Incorrect output with get_attached_file()

I am having troubles with file encodings while retrieving file names with get_attached_file(). The line:

get_attached_file( $attachment_id );

Is getting me results like:

GAC_14_2_Selo-Casa-Azul_Constru?§?￡o-Sustent??vel.pdf

Where it should be like:

GAC_14_2_Selo-Casa-Azul_Constru??o-Sustentável.pdf

The file is correctly stored at the file system; WordPress Media Library also shows correctly; WordPress is at version 4.0.1.

Why is it not working and what should I do to make it work?

Below goes all the my code if it helps.
Its purpose is to regenerate a zip file every time a custom post type post is saved. The zip contains every file attached to the post through Advanced Custom Fields + ACF Repeater.
The code is working: the zip is generated with the files inside it but the filenames are, as shown above, incorrect.

function gerar_zip_dos_materiais( $post_id ) {
// https://stackoverflow.com/questions/23668293/php-dynamically-generated-zip-file-by-ziparchive-cant-be-opened
$materiais = get_field(‘materiais’);
$error = ”;
if ($materiais) {
if(extension_loaded(‘zip’)){

$zip = new ZipArchive(); // Carrega a biblioteca zip
$nome_curto = $slug = basename(get_permalink()); // pega o slug do post
date_default_timezone_set(‘America/Bahia’);
$data_agora = date(‘Ymd_His’); // pega a data do post
$nome_do_zip = $nome_curto . ‘-‘ . $data_agora . ‘.zip’; // Nome do zip
$path = get_site_url();
$url_zipao = $path . ‘/wp-content/uploads/materiais/’ . $nome_do_zip;

if($zip->open($nome_do_zip, ZIPARCHIVE::CREATE)!==TRUE){ // Prepara um zip para carregamento
$error .= “Falhou ao criar o zip desta vez!”;
}

foreach($materiais as $material) {
$nome_subpasta = $material[‘nome_da_aula’];
$documentos = $material[‘conteudos_da_aula’];

foreach ($documentos as $documento) {
$attachment_id = $documento[‘arquivo_do_conteudo’];
$url = wp_get_attachment_url( $attachment_id );
$filename = basename ( get_attached_file( $attachment_id ) );
$path_absoluto_do_arquivo = get_home_path() . str_replace($path.’/’,”,$url);

$zip->addFile( $path_absoluto_do_arquivo, ‘Viviane_Rocha/’ . $nome_curto . ‘/’ . $nome_subpasta . ‘/’ . $filename );
}

}

if ($zip->close() === false) {
exit(“Falou ao fechar o zip desta vez!”);
}

if(file_exists($nome_do_zip)) {
rename($nome_do_zip, ‘../wp-content/uploads/materiais/’.$nome_do_zip);
}

$chave = ‘arquivao’;
$o_zip = $url_zipao;
if ( !isset($o_zip) || !is_string($o_zip) ) {
add_post_meta($post_id, $chave, $o_zip, true);
} else {
update_post_meta($post_id, $chave, $o_zip);
}

} // extension_loaded(‘zip’)
} // $materiais
}

add_action( ‘save_post_materiais’, ‘gerar_zip_dos_materiais’ );