Colloidally stable latex blends of natural rubber (NR) and poly(methyl methacrylate) (PMMA) latexes containing up to 50 wt.% PMMA can be prepared by mixing commercial NR ammoniated latex concentrate and monodisperse PMMA latex dispersion. The clarity and tackiness of the films obtained depend on the PMMA content; films become opaque and non-tacky at >30 wt.% PMMA content. The morphology of these films shows asymmetric distribution of the PMMA particles across the thickness of the film. There is preferential enrichment of PMMA particles at both the air/polymer and glass/polymer interfaces and a predominating NR interior. More PMMA particles are accumulated preferentially at the glass/polymer interface than at the air/polymer interface. The accumulation of the PMMA particles at the interface is strongly dependent on the size and concentration of the PMMA particles. The formation of these asymmetric latex films is explained in terms of the surface energetics, compatibility, T g and density of the polymers, stability of the component latex, surface chemistry and particle size of the latex particles used. Copyright  2001 John Wiley & Sons, Ltd. KEYWORDS: asymmetric latex film; natural rubber latex; poly(methyl methacrylate) latex; latex blend film morphology; natural and synthetic latex blend INTRODUCTIONSynthetic latexes are used extensively in the paints and coating industry. This application requires the latex particles, on drying, to form a continuous film. However, good filmforming latex lacks mechanical strength in its film. Thus, low-T g latexes have good film-forming abilities but the films possess a low Young's modulus. Various techniques have been used to overcome this problem. For example, filmforming aids frequently have been employed to provide a coherent film.1,2 Another approach is the synthesis of waterborne core/shell latex particles with a high-T g polymer core and a film-forming shell that are able to form a film of elastomeric matrix containing a high-modulus inclusion.3,4 Another technique is by physically blending two polymer latexes with different T g values 2,5 in which the soft particles deform and fill the voids between the hard particles. A blend of a low-T g latex with a high-T g polymer is used in latex-based impact modifiers for polymer resins. In polymer blending, one anticipates obtaining different properties in the blend than those of the individual polymer components. Although polymer blending 7 has been studied for many years, much less attention has been paid to synthetic latex blends. One of the main interests in latex blends is the drive towards zero-volatile organic compounds in the organic coating industry.2 Analysis of morphology and transparency of latex blend films by atomic force microscopy (AFM) and scanning electron microscopy (SEM) has provided insight into the interaction between hard and soft latex particles.8 -10 Although diffusion at the particle/particle interface of miscible polymer components during film formation is studied extensively, 11 -15 little is known ab...

No abstract

7b demonstrate the applicability of Raman spectroscopy to the are true polymers; regardless, they are insoluble in most comantilysis of thin heterogeneous deposits on surfaces, a sampb ofbrown mon solvents and can only be removed mechanically. Friction stain or friction polymer produced on sendust (85% Fe, 9% Si, 6 % polymers Can reduce friction and wear and can therefore be A9 surJaces of a simulated read/write head by a magnetic oxide tape beneficial* but can be when reduce sigmaking prior contact with a copper, aluminum or nickel surface was nal transfer from magnetic tape media increasing the head-to-medium spacing. investigated. Raman spectra identi$ed the base jilm of the tape as Ever since Hermance and Egan's paper, many investigapoly(ethyhe terephthalate) or PE7; and the magnetically active luytions of friction polymers have been reported. The particular er~q as containing mostly y-Fe,03. Convmsely, Raman spectra of problem of brown stain has been studied for some years as /~oorun slain showed it to consist mainly of F%04 and organic cornwell. Nevertheless, the orirrin of brown stain and pountls. More brown stain was produced after copper contact than (qter (~lunzinum contact, but only organic deposits were produced aJer nickel contact in these tests. It is speculated on the basis of these sj)cctral data that the inhibiting effect of nickel could be the result of catalytically produced organic materials, which change the tribology on the head surjace and inhibit the fmnation of brown stain or Jiction polymer.