Natural and artificial weathering of low‐density polyethylene (LDPE): Calorimetric analysis

Abstract

Studies of the thermal and photodegradation of two commercial polymers, stabilized and unstabilized low‐density polyethylene, show the effects of weathering on differential scanning calorimetry (DSC) curves. The shape and the size of the melting peak vary significantly in thermal aging and in accelerated photoirradiation, but no change was observed in natural weathering, implying that the crystallinity remains steady in outdoor exposures. The melting temperatures remain steady for all exposure tests. The fall of mechanical properties and the evolution of chemical structure, followed by IR spectroscopy results, especially near the carbonyl regions, were also observed. The resistance to UV light irradiation as probed by deformation at break was superior in stabilized LDPE compared to unstabilized LDPE. Simple correlations observed between the fall of mechanical properties, the rate of oxidation, and morphology. © 1993 John Wiley & Sons, Inc.

Investigating the role of metal oxidation state on the degradation behaviour of LDPE

“…The increase in DSC crystallinity of the samples resulting from xenon exposure is reported in Table 4. Such an increase in crystallinity of polyethylene films upon irradiation has been reported in the literature [15,20]. The increase in crystallinity is an indirect result of the chain scission of the polyethylene molecule in the amorphous regions.…”

“…where DH f(observed) is the enthalpy associated with melting of the material and DH f(100%crystalline) is the enthalpy of 100% crystalline polyethylene, reported in the literature to be 285 J/g [15]. The apparent density was measured using a Sartorius analytical balance (model ME215S) equipped with density measurement accessory (model YDK01).…”

DSC Study of Artificial Thermal Aging of XLPE Insulation Cables

“…The chain scission allows the resulting freed segments to crystallize [10]. The creation of new intermolecular polar bonds, due to carbonyl groups may also lead to this effect [11]. The annealing effect at the oxidation temperature may also contribute to increase the crystallinity [8].…”

Influence of climatic ageing on the mechanical properties and the microstructure of low‐density polyethylene films

“…The mechanical properties of polyethylene have been characterized and modeled by many authors and in particular by one of us 34, 35. It is now well understood that each phase in the semicrystalline microstructure plays an important role as in a nanocomposite material.…”

“…In the first months of the ageing protocol, the increase is rapid. This stiffening is essentially controlled by the secondary crystallization of the amorphous chains whose mobility is enhanced by the chain scission processes 5, 17, 35. Also, several authors proposed that the replacement of CH bonds by CO bonds during the oxidation of the amorphous regions introduces stronger intermolecular bonds and contributes to the modulus increase 9, 31.…”