the highest draw ratios. The γ absorption can be divided into two absorptions, i.e. a low-temperature component due to crystal defects and a high-temperature one due to amorphous regions.     

Nanocrystalline diamond coatings on the interior of WC–Co dies for drawing carbon steel tubes: Enhancement of tube properties

Tungsten carbide (WC–Co) dies are commercially used for the tube drawing process. However they wear out progressively and are unable to meet the high demands required by the industry. In this study, the effect of nanocrystalline diamond (NCD) coatings on the interior of WC–Co drawing dies using a hot filament chemical vapour deposition technique is reported. A field trial was conducted on the production line for drawing AISI 1541 steel tubes to investigate the quality of the drawn tubes. The surface roughness of the tubes drawn through the NCD coated die was lower (R_a = 381 nm) when compared to the tubes drawn through a regular carbide die (R_a = 527 nm). The average residual stress of tubes drawn through the NCD coated drawing die was lowered by 25%. A pin-on-disc sliding wear test, carried out to estimate the coefficient of friction, showed that the coefficient of friction in the case of the NCD coated die was almost half that of the regular WC–Co dies. The excellent thermal conductivity and lower friction coefficient of NCD coatings also helped to decrease the working temperature of the tube drawing process, thereby resulting in a superior product.     

Structure evolution and orientation mechanism of isotactic polypropylene during the two‐stage solid die drawing process

High oriented isotactic polypropylene prepared by self‐designed two‐stage die drawing apparatus was explored through kinds of methods, including differential scanning calorimetry, two‐dimensional wide‐angle X‐ray diffraction, polarized light microscope, and tensile test. The results showed that there was a great difference between the orientation mechanism and structure evolution of two‐stage solid die drawing process and single‐stage solid die drawing process. All samples would undergo free drawing process after die drawing process. Die drawing and free drawing process were of equal importance to single‐stage die drawing process while die drawing process showed an prominent contribution to the two‐stage die drawing process. Drawing speed showed beneficial influence on die drawing process for both single‐ and two‐stage die drawing process routes. Under the same processing condition, tensile strength and modulus of samples prepared by two‐stage die drawing process were higher than those prepared by single‐stage die drawing process and the maximum value could reach 241.93 MPa and 3.57 GPa, respectively. Moreover, two‐stage die drawing samples showed better dimensional stability than single‐stage die drawing samples especially under low draw rate. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46581.     

Synthesis of a cellulose‐grafted polymeric support and its application in the reductions of some carbonyl compounds

The reduction of carbonyl compounds by borohydride supported on a cellulose–anion exchange resin is known. The synthesis of a graft copolymer of cellulose and poly(4‐vinyl pyridine) [CellO‐g‐poly(4‐VP)] has been carried out with ceric ions as a redox initiator. A postgrafting treatment of CellO‐g‐poly(4‐VP) with sodium borohydride has produced CellO‐g‐poly(4‐VP) borane, a polymer‐supported reducing agent. Optimum conditions pertaining to the maximum percentage of grafting have been evaluated as a function of the concentrations of the initiator, monomer, and nitric acid, amount of water, time, and temperature. The maximum percentage of grafting (585%) has been obtained with 0.927 mol/L of 4‐vinyl pyridine and 0.018 mol/L of ceric ammonium nitrate in 120 min at 45°C. The polymeric support, CellO‐g‐poly(4‐VP) borane, has been used for reduction reactions of different carbonyl compounds such as benzaldehyde, cyclohexanone, crotonaldehyde, acetone, and furfural. The graft copolymer has been characterized with IR and thermogravimetric analysis. The grafted cellulose has been found to be thermally stable. The reduced products have been characterized with IR and NMR spectral methods. The reagent has been reused for the reduction of a fresh carbonyl compound, and it has been observed that the polymeric reagent reduces the compounds successfully but with a little lower product yield. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Crystallinity of POM films cast from solution

Summary The process of crystallization and the structure of poly/ oxymethylene/ (POM) films cast from hexafluoroacetone sesquihydrate solutions were studied. The supermolecular structure of thin POM films was studied by the use of polarization microscope. It has been found to consist mainly of spherulites, the size of which are essentially independent of the initial concentration of the solution. Similarly to the findings reported for thin films made of melts, ovoids and spiral ovodis were also found in minor amounts. Two additional formations indicating more complex structure were also detected. Further details of the structures formed could be recognized applying scanning electron microscopy.     

Dielectric properties of polymers at microwave frequencies: a review

A review of the dielectric loss spectra of polymers at microwave frequencies has been carried out. While the main focus of attention is the frequency range from 100 MHz to 100 GHz, loss spectra outside this region are also reviewed because variations in temperature can cause a shift of dielectric loss into or out of the microwave range. A large volume of data for low loss polymers (polyethylene, polypropylene and poly(tetrafluoroethylene)), which are used in the communications industry, was available for review. Other polymers, for which data were available and which have significant loss at microwave frequencies are: polystyrene, poly(vinylchloride), poly(vinylidene chloride), poly(vinylidene fluoride), poly(methyl-methacrylate), poly(methyl acrylate), poly(oxymethylene), poly(ethylene oxide), poly(propylene oxide), polyacetylene, and poly(sulphur nitride). Also, the microwave dielectric properties of engineering thermoplastics such as poly(phenylene oxide), polycarbonate and polysulphane have been reviewed. The origins of microwave dielectric loss in polymers are categorized as: (a) dipolar absorption dispersions in both crystalline and amorphous polymers; (b) dipolar losses due to impurities, additives or fillers in a polymer material; (c) microwave absorption in conducting polymers (polyacetylene and poly(sulphur nitride)) for which the current carriers are electrons; and (d) photon-phonon absorption spectra corresponding to the density of states in amorphous regions of a polymer material.     

Fiber diameter of polybutylene terephthalate melt‐blown nonwovens

A polymer air‐drawing model of Polybutylene Terephthalate (PBT) melt‐blown nonwovens has been established. The predicted fiber diameter coincides with the experimental data. The effects of the processing parameters on the fiber diameter have been investigated. A lower polymer flow rate, a higher initial air velocity, and a larger die‐to‐collector distance can all produce finer fibers, whereas too high an initial air velocity and too large a die‐to‐collector distance contribute little to the polymer drawing of PBT melt‐blown nonwovens. The results show the great potential of this research for the computer‐assisted design of melt‐blowing technology. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1750–1752, 2005     

Analytical and experimental study of the die drawing of circular rods through conical dies

An analysis is presented of the process of die drawing isotropic polymers, in the form of circular rods, to produce highly oriented materials with enhanced mechanical properties. The stresses in a small element of material undergoing the drawing process have been analyzed using a force-equilibrium approach and the initial yield and flow stresses in the material have been predicted from the von-Mises yield criterion. The stress-strain-strain rate characteristics of the polymer used in the analysis were deduced from uniaxial tensile test data obtained at the same temperature at which the die drawing occurred. Experimental results are presented of the stress in polypropylene GSE-108 rods when die drawn at 90°C in a purpose-built die drawing facility. Novel techniques were used to determine the stress and strain distributions along the die. A comparison of the experimental results and the analytical predictions shows good agreement.     

1H‐NMR investigation of the thermooxidation degradation of poly(oxymethylene) copolymers

The thermooxidative degradation of poly(oxymethylene) copolymer (CPOM‐Y) powder was studied in air in 150°C. The effect of the sequence distribution of degraded poly(oxymethylene) (POM) samples on the thermal decomposition behavior was investigated with ¹H‐NMR and gas chromatography/mass spectrometry. The results showed that the degradation process of CPOM‐Y could be divided into three stages with a gradually increasing degradation rate. The change in the sequence molar fractions agreed with the fact that the ethylene oxide (EO) units had higher thermal stability, and the degradation of POM was due to the decomposition of formal units. At the beginning, CPOM‐Y tended to split off formaldehyde, starting at the chain ends, some of which were not ended by EO units. In stage 2, the thermooxidation of POM occurred in the amorphous phase. In stage 3, no obvious rules for the changes in the sequence contents were obtained from NMR results, and this indicated further random chain scission and unzipping occurring heavily in the crystalline bulk. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 577–583, 2004     

Improvement of Flexural Strengths of Poly(L‐lactic acid) by Solid‐State Extrusion, 2. Extrusion Through Rectangular Die

Solid‐state extrusion of poly (L ‐lactic acid) (PLLA) through rectangular die was performed to produce high flexural strength plates that can be used as internal fixation devices. A single‐angle wedge‐shaped rectangular die was utilized having the die exit dimension of 4 mm × 1 mm. Billets were machined out from vacuum compression molded PLLA having different crystallinities to have various thicknesses and thus various imposed draw ratios. Solid‐state extrusion of billets was performed at various drawing rates at 130 °C, above glass transition and below melting temperature. Extruded plates had the width and thickness smaller than the die due to the further drawing outside the die. The decrease in width was larger than the decrease in thickness, and this became more prominent with increasing draw ratio and drawing rate, resulting in a significantly smaller aspect ratio. Contributions of die drawing and further drawing outside the die were estimated from the extruded plate dimensions, by which the drawing rate effect was attributed to the further drawing outside the die. As actual draw ratio increased, crystallinity, melting temperature, crystalline orientation factor, and birefringence increased. Throughout the whole process the decrease in molecular weight was largely suppressed to be about 10%. As billet crystallinity, draw ratio, and drawing rate increased, both flexural strength and flexural modulus increased up to the maxima of 202 MPa and 9.7 GPa, respectively. This enhancement in mechanical properties was correlated with structural developments.

Changes in flexural strength of solid‐state extruded PLLA plates as a function of draw ratio (the effect of drawing rate is co‐plotted by hollow symbols at corresponding draw ratio.).