摘要:

AbstractThe processing properties of low density polyethylene melts, such as drawdown and neck‐in, and the final product properties, such as film haze and gloss, have been successfully correlated with rheological functions and the level of longchain branching. The rheological functions employed are the entrance pressure drop ΔPoand the swell ratio So, determined at a specified shear stress using aft‐orifice with a length/ diameter (L/D) ratio of zero. The calculation of shear stress requires additional measurements using adie with a finiteL/De.g. 20. The rheological functions ΔPo, and Soare governed by the level of high molecular weight species and/or the level of long‐chain branching(LCB). If determined at a constant shear stress, in order to eliminate the effect of viscosity, they are a relative measure of elasticity. Higher ΔP0and Soindicate a higher level of LCB and correlate with poorer optical properties and drawdown

ISSN:0032-3888    

DOI:10.1002/pen.760171102

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractExperimental studies were performed on the effects of postcuring of' styrenated, unsaturated polyesters in nitrogen gas, water or its vapor, hexane vapor, dimethyl sulfoxide (DMSO), and dirnethyl formamide (DMF) all at 100°C It was found that, nitrogen gas and water are inactive, hexane acts as a chain transfer agent, and DMF and DMSO behave as solvents which extract residual styrene monomer and anhydrides from the resins. Post‐treatment in inert media can result in further reaction leading to more complete cure as free radicals and residual monomer continue to react. The post‐curing reaction is a radical copolymerization. Further condepgation polymerisation does not occur. Post‐curing in, hexane vapor1eads to a transfer of the active sites from the radicals to the hexane and to no further radical polymeri

ISSN:0032-3888    

DOI:10.1002/pen.760171103

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractThis paper presents the results of a study onn the effectiveness of ultraviolet absorbers and light stabilizers in preventing the discoloration of flame retardant impact polystyrene. The deleterious effect of certain flame retardants, i.e., aromatic or aliphatic halogenated compounds, on the light stability of this polymer is shown. Light stabilizer systems resulting in substantially improved color stability during light exposure are presented. The beneficial effect df co‐additives, including antioxidants, acid acceptors, epoxies, phosphites, and thiosynergists, on light stability is also discusse

ISSN:0032-3888    

DOI:10.1002/pen.760171104

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractThe dynamic shear properties of a natural rubber and several commercial synthetic polyisoprenes were measured in a Rheometrics mechanical spectrometer. The dynamic viscosity vs angular velocity curve was fitted to the three‐constant Car, reau model. The rheological parameters were correlated with molecular characteristics such as gel content and weight average molecular weight. The viscosity measurements at high shear rate were obtained from capillary rheometry. The viscosity vs shear rate curve at the low shear rate end was found to be superimposible on the plot of dynamic shear viscosity vs twice the angular velocit

ISSN:0032-3888    

DOI:10.1002/pen.760171105

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractCertain steady state viscoelastic parameters, including melt viscosities, normal stress coefficients, and shear compliances, are determined for a series of well‐characterized low, density polyethylene samples, and the results are analyzed. The effects of shear rate, temperature, molecular weight, molecular weight distribution, and the degree of long chain branching are demonstrated. The agreement observed between steady state shear compliance values derived from normal stresses and those obtained from die swell measurements is significan

ISSN:0032-3888    

DOI:10.1002/pen.760171106

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractInvestigated are the swelling and hygroelasticity of a unidirectional glass fiber‐reinforced epoxy composite subjected to boiling water for 24 hrs. By analogy with thermoelasticity, a coefficient of hygroelasticity is defined and shown to be predictable from the coefficients of the constituent materials by Schapery's equations. A mechanism for water penetration into the composite which combines capillarity and diffusion is proposed on the basis of the results of the water take‐up as a function of the composite specimen width (fiber leng

ISSN:0032-3888    

DOI:10.1002/pen.760171107

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractStar‐shaped block copolymers were used as heat activated adhesives in glass to glass joints. The branches consisted in either AB or ABA poly(styrene‐b‐isoprene) block copolymers. Tensile shear strengths of simple lap joints were measured for star block copolymers differing in the length or in the number of branches. Values higher than those of the corresponding linear species were obtained. These results were related to the presence of chemical junction points created by coupling the linear copol

ISSN:0032-3888    

DOI:10.1002/pen.760171108

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractSolution viscosity is known to be sensitive to the nature of solvent and the polymer concentration. The magnitude of such effects, however, is not quantitatively understood. Correlations to predict zero‐shear and shear‐rate dependent viscosity of polymer solutions from polymer solution parameters are presented. Polymer domain volume is found to be the controlling parameter for the zero‐shear viscosity of dilute polymer solutions, that is solutions with insignificant entanglements. At higher concentrations, where polymer‐polymer interactions become significant, it is found that, except for the magnitude of the solvent viscosity, the nature of the solvent is of no consequence. In this region zero‐shear viscosity is correlated as a function of the parametercM5/8, whereCandMrepresent concentration and molecular weight, respectively. A relaxation time such as Bueche's time constant satisfactorily represents the solvent effects on the non‐Newtonian behavior of polymer solutions by incorporating the measured zero‐shear and solven

ISSN:0032-3888    

DOI:10.1002/pen.760171109

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractWhen a polymer melt is forced through the nozzle of an injection molding machine, the material temperature increases significantly. This increase, which is very difficult to measure, is not uniform and local temperature peaks may cause thermal degradation. A method is described for the analysis of timedependent heat transfer and flow in such nozzles. Melts are treated as being inelastic but with viscosities which are nonNewtonian and dependent on both temperature and pressure. Distributions of velocity, temperature and pressure are obtained with the aid of a finite difference method for solving the differential conservation equations' of continuum mechanics. Typical results show that the times required to reach steady flow conditions are small compared with total injection times. Heat transfer is predominantly convective, and flows leaving injection nozzles and entering molds are very far from being thermally fully‐develope

ISSN:0032-3888    

DOI:10.1002/pen.760171110

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760171101

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY