3.1.1. Unfilled HDPE, PP, and their blends
The mechanical properties of the unfilled blends and compos-ites are summarized in Tables 1–3 . The initial HDPE and PP plastics
exhibited very different mechanical performance, with the PP hav-ing much larger moduli and strengths but also lower impact per-formance and strains at yielding and failure (Table 1). The tensile
moduli of the blends without EPDM are clearly proportional to
the relative amounts of HDPE and PP in the blends. Not surpris-ingly, adding 10% of the low modulus EPDM reduces the moduli
of the blends. The reductions in moduli were about 25% in tensile
tests and about 20% in flexural tests. This is a common limitation of
using elastomers as compatibilizers in plastic blends. However, all
moduli for the blends were at least that of the unblended HDPE.
Tensile yield stresses and strains also appear to follow a simple
rule of mixtures. Adding 10% EPDM allows the blends to yield more
easily, at about 16% lower stress, but at about 35–40% higher
strain. The largest yield strains found were for the blends with
25:75 and 50:50 HDPE:PP blend ratios containing EPDM, and ex-ceeded those of the unblended plastics.
Representative tensile curves for the unfilled blends are shown
in Fig. 2 . The large strains exceeded the range of our strain gauge
and the strains shown are nominal strains based on the separation
of the specimen grips. Tests on unfilled HDPE were stopped after
1200% nominal strain. Unlike moduli and yield properties, addi-tions of even 25% PP to HDPE greatly reduced nominal strains at
failure. This negative deviation from a rule of mixtures demon-strates the embrittlement common in incompatible plastic blends
3.1.1. Unfilled HDPE, PP, and their blendsThe mechanical properties of the unfilled blends and compos-ites are summarized in Tables 1–3 . The initial HDPE and PP plasticsexhibited very different mechanical performance, with the PP hav-ing much larger moduli and strengths but also lower impact per-formance and strains at yielding and failure (Table 1). The tensilemoduli of the blends without EPDM are clearly proportional tothe relative amounts of HDPE and PP in the blends. Not surpris-ingly, adding 10% of the low modulus EPDM reduces the moduliof the blends. The reductions in moduli were about 25% in tensiletests and about 20% in flexural tests. This is a common limitation ofusing elastomers as compatibilizers in plastic blends. However, allmoduli for the blends were at least that of the unblended HDPE.Tensile yield stresses and strains also appear to follow a simplerule of mixtures. Adding 10% EPDM allows the blends to yield moreeasily, at about 16% lower stress, but at about 35–40% higherstrain. The largest yield strains found were for the blends with25:75 and 50:50 HDPE:PP blend ratios containing EPDM, and ex-ceeded those of the unblended plastics.Representative tensile curves for the unfilled blends are shownin Fig. 2 . The large strains exceeded the range of our strain gaugeand the strains shown are nominal strains based on the separationof the specimen grips. Tests on unfilled HDPE were stopped after1200% nominal strain. Unlike moduli and yield properties, addi-tions of even 25% PP to HDPE greatly reduced nominal strains atfailure. This negative deviation from a rule of mixtures demon-strates the embrittlement common in incompatible plastic blends
การแปล กรุณารอสักครู่..
