Walter D. Niegisch

THE BIODEGRADABILITY OF SYNTHETIC POLYMERS

Of the large number of plastics produced commercially in this country, three account for about 90% of the plastic found in municipal waste. [1] These three are poly(ethylene) at 38%, poly-(vinyl chloride) at 31% and poly(styrene) at 21%. Because these three plastics make up the bulk of packaging plastics, it was felt that they should be the focus of attention of research and development pertaining to the disposability or recycling of plastic waste.

Crystallography of Poly‐p‐Xylylene

Poly‐p‐xylylene prepared by the vapor‐phase pyrolysis of di‐p‐xylylene affords a linear high‐purity polymer whose crystalline transitions were characterized by x‐ray and electron diffraction, mechanical creep studies, and differential thermal analysis (DTA). Two of the three endotherms observed by DTA correspond to the known alpha and beta polymorphs of poly‐p‐xylylene. The third, occurring at 270°C, is a reversible transition which is regarded as a smectic mesomorphic transition of the stable beta modification. Hence: α→ lim 220∘Cβ1⇋ lim 270∘Cβ2→Tm 420∘C (decomposition). Single crystals precipitated from alpha‐chloronaphthalene were instrumental in characterizing the alpha and beta unit cells. The alpha modification is best represented by an orthorhombic cell with a=21.3, b=33.6, c=6.58 A, for which the theoretical density is 1.141 g·cm−3 at 23°C. The beta modification is hexagonal, with a=20.52±0.05 A and c=6.581±0.020 A, having a theoretical density at 23°C equal to 1.153±0.005 g·cm−3. The fiber repeat...

Hollow Pyramidal Crystals of Polyethylene and a Mechanism of Growth

A hollow pyramidal model for diamond‐shaped single crystals of polyethylene is proposed which accounts for the electron microscope observations and electron diffraction effects presented in this paper and in the literature. The pyramidal shape occurs because the rows of folded molecules along the (110) growth face in each quadrant of the crystal are translated along the molecular chain direction by two carbon‐carbon distances relative to the previous row. This translation presumably occurs in order to relieve steric interferences at the folds or loops of the polymer chain. The resulting triclinic cell, of which the familiar orthorhombic cell is in reality a subcell, has a c dimension equal to the constant fold length of the polymer chain, and remaining parameters of ā=7.84 A, b=5.56 A, α=(90−27.3)°, β=(90−19.0)° and γ=81.5°. The values 19.0 and 27.3 degrees are, respectively, arctan (c/a) and arctan (c/b) of the orthorhombic subcell, so that the (001) planes of the triclinic cell which contain the folds...

Molecular Orientation in Poly‐p‐Xylylene Films

An electron diffraction study of thin (100–200 A) vapor‐deposited films of poly‐p‐xylylene which had been annealed to the beta modification reveals that the majority of crystallites are very specifically oriented with (10·0) prism faces in the plane of the film. Since the polymer chains are aligned in the c‐axis direction [00·1], it follows that the molecules within oriented crystallites are lying in the film plane. A smaller number of crystallites are randomly oriented in these films. These conclusions are qualitatively extended on the basis of x‐ray diffraction data to include films as thick as 4 mil. This study corroborates the hexagonal assignment to the beta cell, with a=20.52 and c=6.581 A. The level of orientation is essentially independent of the nature of the crystalline and amorphous substrates upon which the films were deposited, but is inversely proportional to the partial pressure of the p‐xylylene monomer in the vapor phase above the substrate.