The preparation and tensile properties of polyethylene composites

Abstract

Single polymer composites have been prepared using different morphologies of polyethylene as matrix and as the reinforcement. Depending on annealing conditions, the ultraoriented fibers used as reinforcement can have higher melting points (ca. 139°C) than the matrix made from the same conventionally crystallized high‐density polyethylene (ca. 132°C) or from low‐density polyethylene (ca. 110°C). The optimum temperature has been assessed for bonding to occur by growth of transcrystalline regions from the melt matrix without considerable modulus reduction of the annealed ultraoriented and reinforcement fiber or film. Pullout tests have been used for determining the interfacial shear strength of these single polymer composites. The interfacial shear strength for the high‐density polyethylene films embedded in a low‐density polyethylene matrix is 7.5 MPa and for high‐density polyethylene self‐composites is 17 MPa. These values are greater than the strength for glass‐reinforced resins. The strength is mainly due to the unique epitaxial bonding which gives greater adhesion than the compressive and radial stresses arising from the differential shrinkage of matrix and reinforcement. The tensile modulus of composites prepared from uniaxial and continuous high‐density polyethylene films embedded in low‐density polyethylene obeys the simple law of mixtures and the reinforced low‐density polyethylene modulus is increased by a factor of 10. High strength cross‐ply high‐density‐polyethylene—low‐density‐polyethylene laminates have also been prepared and the mechanical properties have been studied as the film orientation is varied with respect to the tensile axis.

The effect of anhydrous ammonia on the crystalline‐state deformation of nylons 6 and 6,6

“…However, the crystallinity of the former (43.8%) is substantially higher than the hot drawn sample. X-ray diffraction patterns for ammoniated undrawn and drawn samples before ammoniation and after the NH 3 (0140) region to determine the fiber period, and are shown in Figure 8 and Table II. It is well known that nylon 6 can exist in several crystal forms that may vary continuously in crystal perfection, size, and unit cell parameters (12).…”

The water absorption behaviour of all-polypropylene composites and its effect on mechanical properties

“…All-PP composites may have specific ecological advantages over composites based on glass or natural fibres, since they are entirely thermoplastic and can be melted down at the end of the product life without the need for a separate fibre recovery process. Various routes have been proposed so far for the manufacturing of self-reinforced composites [12][13][14][15][16][17][18][19][20][21], and two main routes shall be described briefly here. The 'hot-compaction' process was initially developed at the University of Leeds as a route to self-reinforced polyethylene although it has also been applied to other polymers [15,[22][23][24][25].…”

Resolução lamelar num novo microscópio eletrônico de varredura

“…Alternativamente, o surgimento das primeiras lamelas sobre a fibra poderia ser interpretada como início de fusão ou relaxação superficial da sua estrutura fibrilar (cristais "shish" com cadeias extendidas seriam transformadas em cristais "kebab" com cadeias dobradas), fenômeno detectado anteriormente na literatura 22 . Neste caso, porém, não houve início de fusão na superfície da fibra, uma vez que nenhuma lamela foi encontrada longe do filme de PEAD, Figura 7.…”