Cold forming of plastics part II. Draw forming of laminates containing crosslinkable core

The problems encountered with cold formed thermoplastic material, namely, low heat distortion temperature and stress and solvent crazing, can be overcome by using a laminate consisting of a reinforced thermosetting core sandwiched between two drawable face sheets. This process imposes a restriction on the material by the need for a curing cycle to transform the core into a hard, three dimensional network. To take full advantage of the very fast metal forming technique, the curing should be accomplished outside of the forming apparatus and without external restraint. In order to impart a practical shelf life to the laminate at room temperature, the chemical requirements of the core can only be met with an elevated temperature cure. This in turn places an additional restriction on the face sheets, as they will have to withstand the curing conditions without external constraint and without dimensional changes of the formed part. Finally, the face sheets then have to become an integral part of the formed laminate upon curing of the latter, involving a high adhesive strength between the cured core and the face sheets. The criteria for the selection of the materials for various layers are presented as well as the limitations on the construction of the entire laminate.     

Vacuum forming of thermoplastic foam

The process of thermoforming of foam sheet is analyzed using both finite element modeling and experiments. A simple constitutive model for finite tensile deformations of closed cellular material around its glass transition temperature is proposed, starting from well-known results from Gibson and Ashby (1988). The model is implemented in a finite element code and applied in isothermal vacuum forming simulations. The distributions of thickness and in plane strains are in adequate accordance to the experimental results.     

热塑性聚酯工程塑料的进展

综述了世界上几种热塑性聚酯的生产发展及应用进展，指出聚酯工业的4个主要趋势；生产能力逐渐集中，亚洲生产能力增大；欧美撤出聚酯纤维领域和非纤聚酯比例上升，在应用方面，热塑性聚酯多用于制造片（带）材，中空包装容器，电子、家用电器、汽车、精密仪器部件、薄膜及纤维等领域。     

Deep drawability of biaxially rolled thermoplastic sheets

The deep drawability of biaxially cold-rolled thermoplastic sheets has been studied using polycarbonate, polyvinyl chloride, and acrylonitrile-butadiene-styrene polymers. Each polymer was rolled to two different reductions in thickness. The deep drawability of these rolled sheets was measured by determining the limiting draw ratio using a Swift cup test. Strain ratios were measured in three directions for each of the rolled sheets in order to determine the normal and planar anisotropy of the sheets. It has been determined that the drawability of a sheet can be correlated with the normal anisotropy of the sheet and it is the increase in normal anisotropy of a sheet which increases the drawability of the sheet. It has also been shown that lubrication increases the drawability due to a reduction in punch force.     

Stamp forming of fabric-reinforced thermoplastic composites

A stamp forming technique has been used to process a fabric woven composite made of glass fibers (GF) and polyetherimide (PEI). A hemispherical mold with a built-in hold-down arrangement was designed and used at room temperature to stamp parts from preheated flat preconsolidated laminates. Tensile properties of the material were measured under similar heating conditions as in the relevant stamp-forming process. Stretch in the fiber direction was found to be smaller than the maximum elastic extension of the glass fibers. Reduction of the angle between the crossing fibers was quite large when the satin woven fabric composite was pulled in the 45° direction. The effect of die geometries and original laminate dimensions on the “shear-buckling” were studied. The results described the correlations between processing parameters and fiber buckling. Finally, the local strain of fiber bundles was investigated in relation to different directions of fiber orientation.     

Simulation of compression molding of long-glass-fiber-reinforced thermoplastic sheets

An isothermal two-dimensional shear-thinning model of the compression molding of long-glass-fiber–reinforced thermoplastic is presented. A transverse isotropic behavior is introduced by considering two different pairs of power-law coefficients. First (K₁, m₁) is linked to the shear deformations through the thickness and to the compression deformation; second (K₂, m₂) is associated to the expansion motions in the plane. K₂ is significantly greater than K₁ because of the influence of the glass mat structure, which resists stretching in the plane of the part. These coefficients are determined by fitting the computed and experimental mold closing forces in a circular isothermal compression-molding test. The average velocity through the thickness is obtained by a variational method. Incompressibility is ensured by penalization. A finite element method is used, with a convected mesh and remeshing technique. The agreement between this model and experimental results (shape of the sample, mold closing force, pressure) performed on a rectangular mold is good.     

热塑性塑料激光透射焊接研究

针对混合20%玻纤的丙烯腈-苯乙烯共聚物(AGS)热塑性塑料,进行激光透射焊接试验,得到了线能量对AGS焊接质量的影响规律。在线能量为0.75~1J/mm之间时,剪切强度可达18MPa以上,焊接质量最优。     

热塑性材料产品的收缩与翘曲

本文从材料性能,产品的设计,模具设计及加工工艺四个方面全面阐述了引起产品收缩变形的原因及注意事项。热塑性材料性能对最终制品的尺寸稳定性有影响。结晶材料由于结晶程度的不同而产生的收缩不同会导致产品的翘曲。产品的设计对其尺寸的稳定性也有很大影响,当产品有变厚度的地方,由于冷却不匀,就会同样面临收缩不均匀的问题。改善模具设计也是提高产品尺寸稳定性的关键,象合适的浇口位置能使熔体流动平衡,避免过保压现象。加工工艺参数的优化也能有效地减少不均匀收缩。     

An analysis of stretch forming of thermoplastic composites

Thermoplastic composite sheet materials have found an increasing number of applications through the use of matched‐die compression molding. The combination of high strength, low weight and moderate manufacturing costs makes the material an attractive alternative to sheet metal stampings in a number of applications. However, a significant range of conventional sheet forming techniques may also prove suitable for these materials, provided the effects of strain rate and temperature can be properly understood and exploited, leading to a further reduction of manufacturing costs and an increasing number of potential applications. In this work, limiting strains in biaxial stretch forming were explored using the hemispherical stretch forming test. The materials tested contain 20, 35, and 40 percent by weight of randomly oriented glass fiber in a polypropylene matrix. The forming tests were performed at temperatures ranging from 75°C to 150°C and at punch speeds of 0.01cm/sec, 0.1cm/sec, and 1cm/sec. A rotationally symmetric, anisotropic material model with rate sensitivity was developed and incorporated into an axisymmetric finite element model of the stretch‐forming process. The model parameters were temperature‐dependent, though the temperature distribution in the formed part was assumed to be uniform. Strain distributions in the formed parts are compared to finite element method results, and the results are good up to the point when localized necking begins to dominate the strain distribution. These forming limit strains are compared with predictions based on Marciniak's imperfection theory, with good results.     

Influence of surface photocrosslinking on properties of thermoplastic starch sheets

The surface of glycerol plasticized thermoplastic starch (TPS) sheets was modified by photocrosslinking under ultra violet (UV) irradiation. Sodium benzoate was selected as photosensitizer and induced onto sheet surface layer by soaking the sample sheets in photosensitizer aqueous solution. The effects of concentration of the photosensitizer aqueous solution, soaking time and moisture content in sheets before UV irradiation on the photocrosslinking were investigated. Water contact angle, moisture absorption, and mechanical properties were measured to characterize the influence of the surface photocrosslinking modification on the properties of TPS sheets. The obtained results showed that the surface photocrosslinking treatments markedly reduced the water sensitivity of TPS sheets and enhanced their tensile strength and Young's modulus but decreased the elongation at break. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Photodegradable vinyl plastics. I. Effect of N-halogen additives

The addition of small amounts of N-halogen compounds to polystyrene (PS), Polypropylene (PP), and polyethylene (PE) enhanced the photodegradability of the resultant plastic films. The effectiveness of the additives varied with their structure and with the polymer. A comparison of N-Bromosuccinimide (NBS) with several known photoinitiators showed it to be superior in effectiveness to all but one. Films were irradiated with a 275-watt RS sunlamp for 66–200 hr. Degradation was measured by increase in carbonyl absorbance at 1750–1695 cm^?1 using infrared spectroscopy and by change in viscosity. PS containing NBS underwent a greater molecular weight loss than unmodified PS after UV exposure as determined by viscosity measurements.     

Polyether-based thermoplastic polyurethanes. I. Effect of the hard-segment content

A series of Polyether-based thermoplastic polyurethanes, varying in hard-segment content between 20 and 80 wt. %, was prepared using an (oxypropylene-oxyethylene) diol of M _n = 2000 as the soft segment and 4,4′-diphenylmethane diisocyanate extended with 1,4-butanediol as the hard segment. Physical-mechanical, dynamic-mechanical, and specific heat (DSC) data are used to elucidate the mechanical and morphological behavior of these materials. The polyurethanes varied from soft elastomeric (continuous soft phase) to high-modulus plastic (continuous hard phase) and showed changes in their tensile properties at about 60% hard-segment content, possibly due to phase inversion.     

Engineering plastics from lignin. I. Synthesis of hydroxypropyl lignin

Hydroxypropylation of lignin in a batch reactor under alkaline conditions at 180°C was studied using propylene oxide (PO) by itself, and PO in combination with several ligninlike model compounds and with kraft lignin. While the PO homopolymerization rate increased rapidly at temperatures above 85°C, and was too fast to be determined accurately at 180°C, the addition of model compounds and lignin was found to delay homopolymerization in relation to the presence of ionizable functional groups. The observations are consistent with a reaction mechanism involving first order kinetics with regard to each alkoxide and PO concentrations. Where the reaction rates toward PO increase with increasing pK_a values, the reaction sequence proceeds in the order of declining basicity. Thus lignins with high acidity were found to be subject to greater degrees of modification than those with more neutral character. This explains the earlier observed beneficial effect of lignin carboxylation on the properties of lignin–PO reaction mixtures.     

Flammability of plastics I. relation between pyrolysis and burning

The fundamental basis of the burning of polymers is reviewed and the planning of the present investigations is justified. Preliminary results are given on the effect of chlorinated additives on the pyrolytic decomposition of polyesters.     

Issues in diaphragm forming of continuous fiber reinforced thermoplastic composites

A literature survey is presented on sheet-forming methods and mechanisms for continuous fiber reinforced thermoplastics. The diaphragm forming process is shown to be one of the more promising fabrication routes for complex-curvature structures. The primary deformation mechanisms involved in the sheet-forming processes are identified and discussed. Earlier approaches to develop mathematical models either have been kinematically based or have treated only one of the primary deformation mechanisms. A promising constitutive model for the highly anisotropic behavior of the composite at forming temperature is examined. The composite sheet is assumed to behave as a transversely isotropic Newtonian fluid that is both incompressible and inextensible in the fiber direction. The second section of the paper treats the experimental development of the polymeric diaphragm forming process for thermoplastic composites. The viscoelastic properties of the diaphragm material are characterized by dynamic mechanical analysis. The rate sensitivity of the phenomenon of shear-buckling during forming of certain cross-ply and quasi-isotropic composite laminates is investigated, using a shallow female mold. Finally, the interface condition between the diaphragm and the composite during forming is examined.     

Some properties of thermoplastic mixtures for forming ceramics by extrusion

The change in the rheological properties of mixtures for plastic forming based on cordierite and aluminum nitride as a function of the composition of the thermoplastic binder and the temperature is considered. A supposition on the influence of the ratio between the crystalline and the amorphous components of the thermoplastic dispersion medium on the properties of the mixture is made. Some recommendations on forming of ceramic pieces are given.Translated from Steklo i Keramika, No. 4, pp. 15–17, April, 1995.     

New conducting thermoplastic elastomers. I. Synthesis and chemical characterization

In the last 20 years, much interest has been focused on conducting polymers to find new materials to transfer from research to industry. However, in many cases, as for elastomers for which intrinsically conducting materials are unavailable, it is necessary to use conducting particles that are physically mixed with the polymeric matrix to give loaded rubbers. In this work we report the synthesis and the chemical characterization of an intrinsically conducting material with good mechanical and electrical conduction properties. To achieve such a global goal, we covalently linked, by an amidation reaction, the terminal NH₂ of Emeraldine (EB) and sulfonated Emeraldine (SPAN) to a free carboxylic group belonging to the repetitive unit of a functionalized segmented polyurethane. The reaction was carried out by activating such a carboxylic group with N,N′‐dicyclohexylcarbodiimide and N‐hydroxysuccinimide. The reaction yields and the chemical properties of the polymers were studied by proton and carbon‐13 nuclear magnetic resonance, ultraviolet, and Fourier transform infrared spectroscopy. The average numbers of EB or SPAN aromatic rings per polyether urethane acid (PEUA) repetitive unit, which cannot be assumed to be amidation degree because at this moment the molecular weights of the inserted EB and SPAN chains are unavailable, were 6 in case of the polymer obtained from the pristine Emeraldine and 1 for that obtained from the sulfonated Emeraldine. This result could be because SPAN was used in the acidic form, which depresses the nucleophilicity of the NH₂ group because of the presence of the sulfonic protons. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 857–867, 2002     

Structure-property relationships in thermoplastic elastomers: I. Segmented polyether-polyurethanes

Segmented poly(ether-b-urethanes) have been synthesized with 2000 MW polypropylene oxide coupled with diisocyanates and diol type chain extenders. The diisocyanates used were symmetric rigid 4, 4′-diphenylmethane diisocyanate (MDI), linear aliphatic hexamethylene diisocyanate (HDI), and unsymmetric rigid toluene-2, 4-diisocyanate (TDI). The chain extenders were symmetric N, N′-bis(2-hydroxyethyl) terephthalamide (BT) and N, N′-bis(2-hydroxyethyl)-hydroquinone (BH) unsymmetric N, N′-bis(2-hydroxyethyl)isophthalamide, and linear aliphatic 1, 4-butanediol (B). Hard segment contents ranged from 20 to 40 wt percent. The thermal behavior of these materials is consistent with phase separation into separate hard and soft domains, In order of increasing temperature above the soft segment T_g, there are transitions which occur in the regions ?56 to ?36°C (T_a), 70 to 90°C (T_b), and 138 to 168°C (T_m). The former is probably associated with soft segment change from a viscoelastic to an elastomeric state. Values of T_a are ～ ?51 C and ?56°C for the MDI-BT and HDI-BT polymers, respectively, and are independent of hard segment content. Microscopy showed that the former polymers have spherulitic morphology, so these materials have good microphase separation and exhibit crosslinked elastomeric properties. The TDI-BT or BI and MDI-B polyurethane have composition-independent T_a values of ?41 and ?36°C, respectively. These materials probably have considerable “domain-bound-ary-mixing”. At low hard segment content the MDI-B polymers behave as non-crosslinked elastomers. Only the MDI-BI polymers have _Ta values, which are strongly affected by composition, increasing in magnitude with increasing of hard segment content. This is interpreted as significant “mixing-in-domains” and is supported by morphology observed by microscopy. The next higher transition, T_b, probably involves dissociation of interdomain hydrogen bonding. In the case of the MDI-BT polyurethanes, the spherulites associated with the hard domains had disappeared at 141°C and the few small spherulites in the MDI-BI polymers disappeared at 130°C. The T_b values are 70, 83 to 90, and 100°C for the MDI-B, HDI-BT, and HDI-BI polymers, respectively. The melting transitions occurred between 138 to 168°C for the various polyurethanes except for the MDI-BT systems which decompose before melting. Thermal decomposition is a two-stage process. Hard segments decompose between 200 and 300°C. The initial decomposition temperatures are lowered in the presence of strong acid. Soft segments decompose at higher temperatures. The mechanical properties of the MDI-BI polyurethanes are charateristic of crosslinked elastomer, the results of which will be presented in a subsequent paper.     

Irradiation-modification of starch-containing thermoplastic blends. I. Modification of properties and microstructure

Irradiation-modification of the blends of various starches with a synthetic polymer [poly(ethylene-co-vinyl alcohol)] was carried out using an electron beam. The effect of irradiation on neat starches was studies using gel permeation chromatography. Changes in the thermal and mechanical properties of the blends, as well as in their microstructures, were also evaluated. The data indicate, consistent with other reports in literature, that starch molecules fragment under the effect of ionizing radiation, while the EVOH is relatively unaffected. These substantial (mainly physical) modifications to the starch molecules manifest themselves in changes in the thermal behavior of the blends. Furthermore, the mechanical properties of filaments obtained from molten irradiated pellets were quite different from those of control filaments, at least for some starches. Micrographic examination of some blends indicated a correspondence between a modification in the microstructure of the filaments and a change in their mechanical properties. It seems likely that the enhanced mobility of the fragmented starch molecules in the melt is responsible for these changes in the microstructure and concomitantly, the mechanical properties of the blend. Such an irradiation-based physical modification of starch may be of use in tailoring the properties of commercial blends of starches with synthetic thermoplastics. © 1996 John Wiley & Sons, Inc.