ISSN:0360-8905    

DOI:10.1002/polc.5070580103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

ISSN:0360-8905    

DOI:10.1002/polc.5070580104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

ISSN:0360-8905    

DOI:10.1002/polc.5070580105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

摘要:

AbstractIt is known that in branched polyethylene during cold‐drawing a solid state diffusion of the single chains takes place during which the branches are trapped in the amorphous phase and an equilibrium state of highest possible crystallinity is attained if ϵ ≦ 1.3%. This no longer can be achieved for largerevalues and the sizes D̄002of the microparacrystallites (mPC) in fiber direction attain a definite smallest value of 60 å. This is explained by a feedback of the lateral dimensions of the mPCs which on account of paracrystalline distortions, have sizes of 60‐100 å in a metastable state. The driving force of a minimum surface‐to‐volume ratio stabilizes therefore the D̄002value and constraints the incorporation of more and more branches into the mPCs. Now the volume of the lattice cell increases monotonically withe>0.013 and the melting point decreases according to S

ISSN:0360-8905    

DOI:10.1002/polc.5070580106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

摘要:

AbstractChain molecules of partially crystalline polymers are built up as a three‐dimensional network using one part of their chain segments. The other parts of segments of each molecule are embedded in microparacrystals (mPCs). It is pointed out that the random coil concept is nevertheless a good first approximation for the real conformation of a chain molecule. Its straight segments build up the mPCs. They act as the knots of a three‐dimensional network and explain the phenomenon of the affine transformation and retransformation properties of these structures. On this basis, one can develop a rheology which is in accord with the molecular structure. Mechanical models can be applied, which, contrary to those of conventional methods, substantially contribute Kelvin and Maxwell elements to microdomains and not to volume elements. One microdomain contains at least 106mPCs, including their surrounding network. The positions of the centers of the microdomains obey the rules of affine transformation. They consist of a large number of mPCs. Stretching experiments with linear polyethylene Lupolen 6001H (BASF) are discussed as an example. In the pseudo‐Hooke's law range until elongations of γ ∼ 30%, statistically distributed mPCs in suitable positions are plastically deformed. At longer γ‐values cooperative deformations of layers of mPCs set in and give rise to a necking process. Stretching is thermoreversible under a natural draw ratio because the relaxation time of the Maxwell elements is long enough compared with the time taken for the microdomains to travel through the neck. Their retardation time is calculated and has a minimum value of 2 min, 6 mm behind the beginning

ISSN:0360-8905    

DOI:10.1002/polc.5070580107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

摘要:

AbstractTensile creep of unplasticized and plasticized PVC and toughened polystyrene compounds were recorded as a function of the temperature with the UNIRELAX device developed in our laboratory and produced by Tetrahedron Associates, San Diego, California, U.S.A. The thermomechanical curves obtained this way were found to be governed by the creep process as well as by the recovery of the elastic deformation frozen‐in by processing. Using small stress levels (10 g/mm2) the thermomechanical curve was mainly determined by the recovery of the frozen‐in deformation. Effects of thermal history on the creep thermomechanical curves were studied and interpreted. Using a mathematical formalism derived earlier for amorphous polymers, the curves were computer‐processed in order to separate creep from the recovery of the frozen‐in deformation and to obtain isothermal kinetic

ISSN:0360-8905    

DOI:10.1002/polc.5070580108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

摘要:

AbstractThe hypersonic elastic properties of oriented polymethylmethacrylate (PMMA) have been studied using high contrast (>108) multipass Fabry‐Perot techniques. Four samples of different degrees of orientation (birefringence Δn= −4, −9, −15, −24 × 10−4) were prepared by drawing at 130°C. Measurements of longitudinal sound velocity,VL, as a function of ϕ, the angle between the draw and propagation directions, show an anisotropy which scales with Δ and amounts to 6% in the sample having Δn= 24 × 10−4. At ϕ = 0,VL= 2.80 kilometers per second, (KMS−1), the same as the value in an isotropic sample. The elastic constantsC11andC33are measured as a function of Δn. Data as a function of sound wavelength, Λ, show dispersive effects in bothVLand attenuation αΛ, for Λ>0.7 μ. Over the range 0.7 μ<Λ<1.3 μ, αΛ increases from 0.1 to 0.5 andVLincreases by 8%. Attenuation is consistently higher for ϕ = 0. The data are interpreted in terms of densification (up to 15%) accompanied by void formation on orientation, the structure having characteristic dimensions of approximately 1.5 μ. The structure may be asymmetric with the longer dimension perpendicular to the draw direction. Additional Brillouin peaks may result from sound propagation in the voids (VL= 5.8 KMS−1) in which case the density is approximately 0.3 g cm−3. Measurements of the Landau‐Placzek ratio support these ideas, but evidence from electron micrographs is inconclusive. Dispersion measurements should in principle hel

ISSN:0360-8905    

DOI:10.1002/polc.5070580109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

摘要:

AbstractA structural‐mechanical study of the orientation process in some flexible‐chain semicrystalline polymers has been conducted. By their deformation properties, such polymers may be conditionally divided into two groups: the ultimate draw ratio is 20‐25 for the first group and 6‐10 for the second one, the transformation of the original structure into a microfibrillar one being completed at a draw ratio (λ) of 8‐10 in the polymers of the first type and at a draw ratio of 2‐4 in those of the second type. The low draw ratios characterizing the moment of a virgin neck propagation in the polymers of the second type are considered to be due to a large number of tie molecules in the original su‐permolecular structures. When microfibrils are formed, these molecules are supposed to be included between fibrils.It is shown that a further increase of λ results from the microfibrillar slip. In the polymers of the first type, the slip is, however, relatively easy and is not accompanied by significant changes in the internal structure of microfibrils, because the interfibrillar tie molecules are almost absent in them. In the polymers of the second type, a significant change in the internal cture of microfibrils, associated with a large number of interfibrillar tie molecules, is observed (obliquity of crystallites and an increase of the long period attributed to an increase in the length of the amorphous intrafi‐brjjlar layer).The microfibrillar slip leads to their more dense packing, which results in a sharp increase in the orientation load required for further drawing. This reduces significantly the lifetime of the specimens in high temperature drawing and leads to their fracture by a thermal fluc

ISSN:0360-8905    

DOI:10.1002/polc.5070580110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

摘要:

AbstractUni‐ and biaxial stretching of various polymer films has been studied under well‐defined conditions of temperature and elongational strain rate in order to determine the relationship between stress and recoverable strain for both modes of deformation. The extent of molecular orientation has been investigated with the aid of stress optical methods: In amorphous polymers birefringence was found to be directly proportional to the frozen‐in internal entropic stress irrespective of the latter's relationship with recoverable strain. In a first approximation, molecular orientation can be understood in terms of deformation of a rubberlike network with temporary junction points. The total internal stress in an oriented glassy polymer may be significantly larger than the entropic stress. Experimental methods based on retractive force measurements, able to distinguish between internal stresses of different nature, are described.In uni‐ and biaxially drawn films of polyethylene terephtalate preferred planar orientation of (100) planes has been studied by means of X‐ray diffraction and measurement of the three principal refractive indices. The intrinsic birefringence of completely oriented PET films has been estimated from these measurements with the aid of the Lorentz‐Lorenz theory. The effect of draw ratio and temperature on the rate of crystallization and its consequences (increase of stretching stress and density, decrease of shrinkage) has also been studied.Finally, the effect of molecular orientation on various mechanical properties: modulus, tensile strength, impact resistance, creep compliance, is discussed for both amorphous and semicrystalline polymers, with special emphasis on the predominant influence of amorphous phase

ISSN:0360-8905    

DOI:10.1002/polc.5070580111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY

摘要:

AbstractThe Knopp and Vickers microindentation hardnesses of oriented chain‐extended polyethylene (cold‐drawn, then hydrostatically annealed at 5·35kbar) have been measured to establish correlations with some of the morphological features previously investigated (lamellar thickness, orientation). The irreversible deformation increases with time under load and tends towards a characteristic limiting value for each annealing temperature. This limiting value of microhardness is an increasing function of annealing temperature,TA, and consequently of chain extension, 1. A conspicuous feature of the investigated oriented polyethylene samples is the clear anisotropy exhibited by the indentation pattern. The Vickers microhardness is a maximum when the indenter diagonal lies parallel to the fiber direction and minimum when normal to it. The opposite occurs for the Knoop case. This contrary behavior is due to the shape difference between the two indenters coupled with the high anisotropy of the material. This behavior supports morphological experiments and is a further illustration of the value of this technique in polymer textural stu

ISSN:0360-8905    

DOI:10.1002/polc.5070580112

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1977

数据来源: WILEY