Structure and properties of rubber-modified polypropylene impact blends

Abstract

SynopsisThe state of dispersion of poly(ethy1ene-co-propylene) (PEP) rubber and high-density polyethylene (HDPE) in polypropylene (PP) blends was investigated using scanning electron microscopy to examine solvent-etched microtomed surfaces cut a t low temperatures. The validity of the method was established by comparing the areal fraction of dispersed particles in micrographs with the volume fraction of PEP and HDPE in PP-rich blends. When small amounts of PEP and HDPE were added to PP, they combined to form composite PEP-HDPE particles with characteristic internal structures in a PP matrix. Changes in impact strength and flexural modulus with changes in mixing conditions and blend composition were determined and interpreted in terms of the size, composition, and internal structure of the dispersed particles. Particle growth in the melt limited the impact strength level achieved in molded articles. A simple model proposed for screening rubbers for toughening of brittle plastics successfully predicts that P E P rubber should be an excellent impact modifier for PP.

Study on the mechanical and morphological properties of toughened polypropylene blends for automobile bumpers

“…The HDPE can not initiate crazes nor arrest crack growth as effectively as rubber particles. This behavior may be caused by poor PP-HDPE adhesion as well as by the non-rubberlike characteristics of HDPE [5]. However, as illustrated in Table 2, HDPE used in admixture with POE was an effective toughening agent for PP.…”

Mechanical and morphological characterization of polypropylene toughened with olefinic elastomer

“…Also one should consider that the presence of fewer tertiary hydrogen in these elastomers improve their thermal stability in comparison to EPR's 11 . For PP, a semicrystalline matrix, the most effective particle size range for obtaining the best rubber toughening behaviour observed by various authors [5][6][7][12][13][14][15] is sub-micron in the range of 0.5 to 1.0 µm. The particle size of the elastomer significantly affects the deformation and failure processes being small particle favouring shear yielding while coarser dispersion promotes crazing 7 .…”

“…The improvement of toughness in plastics [1][2][3] and in particular of isotactic polypropylene is a subject of great importance due to its inherent low impact strength, especially in applications that involve sub ambient temperatures [4][5][6][7][8][9][10][11][12][13][14][15] . Polypropylene can be toughened through incorporating low contents of ethylene during its copolymerization, resulting in random or block copolymers 4,5 or by the in situ method, inside the reactor, where are formed dispersed elastomeric domains of ethylene-propylene elastomer (EPR) in a polypropylene matrix, called heterophase polypropylene.…”

Otimização de propriedades mecânicas de misturas ternárias de polipropileno (PP)/borracha de etileno-propileno-dieno (EPDM)/pó de pneus (SRT) sob tração e impacto usando a metodologia da superfície de resposta (MSR)

“…A fim de melhorar tal desempenho, extensa pesquisa vem sendo desenvolvida através de misturas de PP com elastômeros, em particular, a borracha butílica (BR), a borracha de estireno-butadieno (SBR) e a borracha de etileno-propilenodieno não conjugado (EPDM), as quais possuem valores de T g muito baixos. Há ainda técnicas de polimerização in situ com monômeros específicos para o aumento da resistência ao impacto do PP [1][2][3][4][5][6][7][8][9] . Os resíduos de borracha oriundos de pneus inservíveis tornaram-se um passivo ambiental de grande preocupação.…”