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Small and imperfect crystals in polymers reorganize during slow heating. This leads to an increase of their melting point Tm. In order to measure the melting point of the original crystals, high heating rates are needed. This is possible with the modern heat-flow-calorimeters, which work with very small samples. The thermal lag of a DSC cell causes a shift of the melting peak by ΔT to higher temperature. From the theory of a heat-flow-calorimeter, it follows that the error ΔT is proportional to the square root of heating rate. heat of fusion and sample mass. Measurements with sharp melting low molecular weight compounds confirm that this square root relation is quantitatively followed. In order to measure the true melting point of the crystals present in a polymer sample, one has to use different high heating rates and constant sample mass. By plotting the melting peak temperatures as a function of the square root of heating rate and linear extrapolation to zero heating rate, the true melting point is found. This method is applied to HDPE, LDPE and some polyamides.

Drawn fibres of high-density polyethylene, and their crystalline residues obtained by nitric acid digestion of the amorphous phase, exhibit single- or double-peaked melting endotherms depending on the degree of crystallinity of the fibre, the draw ratio and, in the case of some of the crystalline residues, whether or not they have been melted once or twice. The melting behaviour of the drawn fibres and their crystalline residues has been accounted for in terms of the rupture of a fraction of the original lamellar structure and the growth of a new crystalline structure.

Bulk-crystallized high-density polyethylene is subjected to cyclic tensile stress and then irradiated by γ-rays to “spin-label” polymer molecules. The change of crystalline texture in the fatigue process before initiation of necking is detected by the ESR method. The line-resolution parameter of the ESR spectrum, which reflects the degree of regularity of molecular arrangement, first decreases, then increases somewhat, and finally becomes almost constant during fatigue cycling. The concentration of radicals trapped in a fatigued sample is larger than that in the unfatigued one. The excess radicals disappear during heating by a process of low activation energy in the temperature region of the mechanical γ dispersion. The degree of crystallinity evaluated from x-ray diffraction and density scarcely changed during fatigue cycling. The size of the mosaic block crystals estimated from the radical trapping capacity showed a rapid decrease at the initial stage of fatigue. The x-ray paracrystalline analysis indicates a similar but not so drastic decrease. These results lead to the conclusion that the slight disordering of crystalline texture accompanying the decomposition of mosaic block crystals in the lamellae occurs at the initial stage of the fatigue process, following which crystals reform somewhat and then remain unchanged until the initiation of necking.

A torsion pendulum (∼ 1 Hz) has been used to investigate the shear modulus and loss tangent of a number of hydrocarbon polymers as a function of temperature at pressures of up to 1200 atmospheres. Low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), a natural rubber and an ethylene-vinyl acetate copolymer have been studied. The results show that the relaxation temperatures are increased by the application of hydrostatic pressure, by amounts which range between about 5 and 20°C per 1000 atmospheres. However, it has only proved possible to correlate our results with theory in the case of PP because of the lack of other data, in particular the appropriate compressibility and thermal expansion coefficients. The results also show that if the crystallinity of LDPE and PP is reduced the α relaxations are resolvable into two distinct processes.

Yield studies including uniaxial tension, uniaxial compression and biaxial stress states (developed with internally pressurized thin wall tubes) were conducted with high density polyethylene. The experimental results are compared with a predicted yield locus based upon a pressure-modified von Mises criterion. Agreement was quite reasonable although a slight degree of anisotropy was noted in the test material. Since this same yield criterion has earlier been shown to provide excellent agreement with glassy amorphous polymers it appears unnecessary to employ different criteria for different polymers if one is concerned with macroscopic yielding.

High and low density polyethylenes (HDPE and LDPE) were studied by rapid sedimentation and nuclear magnetic relaxation. A correlation was established between results obtained by studies of PE by various methods. It was shown that HDPE specimens of different cracking stabilities have different MWD. Short chain branching of LDPE macromolecules may be evaluated by spin-lattice relaxation.

Specific volume change and stress-strain data were obtained simultaneously during tensile deformation on several plastics known to be resistant to impact loading. Tensile deformation rates of 20 percent/minute and 106 percent/minute and temperatures of −190° to 55°C were employed. A common sequence of deformation modes was observed in all materials studied (rubber modified acrylics and styrene, ABS materials, polycarbonate, impact grade polypropylenes, and high density polyethylene). In all cases the major mode of deformation to failure at low rates and/or higher temperatures is volume conserving and primarily a shear flow process. At higher rates of deformation or lower temperatures, a transition occurs and the specific volume of the material increases in direct proportionality to the tensile strain above the apparent yield point. Volume increases of 17 to 50% were observed and these were equal to 85 percent or more of the observed tensile strain at failure. These observations indicate that microcavitation may be the major process available for the absorption of mechanical energy at impact rates in plastic materials.

TheYoungs modulus of HDPE filaments cold-drawn to different extents has been determined. The orientation distribution of the crystallites, of the total molecules and of the amorphous regions have been quantitatively determined. Using a simple one-phase model to predict theYoungs moduli, it is shown that the modulus is related primarily to the average orientation of the molecules in the amorphous regions.

An intergrated vacuum distillation gas chromatographic method has ben developed for measuring total volatiles content and absolute levels of specific volatiles in polymers and other relatively non-volatile matrices. The method is very versatile and is used for the simultanoues determination of moisture and organic volatiles over the range 0.0005% to 40% by weight with a precision of 4% relative The lower limit of detection for hydrocarbon volatiles is 1 ppb* with flame ionization detection. Specific applications to the quantitative determination of hydrocarbon volatiles in high-density polyethylene (HDPE), moisture and hexane in atactic polypropylene, and a trace odorant in HDPE are presented.

The stress state of four rheologically characterized polymer melts—low‐density polyethylene (LDPE), high‐density polyethylene (HDPE), polystyrene (PS), and poly(methyl methacrylate) (PMMA)—in laminar shearing flow was completely determined by measuring the non‐Newtonian viscosity μ and the first and second normal stress differences N1 and N2. The mean N2 function was negative and about 0.1–0.3 the value of N1. The measurements were made in a Weissenberg rheogoniometer using cone‐ and parallel‐plate geometries. Additional viscosity measurements were made in a capillary rheometer. An experimental study of interface distortion in the stratified two‐phase flow has been carried out using these melts. It was found in the stratified flow experiments that the lower viscosity melts exhibited concave interfaces and encapsulated the higher viscosity melts irrespective of the relative values of N1 and N2. The rate of interface distortion and encapsulation increases with increasing viscosity differences. The pressure ...

A study was made of the supermolecular structures formed in two component mixtures of isotactic polypropylene with low and high density polyethylene relative to the composition of the mixtures and the conditions of heat treatment. The size, shape and degree of order of the supermolecular structures were determined by the low angle light scattering method. The influence of the composition of the mixtures on the processes of melting and crystallization of the individual components was determined. The experimental results point to the microheterogeneous character of the mixtures in the solid state.

Extended-chain high-density polyethylene prepared through crystallization at high pressure is substantially stiffer and somewhat stronger than normal folded-chain HDPE. With weight-average molecular weight in the range normal for molding or extrusion resins, the extended-chain material is inductile and brittle; but with molecular weight near 2,000,000, the resin can be rigid and tough. This rigid, tough material can be converted to articles through some of the solid-state processes developed for metals. The volume–temperature behavior of HDPE at 5000 atmospheres appears to reflect a polymorphic transition between orthorhombic and triclinic phases.

This simply built device for shipboard use incorporates a tilt adjustable 57-liter drum and an effluent collector of high density polyethylene. The nonmetallic construction removes possible sources of heavy metals contamination; an enclosed elutriation drum top helps prevent spillage.

The steady shear viscosities of high density polyethylene disolved in highly branched isoparaffin solvents have been measured with a high-pressure autoclave viscometer at temperatures ranging from 150 to 250°C and over a range of shear rates from 0.02 to 170 sec−1. Laboratory measurements on solutions ranging from 15 to 67 wt percent polymer were used to develop and calibrate a mathematical model for solution viscosity intended for a range of from 10 to 100 wt percent polymer. The foundation for the model consists fo two equations: the modified Martin equation is used to describe the effect of concentration, and the Sabia equation is used to describe pseudoplastic behavior. The model correlates viscosities that can range over nine orders of magnitude with sufficient accuracy for most process design work, averaging less than 10 percent error. Both the data and the model indicate that at constant stress the activation energies (EA) for the effect of temperature on viscosity are higher for solutions in the midrange of composition than for either of the pure components. This peak in EA is related to the density difference between polymer and solvent.

The critical resolved shear stress (C.R.S.S.) for (010) [001] slip in oriented high- density polyethylene (HDPE) has been measured as a function of temperature between 0° and 100°C. The variation of the C.R.S.S. with temperature has been interpreted in terms of yield by means of the thermal activation of dislocations at the edges of the crystal platelets under the action of an applied shear stress.

In this paper, the dose dependence and the load dependence of friction, and also the relation between the coefficient of friction μ and S/P (S : shearing strength ; P : hardness or yield pressure), of linear polymers irradiated by cobalt-60 γ-ray, from 5×107 r up to 2.5×109 r, including non-irradiated specimens, are examined. The μ of crosslinking polymers of polyamide and high density polyethylene increases from two to four times, and that of low density polyethylene decreases gradually to about one half that of the non-irradiated specimen, with increasing radiation dose, and the increase of that of degradated polymers of fluorocarbons is less than above. The dose dependence curve of coefficient α, which is decided by μ∝W-α, is similar to the reversed curves of those of stiffness, hardness and shearing strength. The μ and S/P are nearly in accord qualitively, but not quantitatively.

The gas chromatographic (GC) method for thermodynamic measurements of polymer-solvent systems at finite concentration has been improved to extend its operating range from atmospheric pressure to over 70 atm and over 240°C. This paper describes the design and opertion of the equipment and the mathematical treatment of the GC data, and presents experimental results for n-hexane and isooctane in high density polyethylene. These results include the solubility isotherms, activity coefficients, and polymer-solvent interaction parameters. The activity coefficients covering a range from 4 to 70 atm for n-hexane in the polymer solution were correlated successfully as a function of composition using a two-parameter segment interaction equation.

The influence of the type of polyethylene on the rate and yield of grafting of styrene was studied by using simultaneous irradiation with γ-rays and also pre-irradiation in vacuo. By both methods, the grafting yield was found to be higher in high density polyethylene, except at low temperature with thick samples. The effect of the foil thickness is the same for both methods: the grafting yield generally increases with increase in foil thickness. It is assumed that the advantageous effect of higher crystallinity and of greater thickness on the grafting rate can be explained by the greater rigidity of the polymeric matrix. This causes a lower degree of swelling, a greater gel effect and perhaps a better utilization of the radicals. In these cases, the structure of the polyethylene affects kinetic parameters, mainly the termination rate constant. During grafting, probably through the mechanical action of the growing and swelling chains, some free radicals trapped in the crystalline regions may become accessible for grafting. The creation of new grafting sites is not excluded. A rise in temperature diminishes the rigidity of the matrix: the overall grafting rate decreases and the effects of crystallinity and of sample thickness become less marked. By further increase of the rigidity of the matrix, the pressure exerted by the growing and swelling chains is incapable of loosening the structure. The grafting becomes limited by the structure; only low grafting yields and rates can be obtained. This is the case with high density polyethylene at low temperature, where the grafting yield decreases steeply with thickness. As could be expected, a rise in temperature has, in this case, the opposite effect on the rate: grafting is favoured at higher temperatures.

The effect of heterogeneity on the flow behavior of high density polyethylene (HDPE) has been studied by systematically homogenizing heterogeneous blends and observing the effect on the basic rheological parameters and on the extrudate surface appearance. Ample evidence is presented to show that heterogeneity causes substantial changes in the flow behavior although molecular parameters obtained through solution studies are unchanged. A simplified mathematical model which clearly illustrates the effects of the size of these flow units on the flow behavior is presented.

In the presence of oxygen, the radicals produced by irradiation in high density polyethylene become trapped for a long time and can not immediately crosslink but react on oxygen to form carbonyl groups. If quick-heating was applied to the polymer followed by irradiation, the trapped radicals are set free to move and to form crosslinks. This reaction is accompanied by the decrease in crystallinity. While, the per cent gel corresponding to the degree of crosslinking is less in the case when polyethylene is irradiated in higher crystalline state than when it is done in lower crystalline one for the same irradiation dose. It may be expected therefore that several heat-treatments during irradiation would improve the effect of irradiation.The authors reported previously that the effect of heat-treatments on tearing properties of irradiated and/or rolled polyethylene. Now, it is the purpose of this paper to study and show the same effect on tensile properties of irradiated or rolled and then irradiated polyethylene using an instron tensile tester. Test temperature was limited to 30°C and cross-head speed was made 100%/min.The results obtained from the experiments are as follows: The yield point becomes higher generally when the heat-treatments are performed ten times than when they are given once (All the specimens are heat-treated once at least following the irradiation to eliminate the time effect). Especially, it is worth nothing that the irradiation dose, at which the yield point ratio takes the maximum value, becomes smaller gradually with the repetition of heat-treatments for the specimen rolled and cut in 0° direction to the direction of rolling and then irradiated.

The process of solid state extrusion of high density polyethylene was analyzed by assuming pure plastic behavior of the polymer. The agreement between the values calculated on the basis of the tensile data and that observed in extrusion experiments confirmed the assumed plastic nature of the polymer. The equation examined will be efficient as a starting point for detailed studies of solid state extrusion.Solid state extrusion of 6-nylon was also tried. It was successful only at the relatively low degrees of processing even at the temperatures close to the melting point. This fact makes contrast to that of polyethylene, in which extrudates of high degrees of processing was obtainable at the temperatures above 80°C.

Experimental studies were conducted on lapped high-density polyethylene tape dielectric pressurized mainly with SF6 to clarify its performance under conditions of overvoltage in EHV systems.

HDPEの射出成形品の成形収縮は金型内の樹脂圧力挙動, 成形方法および成形条件に強く依存する。本報ではクッション量, 初期充てん量, スクリュー前進時間および保持圧力が成形収縮に及ぼす影響を検討した。この場合保持圧時間中の保持圧力を一定に保つため, クッションを用いた。保持圧力は金型内の圧力プロフィルの静圧に大きな影響を与え, 収縮率を大きく変化させる。保持圧力の増大は樹脂の流れ方向およびそれと直角方向の収縮率を減少させるが, 収縮率の異方性をも増大させる。収縮率と圧力の残存時間から得られる固化時間は加熱筒温度および金型温度の上昇により延長されるが, これらは計算値とかなりよい一致を示す。収縮率の異方性をもたらす流動配向は樹脂温度と充てん過程での推進力に強く支配されていると思われる。

Solid-state extrusion of some crystalline polymers, such as high density polyethylene, isotactic polypropylene and nylon 6, were analyzed on the basis of the upper bound theorem. The method of practical application of the theorem was the same as that described by Avitzur, and an improvement was added by taking into account of the strain hardening effect of the polymeric materials. The agreement between calculated and observed results was fairly good with the frictional coefficient of the values coincident with those estimated in previous papers with the other approach. And the cause of the increase of the extrusion pressure with increasing die taper angle was confirmed as due to the discontinuous change of the velocity distributions, especially around the exit of the die.

The melting characteristics of high-density polyethylene have been shown to be dependent on molecular weight and molecular weight distribution as well as on annealing and crystallizing history. The phenomenon of double melting endotherms is explained on the basis of a molecular weight fractionation process occurring during annealing and crystallization in which there is preferential crystallization of low or high molecular weight species according to the temperature. Reference is made to other polymers exhibiting similar behaviour.

The previous paper presented a study of the radical species in irradiated Marlex‐50 at low dose levels. This paper extends that study to a level of 4000 megaroentgens. The kind and relative number of each radical trapped at room temperature (RT) depends on the degree and tightness of the crystalline and crosslinked fractions during irradiation. At least two of three distinct species, having different hyperfine structures (six‐, five‐, and a single‐line) are present in varying concentrations at all doses. The six‐ and five‐line radicals are trapped in the crystal, whereas the single‐line radical is trapped in the highly crosslinked medium. During irradiation at RT and liquid‐nitrogen (LN) temperature, the crystal is not as effective in trapping the six‐line radical as in the absence of irradiation. At 640 megaroentgens the six‐line radical does not survive during irradiation at RT, leaving the five‐ and single‐line radicals above this level. The single‐line radical appears at 320 megaroentgens and increase...

Statistical analysis of inherent viscosities (LVN), shear modulus (G*), and melting temperature (Tm) interval data for isotactic polypropylene–linear polyethylene (HDPE) blends was performed in order to verify their microheterogeneity. High shear measurements in viscometric (Poiseuille's) flow were carried out on four replicated compositions of the blends. Least-squares treatment of the results yielded power law parameters for the blends differing in composition. The significance of differences between the blends of various HDPE content was tested using the multiple-range (Duncan's) test, and tentative conclusions are drawn on the composition dependence of the melt flow viscosities of the blends.

イミダゾリン型両性界面活性剤Ca塩(No.433)を練込んだ高密度ポリエチレンの吹込成形によるビン容器の製造を半工業的な規模で行なって,液体合成洗剤の容器としての性能を検討した。成形ビンの帯電防止性は表面固有抵抗,摩擦帯電圧,電荷の漏洩によってしらべたが良好と認められた。プラスチック性能は物性,表面粗度,圧縮強度,口径寸法,肉厚,変形試験,落下試験,印刷性の面で実用的に詳しく検討されたが,内部用帯電防止剤として,No.433を1.0%添加量で練込んでも悪影響は全く認められず,むしろ向上する場合もあることを知った。本報でつくったビン容器のホコリ付着については次報でくわしく検討されるはずである。

The authors previously reported a method for molecular weight and long-chain branching distributions using GPC and intrinsic viscosity measurements on whole polymer and fractions [1]. The method does not require prior knowledge of the functional relationship between branching frequency and molecular weight. Applications included “randomly” branched polymers, prepared by free radical initiation, and anionically polymerized macromolecules branched by various techniques leading to specific distributions of branches. Additional examples are given in the present report. The technique has been applied both without and with GPC band spreading correction. The effect of this correction on the resulting estimate of the long-chain branching distribution is insignificant. When the method is applied to whole polymer only (without preparative fractionation), an average branching factor is obtained, which serves as a useful partial characterization of long-chain branching. Use of this alternative is discussed and illustrated with examples of low and high density polyethylene, branched styrene-butadiene block copolymers, star-branched polybutadiene and others. For the special case of statistically random branching, the average branching factor may be converted to a branching frequency by a straightforward computer program, leading to a description of branching similar to that of Drott and Mendelson [2].

The dynamic Young's modulus and the mechanical damping of the low density polyethylene (Alkathene) and the high density polyethylene (Marlex 50 and Hostalen) subjected to electron irradiation have been measured at a frequency of 0.2 c/s over a temperature range of 20 to 180°C. A remarkable change in the mechanical properties of irradiated high density polyethylene was observed after heat treatment. After an initial heating of an irradiated specimen above its melting point the elastic modulus at lower temperature decreases and the curve of mechanical damping vs. temperature changes. Two peaks appearing in the damping vs. temperature curve may be associated with the melting process of two groups of small and large size crystals. The crosslinks introduced by electron irradiation at room temperature prevent the large crystals of polyethylene from regaining their original size after attaining the rubber state due to melting. The heat treatment, therefore, produces a larger number of crystals of small size and fewer large crystals, which appears to conform with the tendency to an increase of height and width of the damping peak at lower temperature and a decrease of height of the damping peak at higher temperature.

The property of environmental stress cracking is a critical performance factor in the polyethylene product areas of rigid and flexible containers, wire and cable insulation and pipe or conduit. It has been known for quite some time that the addition of an elastomeric material to polyethylene can improve its resistance to environmental stress cracking. However, the information reported in the literature on the subject is rather limited and as far as can be determined no attempt has been made to determine the rubber variables affecting the environmental stress cracking performance of polyethylene. In studying the effect of rubber on the environmental stress crack resistance (ESCR) of low and high density polyethylene, the choice of base resin is important. With some resins the addition of rubber doubles the ESCR while with others a fiftyfold improvement can be effected. Of the elastomers investigated in this study, Enjay Butyl 007 a copolymer of isobutylene and isoprene gave the greatest stress-crack improvement in both low and high density polyethylene. Evaluation of a series of polyisobutylenes indicate that the higher its molecular weight the more effective its performance as a stress crack additive. The effect of rubber on other properties of the polyethylenes such as melt index, stiffness, permeability, chemical resistance, brittle point temperature, and impact strength is also discussed.

Some organic pigments, present in very small amounts (0.1 to 0.2%), can cause warpage and shrinkage phenomena in moulded parts of linear polyethylene. Investigations on such phenomena have been carried out by dilatometric and morphological analysis. The influence on polyethylene crystallisation kinetics and morphology of such organic and inorganic pigments, which do not cause any deformation effect, has been studied. The experimental results show that only organic pigments increase the crystallisation rate, by acting as nucleating agents; in these cases, moreover, the crystalline grain is smaller and the typical morphology of polyethylene crystallised in bulk is altered. A possible correlation between the nucleating action and the warpage effect of organic pigments on moulded polyethylene is discussed.

Selection of suitable packaging film is necessary to minimize the deteriorative changes of foods. Packaging films differ for different food products. Flexible packaging films are now widely used instead of hard packages for processed dry food products. In this study attempt has been made to select a suitable packaging film for dry coriander powder at ambient temperature. Three types of packaging films like heat sealable laminated aluminium foil, high density polythene (HDPE) and poly propylene (PP) were chosen. The changes in water activity, total ash, acid insoluble ash and consequent effect on sensory qualities like texture, colour, flavour and appearance of coriander powder were investigated at an interval of two months during one year storage period. Bangladesh J. Sci. Ind. Res. 42(1), 53-58, 2007

The paper presents the “Thermophysical Profiles” of selected plastics and discusses their significance in correlating the mechanical properties with the molecular and crystalline structure of these polymers. The profiles were obtained with a new instrument, by imposing a fixed, forced elastic vibration on the speciments' surface and by recording continuously the energy absorbed by the specimens through a temperature range from −200°F to +500°F The profiles locate the first and second order transition points of the test materials (defining, thus, the temperature limits of their use) and indicate the change in modulus with temperature in the viscoelastic region of the polymers. Profiles of the following materials are discussed, low and high density polyethylene, polypropylene and PVC films and unfilled samples of cast epoxy and polyester resins.

Two groups of dielectric absorption are observed in the impurity (surfactant=metal salt of imidazoline type amphoteric agent) doped high and low density polyethylene. One of them has the loss maximum dependent on the amount of the impurity and is imputed to the relaxation of a dipole orientation of the impurity. Another shows an odd behavior named retrogressing phenomenon near the melting point of polyethylene (90°C for low density polyethylene and 120°C for high density polyethylene) and can not be detected in the amorphous polystyrene depoed with the same impurity. An interfacial polarization is proposed assuming a model, crystalline part of polyethylene being covered with a surfactant dense layer. This model is justified semi-quantitatively by the Miles and Robertson theory. The retrogressing phenomenon is explained by the change of the layer thickness that affects the dielectric relaxation time of this model.

18. G. W. SCHULZ and V. A. HANG, Z. phys. Chem. 34: 328, 1962 19. T. G. FOX, Polymer 83: 111, 1962 20. U. BAUMAN, H. SCHREIBEI{ and K. TESSMAR, Makromolek. Chem. 36: 81, 1960 21. W. R. KRIGBAUM and P. J. FLORY, J. Polymer Sci. 11: 37, 1953 22. W. R. KRIGBAUM and D. K. CORPENTER, Z. phys. Chem. 59: 1168, 1955 23. V. CRESCENZI and P. J. FLORY, J. Amer. Chem. Soc. 86: 141, 1964 24. U. BIANCHI, W. MAGNOSCO and C. ROSSI, Chim. Ind. (Milan) 40: 263, 1958

Thermal degradation experimant of high density polyethyiene was carried out by using a continuous flow reactor in the temperature range of 4000 to 4450C under a. tmospher. jc pressure to investigate the rate of thermal degradation and properties of decomposition products at the steady state.The products of thermal degradation were separated into two parts, the one, vol, atile gaseous product at 25C and the other, less-volatile Qily product. The gaseoms product wasi. analyzed by gas chromatography and was found to be ceRsisted ef H2 and CitvC6 hydrocarbens, having the average molecular weight of 35 to 37. The composition of gaseotis products did not change appreeiably with the degradatien temperature. The oily product was found to be consisted of a wide spectrum of hydrocarbon fragment, saturated and unsatutated, varying in carbon numbers from 3 to 30 (see Fig.6, 7). The average molecular weight ef the oily product varied from 180 to 232 withx, degradatiop temperature (see Fig.9). Other physical properties of eily products are shown in Table 3.The average yield of product oil was 94.5% of the total products in the temperature range investigated. The reactor content was the degraded polymer and its molecular weight was decreased to about 1200. Some physical properties of the reactor contents are shown in Table 3. The correlation between the rate of decomposition of the polyethylene and the rate of formation of double bonds, was also investigated. Both rates are plotted in Fig, 4 as a function of the degradation temperature. Carbon-carbon double bonds were found in gaseous products, only product and reactor contents, but as shown in Fig.5, the increase in double bonds of the reactor content was negligible. The activation energies of thermal degradation of the polyethylene, calculated on the basis of the above two rates, were 47.5 kcal/mol and 49.4 kcal/mol, respectively.

Wear by roll-formation is common among polymers when bulk deformation and “give” exist. The necessary condition for such wear is that the strength of an asperity of a given polymer will be lower than both the strength of the opposing asperity of the other polymer and the interfacial friction force over the relevant surface of both asperities. Ductility, manifested by roll-formation, was observed in high density polyethylene (HDPE), polypropylene (PP), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), Nylon 6, polyethylene terephthalate (PET), polyamide imide(PAI), polybutadiene(PBD), and polymethylmethacrylate(PMMA). Ductility, manifested by the shear of a whole surface layer, was observed, also, in polystyrene(PS). Ductile wear of brittle polymers is shown to be dependent on ( ΔH ∗ a −U 0 ) and the product of the applied stress and the volume that can undergo cooperative ductile deformation independently from other, adjacent or close, such volumes.

The self-seeding crystallisation technique is applied to a dilute solution of polyethylene in xylene containing, in suspension, foreign particles; data concerning some pigments usually employed for colouring the plastics are reported. It is shown that this method allows easy demonstration of the interactions existing between the dissolved polymer and the pigment; at the same time, it is possible to study the morphology which is evolved as a consequence of these interactions under particularly simple conditions as only a small amount of polymer crystallises on the pigment particles. The behaviour of several pigments is consistent with the results obtained by crystallising the bulk polyethylene coloured with the same pigments. Some unusual morphologies are made evident.

The deformation of samples of oriented high-density polyethylene has been analysed in terms of three principal deformation mechanisms,fibrillar slip, lamella slip andchain slip. From a study of small- and wide-angle X-ray diffraction patterns it is possible to deduce which mechanism or mechanisms are operating in particular cases. Material prepared in three different ways has been examined and it appears that in all three cases the primary mechanism for plastic deformation is [001] chain slip.

Dilute solution properties of twenty-five PVC fractions prepared from commercial and experimental bulk-polymerized PVC samples have been investigated by means of light-scattering, viscometry and exclusion-chromatography The following Mark—Houwink—Sakadura relationships: []2YC = 1,63 10—2 M°76° x 1.017 c.gs. I 125t — 2 ir2 At 0.725 >< 1 02 Lflicyclohexanone — : ' c.g.s. have been found to be valid in a range of Mw-values between 6400 and 650000. The validity of various extrapolation procedures, proposed in order to calculate unperturbed dimensions and polymer-solvent interaction para meters from the empirical viscosity-molecular weight relationship, has been examined The Kurata—Stockmayer method applied to the measurements in tetrahydrofuran yields a Krvalue equal to 0.14 c.g.s. The polymer—solvent interaction parameter derived by the same method is not in agreement with the one deduced from second virial coefficient measurements. Molecular weight distributions determined in commercial PVC samples can be adequately represented, in a first approximation, by the usual exponential distribution function, first. proposed by Schulz. The chromatographic determination of MWD and its effect on the viscosity—molecular weight relationship are discussed. Finally, the possible occurrence of long chain branching in PVC has been investigated by means of an experimental study of the structure and properties of various polyethylene samples obtained by reduction with LiAIH4 of commercial PVC polymers. The melting temperatures and the intrinsic viscosity -molecular weight relationship for the polyethylene samples, so obtained, were found to be identical with those of High Density Polyethylene. It is concluded that most PVC polymers contain only very few long branches, if any INTRODUCTION Dilute solution properties of polymers may provide quantitative information on the size, shape and structure of the dissolved macromolecules as well as on the importance of polymer—polymer and polymer—solvent

The melting of solids under shear conditions is an important operation in the processing of most thermoplastics. In this study, solid blocks of high density polyethylene were melted on a hot, moving surface over a range of surface temperatures and velocities. The conservation equations for mass, momentum, and energy were applied to the molten layer and then simplified by an order of magnitude analysis. A general model that included all significant terms gave rates of melting that agreed closely with the measured rates. A simpler model that was analogous to present extruder models predicted melting rates that were ten to twenty-five percent lower than the experimental values. Models for polymers with low to moderate crystallinity should be modified to account for physical removal of amorphous material by shear forces.

The dynamic viscosity η' and rigidity G' have been measured by means of the rotational cylinder type rheometer described elsewhere for seven types (A to G) of high-density polyethylene manufactured by three different processes. The measurements have been carried out in a frequency range from 0.001 to 0.5cps at five temperatures ranging from 180 to 260°C.These materials do not necessarily have the same frequency dependence of η' and G', and can be classified into four groups. Polymers D and E have the same frequency dependence of η' and G' in the frequency range covered by the experiment and η' vs. ω or G' vs. ω curve (ω denotes angular frequency) can be superposed into a composite curve by shifting them along a straight line having the slope of -1 or the abscissa. This also holds for polymers F and G, but the η' and G' curves for these polymers intersect with those for polymers D and E. The polymers A and B have the same frequency dependences of η' and G' on each other but are different from the above materials.The polymer C is quite different from others. The frequency dependence of η' for this polymer is much larger and that of G' is much smaller than the other materials.In some cases, the difference in the frequency dependence of η' and G' for different materials may be ascribed to the presence and the nature of double bonds included in the polymer chains as verified from the infrared spectrum. In other cases, the difference may be due to the difference in the molecular weight distribution as elucidated by the fractionation with the column method and turbidity titration.The frequency dependence of η' for the polymer having bimodal distribution is greater than for the polymer having normal distribution, and that of G' is reverse. The absolute values of η' and G' for the polymer having bimodal distribution tend to be higher than the normal for a given weight-average molecular weight. Moreover, the polymer having bimodal distribution have larger shift factor and lower fluidity than the normal, indicating that the molecular weight distribution is very important to the flow properties of polymer melts.

市販高密度ポリエチレンwhole polymerおよびその分別物の融液のレオロジーについて粘度と法線応力の測定を行なった。粘度測定にはcone-plate型とcapillary型粘度計を使用した。法線応力は圧力分布が検出できるように改良された平行円板型レオメーターを使用して測定した。その結果, 定常流粘度の非ニュートン性や法線応力は分子量分布 (Mz/Mw) によって大きく影響され, Mz/Mwが大きいほうが非ニュートン性も著しく, 法線応力も大きいことがわかった。

This paper describes an experimental study of the friction and transfer of some thermo­plastic polymers sliding over clean surfaces. With PTFE and high density polyethylene sliding at low speeds on smooth surfaces of glass or polished metals there is a marked dif­ference between static and kinetic friction. The static friction is of the order of μ ═ 0.2 and is accompanied by transfer of lumps of polymer several hundred angstroms thick. This frictional behaviour is ‘normal' and may be explained in terms of the bulk properties of the polymers. However, once sliding has commenced and the slider acquires a preferred orienta­tion the friction falls to a much lower value ( μ < 0.1) and the transfer is either in the form of an extremely thin film (PTFE) or discrete streaks less than 10 nm thick (PE). This behaviour does not depend on the degree of crystallinity or on the crystalline texture of the polymer. If the molecular structure is changed by introducing an appreciable number of bulky side groups (e. g. TFE-HFP copolymers, PCTFE or low density PE) the kinetic friction remains the same as the static value. The friction and transfer are those of ‘normal’ polymers and resemble polypropylene and amorphous polymers such as PMMA and PVC in their be­haviour. The results suggest that the low friction and light transfer of PTFE and high density PE during sliding are essentially due to their smooth molecular profiles.

A high-density polyethylene prepared at low pressures is characterized with respect to density, microscopic examination, mechanical properties, and diffusion. The data for the slowly cooled, nonisothermally crystallized polymer clearly indicate that the method of preparation grossly affects the final properties of the polymer.

High density polyethylene film in a wide temperature range may be easily drawn by neck propagation to draw ratios between 7 and 30. Lower draw ratios between 1 and 10 may be obtained by rolling. The two types of plastic deformation differ to some extent in crystal lattice and lamella orientation but are rather similar as far as long period and the number of tie molecules are concerned. At large draw ratio the long period depends nearly uniquely on the temperature of drawing or rolling and is independent of the long period of the starting material. At low draw ratio the opposite is true. The number of tie molecules increases with the draw ratio and finally reaches a limiting value, but does not depend on the temperature of drawing or rolling in the temperature range investigated. The longitudinal elastic modulus and tensile strength of the samples seem to be roughly proportional to the number of tie molecules.